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Linear, Graft, and Beyond: Multiblock Copolymers as Next-Generation Compatibilizers
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JACS Au

Cite this: JACS Au 2022, 2, 2, 310–321
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https://doi.org/10.1021/jacsau.1c00500
Published January 31, 2022

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Abstract

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Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technological breakthroughs on various fronts. Mechanical recycling of plastic waste into polymer blends is one method expected to contribute to a solution. Due to phase separation of individual components, mechanical recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further technical development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concentrations as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising solution to help close the loop on plastic waste. While a complete discussion of the implementation of this technology would entail infrastructural, policy, and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the technical advancements of block copolymer compatibilizers.

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1. Introduction

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1.1. Motivation

In 1908, Jacques E. Brandenberger invented “cellophane” as the first clear polymer film and unknowingly launched what would soon become a multibillion-dollar industry. (1,2) Today, single-use plastic packaging is ubiquitously found in everything from sterile medical supplies to individually wrapped fruits at the market. Thermoplastics─a class of polymers named for their ability to flow when sufficiently heated─have provided a low-cost solution to meet this growing demand for packaging. Unfortunately, less than 10% of all consumer generated plastic waste is recycled in the United States (3) leading to an unsustainable accumulation of plastic waste in landfills and ecosystems. (4) Not surprisingly, a wide variety of polymers comprise this plastic waste with the most common commercial polymers being highlighted in Figure 1.

Figure 1

Figure 1. Structures, names, and recycling codes for common polymers discussed in this perspective.

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Each of the polymers presented in Figure 1 differs in structure and/or chemical composition, resulting in a range of thermal and mechanical properties. Even polymers with the same repeat unit can have different properties depending on the molecular architecture, molar mass, and crystallinity, such as for high-density PE and low-density PE. While single polymers may be perfectly suited for a particular application and processing method, the performance demands of many products often require combinations. A prominant example is multicomponent products such as multilayer packaging where different polymers, and other materials like paper and foil, are combined to achieve the aggregate desired performance. For example, meeting food packaging requirements, including good containment, security, processability, durability, and low water/oxygen permeability, often necessitates between three and seven distinct layers. (5) Films with nonpolymeric materials present an entirely separate set of challenges to recycling, but for simplicity the following discussions will only focus on purely polymeric multilayer packaging materials. Such packaging also typically introduces adhesives and other additives between and within different polymer layers. (6) Whether combined before or after consumer use, the majority of thermoplastics end up as mixed plastic waste streams, and recovering valuable materials from this mixed waste stream has proven challenging.
Given that thermoplastics flow when heated, it would be convenient if mixed plastic waste streams could be simply mechanically recycled (i.e., melted and reprocessed) into a multicomponent plastic resin for use in other applications. However, due to the small entropy change upon mixing molecules of high molar mass, most polymers are thermodynamically immiscible. (7) This is even true for some polymers with similar chemical structures; for example, PE and PP are both comprised entirely of hydrogen and aliphatic carbons, yet they are immiscible. (8) For this reason, mechanical recycling typically does not result in a homogeneous material but instead produces large phase-separated domains of each component. The interfaces between these domains are typically weak due to sharp compositional gradients that preclude polymer chain entanglements and cocrystallization across the interface, compromising the mechanical performance. There is strong motivation to develop methods to “compatibilize” polymer blends to valorize the enormous quantities of otherwise unusable plastic waste. While “compatible” is sometimes used interchangeably with “miscible”, herein compatibilization refers specifically to a reduction of interfacial tension and domain size, and an increase in interfacial adhesion that leads to an improvement in polymer blend mechanical performance. (9) Compatibilized blends, due to their distinct domains, retain thermal properties of each individual component, instead of amalgamation of thermal transitions often observed in miscible blends. Many research efforts have sought to address these issues by developing additives and processing approaches that not only strengthen interfaces by compatibilizing two or more disparate polymers, but also fit easily into existing infrastructure for mechanical recycling. In the following sections, we will briefly review the use of block copolymers (BCPs) for compatibilizing polymer blends before discussing recent investigations leveraging multiblock copolymers (MBCPs).

1.2. Conventional Approaches to Compatibilization

A conventional approach for compatibilizing a binary blend of polymers is to introduce an interfacially active polymer, termed a “compatibilizer”, that is often comprised of two polymer blocks, each miscible with one polymer blend component. The blocks can be chemically identical to or structurally similar to a blend component or can possess functionalities that enable chemical interactions with specific blend components, all promoting miscibility of one block into each polymer blend component. (10,11) This can be realized via two distinct routes: (1) incorporating preformed BCP into the blend and (2) inducing reactions at polymer–polymer interfaces to form BCP in situ. Regardless of how they are generated, BCP compatibilizers are effective only by localizing at interfaces where they can interact with both homopolymer domains, thereby forming a “tether” across the interface. (12) This idea is shown schematically in Figure 2. The mechanism of the BCP increasing interfacial adhesion between the homopolymers generally consists of entanglement formation or cocrystallization of the BCP with each homopolymer domain. The absence of these two mechanisms generally produces relatively weak interfacial adhesion where the interface fails by chain pullout. (13)

Figure 2

Figure 2. Illustration of a polymer–polymer interface being stabilized with a (i) diblock copolymer, (ii) triblock copolymer, and (iii) grafted copolymer.

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The idea of using BCPs, both preformed and formed in situ, to compatibilize binary polymer blends has been actively studied since the 1970s. (14−17) Compared to forming copolymers in situ, the use of premade diblock copolymers can afford more well-defined systems in terms of molecular structure and composition which allow for more methodical investigations of the structure–property relationships of BCP compatibilizers. For example, reactive formation of the PE-iPP diblock in situ is challenging because it requires installation of complementary functional groups on each block precursor; on the other hand, synthesizing a premade PE-iPP diblock can be readily achieved with good control of molecular architecture. (18) While early reports suggested there might exist an optimal block length for compatibilization, (19) later investigations revealed a more nuanced trade-off in molecular weight. (15) Lower molecular weight copolymers show enhanced diffusivity and can more easily localize at the interface, but they do not provide the same stabilizing effect as higher molecular weight analogues. (20) The reduced performance of lower molecular weight blocks has been attributed to being less capable of spanning the interface and less effective “anchoring” in the homopolymer domains by cocrystallization and/or entanglements. However, at higher BCP molecular weights, the critical micelle concentration (CMC) is substantially reduced for the BCP in each homopolymer and BCP micelles diffuse to the interface more slowly, all promoting a less effective compatibilizer. (15,21−23) Therefore, while the concept of an “optimal” molecular weight is enticing, the reality is that compatibilizer design requires consideration of the specific material system. Beyond these material considerations, there is also the added complexity of differences in processing that can dictate system performance (e.g., stage mixing before compounding often improves localization to the interface). (24,25)
Similar questions have been posed regarding the necessity of a BCP architecture for stabilizing interfaces. Using a PS-PMMA system, Lee et al. demonstrated that, while random copolymers can localize to the blend interface, they do not achieve similar stabilizing effects supporting the notion that sufficiently large blocks are required in order to achieve compatibilization. (26) It should be noted that many copolymers (including random copolymers) can reduce the dispersed particle size in polymer blends but do not necessarily stabilize the disperse phase from coalescing during subsequent processing. (27) Efficient compatibilization is only realized when both domain size reduction and stabilization occur. Interestingly, Fayt et al. showed that a “tapered” transition between the blocks of a copolymer could further improve compatibilization relative to analogues with two distinct blocks. (28) Other investigations in the area, both experimentally (29) and computationally, (30,31) have confirmed that interfacial activity and phase separation are strongly effected by subtle differences in block structure (e.g., degree of tapering). These encouraging results suggest that developing architectural complexity beyond a simple diblock could have significant impact on blend performance and is still an active area of investigation. (32,33)
The emphasis on diblock compatibilizers stems from both synthetic convenience and by analogy to traditional surfactants as well as early assertions that the diblock architecture outperformed other polymer architectures (i.e., graft copolymers and linear triblock copolymers). (11,28,34) Early studies made claims that increasing the number of blocks had little, even detrimental, impact on interfacial adhesion of incompatible polymers; however, the polymers used in these studies were limited to triblocks. (28) More recent studies investigating MBCP compatibilizers with four or more blocks─enabled by synthetic advancements─have revealed that MBCPs actually outperform traditional diblocks. (18,35−37) These and other recent advances are discussed in depth in later sections of this perspective.
The other main strategy for introducing compatibilizers is to form them in situ via coupling reactions at the blend interface. (38) This can be achieved in a variety of ways but typically includes a homopolymer with reactive handles which can couple with complementary functionalities of another homopolymer. All of the polymer architectures given in Figure 2 could be generated in situ if the polymer precursors are appropriately designed to participate in a coupling reaction. Fortuitously, compounding supplies the required heat and mixing to drive the chemical reaction, while mixing also disperses the phases during the mechanical recycling process, allowing for copolymer formation and blend compatibilization to occur in a single step. Therefore, unlike premade BCP compatibilizers which require additional synthesis and isolation prior to addition, reactive graft copolymers can often be implemented more readily. Intuitively, optimal copolymer formation can be achieved if the homopolymers being blended intrinsically contain complementary functional groups, but this approach must be implemented during the original production of the virgin materials and is therefore not generally applicable to the compatibilization of mixed waste streams.
Compatibilizers formed in situ have several other influences on the kinetics of compatibilization compared to premade compatibilizers. Since premade compatibilizers must localize to the blend interface─with no chemical reaction necessary for their formation─the primary influence on how fast the system can compatibilize is the diffusivity of the compatibilizer to the blend interface. For in situ formed compatibilizers, the transport of the reactive precursors and rate of formation at the interface both influence the rate at which the system can compatibilize. For example, if the reactive groups can form the compatibilizer significantly faster than the rate of droplet breakup during processing, then the result is less efficient dispersion of the minority phase. (39) The predominant lesson being that the reaction rate must be balanced with the rate of growth of interfacial area (i.e., reduction in droplet size) during processing to optimize in situ blend compatibilization.
Leveraging functional groups inherent to the polymer (e.g., amine end-groups on nylons) to drive reactions with a complementary functionalized additive (e.g., maleic anhydride-grafted polymers) has been demonstrated to effectively compatibilize polymer blends. (17,40) The most prevalent of these coupling chemistries is the amine-anhydride reaction due to its high reactivity and well-established synthetic methods for generating polymers with the required functionalities. (38,41) Reactive compatibilization has been implemented industrially to compatibilize recycled mixed plastic at concentrations between 5 to 20 wt % of reactive resin. (42−44) Extensive efforts have been made to quantify the reactivity of various other reactive handles by monitoring the coupling reactions as graft or block compatibilizers are formed, (45) as well as quantifying the difference in reactivity of end-functionalized versus pendant-functionalized polymers. (46) Because reactive compatibilization can result in various types of copolymers, developing a more rigorous understanding of the consequences and performance of copolymer architecture (i.e., graft vs linear) is necessary. Similarly, graft copolymers have structural parameters such as grafting density, graft distribution, and molecular weight of grafted chains that all influence their performance as compatibilizers, and more work is necessary to elucidate the underlying structure-performance relationships. (46−48)

2. Synthetic Methods

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The discovery of living polymerizations by Szwarc et al. enabled access to well-defined block and graft copolymers that catalyzed decades of innovation. (49) The further development and refinement of these methods led to various technological advances, including thermoplastic elastomers (50) and, later on, BCP compatibilizers. (6) In the time since, the combined contribution of many researchers have expanded the range of accessible polymer architectures enormously, (51) but our understanding of the effect of architecture on compatibilizer performance has lagged behind. In Figure 3, a series of increasingly complex architectures that can be formed with only two distinct blocks is shown to illustrate the immense variety within this space. The discrepancy between our extensive synthetic capability and physical understanding poses an exciting opportunity to investigate and potentially implement new polymer architectures as novel compatibilizers.

Figure 3

Figure 3. Diverse range of possible copolymer architectures using only two distinct blocks.

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Several reviews exist that thoroughly discuss recent innovations in living polymerization chemistry, (52−54) MBCP synthesis, (55) and coupling reactions, (56,57) so herein we will only highlight several key examples of how synthetic developments have enabled advancements in the field of blend compatibilization. Early studies largely focused on amorphous polymer compatibilizers (as those polymers could be directly attained from anionic polymerization), but the development of improved catalysts and chemistries have enabled the study of semicrystalline blends which are far more industrially relevant. For example, a synthetic strategy developed by Lee et al. to generate multiblock PLA-PB copolymers via a condensation polymerization of two hydroxy-terminated macromonomers with a diacyl chloride (58) inspired a recent method by Nomura et al. that generated PET-PE MBCP compatibilizers. (36) While PET-PE MBCPs have previously been generated in situ, (59−61) the establishment of a robust synthetic method for their ex situ synthesis allows for a more methodical study of the structure–property relationship of these materials. (36) Similarly, Wang et al. demonstrated the first synthesis of well-defined PE-g-aPP copolymers (with molar mass dispersities, Đ < 2). (62) This advancement was made possible by the synthesis of a cyclooctene (COE)-terminated aPP macromonomer, which allowed for a grafting-through copolymerization with COE; a subsequent hydrogenation step transformed the PCOE-g-aPP into the desired PE-g-aPP. (62) While similar syntheses have been demonstrated, (63,64) the use of a COE-terminated macromonomer allowed for a graft-through approach that gave researchers unprecedented control over side chain length and grafting density in a well-defined PE-g-aPP copolymer. (62) Beyond these academic developments, ongoing efforts at Dow have developed a method for generating olefinic BCPs using a known metallocene catalyst combined with an innovative “chain shuttling agent” (65) to be used as compatibilizers (66) and tie layers. (67) From these examples, it is clear that synthetic innovations do not necessarily stem from a dramatic or singular discovery but instead usually arise from the refinement and creative application of previous syntheses.
Because of the incredible diversity in structure, number, and connectivity of blocks in BCPs, investigation in this field is guided primarily by (1) available synthetic routes for achieving the desired molecular architecture and (2) predictive theoretical models that enable rational molecular design. (27) With the increased accessibility of polymer architectures, questions arise regarding how to make appropriate comparisons between them. For example, what would be the appropriate diblock copolymer comparison for a multiblock grafted copolymer? How can performance metrics between structurally dissimilar architectures be standardized to allow for relevant comparison? Seemingly small structural changes, like the addition of a block or a difference in block connectivity or sequence, can have repercussions on properties. While it has been shown that molecular weight dispersity can drive large changes in bulk self-assembly, (68−70) only recently has polydispersity been investigated in the context of blend compatibilization. (71) Similar investigations are now taking place around the use of MBCP compatibilizers and the results show great promise. (18,35,36,58)

3. Linear Multiblock Copolymer Compatibilizers

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When considering systems beyond the conventional diblock, an immediately evident possibility is the MBCP architecture. The simplest MBCP architecture is an extension of the conventional diblock copolymer, where blocks are connected linearly to generate a linear multiblock copolymer (lMBCP). One can imagine that lMBCPs could similarly segregate to an interface to span and reinforce two homopolymer domains; rather than crossing the interface a single time as with a diblock copolymer, lMBCPs can cross the interface multiple times, effectively “stitching” the domains together. Assuming localization to the interface and appropriate segregation of the multiblock components to their respective homopolymer domains, the number of interface crossings scales with number of blocks (n) in the copolymer. This is shown schematically in Figure 4.

Figure 4

Figure 4. Depiction of several MBCPs (n > 2) stabilizing a polymer–polymer interface, highlighting the increased number of interface crossings per molecule with an increased number of blocks.

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Eagan and Xu et al. synthesized both tetrablock and hexablock PE-iPP copolymers directly from ethylene and propylene monomers using a hafnium-based living catalyst. (18,35) To simulate recycling, HDPE/iPP blends were prepared by melt blending with lMBCP additives in a single microcompounding step. As shown in Figure 5, the blends achieved a strain-at-break of ∼500% with only 1 wt % of the lMBCP compatibilizer, a significant improvement from the ∼10% strain-at-break for neat blends prepared without compatibilizer. (18) Also, the interfacial adhesion between HDPE and iPP films was significantly strengthened when a PE-iPP lMBCP was employed as a tie layer in multilayer laminates (peel strength > 6 vs < 0.5 N/mm for HDPE/iPP films). In the same work, researchers found that a traditional diblock copolymer with comparable block length performs worse as both a compatibilizer (Figure 5, strain at break 90% vs 500% for lMBCP) and a tie layer (peel strength ∼ 1 vs > 6 N/mm for lMBCP). For these diblock copolymers to show comparable performance they must be higher in molecular weight and concentration (ca. 5 wt %) than analogous MBCPs. Similarly, Nomura et al. synthesized PET-PE MBCPs for compatibilizing a PET/LLDPE system. They found that 2 wt % addition of lMBCP could convert brittle 80/20 PET/LLDPE blends (strain at break ∼10%) to ductile compatibilized blends (strain at break ∼400%). In contrast, analogous blends containing triblock copolymer with comparable block length exhibited strain at break of only ∼13%. In addition, as an interfacial tie layer, lMBCP increased the interfacial adhesion between PET and LLDPE over two orders of magnitude, while the triblock copolymer counterpart only increased adhesion by four times, compared to without a tie layer. These results also indicate that lMBCPs outperform triblock copolymers at comparable block length. (36) It is clear from these findings that lMBCPs compatibilizers pose a competitive alternative to traditional diblock copolymers, but more work remains to understand the underlying mechanisms of their enhanced performance as well as the limits of the architectural advantage (e.g., the trade-off between anchoring ability and diffusivity when increasing block number and molecular weight).

Figure 5

Figure 5. Uniaxial tensile elongation of PE/iPP materials and blends. Materials were melt-blended at 190 °C without BCPs (black) or with 1 wt % diblock (green), 1 wt % tetrablock (orange), or 5 wt % tetrablock copolymers (purple). These materials were then compression molded into tensile specimens at 180 °C and tensile tested at a rate of 100%/min (Adapted with permission from the work of Eagan et al. (35) Copyright 2017 AAAS).

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3.1. Mechanisms of Enhanced Compatibilizer Performance

In diblock copolymers, the performance is determined largely by two factors: areal density (which scales with localization at the interface) and molecular weight (which dictates the polymer–polymer interaction in the homopolymer domains). (19,72) As shown in Figure 4, lMBCPs can cross the interface between two homopolymers multiple times. In a conventional diblock copolymer, a sufficiently high block length can result in entanglement of the blocks with the homopolymer domains, thereby strengthening the interface and reducing the possibility of failure by chain pullout. Based on theories concerning chain entanglements in homopolymers, a critical molecular weight (Mc), determined to be two to three times the molecular weight between entanglements (Me), is often required to observe the effects of entanglement. (73) When considering entanglement across an interface, a shift in interfacial failure mechanism can be observed at four to five times the molecular weight of entanglement. (72) In the case of lMBCP, entanglements can also be formed with midblocks which results in the possibility of “trapped entanglements”, instead of only end-blocks as for diblock copolymers, shown schematically in Figure 6. Eastwood et al. experimentally probed this question of midblock entanglement in lMBCP compatibilizers using diblocks and pentablocks and found that the failure mechanism changed at much lower molecular weights for midblocks than for chain ends (100 kg/mol for diblocks vs 30 kg/mol for pentablocks), suggesting that the conformational constraints imposed by molecular self-assembly characteristics at the interface improve midblock entanglement. (73) This phenomenon has been predicted by Monte Carlo simulations of MBCP systems. (74) While it is well understood that the chain ends of BCPs can fail by chain-pullout, the behavior of entangled midblocks (e.g., relaxation time and failure mechanism) and the molecular weight dependence of these phenomena remain opportunities for further investigation. (73) Quantifying how entanglements scale with lMBCP structure will prove key to designing optimized MBCP to compatibilize complex polymer blends.

Figure 6

Figure 6. Schematics of lMBCP forming trapped entanglements and cocrystallizing with homopolymers.

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For semicrystalline polymers (e.g., PE, iPP, PET), another anchoring mechanism is available between the lMBCP and the homopolymers: cocrystallization (Figure 6). The block molecular weight necessary for cocrystallization to occur is typically higher than that for trapped entanglements because (1) polymer chains must fold into the crystal structure and (2) the BCP needs to be long enough to span the amorphous interfacial width to colocate with the crystalline homopolymer domains. (18) When using a PE-iPP lMBCP with sufficiently large blocks as a tie layer between iPP and HDPE films, Xu et al. observed crystal formation near the interfaces between lMBCP and the homopolymers and proposed cocrystallization as contributing to the observed toughening. (18) However, further experimentation is needed to definitively confirm that the lMBCP is incorporated into the crystalline domains of the homopolymers, possibly through polymer labeling and high spatial-resolution analytical techniques. With cocrystallization, it has been shown for polyethylene and its copolymers containing small amounts of acetate or ethyl branches that the temperature at which the crystallite melts can become intermediary to that of the two individual components. (75) This effect, while small, in compatibilized blends where the vast majority of crystallites are usually composed of homopolymer, could provide an interesting property to study further in the presence of cocrystallizable MBCPs. Further, when crystallization occurs near an interface between two polymer domains with sufficient differences in crystallization rates, the volume contraction associated with crystallization can effectively pull material across the interface (a process known an “local crystallization”). (76) This process can presumably occur concurrent to cocrystallization but has only been demonstrated at noncompatibilized polymer interfaces. Investigating this phenomenon with lMBCP compatibilized interfaces could give insight into toughening mechanisms.
MBCPs have achieved successful compatibilization at impressively low concentrations (ca. 0.5 wt % or lower) (36) relative to the current industrially utilized reactive compatibilizers (5–20 wt %). (42−44) This is a very encouraging indication that this technology could be realized industrially as it would reduce the amount of required additive and therefore lower the cost of implementation. A possible explanation for the increased efficiency of lMBCPs is that they can more easily localize to the interface (thereby outcompeting micellization). Micellization of diblock copolymers in homopolymers has been rigorously investigated. It has been observed that diblock copolymers readily form micelles in the major blend components─a feature that reduces compatibilization─and the tendency of micelle formation further increases with higher molecular weight. In contrast, there have been few studies on the micellization behavior of lMBCP in homopolymers. To help bridge this gap in our understanding, more systematic investigations on micellization as a function of MBCP physical parameters (e.g., block asymmetry, block molecular weight, number of blocks) are needed. A clear understanding of the design space of MBCPs will help understand the apparent high efficiency displayed by many MBCP compatibilizers and translate this technology to recycling solutions.

3.2. Future Work and Challenges

With the recently demonstrated successes of lMBCP as polymer blend compatibilizers, these materials are quickly gaining interest as a research area rife with opportunity. As discussed previously, trapped entanglements and cocrystallization of an lMBCP with a homopolymer can occur simultaneously to synergistically strengthen interfaces, but future experiments could work toward isolating either mechanism to better understand its contribution to overall performance. For example, polymer crystallinity is strongly process- and molecular architecture-dependent; therefore, with strategic material design and clever manipulation of processing conditions, the two mechanisms may be decoupled. This would enable a great opportunity for investigating their interplay in defining blend performance. Studies in this direction have revealed the limitations of current characterization techniques (e.g., peel tests) (18) suggesting that development in both the materials of study and methods of study will be necessary to elucidate a clearer understanding of the system. Further, the use of amorphous model blends entirely eliminates the possibility of cocrystallization, thereby isolating the contribution of trapped entanglements. Strategic investigation of an amorphous system could yield many insights into the nature of trapped entanglements in MBCP-compatibilized blends.
Beyond these opportunities, many challenges still exist to further develop a theoretical framework for guiding material design of lMBCP compatibilizers. In blend compatibilization, vigorous melt mixing aids transport and migration of compatibilizer to the interface. Preliminary work seems to suggest that lMBCPs are more effective than diblock copolymers at localizing to the interface, but direct observation of the relative transport through homopolymers to interfaces has not yet been realized. Further, a complete physical understanding of factors driving the difference in localization is lacking yet would be incredibly beneficial for molecular (re)design of optimal compatibilizers. For example, factors like micelle formation and segregation strength affect the ability to localize to an interface but are strongly coupled and require careful study to deconvolute. (77) Importantly, there is a wealth of theory and simulation studies aimed at understanding the behavior of diblock copolymers in homopolymers blends, (32,74,78−81) but fewer have extended these investigations to lMBCPs. (82−84) Some simulation work has been done on MBCPs in solution, (85,86) highlighting some of their interesting assembly behavior, and applying similar efforts to MBCPs in homopolymer could be highly informative in the field for guiding experimental work.
Translating a mechanistic understanding into an efficient processing technique is also critical for further developing this technology. For example, if lMBCPs segregate efficiently to polymer–polymer interfaces, should they be incorporated directly into homopolymers as latent compatibilizers for ready to recycle opportunities after their initial use? Alternatively, given their competitive performance as adhesive tie layers, should lMBCPs be incorporated into products as tie layers in place of conventional adhesives such that they can readily compatibilize the resulting mixed polymer waste stream after use? Already there are innovative commercial products exploring these ideas with olefinic BCPs, but numerous opportunities for industrial and academic study still remain.

4. Grafted Multiblock Copolymer Compatibilizers

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Another polymer architecture that has garnered interest for its potential use as a compatibilizer is the grafted multiblock copolymer (gMBCP). Recalling Figure 2iii, these molecules consist of a polymer backbone that is miscible with one phase of the blend and has grafted side chain polymers that are miscible with the other polymer in the blend. While these polymers can also be considered MBCPs owing to the multiple blocks that comprise them, they differ from lMBCP in their block interconnectivity. In contrast to lMBCP compatibilizers that cross back and forth across the interface, gMBCP compatibilizers have multiple grafted chains which can only cross the interface once, with the chain-ends of one block type located in one of the blend components. As a result of this architectural difference, only the backbone of gMBCP compatibilizers can form trapped entanglements, as opposed to both block types in lMBCPs. However, because gMBCPs have multiple grafted blocks, a single gMBCP may stitch the interface more than once. (87) This effect seems to be supported by other studies that have shown increased compatibilization with increasing grafting density, paralleling the argument of increased blocks in lMBCPs. (64) Another important consideration in the case of gMBCPs is the choice of which polymer should compose the backbone block versus grafted blocks because of the difference in their interactions with the homopolymer. The backbone of a gMBCP is constrained nearer to the interface and presents the opportunity for trapped entanglements, whereas the gMBCP grafted blocks consist of a single chain-end with more conformational freedom (shown in Figure 7). As a result of this asymmetry, differences arise when the backbones are included in the major phase versus the minor phase of a blend that should be considered when designing gMBCP. Though the aforementioned studies focused on preformed gMBCPs, these molecules are often generated in situ. While it is certainly more convenient for processing to form gMBCPs in situ, it also makes it more challenging to elucidate structure–performance relationships because the compatibilizers are not being isolated and rigorously characterized. For this reason, many investigations use polymer syntheses that allow for precise architectural control to help probe the variable space thereby informing future design of reactive systems.

Figure 7

Figure 7. Schematic of reactively formed graft copolymers. Reactive groups must both be present at the interface to form the compatibilizer.

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4.1. Premade Versus Reactive Graft Multiblock Copolymer Compatibilizers

Like linear copolymers, graft copolymer compatibilizers can either be premade prior to melt mixing or formed in situ through reactions between functional groups on each polymer (Figure 7). Premade graft copolymers can be synthesized through a variety of methods such as graft-to (i.e., reacting an end-functionalized chain with dispersed functionalities on a backbone) (46) or by graft-from (i.e., using functional groups along the backbone to initiate the growth of the pendant chains). (88) With recent advances in catalyst technology, it is now also possible to synthesize macromonomers containing the desired graft chain, and copolymerize these macromonomers with a graft-through approach. (55) Premade graft copolymers and the controlled polymerization techniques used to make them provide the framework for systematic studies of the variables that affect compatibilization (e.g., backbone/side chain length and grafting density/spacing). Recent work in this field has shown that the addition of PE-g-iPP (gMBCP) to a 70/30 blend of HDPE/iPP increased strain at break from 18 to ∼900% and more than halved the average minority component droplet size. (64) Moreover, it was shown that increasing the number and length of grafted chains─thereby increasing the number and strength of “anchors” afforded by entanglements and/or cocrystallization on each side of the interface─led to improved mechanical performance. Studies like this have started to explore the structural parameter space that can be accessed through new synthetic methods and are crucial for developing the necessary understanding to allow for rational design of compatibilizers in the future.
The insight gained from these investigations on premade gMBCPs can be applied to systems that reactively form gMBCPs. The precursors to these reactively formed copolymers are typically functionalized versions of an unreactive phase (often a polyolefin like PE) which has had functional groups incorporated into the backbone by either copolymerization or grafting techniques. (6) One advantage of using these functionalized polymers to form graft copolymers in situ is that there is already a library of these functional polymers to choose from due to their use as tie layers in multilayer films. (6) Moreover, we believe that forward-thinking design of multilayer systems to incorporate these functionalized polymers as tie layers that can function downstream as compatibilizers can open up new and exciting recycling pathways. This idea of integrating compatibilizers into tie layers is already being employed industrially to allow multilayer packaging films to enter recycling streams. (67,89)
Along with the design factors associated with premade graft copolymers, reactive systems bring an added layer of complexity in the form of reaction rates for generating in situ gMBCPs. In a 2001 study, Orr et al. characterized a wide array of functional pairs commonly used for in situ compatibilization. (45) They found that an amine/anhydride had by far the fastest reaction rate, with the next fastest reaction measured (acid/epoxy) being almost two orders of magnitude slower. These results explain why anhydride functionalized polymers are utilized in most multilayer materials. However, we believe that by understanding the other underlying factors controlling reactivity, compatibilizers derived from slower coupling chemistries may become more viable. Functional groups with reduced reactivity tend to be more shelf-stable and less expensive, making them more attractive. The intrinsic reactivity of a functional group pair is thermodynamically driven, but the apparent reaction rate is largely governed by kinetic factors. Therefore, less reactive pairs can be accelerated by increasing the availability of functional groups at the interface. It has been found that droplet size distributions decrease when a reactive backbone is mixed directly with its complementary phase (i.e., mixing it in the phase with complementary reactive groups) as compared to premixing it with the phase it matches (i.e., putting it in the miscible phase and hoping it finds its way to the interface to react). (43) Likewise, aggressive mixing can help mitigate slow intrinsic reaction rates, having been shown to increase effective reaction rates by almost two orders of magnitude compared with static annealing. (46) These results suggest that reactive gMBCP performance is determined not just by the final polymer structure but by the processing conditions used to drive the copolymer formation. These preliminary findings indicate that gMBCPs could offer competitive performance to lMBCPs, but further investigations are necessary to understand and optimize the design of these compounds.

4.2. Future Work and Challenges

Despite their prevalence as compatibilizers and tie layers, a systematic understanding of the factors surrounding the compatibilization efficiency of gMBCPs has not yet been established. Current studies with tightly controlled graft architecture have had the copolymer backbone miscible with the majority component of the blend, but could similar improvements in performance be gained with the backbone in the minority phase and grafted side chains extending into the matrix? Similarly, how would performance be affected if both variants of the grafted copolymers (backbone in majority phase and backbone in minority phase) were concurrently introduced to a blend? It has been shown that, when the grafted side chains are miscible with the dispersed phase (and the backbone with the matrix), compatibilization decreases due to chain pullout of the grafts, (90) so more deeply exploring the effects of this asymmetry is imperative for understanding gMBCP function. This asymmetry can be taken a step further by introducing grafted chains that are copolymers themselves. Leveraging insights gained from investigations of BCP compatibilizers, random copolymer grafted side chains could be introduced to increase the width of the interfacial region; tapered copolymer grafted side chains could also be studied for their previously demonstrated improvements to compatibilization.
More questions arise as to how transport of these graft polymers can be manipulated to maximize the amount of polymer that localizes to the interface. Specifically, it would be interesting to explore the effect of polymer miscibility (of both the backbone and the side chains) on localization behavior as well as differences in micellization behavior of gMBCPs formed in situ versus ex situ. In reactive systems requiring small molecule catalysts, it was seen that the most effective catalysts were those with solubility parameters in between the two polymers being compatibilized, causing them to localize at the interface (an analogous trend to what has been observed with diblock copolymers). (91) Could strategies for tethering catalysts be used to improve reaction rates and circumvent solubility issues? Similarly, it has been observed that higher molecular weight polymer backbones can improve segregation to the interface and toughening of the interface (through previously described entanglement/cocrystallization mechanisms) but can hinder diffusion through the bulk. While it is known that higher molecular weight can promote micellization in diblock copolymers, it is not yet clear if the same is true for gMBCPs nor how limiting micellization of gMBCPs might be for compatibilization. Is there an optimal backbone length and/or grafting density to maximize localization to the interface? Or is it a nuanced relationship that must consider the identity of the backbone and the immiscible phase? Encouraged by preliminary studies, we believe the opportunities for gMBCP compatibilizers are plenty, but to achieve them we must first take a step back and closely consider the roles of the building blocks of the system.

5. Beyond Binary Blends

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As the value of BCPs becomes more and more apparent for use as compatibilizers in mixed waste stream recycling, questions arise as to future directions and commercial implementation of these materials. To this point, the majority of studies have focused mostly on two phase systems (often some mixture of a polyolefin and either another polyolefin, (18,35,92) a polyurethane, (93−95) a polyester, (36,96,97) or a polyamide (24,98,99)). However, a simple examination of the contents of any recycling bin reveals a wide array of materials that may at some point end up in a solid plastic waste stream together. Though current separation techniques (e.g., flotation, physical sorting, etc.) can enrich streams toward a single material, remaining impurities are highly variable in time and by source and difficult to predict. The net result of these difficulties is a highly inefficient process. This dilemma highlights a major need for advancing recycling technology. To date, significant advances have been made with model, virgin polymers, and their blends, but it is as of yet unclear how these will translate to real waste streams. The establishment of a series of models for more realistic plastic waste stream standards would allow researchers to study more relevant systems while enabling comparisons across laboratories. However, this is a formidable task as it is difficult to imagine what a prototypical realistic model waste stream might look like. Is it majority polyolefin? Are ternary blends or higher order mixtures most appropriate? These are complex questions from a materials standpoint that are necessarily intertwined with societal behaviors, industrial practices, and waste collection infrastructure which complicate an already convoluted problem. (100)
Importantly, strategies are emerging to address blends that are beyond binary. Recent work has demonstrated gMBCP compatibilizers can be effective for ternary PP/PA6/PS (101) (as shown in Figure 8) and PP/PA6/SEBS (102) blends. These blend compositions were specifically chosen to contain three mutually immiscible components because if any two components were miscible then it could be approximated as a binary blend and not a true ternary blend. Further, the blend choice encompasses the three major divisions of commercial consumer plastics: polyolefins, engineering plastics, and styrene-based polymers. This work represents an ambitious new direction in the field of using highly tailored MBCP compatibilizers to address more complex multicomponent blends that better simulate real-life waste streams. The compatibilizer precursor that is dispersed into the ternary blend is a polypropylene backbone grafted with side chains of maleic anhydride-styrene copolymers (PP-g-(MAH-co-PS)); the maleic anhydride can react in situ with amine groups on PA6 to generate the final gMBCP structure (PP-g-((MAH-g-PA6)-co-PS)). This synthetic approach of having reactive grafting groups within a grafted side chain shows great promise and could theoretically be extended to blends with even more than three components. As shown in Figure 8, when compatibilizing ternary systems there are many more interactions that must be taken into consideration. While this inherently complicates the design of compatibilizers, MBCPs offer an efficient materials platform for encoding various interactions and parameters into a single molecule.

Figure 8

Figure 8. Interplay between phases and compatibilizer in preliminary ternary system studies (Adapted with permission from ref (101). Copyright 2011 Elsevier Ltd.).

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Considering the aforementioned demonstrations of reactive gMBCP compatibilizers for ternary blends, the question naturally arises about whether a premade MBCP compatibilizer (linear or graft) with three or more distinct polymer chemistries could also be effective for multicomponent blends. As shown in Figure 3, there exists a wide range of potential connectivity for diblock copolymers, but for MBCPs the potential connectivity and order of the blocks expands exponentially. (51) For example, moving from a diblock to a triblock expands the potential unique connectivities from one to three (i.e., while a linear diblock will always be an AB copolymer, a linear triblock can exist as ABC, ACB, and CAB copolymers). Moving from a linear polymer to more complex architectures (e.g., grafted copolymer and star copolymer) further confounds the possibilities. Given the enormity of possible polymer and architecture combinations, discovering effective compatibilizers will require strategic and targeted investigations. One particularly interesting architecture is the miktoarm star copolymer (where mikto means “mixed”). One can imagine a single star copolymer with a separate arm for each of several major recyclable polymer classes working as a “one-size-fits-all” compatibilizer. Similarly, a graft copolymer system with various arms of distinct polymer types (i.e., a “mikto”-grafted MBCP) could be developed to address multicomponent blends. And there is no reason to limit these systems to homopolymer side chains; a star or grafted MBCP could be composed of diblock, gradient, or even random copolymer side chains to improve interactions with specific interfaces. While it is unknown whether these molecular designs could outperform conventional compatibilizers, they illustrate the numerous opportunities for impactful investigation on polymer architecture in this field. With the many developments in polymer synthesis, newly accessible structures could bring us closer to a “universal compatibilizer”, but first, the basic principles surrounding the effectiveness of these new and exciting architectures must be understood.

6. Outlook

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In recent years, lMBCP and gMBCP architectures have been used to compatibilize polymer blends and multilayer films. In the absence of compatibilizers, polymer blends have poor mechanical performance due to poor stress transfer across the interface. However, MBCP compatibilizers have been shown to effectively mitigate this issue by improving interfacial adhesion, at concentrations lower than those necessary for diblock copolymer compatibilizers. These results demonstrate the great potential of MBCPs for opening new pathways to recycle mixed plastic waste. Mechanical mixing has historically been viewed as “downcycling” because the resulting blends generally had inadequate properties due to degradation, additives, and molecular weight variability. With the development and optimization of modern compatibilizers, this old paradigm is quickly shifting. Properly compatibilized blends can have properties intermediate to their constituent parts and well within range of some commercial materials. Just like any other materials selection process in product design, we need to recognize that compatibilizers are not a one-size-fits all solution for all mixtures, rather successful outcomes require strategic implementation derived from leaning on knowledge of polymer chemistry, physics, and processing. Ultimately, the combination of compatibilization techniques and appropriate choice of application could valorize much of the solid plastic waste that is currently being lost to the environment, burned for energy, or deposited in landfills.
This is an area rich with many fundamental questions that need to be answered. For both lMBCPs and gMBCPs, we need to develop a better understanding of their diffusion, micellization, and localization behavior, both in homopolymer and in mixed blends, as well as the underlying mechanisms of their stabilization. Simultaneously, we must develop effective methods for incorporating compatibilizers into real life waste streams. In the same vein, extending fundamental research efforts from binary blends into the reality of multicomponent waste streams will be crucial to their successful implementation. Not only will these streams have multiple plastic components, but also various additives, such as pigments, dyes, stabilizers, nucleating agents, and particulates, that will complicate compatibilization. MBCPs offer a potentially exciting material solution to these issues, but our nascent understanding of their use as compatibilizers requires further development. With the multitudinous synthetic advancements of recent years, researchers are granted enormous freedom and flexibility in the design of these molecules which greatly enables new studies. Overall, progress in the field of BCP compatibilizers is guiding us toward a path for bringing plastic waste into a circular economy, but many exciting challenges lie ahead before we can close the loop.

Author Information

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  • Corresponding Author
  • Authors
    • Jeffrey L. Self - Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States;  Orcidhttps://orcid.org/0000-0002-9394-4582
    • Aristotle J. Zervoudakis - Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States;  Orcidhttps://orcid.org/0000-0002-4758-1784
    • Xiayu Peng - Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States;  Orcidhttps://orcid.org/0000-0002-6216-7493
    • William R. Lenart - Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States;  Orcidhttps://orcid.org/0000-0002-3660-256X
    • Christopher W. Macosko - Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States;  Orcidhttps://orcid.org/0000-0002-2892-3267
  • Author Contributions

    J.L.S., A.J.Z., X.P., and W.R.L. made equal contributions. The manuscript was written through contributions of all authors.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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We acknowledge our principal funding source, the National Science Foundation Center for Sustainable Polymers at the University of Minnesota, which is a National Science Foundation supported Center for Chemical Innovation (CHE-1901635).

References

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    Macromolecules (Washington, DC, United States) (2018), 51 (21), 8585-8596CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A series of isotactic polypropylene (iPP) and polyethylene (PE) diblock, tetrablock, and hexablock copolymers (BCPs) were synthesized with tunable mol. wts. using a hafnium pyridylamine catalyst. The BCPs were melt blended with 70 wt. % high-d. PE (HDPE) and 30 wt. % iPP com. homopolymers at concns. between 0.2 and 5 wt. %. The resulting blend morphologies were investigated using TEM, revealing uniformly dispersed iPP droplets ranging progressively in size with increasing BCP content from three-quarters to one-quarter of the diam. of the uncompatibilized mixt. Tensile tests revealed a dramatic enhancement in toughness based on the strain at break which increased from 10% for the unmodified blend to more than 300% with just 0.2 wt. % BCP and over 500% with the addn. of 0.5 wt % BCP or greater. Incorporation of BCPs in blends also improved the impact toughness, doubling the Izod impact strength to a level comparable to the neat HDPE with just 1 wt. % additive. These improved blend properties are attributed to enhanced interfacial strength, which was independently probed using T-peel adhesion measurements performed on laminates composed of HDPE/BCP/iPP trilayers. Thin (ca. ≤100 nm thick) BCP films, fabricated by high-temp. spin coating and molded between the homopolymer films, significantly altered the laminate peel strength, depending on the mol. wt. and mol. architecture of the block copolymer. Multilayer laminates contg. no BCP or low mol. wt. diblock copolymer sepd. by adhesive failure during peel testing. Sufficiently high mol. wt. iPP-PE diblock copolymers and iPP-PE-iPP-PE tetrablock copolymers with significantly lower block mol. wts. exhibited cohesive failure of the HDPE film rather than adhesive failure. We propose adhesion mechanisms based on mol. entanglements and cocrystn. for tetrablocks and diblocks, resp., to account for these findings. These results demonstrate exciting opportunities to recycle the world's top two polymers through simple melt blending, obviating the need to sep. these plastics in mixed waste streams.
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    Gaylord, N. G. Compatibilization Concepts in Polymer Applications. Advances in Chemistry 1975, 142, 76– 84,  DOI: 10.1021/ba-1975-0142.ch007
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    Compatibilization concepts in polymer applications
    Gaylord, Norman G.
    Advances in Chemistry Series (1975), 142 (Copolym., Polyblends, Compos., Sym., 1974), 76-84CODEN: ADCSAJ; ISSN:0065-2393.
    A review with 21 refs. Introduction of a compatibilizing agent, i.e. block or graft copolymers having segments of similar structure or soly. parameter, permitted the blending of incompatible polymers and enhanced the dispersion of fillers and reinforcing agents.
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    Macosko, C. W.; Guégan, P.; Khandpur, A. K.; Nakayama, A.; Marechal, P.; Inoue, T. Compatibilizers for Melt Blending: Premade Block Copolymers. Macromolecules 1996, 29 (17), 5590– 5598,  DOI: 10.1021/ma9602482
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    Compatibilizers for Melt Blending: Premade Block Copolymers
    Macosko, C. W.; Guegan, Philippe; Khandpur, Ashish K.; Nakayama, Akinari; Marechal, Philippe; Inoue, Takashi
    Macromolecules (1996), 29 (17), 5590-5598CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Poly(Me methacrylate) (PMMA) was melt mixed 30:70 into polystyrene (PS) with and without sym. P(S-b-MMA) diblock copolymers. The mol. wt. of the components was varied. After 5 min of shear mixing, the PMMA was dispersed into roughly spherical, submicron particles. Particle size was measured by light scattering and transmission electron microscopy. As little as 1% copolymer led to a significant redn. in PMMA particle size, although larger amts. were needed to make the particles stable to annealing (180° for 15 min). The main role of block copolymers in controlling morphol. appears to be in preventing coalescence. Preventing dynamic coalescence leads to size redn., while preventing static coalescence results in stability or compatibilization. We est. that less than 5% of the interface needs to be covered to prevent dynamic coalescence while ∼20% is necessary to impart static stability. Mobility, crit. micelle concn., and mol. wt. of the block copolymer also appear to be important. Lowering the mol. wt. of the PMMA phase from 43,000 to 11,000 resulted in dramatically lower particle size (700 vs 60 nm). These variables are discussed in terms of a qual. balance between rate of diffusion and rate of area generation during blending.
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    Noolandi, J.; Hong, K. M. Interfacial Properties of Immiscible Homopolymer Blends in the Presence of Block Copolymers. Macromolecules 1982, 15 (2), 482– 492,  DOI: 10.1021/ma00230a054
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    Interfacial properties of immiscible homopolymer blends in the presence of block copolymers
    Noolandi, J.; Hong, K. M.
    Macromolecules (1982), 15 (2), 482-92CODEN: MAMOBX; ISSN:0024-9297.
    The emulsifying effect of block copolymers in immiscible homopolymer blends was studied using a formalism for inhomogeneous, multicomponent polymer systems previously developed. The redn. in interfacial tension with increasing block polymer concn. was calcd. for a range of copolymer and homopolymer mol. wt. and compared with the data of G. Riess et al. (1980) for polystyrene [9003-53-6]-polybutadiene [9003-17-2]-butadiene-styrene block polymer [9003-55-8] blends. The calcd. interfacial d. profiles show increasing exclusion of homopolymers from the interphase region with increasing block polymer mol. wt. The crit. concn. of block polymer for micellar aggregation in the bulk of the homopolymer was detd.
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    Galloway, J. A.; Jeon, H. K.; Bell, J. R.; Macosko, C. W. Block Copolymer Compatibilization of Cocontinuous Polymer Blends. Polymer 2005, 46 (1), 183– 191,  DOI: 10.1016/j.polymer.2004.10.061
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    Block copolymer compatibilization of cocontinuous polymer blends
    Galloway, Jeffrey A.; Jeon, Hyun K.; Bell, Joel R.; Macosko, Christopher W.
    Polymer (2005), 46 (1), 183-191CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    The effect of block copolymers on the cocontinuous morphol. of 50/50 (wt./wt.) polystyrene (PS)/high d. polyethylene (HDPE) blends was investigated using sym. polystyrene-polyethylene block copolymers (PS-PE) with mol. wts. varying from 6 to 200 kg/mol. The coarsening rate during annealing was compared to the Doi-Ohta theory. An intermediate mol. wt. PS-PE, 40 kg/mol, showed remarkable results in reducing the phase size and stabilizing the blend morphol. during annealing. Mixing small amts. of 6, 100 or 200 kg/mol PS-PE in the blend did not reduce the phase size significantly, but did decrease the coarsening rate during annealing. In stabilizing the morphol., 6 kg/mol PS-PE was inferior to 100 and 200 kg/mol. The existence of an optimal mol. wt. block copolymer is due to a balance between the ability of the block copolymer to reach the interface and its relative stabilization effect at the interface.
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    Chang, K.; Macosko, C. W.; Morse, D. C. Interfacial Tension Measurement and Micellization in a Polymer Blend with Copolymer Surfactant: A False Critical Micelle Concentration. Macromolecules 2015, 48 (22), 8154– 8168,  DOI: 10.1021/acs.macromol.5b01268
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    Interfacial Tension Measurement and Micellization in a Polymer Blend with Copolymer Surfactant: A False Critical Micelle Concentration
    Chang, Kwanho; Macosko, Christopher W.; Morse, David C.
    Macromolecules (Washington, DC, United States) (2015), 48 (22), 8154-8168CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The interfacial tension between polystyrene (PS) and polybutadiene (PB) homopolymers is measured in the presence of a nearly sym. poly(styrene-b-butadiene) (SB) copolymer and compared to independent measurements of the crit. micelle concn. (CMC) by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), and to SCF theory (SCFT) predictions. Interfacial tension is measured with a spinning drop tensiometer (SDT) contg. a drop of PB in a PS matrix, using samples in which varying concns. of SB copolymer were initially added to either PS or PB. When SB is premixed with PS, the dependence of the interfacial tension γ upon copolymer concn. c is qual. similar to that expected in equil., showing a decrease of γ with increasing c for c less than an apparent CMC and then satg. at higher concns. TEM and SAXS studies of a binary mixt. of the same copolymer and PS homopolymer show, however, that the true CMC in PS is much lower than the apparent CMC inferred from these SDT expts. We analyze the role of transport limitations in this expt. and propose that this discrepancy may be a result of a suppressed copolymer chem. potential near the interface due to continual diffusion of copolymer into the PB drop.
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    Willis, J. M.; Favis, B. D. Processing-morphology Relationships of Compatibilized Polyolefin/Polyamide Blends. Part I: The Effect of an Lonomer Compatibilizer on Blend Morphology. Polym. Eng. Sci. 1988, 28 (21), 1416– 1426,  DOI: 10.1002/pen.760282111
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    Processing-morphology relationships of compatibilized polyolefin/polyamide blends. Part I. The effect of an ionomer compatibilizer on blend morphology
    Willis, J. M.; Favis, B. D.
    Polymer Engineering and Science (1988), 28 (21), 1416-26CODEN: PYESAZ; ISSN:0032-3888.
    The addn. of Surlyn 9020 (I) compatibilizer to HDPE- and isotactic polypropylene-nylon 6 blends increased the dispersion and decreased the particle size of the dispersed phase as shown by SEM of the fracture-surface morphol. For a dispersed phase content of 10%, a max. redn. in phase size was obsd. when only 0.5% I was added to the blend. Mol. interaction between I and nylon 6 resulted in a greater redn. in the phase size of dispersed nylon compared to that of dispersed polyolefin. Flocculation of the nylon dispersed phase was obsd. at high I concns. The blend morphol. was also dependent on the mode of addn. of I. In comparison to 1-step mixing, blends prepd. by 2-step or batch mixing exhibited a smaller dispersed phase when nylon was the matrix and a larger particle size when nylon was the minor phase.
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    Zhang, C. L.; Feng, L. F.; Gu, X. P.; Hoppe, S.; Hu, G. H. Efficiency of Graft Copolymers as Compatibilizers for Immiscible Polymer Blends. Polymer 2007, 48 (20), 5940– 5949,  DOI: 10.1016/j.polymer.2007.07.042
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    Efficiency of graft copolymers as compatibilizers for immiscible polymer blends
    Zhang, Cai-Liang; Feng, Lian-Fang; Gu, Xue-Ping; Hoppe, Sandrine; Hu, Guo-Hua
    Polymer (2007), 48 (20), 5940-5949CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    This work was aimed at studying the emulsification efficiency of graft copolymers and the effect of feeding mode on the emulsification efficiency using the emulsification curve approach. The blends were composed of polystyrene (PS) and polyamide 6 (PA6). PS was always the matrix and PA6 the dispersed phase. A series of graft copolymers of PS and PA6, denoted as PS-g-PA6, with different mol. structures were used as emulsifiers. Feeding mode had a very significant effect on the size of the dispersed phase domains at short mixing time and its effect decreased or became negligible at long mixing time. This indicates that feeding mode affected mostly the time necessary for the PS-g-PA6 emulsifier to reach and emulsify the PS/PA6 interfaces. The mol. structure of the PS-g-PA6 graft copolymer also had a profound effect on its emulsification efficiency. The longer the PA6 grafts (from 1.7 to 5.1 kg/mol), the higher the emulsification efficiency. On the other hand, the no. of PA6 grafts had little effect on the emulsification efficiency when the PA6 grafts were short (1.6-1.7 kg/mol). The effect of the blend compn. was also investigated.
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    Lee, M. S.; Lodge, T. P.; Macosko, C. W. Can Random Copolymers Serve as Effective Polymeric Compatibilizers?. J. Polym. Sci., Part B: Polym. Phys. 1997, 35 (17), 2835– 2842,  DOI: 10.1002/(SICI)1099-0488(199712)35:17<2835::AID-POLB8>3.0.CO;2-P
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    Can random copolymers serve as effective polymeric compatibilizers?
    Lee, M. S.; Lodge, T. P.; Macosko, C. W.
    Journal of Polymer Science, Part B: Polymer Physics (1997), 35 (17), 2835-2842CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
    We investigate the compatibilizing performance of a random copolymer in the melt state, using transmission electron microscopy. Blends of polystyrene (PS) and poly(Me methacrylate) (PMMA) are chosen as a model system, and a random copolymer of styrene and Me methacrylate (SMMA) with 70 wt% styrene is used as a compatibilizer. From TEM photographs it is clear that SMMA moves to the interface between PS and PMMA domains during melt mixing, and forms encapsulating layers. However, the characteristic size of the dispersed phase increases gradually with annealing time for all blend systems studied. This demonstrates that the encapsulating layer of SMMA does not provide stability against static coalescence, which calls into question the effectiveness of random copolymers as practical compatibilizers. We interpret the encapsulation by random copolymers in terms of a simple model for ternary polymer blends.
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    Sundararaj, U.; Macosko, C. W. Drop Breakup and Coalescence in Polymer Blends: The Effects of Concentration and Compatibilization. Macromolecules 1995, 28 (8), 2647– 2657,  DOI: 10.1021/ma00112a009
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    Drop Breakup and Coalescence in Polymer Blends: The Effects of Concentration and Compatibilization
    Sundararaj, Uttandaraman; Macosko, C. W.
    Macromolecules (1995), 28 (8), 2647-57CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A limiting dispersed phase particle size exists at low concns. for polymer blends mixed in an internal batch mixer and 2 types of twin-screw extruders. The Taylor limit for breakup of a single drop in a matrix under-predicts the limiting particle size; this discrepancy is attributed to viscoelastic effects. For uncompatibilized blends, the final particle size increases with the dispersed phase concn. due to increased coalescence. The particle size distribution also broadens at higher concns. Using in-situ reaction during blending or adding pre-made diblock copolymers suppresses coalescence resulting in smaller particle size and narrower particle size distribution. Using pre-made block copolymers is not as efficient in stabilizing morphol. as using reactive polymers. The main advantage of using compatibilizers in polymer blends is the suppression of coalescence achieved through stabilizing the interface, not a redn. in the interfacial tension. There is a crit. shear rate in polymer systems where a min. particle size is achieved. A qual. explanation of why this occurs is given based on droplet elasticity.
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    Fayt, R.; Jerome, R.; Teyssié, P. Molecular Design of Multicomponent Polymer Systems, 13. Control of the Morphology of Polyethylene/Polystyrene Blends by Block Copolymers. Die Makromol. Chemie 1986, 187 (4), 837– 852,  DOI: 10.1002/macp.1986.021870414
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    Lefebvre, M. D.; Dettmer, C. M.; McSwain, R. L.; Xu, C.; Davila, J. R.; Composto, R. J.; Nguyen, S. T.; Shull, K. R. Effect of Sequence Distribution on Copolymer Interfacial Activity. Macromolecules 2005, 38 (25), 10494– 10502,  DOI: 10.1021/ma0509762
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    Effect of Sequence Distribution on Copolymer Interfacial Activity
    Lefebvre, Michelle D.; Dettmer, Christine M.; McSwain, Rachel L.; Xu, Chen; Davila, Jonathan R.; Composto, Russell J.; Nguyen, SonBinh T.; Shull, Kenneth R.
    Macromolecules (2005), 38 (25), 10494-10502CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Interfacial segregation of diblock, gradient, and random copolymers was measured using forward recoil spectrometry. The polymers were synthesized by a ring-opening metathesis polymn., allowing a high degree of control over the sequence distribution. The norbornene-based monomers have reactivity ratios close to unity, which makes them ideal for facile tailoring of different gradient copolymer profiles. The copolymers form a good weakly segregating model system for which we can obtain an est. of the interaction parameter χ. Mean-field theory was used to describe the interfacial segregation results and to relate the measured quantities to the detailed mol. structure of the interface. The diblock copolymer forms a monolayer at the interface and significantly reduces the interfacial tension, while the random copolymer forms an interfacial wetting layer. The gradient copolymer exhibits intermediate behavior, forming a monolayer with a larger interfacial width than that of the diblock copolymer.
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    Lefebvre, M. D.; Olvera de la Cruz, M.; Shull, K. R. Phase Segregation in Gradient Copolymer Melts. Macromolecules 2004, 37 (3), 1118– 1123,  DOI: 10.1021/ma035141a
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    Phase Segregation in Gradient Copolymer Melts
    Lefebvre, Michelle D.; Olvera de la Cruz, Monica; Shull, Kenneth R.
    Macromolecules (2004), 37 (3), 1118-1123CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Local segregation in melts of copolymers with compn. gradients along their backbones is analyzed. The transition to a lamellar periodic structure as the effective degree of incompatibility χN increases is studied for sym. copolymers with various compn. gradients. A numerical self-consistent mean-field (SCMF) technique is used to characterize the ordered lamellar state in the weak and strong segregation regimes, and the RPA is used to calc. the scattering function anal. and find the location of the crit. order-disorder transition for each melt. The crit. point increases from (χN)c = 10.495 for block copolymers to (χN)c = 29.25 for a fully tapered linear gradient copolymer. For broad compn. gradients the equil. lamellar repeat length is shorter for a given value of χN, and the unit cell compn. profile is more sinusoidal. The dependence of the equil. repeat distance on χN is nearly universal when renormalized by the crit. point of each copolymer.
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    Shull, K. R. Interfacial Activity of Gradient Copolymers. Macromolecules 2002, 35 (22), 8631– 8639,  DOI: 10.1021/ma020698w
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    Interfacial Activity of Gradient Copolymers
    Shull, Kenneth R.
    Macromolecules (2002), 35 (22), 8631-8639CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Numerical SCF theory is used to study the equil. segregation of A/B gradient copolymers to the interface between immiscible A and B homopolymers. A generalized SCF theory is developed that allows arbitrary compn. gradients to be investigated. The focus of this paper is on sym. copolymers consisting of equal amts. of A and B repeat units, with a linear or hyperbolic tangent compn. gradient. A gradient parameter, λ, is introduced that describes the length of the compn. gradient relative to the length of the entire copolymer mol. Crit. values of the copolymer chem. potential corresponding to the formation of copolymer micelles, or to a vanishing interfacial free energy between A and B homopolymer phases, decrease with λ, and are about 1.6kBT lower for λ = 1 than for λ = 0. The width of the concn. profile of A or B repeat units within a lamellar copolymer phase, or across an emulsified interface, increases with λ, and is equal to about twice the copolymer radius of gyration for λ = 1.
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    Levine, W. G.; Seo, Y.; Brown, J. R.; Hall, L. M. Effect of Sequence Dispersity on Morphology of Tapered Diblock Copolymers from Molecular Dynamics Simulations. J. Chem. Phys. 2016, 145 (23), 234907,  DOI: 10.1063/1.4972141
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    Effect of sequence dispersity on morphology of tapered diblock copolymers from molecular dynamics simulations
    Levine, William G.; Seo, Youngmi; Brown, Jonathan R.; Hall, Lisa M.
    Journal of Chemical Physics (2016), 145 (23), 234907/1-234907/8CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Tapered diblock copolymers are similar to typical AB diblock copolymers but have an added transition region between the two blocks which changes gradually in compn. from pure A to pure B. This tapered region can be varied from 0% (true diblock) to 100% (gradient copolymer) of the polymer length, and this allows some control over the microphase sepd. domain spacing and other material properties. We perform mol. dynamics simulations of linearly tapered block copolymers with tapers of various lengths, initialized from fluids d. functional theory predictions. To investigate the effect of sequence dispersity, we compare systems composed of identical polymers, whose taper has a fixed sequence that most closely approximates a linear gradient, with sequentially disperse polymers, whose sequences are created statistically to yield the appropriate ensemble av. linear gradient. Esp. at high segregation strength, we find clear differences in polymer conformations and microstructures between these systems. Importantly, the statistical polymers are able to find more favorable conformations given their sequence, for instance, a statistical polymer with a larger fraction of A than the median will tend towards the A lamellae. The conformations of the statistically different polymers can thus be less stretched, and these systems have higher overall d. Consequently, the lamellae formed by statistical polymers have smaller domain spacing with sharper interfaces. (c) 2016 American Institute of Physics.
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    Von Tiedemann, P.; Blankenburg, J.; Maciol, K.; Johann, T.; Müller, A. H. E.; Frey, H. Copolymerization of Isoprene with P-Alkylstyrene Monomers: Disparate Reactivity Ratios and the Shape of the Gradient. Macromolecules 2019, 52 (3), 796– 806,  DOI: 10.1021/acs.macromol.8b02280
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    Copolymerization of Isoprene with p-Alkylstyrene Monomers: Disparate Reactivity Ratios and the Shape of the Gradient
    von Tiedemann, Philipp; Blankenburg, Jan; Maciol, Kamil; Johann, Tobias; Mueller, Axel H. E.; Frey, Holger
    Macromolecules (Washington, DC, United States) (2019), 52 (3), 796-806CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    The statistical copolymn. of isoprene with p-ethyl- (p-ES), p-isopropyl- (p-iPS), and p-tert-butylstyrene (p-tBS) initiated by sec-butyllithium in cyclohexane was studied with respect to kinetics, reactivity ratios, and formation of tapered block copolymers with pronounced monomer gradient. An efficient synthetic route to the monomers was developed on a multigram scale, relying on the pptn. of the side-product triphenylphosphine oxide at low temp. The copolymn. kinetics and resulting mol. wt. distributions were analyzed. The dispersity, D, of the copolymers depends on the p-alkyl substituent, the d.p. Pn and the comonomer mole fraction, X. In situ1H NMR kinetics characterization revealed a strong gradient structure for all three copolymer systems (rI = 21.9, rp-ES = 0.022; rI = 19.7, rp-iPS = 0.027; rI = 19.8, rp-tBS = 0.022). The rate of crossover from a polyisoprenyllithium chain end (I) to a p-alkylstyrene (S) unit relative to the alkylstyrene homopolymn., kIS/kSS (in 10-3 (L mol-1)-1/4), decreases in the order p-MS (19.1) > p-ES (11.3) > p-iPS (5.71) ≈ p-tBS (5.63), supporting the obsd., increasingly bimodal character of the mol. wt. distributions and the higher dispersity. Thermogravimetric anal. revealed that all poly(p-alkylstyrene) homopolymers are stable up to 300°C.
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    Fayt, R.; Jérôme, R.; Teyssié, P. Interface Modification in Polymer Blends. Multiphase Polymers: Blends and Ionomers 1989, 58, 38– 66,  DOI: 10.1021/bk-1989-0395.ch002
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    Eagan, J. M.; Xu, J.; Di Girolamo, R.; Thurber, C. M.; Macosko, C. W.; LaPointe, A. M.; Bates, F. S.; Coates, G. W. Combining Polyethylene and Polypropylene: Enhanced Performance with PE/ i PP Multiblock Polymers. Science 2017, 355 (6327), 814– 816,  DOI: 10.1126/science.aah5744
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    Combining polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers
    Eagan, James M.; Xu, Jun; Di Girolamo, Rocco; Thurber, Christopher M.; Macosko, Christopher W.; La Pointe, Anne M.; Bates, Frank S.; Coates, Geoffrey W.
    Science (Washington, DC, United States) (2017), 355 (6327), 814-816CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Polyethylene (PE) and isotactic polypropylene (iPP) constitute nearly two-thirds of the world's plastic. Despite their similar hydrocarbon makeup, the polymers are immiscible with one another. Thus, common grades of PE and iPP do not adhere or blend, creating challenges for recycling these materials. We synthesized PE/iPP multiblock copolymers using an isoselective alkene polymn. initiator. These polymers can weld common grades of com. PE and iPP together, depending on the mol. wts. and architecture of the block copolymers. Interfacial compatibilization of phase-sepd. PE and iPP with tetrablock copolymers enables morphol. control, transforming brittle materials into mech. tough blends.
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    Nomura, K.; Peng, X.; Kim, H.; Jin, K.; Kim, H. J.; Bratton, A. F.; Bond, C. R.; Broman, A. E.; Miller, K. M.; Ellison, C. J. Multiblock Copolymers for Recycling Polyethylene-Poly(Ethylene Terephthalate) Mixed Waste. ACS Appl. Mater. Interfaces 2020, 12 (8), 9726– 9735,  DOI: 10.1021/acsami.9b20242
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    Multiblock Copolymers for Recycling Polyethylene-Poly(ethylene terephthalate) Mixed Waste
    Nomura, Keiichiro; Peng, Xiayu; Kim, Hanim; Jin, Kailong; Kim, Hee Joong; Bratton, Abigail F.; Bond, Christopher R.; Broman, Amelia E.; Miller, Kevin M.; Ellison, Christopher J.
    ACS Applied Materials & Interfaces (2020), 12 (8), 9726-9735CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Plastic pollution is one of the most pressing global environmental issues we face today, in part due to the continued rise in prodn. and use of disposable plastic products. Polyolefins and polyesters are two of the most prevalent polymers in the world accounting for ∼80% of total nonfiber plastic prodn. Recycling, despite being intrinsically environmentally friendly and sometimes economically viable, remains at a surprisingly low level (<9% in the U.S.) with most plastic waste ending up in landfills. One reason for this low rate of recycling stems from the challenge of recycling mixed waste streams and multicomponent plastics. In mixed waste streams, phys. presorting of components prior to recycling requires significant effort, which translates to added cost. For multicomponent plastics (e.g., multilayer films such as food wrappers), the individual plastic components cannot be efficiently phys. sepd., and they are immiscible with poor interfacial adhesion when melt reprocessed. Thus, direct recycling of mixed plastics by melt reprocessing results in products that lack desired end-use properties. In this study, we describe the synthesis of novel poly(ethylene terephthalate)-polyethylene multiblock copolymers (PET-PE MBCPs) and evaluate their utility as adhesive tie layers in multilayer films and compatibilizer additives for melt reprocessed blends. PET and PE are targeted because they are two of the most prevalent com. polymers in the world and are high vol. waste streams. The work described here demonstrates two key findings. First, the PET-PE MBCPs serve as effective adhesive tie layers between neat PET/PE films with adhesive strength comparable to that of com. available adhesives. Second, PET/PE (80/20 wt %) blends contg. ∼0.5 wt % PET-PE MBCP were melt mixed to mimic recycling mixed plastic waste, and they were found to exhibit mech. properties better than neat PET. Overall, this study demonstrates that PET-PE MBCPs could significantly enhance the ability to recycle PET/PE mixed waste streams by serving the role as both an adhesive promoting layer and a compatibilizer additive.
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    Klimovica, K.; Pan, S.; Lin, T. W.; Peng, X.; Ellison, C. J.; Lapointe, A. M.; Bates, F. S.; Coates, G. W. Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers. ACS Macro Lett. 2020, 9 (8), 1161– 1166,  DOI: 10.1021/acsmacrolett.0c00339
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    Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers
    Klimovica, Kristine; Pan, Sanshui; Lin, Ting-Wei; Peng, Xiayu; Ellison, Christopher J.; LaPointe, Anne M.; Bates, Frank S.; Coates, Geoffrey W.
    ACS Macro Letters (2020), 9 (8), 1161-1166CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges assocd. with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepd. using a grafting-through strategy by copolymn. of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (Mn = 6-28 kg/mol), graft nos., and graft spacings were prepd. These graft copolymers were melt-blended with high-d. polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 wt./wt.) and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt. % loading, with higher tensile strength obsd. for larger block nos. and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.
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    Blends of 90% nylon-6 and 10% EPDM rubber were prepd. The rubber was grafted with various amts. of maleic anhydride (I) with the aid of a peroxide. The initial moduli and the melt viscosities of the rubbers were affected slightly by the I and peroxide concns. The effect of I concn. on the blending process and the impact behavior was studied. The interfacial layer was investigated using IR spectroscopy and elemental anal. The I grafted onto the rubber reacted with the nylon during the blending process. With the I-grafted rubbers, a much finer dispersion could be obtained. However, the concn. of the coupling agent, within the range 0.13 to 0.89% grafted onto the rubber, had hardly any influence on either the dispersion process or the impact behavior of the blends.
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    The rates of nine melt coupling reactions were measured by reacting terminally functional polymer chains. The functional groups are carboxylic acid, oxazoline, epoxy, arom. primary amine, aliph. primary amine, hydroxyl and cyclic anhydride. The functional groups were attached to the end of polystyrene (PS) and poly(Me methacrylate) (PMMA) chains with most expts. performed at mol. wts. of about 25,000 g/mol and temp. of 180°. Reactions were performed homogeneously by blending stoichiometric amts. of the same type of polymer contg. complementary functional groups. Reaction rates were detd. from the amt. of coupled chains via gel permeation chromatog. The functional group pairs, in order of increasing reactivity, are acid/amine, hydroxyl/(anhydride or acid), arom. amine/epoxy, aliph. amine/epoxy, acid/oxazoline, acid/epoxy, arom. amine/anhydride, aliph. amine/anhydride. This is in general agreement with results for very dil. small mol. analogs. Some expts. performed at higher mol. wts. gave similar results. Coupling between aliph. amine terminal and cyclic anhydride terminal chains was found to be extremely fast; complete conversion occurred in <30 s. Diln. studies and comparison to theory indicate that this reaction was not diffusion controlled. Mixing and diffusion are rapid enough to bring every chain end in contact within 15 s.
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    Coupling Reactions of End- vs Mid-Functional Polymers
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    Reactive compatibilization of immiscible polymer blends is typically accomplished by grafting reactions between functional groups distributed randomly on one polymer and end-functional groups on the other polymer. A no. of model studies have focused on end coupling in polymer melts. In this work we compare directly reaction rate consts. for an end-functional chain reacting with an end-functional chain, kE, vs reacting with a mid-functional chain, kM, using competitive reaction of phthalic anhydride end- and mid-functional poly(Me methacrylate) (PMMA-eAn and PMMA-mAn) with amine terminal PMMA and polystyrene (PMMA-NH2 and PS-NH2). PMMA-eAn was labeled with 7-nitrobenz-2-oxa-1,3-diazole (NBD) while PMMA-mAn was labeled with anthracene. We measured the extent of coupling to block and graft copolymers selectively at the characteristic excitation and emission wavelengths of NBD and anthracene using a fluorescence detector coupled with GPC. We found that coupling with the mid-functional PMMA was slower under all reaction conditions studied and had the increasing order of kE/kM: homogeneous melt (1.7), soln. (2.8), heterogeneous blend prepd. in the mixer (2.6-3.2), and static flat interface (>10). The kinetic excluded-vol. effect and steric hindrance due to the polymer chain are considered to be the reasons for kE/kM > 1 in the homogeneous case. kE/kM in soln. was in agreement with the value (2.1) predicted by the kinetic excluded-vol. theory. The large value of kE/kM in the static flat interface was attributed to end-group segregation at the interface. Interestingly, we found that flow affected the interfacial reaction tremendously, resulting in over 1000 times higher rate const. in heterogeneous melt blending than that in the static bilayer film.
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    Kim, S.; Kim, J. K.; Park, C. E. Effect of Molecular Architecture of in situ Reactive Compatibilizer on the Morphology and Interfacial Activity of an Immiscible. Polyolefin/Polystyrene Blend 1997, 38 (8), 1809– 1815,  DOI: 10.1016/S0032-3861(96)00714-8
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    An ω-Isocyanate PMMA, an α-anhydride PMMA, and a styrene-styrylamine copolymer (PS-co-PSNH2) were prepd. by atom transfer radical polymn. (ATRP) with controlled mol. wt. (104 and 3.5 × 104) and low polydispersity (1.2). The functionalized compds. were used as precursors of PS-g-PMMA copolymers via reaction in the melt (170°, for 10 min) under moderate shear rate. The well-controlled mol. characteristics of the precursors allow for study of the effect of interfacial reaction kinetics on phase morphol. When the grafting reaction is fast (NH2/anhydride pair) and low mol. wt. chains are used, the interfacial reaction is quasi-complete and a nanophase morphol. is obsd., whereas limited reaction and formation of microphases are obsd. in all the other cases. A high reaction yield requires that the functional groups are highly reactive and that the interface is available to the functional polymers for the reaction to progress. Then, the nanophase morphol. is that of the copolymer formed by the interfacial reaction. A low reaction yield is dictated by either a slow interfacial reaction or a slow diffusion of the copolymer away from the interface. In the latter case, the phases formed by the unreacted precursors are stabilized by the copolymer which resides at the interface.
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    The polymerization of styrene (I) in tetrahydrofuran (II) initiated by Na naphthyl (III) with the exclusion of air and H2O constitutes a "living" polymer system. The propagating anion chain (IV) has the structure Ph-CH-CH2-CH2CH-Ph. No proton is available from II for chain termination, nor is electron transfer from IV to II energetically feasible. IV, therefore, continues to grow until I is exhausted without ever losing its anion centers. This is proved by the immediate conversion of the green color of III to red when I is added in the described system. The red color (that of neg. benzyl ions) persists for days in the absence of air and moisture. The addn. of I and II to IV results in further polymerization as shown by viscosity changes and gives further evidence of the existence of "living" ends in IV. Block polymers were prepd. by the addn. of isoprene to IV. H2O provides protons that terminate IV with no increase in viscosity. O terminates IV by radical formation followed by dimerization and a viscosity increase.
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    A review. Advances in synthetic polymer chem. have unleashed seemingly unlimited strategies for producing block polymers with arbitrary nos. (n) and types (k) of unique sequences of repeating units. Increasing (k,n) leads to a geometric expansion of possible mol. architectures, beyond conventional ABA-type triblock copolymers (k = 2, n = 3), offering alluring opportunities to generate exquisitely tailored materials with unparalleled control over nanoscale-domain geometry, packing symmetry, and chem. compn. Transforming this potential into targeted structures endowed with useful properties hinges on imaginative mol. designs guided by predictive theory and computer simulation. Here, we review recent developments in the field of block polymers.
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    Wang, W.; Lu, W.; Goodwin, A.; Wang, H.; Yin, P.; Kang, N.-G.; Hong, K.; Mays, J. W. Recent Advances in Thermoplastic Elastomers from Living Polymerizations: Macromolecular Architectures and Supramolecular Chemistry. Prog. Polym. Sci. 2019, 95, 1– 31,  DOI: 10.1016/j.progpolymsci.2019.04.002
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    Recent advances in thermoplastic elastomers from living polymerizations: Macromolecular architectures and supramolecular chemistry
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    Progress in Polymer Science (2019), 95 (), 1-31CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Thermoplastic elastomers (TPEs) have found use in a wide range of applications, such as adhesives, elastomers, coatings, fibers, and in additive manufg. techniques such as 3D printing. Despite their omnipresence, the need for advanced TPEs with adaptive properties is continuously growing. Along with a brief historical introduction, this review presents an overview of typical structure-property relationships for various TPEs and discusses the design principles of TPEs from a synthetic chem. perspective. Recent advances in TPEs with different macromol. architectures, including linear ABA triblock copolymers, ABC triblock terpolymers, multiblock copolymers, star copolymers, graft copolymers, bottlebrush polymers, and hyperbranched polymers are reviewed. Service temps. and mech. properties of the different materials are compared in each section. Incorporating various supramol. interactions into different macromol. architectures as a means to further extend the range of TPE applications is also discussed. Future opportunities for TPE research in both academia and industry are addressed as perspectives.
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    Chen, Y.; Zhang, L.; Jin, Y.; Lin, X.; Chen, M. Recent Advances in Living Cationic Polymerization with Emerging Initiation/Controlling Systems. Macromol. Rapid Commun. 2021, 42 (13), 2100148,  DOI: 10.1002/marc.202100148
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    A review. While the conventional living cationic polymn. (LCP) provided opportunities to synthesizing well-defined polymers with predetd. mol. wts., desirable chem. structures and narrow dispersity, it is still important to continuously innovate new synthetic methods to meet the increasing requirements in advanced material engineering. Consequently, a variety of novel initiation/controlling systems have be demonstrated recently, which have enabled LCP with spatiotemporal control, broadened scopes of monomers and terminals, more user-friendly operations and reaction conditions, as well as improved thermomech. properties for obtained polymers. In this work, recent advances in LCP is summarized with emerging initiation/controlling systems, including chem.-initiated/controlled cationic reversible addn.-fragmentation chain transfer (RAFT) polymn., photoinitiated/controlled LCP, electrochem.-controlled LCP, thionyl/selenium halide-initiated LCP, org. acid-assisted LCP, and stereoselective LCP. It is hoped that this summary will provide useful knowledge to people in related fields and stimulate new ideas to promote the development and application of LCP in both academia and industry.
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    Grubbs, R. B.; Grubbs, R. H. 50th Anniversary Perspective: Living Polymerization - Emphasizing the Molecule in Macromolecules. Macromolecules 2017, 50 (18), 6979– 6997,  DOI: 10.1021/acs.macromol.7b01440
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    A review. The ideal of living polymn. has defined research in polymer chem. over the past 50 years. In this Perspective, we present the case that this concept has enabled the treatment of polymers as org. mols., rather than impure mixts. of species, and allowed the translation of methods developed by synthetic org. chemists into ever more accessible living and/or controlled polymn. methods. The concurrent development of rapid anal. methods for screening new polymn. methods for living characteristics, chiefly size exclusion chromatog., has greatly aided in the expansion of living polymn. methods.
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    A review. Multiblock copolymers (MBCs) are an emerging class of synthetic polymers that exhibit different macromol. architectures and behaviors to those of homopolymers or di/triblock copolymers. Owing to the rapidly expanding field of synthetic methodologies applied in the field of polymer chem., sequenced controlled MBCs are becoming the new functional materials of this decade. MBCs can now be synthesized with precision and control unlike before and yet some of the synthetic limitations remain a challenge. In this review article, we summarise the various synthetic methodologies that have been reported to date with recent advances in different polymn. techniques and applications.
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    Hu, L.; Vuillaume, P. Y. Reactive Compatibilization of Polymer Blends by Coupling Agents and Interchange Catalysts. Compat. Polym. Blends Micro Nano Scale Phase Morphol. Interphase Charact. Prop. 2020, 205– 248,  DOI: 10.1016/B978-0-12-816006-0.00007-4
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    Geng, Z.; Shin, J. J.; Xi, Y.; Hawker, C. J. Click Chemistry Strategies for the Accelerated Synthesis of Functional Macromolecules. J. Polym. Sci. 2021, 59, 963– 1042,  DOI: 10.1002/pol.20210126
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    A review. Click chem. is one of the most powerful strategies for constructing polymeric soft materials with precise control over architecture and functionality. In this review, we provide a comprehensive summary of the state-of-the art for synthesizing functional polymers and their expanding range of applications. The synthetic and mechanistic aspects are discussed for key reactions that fulfill "click" requirements and their applications in construction of macromols. with linear, branched, and other complex architectures are described.
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    Lee, I.; Panthani, T. R.; Bates, F. S. Sustainable Poly(Lactide- b -Butadiene) Multiblock Copolymers with Enhanced Mechanical Properties. Macromolecules 2013, 46 (18), 7387– 7398,  DOI: 10.1021/ma401508b
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    Sustainable Poly(lactide-b-butadiene) Multiblock Copolymers with Enhanced Mechanical Properties
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    To develop mech. improved polylactide (PLA)-based sustainable polymers, a series of poly-(lactide-b-butadiene) (PLA-PB) multiblock copolymers were synthesized in a two-step procedure: PLA-PB-PLA (LBL) triblock copolymers were prepd. using ring-opening polymn. of D,L-lactide, followed by chain extension of LBL triblock polymers with toluene-2,4-diisocyanate (TDI) and terephthaloyl chloride (TCl). Mol. characterization revealed that the synthetic procedures yielded the desired triblock and multiblock copolymers with a compn. range of 0.5 ≤ fPLA ≤ 0.9. Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) demonstrated nearly identical, well-ordered, morphologies in the homologous triblock and multiblock copolymer materials, in sharp contrast with the findings of a recent study involving poly-(styrene-b-butadiene) (PS-PB) multiblock polymers. These results indicate a transition from classically ordered morphologies to a state of bicontinuous disorder for multiblocks contg. 〈n'〉 ≥ 10, where 〈n'〉 is the av. total no. of blocks. Lamellae (fPLA = 0.6) and cylinder (fPLA = 0.7 and 0.8) forming PLA-PB multiblock copolymers exhibited dramatically enhanced mech. properties compared to the corresponding LBL triblock copolymers. However, this toughening effect was not evident in samples contg. a spherical morphol. (fPLA = 0.9). These findings demonstrate a com. viable approach to prepg. sustainable plastics with competitive mech. properties.
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    Pawlak, A.; Morawiec, J.; Pazzagli, F.; Pracella, M.; Galeski, A. Recycling of Postconsumer Poly(Ethylene Terephthalate) and High-Density Polyethylene by Compatibilized Blending. J. Appl. Polym. Sci. 2002, 86 (6), 1473– 1485,  DOI: 10.1002/app.11307
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    Recycling of postconsumer poly(ethylene terephthalate) and high-density polyethylene by compatibilized blending
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    Two methods for recycling scrap PET and HDPE were analyzed: blending incompletely segregated polymers with a compatibilizer or blending nonsegregated polymers with a small amt. of another compatibilizer. The advancement of the compatibilization reaction in a twin-screw extruder depended on the residence time and intensity of mixing according to melt viscosity measurements and SEM observations. The acceptable mech. properties for systems with various PET contents were obtained in blends compatibilized with ethylene-glycidyl methacrylate copolymer (EGMA) and maleated SEBS rubber. For a blend contg. 75% PET and 25% HDPE, the optimum content of EGMA was ∼4 pph, and a film was produced with this compn. Admixts. present in recycled HDPE migrated to PET during blending and accelerated the hydrolysis of PET. As a result of migration, differences in the mech. properties of the blends were obsd., depending on the brand of recycled HDPE used. EGMA also was successfully used for the improvement of the mech. properties of a nonsegregated mixt. based on PET. Tensile properties of two compatibilized PET-rich and HDPE-rich commingled scraps indicated the possibility of using these blends for film extrusion, with potential applications in the packaging of tech. products.
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    Zhang, Y.; Zhang, H.; Guo, W.; Wu, C. Effects of Different Types of Polyethylene on the Morphology and Properties of Recycled Poly(Ethylene Terephthalate)/Polyethylene Compatibilized Blends. Polym. Adv. Technol. 2011, 22 (12), 1851– 1858,  DOI: 10.1002/pat.1683
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    Effects of different types of polyethylene on the morphology and properties of recycled poly(ethylene terephthalate)/polyethylene compatibilized blends
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    Recycled poly(ethylene terephthalate) (R-PET) was blended with four types of polyethylene (PE), linear low d. polyethylene (LLDPE; LL0209AA, Fs150), low d. polyethylene (LDPE; F101-1), and metallocene-LLDPE (m-LLDPE; Fv203) by co-rotating twin-screw extruder. Maleic anhydride-grafted poly(styrene-ethylene/butyldiene-styrene) (SEBS-g-MA) was added as compatibilizer. R-PET/PE/SEBS-g-MA blends were examd. by SEM, differential scanning calorimeter (DSC), dynamic mech. anal. (DMA), and mech. property testing. The results indicated that the morphol. and properties of the blends depended to a great extent on the miscibility between the olefin segments of SEBS-g-MA and PE. Due to the proper interaction between SEBS-g-MA and LDPE (F101-1), most SEBS-g-MA, located at the interface between two phases of PET and LDPE to increase the interfacial adhesion, lead to better mech. properties of R-PET/LDPE (F101-1) blend. However, both the poor miscibility of SEBS-g-MA with LLDPE (LL0209AA) and the excessive miscibility of SEBS-g-MA with LLDPE (Fs150) and m-LLDPE (Fv203) reduced the compatibilization effect of SEBS-g-MA. DSC results showed that the interaction between SEBS-g-MA and PE obviously affected the crystn. of PET and PE. DMA results indicated that PE had more influence on the movement of SEBS-g-MA than PE did. Copyright © 2010 John Wiley & Sons, Ltd.
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    Todd, A. D.; McEneany, R. J.; Topolkaraev, V. A.; Macosko, C. W.; Hillmyer, M. A. Reactive Compatibilization of Poly(Ethylene Terephthalate) and High-Density Polyethylene Using Amino-Telechelic Polyethylene. Macromolecules 2016, 49 (23), 8988– 8994,  DOI: 10.1021/acs.macromol.6b02080
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    Macromolecules (Washington, DC, United States) (2016), 49 (23), 8988-8994CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Low molar mass (3-17 kg/mol) amino-telechelic polyethylene (ATPE) was used to reactively compatibilize polyethylene terephthalate (PET) and high d. polyethylene (HDPE) via ester aminolysis of PET. A tert-butyl-oxycarbonyl (Boc)-protected polyethylene precursor was thermolytically deprotected during the melt-blending process to render the reactive amine termini. Spectroscopic anal. of a model reaction confirmed the presence of amide functionality in the resultant material. Through blending studies, we found that low loadings of ATPE (0.5 wt %) significantly reduced the vol. of the dispersed HDPE phase particles by a factor of 8 when compared to a binary PET/HDPE blend as assessed by SEM. Mech. anal. of the ATPE-compatibilized blends showed a 12-fold increase in the elongation at break over the unmodified PET/HDPE blend. Ultimately, the results here offer a new approach to reactively compatibilize and toughen PET/HDPE blends and opens the door for other uses of amino-telechelic polyethylene.
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    Wang, H.; Onbulak, S.; Weigand, S.; Bates, F. S.; Hillmyer, M. A. Polyolefin Graft Copolymers through a Ring-Opening Metathesis Grafting through Approach. Polym. Chem. 2021, 12 (14), 2075– 2083,  DOI: 10.1039/D0PY01728K
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    Polyolefin graft copolymers through a ring-opening metathesis grafting through approach
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    Polymer Chemistry (2021), 12 (14), 2075-2083CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A series of polyethylene-graft-atactic polypropylene (PE-g-aPP) graft copolymers were synthesized by grafting through copolymn. of a cyclooctene terminated aPP macromonomer and cyclooctene using ring opening metathesis polymn. (ROMP) and subsequent hydrogenation. The macromonomer was prepd. by a facile alkoxycarbonylation reaction between 1,5-cyclooctadiene, hydroxyl terminated aPP and carbon monoxide. Near complete monomer conversion, a near random graft distribution, and relatively low dispersity were achieved. Thermal anal. of the graft polymers indicates decreasing Tm and Tg as the wt. percentage of aPP increases. The percent Xc of PE decreases as aPP content increases, confirmed by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS) characterization. The normalized percent crystallinity (Xc,norm) indicates that changing side chain nos. and/or length of aPP do not have a significant impact on PE Xc. Small angle X-ray scattering indicates the PE lamellae crystals in the graft copolymers have similar interlamellar spacing but decreased thickness as aPP content increases. In addn., the linear viscoelastic behavior shows that the PE-g-aPP graft copolymers exhibit greatly enhanced dynamic modulus and complex viscosity compared to the linear PE, and the effect increases as side chain no. and/or length increases. This work is important for further development of graft polymers for direct recycling of ubiquitous polyolefins from mixed polyolefin waste.
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    Rose, J. M.; Mourey, T. H.; Slater, L. A.; Keresztes, I.; Fetters, L. J.; Coates, G. W. Poly(Ethylene-Co-Propylene Macromonomer)s: Synthesis and Evidence for Starlike Conformations in Dilute Solution. Macromolecules 2008, 41 (3), 559– 567,  DOI: 10.1021/ma702190c
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    Poly(ethylene-co-propylene macromonomer)s: Synthesis and Evidence for Starlike Conformations in Dilute Solution
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    Macromolecules (Washington, DC, United States) (2008), 41 (3), 559-567CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    By use of two sequential coordination-insertion polymns., a series of ethylene-co-propylene-based comb polymers was synthesized. First, poly(ethylene-co-propylene) macromonomers featuring one unsatd. chain end were synthesized using a titanium bis(phenoxyimine) catalyst. The macromonomers were then homopolymd. using a living nickel α-diimine catalyst. The mol. wt. and corresponding no. of arms for each poly(macromonomer) were detd. using size-exclusion chromatog. with viscometry detection and universal calibration. Viscosity-mol. wt. conformation plots for the poly(macromonomer)s revealed compact soln. structures. The viscometric radius for each poly(macromonomer) (Rv) and corresponding linear macromonomer (Rv)a was detd. and the ratio (Rv)/(Rv)a for each pair was compared to those of a variety of polyisoprene-based star polymers with similar functionality. The comparison revealed that despite the obvious comb topol. of the poly(macromonomer)s their dil. soln. conformations correspond reasonably well to the bona fide polyisoprene stars.
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    Klimovica, K.; Pan, S.; Lin, T. W.; Peng, X.; Ellison, C. J.; Lapointe, A. M.; Bates, F. S.; Coates, G. W. Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers. ACS Macro Lett. 2020, 9 (8), 1161– 1166,  DOI: 10.1021/acsmacrolett.0c00339
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    Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers
    Klimovica, Kristine; Pan, Sanshui; Lin, Ting-Wei; Peng, Xiayu; Ellison, Christopher J.; LaPointe, Anne M.; Bates, Frank S.; Coates, Geoffrey W.
    ACS Macro Letters (2020), 9 (8), 1161-1166CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges assocd. with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepd. using a grafting-through strategy by copolymn. of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (Mn = 6-28 kg/mol), graft nos., and graft spacings were prepd. These graft copolymers were melt-blended with high-d. polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 wt./wt.) and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt. % loading, with higher tensile strength obsd. for larger block nos. and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.
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    Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. Catalytic Production of Olefin Block Copolymers via Chain Shuttling Polymerization. Science 2006, 312 (5774), 714– 719,  DOI: 10.1126/science.1125268
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    Catalytic Production of Olefin Block Copolymers via Chain Shuttling Polymerization
    Arriola, Daniel J.; Carnahan, Edmund M.; Hustad, Phillip D.; Kuhlman, Roger L.; Wenzel, Timothy T.
    Science (Washington, DC, United States) (2006), 312 (5774), 714-719CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    We report a catalytic system that produces olefin block copolymers with alternating semicryst. and amorphous segments, achieved by varying the ratio of α-olefin to ethylene in the two types of blocks. The system uses a chain shuttling agent to transfer growing chains between two distinct catalysts with different monomer selectivities in a single polymn. reactor. The block copolymers simultaneously have high melting temps. and low glass transition temps., and therefore they maintain excellent elastomeric properties at high temps. Furthermore, the materials are effectively produced in economically favorable, continuous polymn. processes.
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    Shan, C. L. P.; Walton, K. L.; Marchand, G. R.; Carnahan, E. M.; Karjala, T. Crystalline Block Composites as Compatibilizers. US Patent US8822599B2, 2014.
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    Hu, Y.; Conley, B.; Walton, K. L.; Shan, C. L. P.; Marchand, G. R.; Patel, R. M.; Kupsch, E.-M.; Walther, B. W. Multilayered Polyolefin-Based Films. US Patent US9511567B2, 2013.
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    Listak, J.; Jakubowski, W.; Mueller, L.; Plichta, A.; Matyjaszewski, K.; Bockstaller, M. R. Effect of Symmetry of Molecular Weight Distribution in Block Copolymers on Formation of “Metastable” Morphologies. Macromolecules 2008, 41 (15), 5919– 5927,  DOI: 10.1021/ma800816j
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    Effect of Symmetry of Molecular Weight Distribution in Block Copolymers on Formation of "Metastable" Morphologies
    Listak, Jessica; Jakubowski, Wojciech; Mueller, Laura; Plichta, Andrzej; Matyjaszewski, Krzysztof; Bockstaller, Michael R.
    Macromolecules (Washington, DC, United States) (2008), 41 (15), 5919-5927CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Polystyrene-b-poly(Me acrylate) (PS-PMA) copolymers were synthesized using activators regenerated by electron transfer (ARGET) for atom transfer radical polymn. (ATRP). Polydispersity of the PMA block was varied by adjusting the amt. of copper catalyst in ARGET ATRP, and the resulting mol. wt. distributions were approx. sym. At a compn. of 35 vol. % of PMA, the formation of a hexagonally perforated lamellar (HPL) morphol. was obsd. for a polydisperse PS-PMA copolymer for short- and long-term solvent-casting conditions. No order-order transitions were obsd. at elevated temps. or after prolonged thermal annealing. The obsd. stabilization of the HPL morphol.-that is considered to be metastable in narrow-disperse diblock copolymers and diblock copolymers with selective block polydispersity given by a Schulz-Zimm distribution-suggests that the skewness of the distribution of block mol. wts. is an important parameter for the structure selection during the microphase sepn. process. In particular, near-sym. block mol. wt. distributions (as realized by the ARGET ATRP technique) facilitate the stabilization of microdomain morphologies with increased std. deviation of mean curvature. The results point to the relevance of controlling both the width and symmetry of mol. wt. distribution as a potential route toward the tailored synthesis of non-regular microstructures with particular topol. properties that might be of future technol. interest.
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    Lynd, N. A.; Meuler, A. J.; Hillmyer, M. A. Polydispersity and Block Copolymer Self-Assembly. Prog. Polym. Sci. 2008, 33 (9), 875– 893,  DOI: 10.1016/j.progpolymsci.2008.07.003
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    Polydispersity and block copolymer self-assembly
    Lynd, Nathaniel A.; Meuler, Adam J.; Hillmyer, Marc A.
    Progress in Polymer Science (2008), 33 (9), 875-893CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Block copolymers consist of two or more chem. distinct polymers that are covalently bound. These materials self-assemble into fascinating mesostructures with features on the nanometer length scale and have been the subject of intense research interest for about four decades. These efforts have generally focused on model block copolymer systems where the mol. wt. distributions of all blocks are very narrow. Traditionally, many block copolymer systems have been prepd. by living anionic polymn. and thus usually exhibit narrow mol. wt. distributions in all blocks. Therefore, the assumption of monodisperse blocks that greatly simplifies theor. work is on solid exptl. ground. Prepn. of block copolymers with relatively broad mol. wt. distributions in one or more block has become increasingly common, however, as use of synthetic techniques such as controlled radical polymn. has proliferated. A review. Advances in these techniques have increased the no. of monomers readily incorporated into block copolymers and potentially will drive com. costs down. These polymn. strategies often, however, result in broader mol. wt. distributions than are typically obtained using living anionic, cationic, or metal-catalyzed techniques; understanding polydispersity effects should aid deployment of these block copolymers in advanced materials applications. This review describes both theor. and exptl. investigations of the effects of polydispersity on the melt-phase morphol. behavior of block copolymers. The summary includes research efforts focused on both continuous mol. wt. distributions and multicomponent blends. The review concludes with a summary and outlook on the potential utility of polydispersity as a tool to tune the morphol. behavior of block copolymers.
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    Hillmyer, M. A. Polydisperse Block Copolymers: Don’t Throw Them Away. J. Polym. Sci., Part B: Polym. Phys. 2007, 45 (24), 3249– 3251,  DOI: 10.1002/polb.21323
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    A review. The relevance of block copolymers with continuous distribution of mol. wt. and block compns. is discussed with focus on applicability of these properties to new materials. Organized microstructures upon self assembly; phase behavior; processing; and reproducibility of polymn. procedures are also discussed.
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    Chen, H.; Ginzburg, V. Reaction: Size Distribution in Olefin Block Copolymers: Not Bad at All. Chem. 2019, 5 (3), 491– 492,  DOI: 10.1016/j.chempr.2019.02.018
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    Reaction: Size Distribution in Olefin Block Copolymers: Not Bad at All
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    Hongyu Chen completed his PhD in macromol. science at Case Western Reserve University in 2010. He is a fellow of the Dow Chem. Company, where he focuses on developing new products. He is also a fellow of the American Phys. Society and American Chem. Society. Valeriy Ginzburg completed his PhD in polymer physics at the Moscow Institute of Physics and Technol. in 1992. He is a senior scientist at the Dow Chem. Company and a fellow of the American Phys. Society.
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    Creton, C.; Kramer, E. J.; Brown, H. R.; Hui, C.-Y. Adhesion and Fracture of Interfaces Between Immiscible Polymers: From the Molecular to the Continuum Scal. Adv. Polym. Sci. 2001, 156, 53– 136,  DOI: 10.1007/3-540-45141-2_2
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    Eastwood, E. A.; Dadmun, M. D. Multiblock Copolymers in the Compatibilization of Polystyrene and Poly(Methyl Methacrylate) Blends: Role of Polymer Architecture. Macromolecules 2002, 35 (13), 5069– 5077,  DOI: 10.1021/ma011701z
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    Multiblock copolymers in the compatibilization of polystyrene and poly(methyl methacrylate) blends: role of polymer architecture
    Eastwood, E. A.; Dadmun, M. D.
    Macromolecules (2002), 35 (13), 5069-5077CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    An asym. double cantilever beam (ADCB) was utilized to det. the ability of a series of styrene and Me methacrylate copolymers with varying architectures to compatibilize the polystyrene/poly(Me methacrylate) interface. Diblock, triblock, pentablock, and heptablock multiblock copolymers with similar mol. wts. were compared to a random copolymer. When the surface is satd. with copolymer, PS/PMMA interfaces compatibilized with pentablock copolymers [S-M-S-M-S(30) and M-S-M-S-M(30)] were the strongest, followed by triblock [S-M-S(50) and M-S-M(50)] and then diblock [S-M(100)]. The least blocky structures, heptablocks [S-M-S-M-S-M-S(21) and M-S-M-S-M-S(21)] and random, provided the weakest interfaces under similar conditions. The ability of the multiblock copolymers to strengthen the PS/PMMA interfaces was attributed to multiple interface crossings and blocks of monomers that are able to anchor into the homopolymers. The results suggest that block lengths with mol. wt. greater than 21 000 are required for adequate anchoring into the PS/PMMA homopolymer phases. Surprisingly, a dependence of the interfacial fracture toughness on copolymer compn. was not obsd. for the multiblock copolymers studied. Both styrene-centered and Me methacrylate-centered multiblock copolymers gave comparable results even though the compns. of the comparable copolymers differed greatly, as much as 70/30 to 30/70. In addn., increasing block lengths in multiblock copolymers of a given architecture increased interfacial adhesion.
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    Gersappe, D.; Harm, P. K.; Irvine, D.; Balazs, A. C. Contrasting the Compatibilizing Activity of Comb and Linear Copolymers. Macromolecules 1994, 27 (3), 720– 724,  DOI: 10.1021/ma00081a015
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    Macromolecules (1994), 27 (3), 720-4CODEN: MAMOBX; ISSN:0024-9297.
    Using Monte Carlo computer simulations, the authors compared the interfacial behavior of various comb and linear copolymers at a penetrable interface, which represented the boundary between two incompatible homopolymers, A and B. The backbone of the combs was composed of A sites (the majority of the species in the comb), while the teeth were composed of B sites. The authors varied the no. and length of the teeth and found that combs with fewer, longer teeth could more readily localize at the interface than combs with multiple, short teeth. In addn., combs would more readily localize at the interface than comparable linear multiblocks. The findings highlighted the importance of mol. architecture in detg. the interfacial activity of copolymers. The results also provided guidelines for fabricating copolymers that acted as optimal compatibilizers between immiscible polymers.
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    Alamo, R. G.; Glaser, R. H.; Mandelkern, L. The Cocrystallization of Polymers: Polyethylene and Its Copolymers. J. Polym. Sci., Part B: Polym. Phys. 1988, 26 (10), 2169– 2195,  DOI: 10.1002/polb.1988.090261011
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    The cocrystn. of both homopolymer-copolymer mixts. and copolymer mixts. of polyethylene were studied. Mol. wt. and compn. fractions were used exclusively. Mol. wts. of the components were matched so that attention is given to the influence of chain structure. DSC and selective extn. techniques were used to assess whether cocrystn. occurs. Linear polyethylene, and random copolymers which contained ≤2 mol% of either Et or acetate branches, cocrystd. upon rapid crystn. from the melt. When the branching content became ≥3 mol%, cocrystn. did not occur. Copolymers contg. ∼1-2 mol% cocrystd. with one another. However, copolymers contg. higher counit contents did not cocrystallize with one another or with samples contg. a smaller amt. of counit. These results were explained on the basis of the concn. of eligible sequences that were available for crystn.
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    Yuan, B.-L.; Wool, R. P. Strength Development at Incompatible Semicrystalline Polymer Interfaces. Polym. Eng. Sci. 1990, 30 (22), 1454– 1464,  DOI: 10.1002/pen.760302206
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    The structure of an interface that develops from laminating isotactic polypropylene (I)-polyethylene (II) by hot compression-molding was analyzed by optical and electron microscopy. The interface strength (S) was measured by means of a butt-joint specimen. For the laminate formed by isothermal crystn. above the II m.p., S increased with time due to the formation of II influxes between the I spherulites. The interspherulitic influxes broke up the sharp I-II interface plane and provided considerable strength by mech. interlocking. Intraspherulitic entanglements were also noted for I spherulites nucleated near the interface. Fast crystn. prevented the formation of influxes and resulted in a weak interface. For the nonisothermal crystn. case during cooling at 10°/min, the morphol. of a I-HDPE interface was different from that of a I-linear LDPE interface. The difference in crystn. temps. and growth rates between I and HDPE during rapid cooling permitted the HDPE to crystallize first, which prevented the formation of influxes. With I-linear LDPE, the I crystd. first, allowing some influxes to develop. To obtain good mech. properties for a given I-II couple, one can control the processing thermal history to optimize the development of influxes and mech. strength at the interface.
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    Schnell, R.; Stamm, M.; Rauch, F. Segregation of Diblock Copolymers to the Interface between Weakly Incompatible Polymers. Macromol. Chem. Phys. 1999, 200 (7), 1806– 1812,  DOI: 10.1002/(SICI)1521-3935(19990701)200:7<1806::AID-MACP1806>3.0.CO;2-9
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    The interface between thin films of polystyrene (PS) and poly(p-methylstyrene) (PpMS) was investigated in the presence of the diblock copolymer P(S-b-pMS). The use of neutron reflectivity and 15N nuclear reaction anal. in combination with suitable deuteration of the components provides information on the interface width and the distribution of the diblock copolymer at the interface. By variation of the mol. wt. of the homopolymers, compatibility can be changed from compatible to incompatible. Depending on mol. wt. the diblock copolymers segregate to the interface between the incompatible phases, while in weakly incompatible systems (χN = 3) copolymers are dissolved to a considerable amt. in the homopolymer phases. At large copolymer concn. even full compatibility of components can be achieved, which is in good agreement with mean field predictions.
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    Shull, K. R.; Kramer, E. J.; Hadziioannou, G.; Tang, W. Segregation of Block Copolymers to Interfaces between Immiscible Homopolymers. Macromolecules 1990, 23 (22), 4780– 4787,  DOI: 10.1021/ma00224a006
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    Macromolecules (1990), 23 (22), 4780-7CODEN: MAMOBX; ISSN:0024-9297.
    Predictions from a mean-field theory for the dependence of the segregation of perdeuterostyrene-2-vinylpyridine diblock copolymer (I) to the interface in polystyrene (II)-poly(2-vinylpyridine) immiscible blends on the equil. I concn. in the II phase were quant. accurate for values of I chem. potential which were below the limiting value assocd. with the formation of I micelles. Segregation behavior in the regime where micelles were present was complicated by a strong tendency for micelles to segregate to the free II surface and by a weaker tendency for micelles to segregate to the interfacial region. I chem. potentials at the micelle transition were detd.
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    Semenov, A. N. Theory of Diblock-Copolymer Segregation to the Interface and Free Surface of a Homopolymer Layer. Macromolecules 1992, 25 (19), 4967– 4977,  DOI: 10.1021/ma00045a024
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    Equil. and dynamics of block copolymer chains in a homopolymer layer (between the interface with another homopolymer and the free surface) are considered. An anal. mean-field theory for equil. copolymer segregation to the interface is presented, the results being in good agreement with those of another theor. approach and with exptl. data. The dynamics of an interface copolymer excess are also considered. The situation above the crit. micelle concn. (CMC) is also analyzed. Copolymer micelles usually strongly attract each other, tending to form a sep. micellar macrophase. Primings of the copolymer phase are attracted to the free surface and (somewhat weaker) to the interface; the superwetting of the free surface by the micellar phase is expected for copolymer mol. wts. exceeding some crit. value. The formation of micelles is an activation process usually with a high energy of activation; the apparent CMC might be appreciably greater than the equil. CMC. For high enough copolymer mol. wts., the micellar geometry should be dynamically controlled; in that case the formation of spherical micelles dominates over other geometries in a wide range of copolymer compns. including sym. copolymers (provided that the copolymer vol. fraction is small). The micellar contribution to the free surface and interface excesses is due to higher rate of the micelles' formation at the surfaces.
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    Kim, S. H.; Jo, W. H. A Monte Carlo Simulation of Polymer/Polymer Interface in the Presence of Block Copolymer. I. Effects of the Chain Length of Block Copolymer and Interaction Energy. J. Chem. Phys. 1999, 110 (24), 12193– 12201,  DOI: 10.1063/1.479156
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    A Monte Carlo simulation for the segregation behavior of sym. diblock copolymer at the interface between immiscible homopolymers was performed on a simplified lattice model. The simulation results show that the segregation behavior of block copolymer is significantly dependent on the mol. parameters, such as the chain length Nc of block copolymer and the interaction energy εAB between A and B segments. In a weakly repulsive system with εAB=0.1, the block copolymers are more strongly segregated at the interface with increasing the chain length when the block length is shorter than and comparable to the homopolymer length. However, when the block length becomes longer than the homopolymer length, the concn. of copolymer segments at the interface rather decreases and its distribution becomes broadened. In a strongly repulsive system with εAB=0.5, the distribution of copolymer segments at the interface becomes broader as the chain length of block copolymer increases. This behavior is closely related to the stretching and orientation of block copolymer chains at the interface and to the extent of penetration of homopolymers into the copolymer layer. These simulation results are in excellent agreement with the numerical predictions by the self-consistent mean field theory.
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    Cho, D.; Hu, W.; Koberstein, J. T.; Lingelser, J. P.; Gallot, Y. Segregation Dynamics of Block Copolymers to Immiscible Polymer Blend Interfaces. Macromolecules 2000, 33 (14), 5245– 5251,  DOI: 10.1021/ma981699k
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    Dynamic interfacial tension measurements were used to characterize segregation rates of diblock copolymers to a polymer-polymer interface. The system studied is a poly(styrene-b-dimethylsiloxane) [P(S-b-DMS); Mn = 13 000] sym. diblock copolymer added to a molten blend of the corresponding immiscible homopolymers. Interfacial tension was measured by the pendant drop technique with poly(styrene) [PS; Mn = 4000] as the pendant drop phase and a mixt. of poly(dimethylsiloxane) [PDMS; Mn = 1600] with silane-terminated P(S-b-DMS) as the surrounding phase. The pendant drop technique is found to suffer from two intrinsic limitations in this application: short time data are inaccessible due to the finite time required for the drop shape to equilibrate, and long time data may not be readily analyzed as a result of the finite drop size. Intermediate time data were compared to the predictions of diffusion-limited segregation models proposed by A.Budkowski, A. Losch, and J. Klein (BLK, (1995)) and by A. Semenov (1992) that were modified to treat interfacial tension data. The apparent block copolymer diffusion coeff. obtained from the two analyses fall in the range of 10-5-10-6 cm2/s, in agreement with the estd. self-diffusion coeff. of the PDMS homopolymer matrix.
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    Monte Carlo simulations were used to examine the behavior of a single multiblock AB copolymer near the penetrable interface between two immiscible fluids, A and B. The values of χAB, the interaction energy between comonomer and fluid, necessary to localize the chain at the fluid-fluid boundary were detd. and the dependence of this value on the block length was investigated. Once localized at the interface, how the conformation of the multiblock copolymer was perturbed from its random coil dimensions was calcd. The interfacial behavior of the multiblock chain for a range of χAB values and for different block length was then compared. These results were compared with the properties of various diblocks at such an interface. The behavior of several multiblocks at the fluid-fluid surface was examd. The findings of the simulations were helpful in contrasting the compatibilizing activity of diblock and multiblock copolymers.
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    Liu, D.; Gong, K.; Lin, Y.; Bo, H.; Liu, T.; Duan, X. Effects of Repulsion Parameter and Chain Length of Homopolymers on Interfacial Properties of An/Ax/2BxAx/2/Bm Blends: A DPD Simulation Study. Polymers (Basel) 2021, 13 (14), 2333,  DOI: 10.3390/polym13142333
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    Effects of Repulsion Parameter and Chain Length of Homopolymers on Interfacial Properties of An/Ax/2BxAx/2/Bm Blends: A DPD Simulation Study
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    Polymers (Basel, Switzerland) (2021), 13 (14), 2333CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
    We explored the effects of the repulsion parameter (aAB) and chain length (NHA or NHB) of homopolymers on the interfacial properties of An/Ax/2BxAx/2/Bm ternary polymeric blends using dissipative particle dynamics (DPD) simulations. Our simulations show that: (i) The ternary blends exhibit the significant segregation at the repulsion parameter (aAB = 40). (ii) Both the interfacial tension and the d. of triblock copolymer at the center of the interface increase to a plateau with increasing the homopolymer chain length, which indicates that the triblock copolymers with shorter chain length exhibit better performance as the compatibilizers for stabilizing the blends. (iii) For the case of NHA = 4 (chain length of homopolymers An) and NHB (chain length of homopolymers Bm) ranging from 16 to 64, the blends exhibit larger interfacial widths with a weakened correlation between bead An and Bm of homopolymers, which indicates that the triblock copolymer compatibilizers (Ax/2BxAx/2) show better performance in reducing the interfacial tension. The effectiveness of triblock copolymer compatibilizers is, thus, controlled by the regulation of repulsion parameters and the homopolymer chain length. This work raises important considerations concerning the use of the triblock copolymer as compatibilizers in the immiscible homopolymer blend systems.
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    Liu, D.; Gong, K.; Lin, Y.; Liu, T.; Liu, Y.; Duan, X. Dissipative Particle Dynamics Study on Interfacial Properties of Symmetric Ternary Polymeric Blends. Polymers (Basel) 2021, 13 (9), 1516,  DOI: 10.3390/polym13091516
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    Dissipative particle dynamics study on interfacial properties of symmetric ternary polymeric blends
    Liu, Dongmei; Gong, Kai; Lin, Ye; Liu, Tao; Liu, Yu.; Duan, Xiaozheng
    Polymers (Basel, Switzerland) (2021), 13 (9), 1516CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
    We investigated the interfacial properties of sym. ternary An/AmBm/Bn and An/Am/2BmAm/2/Bn polymeric blends by means of dissipative particle dynamics (DPD) simulations. We systematically analyzed the effects of compn., chain length, and concn. of the copolymers on the interfacial tensions, interfacial widths, and the structures of each polymer component in the blends. Our simulations show that: (i) the efficiency of the copolymers in reducing the interfacial tension is highly dependent on their compns. The triblock copolymers are more effective in reducing the interfacial tension compared to that of the diblock copolymers at the same chain length and concn.; (ii) the interfacial tension of the blends increases with increases in the triblock copolymer chain length, which indicates that the triblock copolymers with a shorter chain length exhibit a better performance as the compatibilizers compared to that of their counterparts with longer chain lengths; and (iii) elevating the triblock copolymer concn. can promote copolymer enrichment at the center of the interface, which enlarges the width of the phase interfaces and reduces the interfacial tension. These findings illustrate the correlations between the efficiency of copolymer compatibilizers and their detailed mol. parameters.
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    Gindy, M. E.; Prud’homme, R. K.; Panagiotopoulos, A. Z. Phase Behavior and Structure Formation in Linear Multiblock Copolymer Solutions by Monte Carlo Simulation. J. Chem. Phys. 2008, 128, 164906,  DOI: 10.1063/1.2905231
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    Phase behavior and structure formation in linear multiblock copolymer solutions by Monte Carlo simulation
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    Journal of Chemical Physics (2008), 128 (16), 164906/1-164906/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The soln. phase behavior of short, strictly alternating multiblock copolymers of type (AnBn)m was studied using lattice Monte Carlo simulations. The polymer mols. were modeled as flexible chains in a monomeric solvent selective for block type A. The degree of block polymn. n and the no. of diblock units per chain m were treated as variables. The authors show that within the regime of parameters accessible to this study, the thermodn. phase transition type is dependent on the ratio of m/n. The simulations show microscopic phase sepn. into roughly spherical aggregates for m/n ratios less than a crit. value and first-order macroscopic pptn. otherwise. In general, increasing m at fixed n, or n at fixed m, promotes the tendency toward macroscopic phase pptn. The enthalpic driving force of phase change is found to universally scale with chain length for all multiblock systems considered and is independent of the existence of a true phase transition. For aggregate forming systems at low amphiphile concns., multiblock chains are shown to self-assemble into intramol., multichain clusters. Predictions for microstructural dimensions, including crit. micelle concn., equil. size, shape, aggregation parameters, and d. distributions, are provided. At increasing amphiphile d., interaggregate bridging is shown to result in the formation of networked structures, leading to an eventual soln.-gel transition. The gel is swollen and consists of highly interconnected aggregates of approx. spherical morphol. Qual. agreement is found between exptl. obsd. phys. property changes and phase transitions predicted by simulations. Thus, a potential application of the simulations is the design of multiblock copolymer systems which can be optimized with regard to soln. phase behavior and ultimately phys. and mech. properties. (c) 2008 American Institute of Physics.
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    Halperin, A. On the Collapse of Multiblock Copolymers. Macromolecules 1991, 24 (6), 1418– 1419,  DOI: 10.1021/ma00006a033
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    On the collapse of multiblock copolymers
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    Macromolecules (1991), 24 (6), 1418-19CODEN: MAMOBX; ISSN:0024-9297.
    The formation of intramol. micelles in (AB)n multiblock polymers immersed in a highly selective solvent was considered. For flexible chains comprising sol. A blocks and insol. B blocks consisting of NA and NB monomer units such that NA » NB » 1, 2 simple limits emerged: (1) for n ≈ NB4/5, a single starlike mol. micelle is formed, and (2) for n » NB4/5, a string of starlike micelles is expected. In case (1), the chain dimensions scaled as n1/5NA3/5, while in case (2), a n3/5NA3/5NB-8/25 behavior is expected.
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    López-Barrón, C. R.; Tsou, A. H. Strain Hardening of Polyethylene/Polypropylene Blends via Interfacial Reinforcement with Poly(Ethylene- Cb -Propylene) Comb Block Copolymers. Macromolecules 2017, 50 (7), 2986– 2995,  DOI: 10.1021/acs.macromol.7b00264
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    Strain Hardening of Polyethylene/Polypropylene Blends via Interfacial Reinforcement with Poly(ethylene-cb-propylene) Comb Block Copolymers
    Lopez-Barron, Carlos R.; Tsou, Andy H.
    Macromolecules (Washington, DC, United States) (2017), 50 (7), 2986-2995CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    A poly(ethylene-cb-propylene) comb block copolymer (P(E-cb-P)), prepd. by copolymn. of vinyl-terminated atactic polypropylene and ethylene, was used to compatibilize immiscible blends of high-d. polyethylene (HDPE) and isotactic polypropylene (iPP). Addn. of 5 wt % P(E-cb-P) resulted in 5-fold microdomain size redns. and the concomitant increase in the elastic modulus, as typically obsd. in immiscible blends compatibilized with linear block copolymers. We report an unexpected phenomenon, namely, the development of extensional flow hardening by the addn. of P(E-cb-P) to the HDPE/iPP blends. This unprecedented effect is stronger in blends with cocontinuous morphol. (50/50 HDPE/iPP) than in blends with matrix-droplet morphol. (75/25 or 25/75 HDPE/iPP). We postulate that the melt strength enhancement and extensional strain hardening obsd. in the compatibilized blends may arise from the interfacial stiffening as a result of the interfacial stitching by the P(E-cb-P) comb block copolymer. This interfacial stitched network acts as an elastic membrane that resists interfacial deformations. Entanglements of the PP comb arms with iPP generates interfacial stitches which, in turn, could lead to the stretching of the PE backbone of the P(E-cb-P) comb block at large interfacial deformations and, hence, extensional flow hardening.
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    Datta, S.; Lohse, D. J. Graft Copolymer Compatibilizers for Blends of Isotactic Polypropylene and Ethene-Propene Copolymers. 2. Functional Polymers Approach. Macromolecules 1993, 26 (8), 2064– 2076,  DOI: 10.1021/ma00060a040
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    Graft copolymer compatibilizers for blends of isotactic polypropylene and ethene-propene copolymers. 2. Functional polymers approach
    Datta, Sudhin; Lohse, David J.
    Macromolecules (1993), 26 (8), 2064-76CODEN: MAMOBX; ISSN:0024-9297.
    A graft polymer with isotactic polypropylene (I) arms pendent from an ethene-propene copolymer (II) backbone was made and it effectively compatibilized I-II blends. The graft copolymer was made by treatment of maleated I with II contg. 5-(methylamino)-2-norbornene groups, either in soln. or in the melt state. The addn. of <10% of this graft polymer to a I-II blend had a large effect on its morphol. and properties. Not only did the size of dispersed II phase domains shrink by a factor of 4 when the compatibilizer is added, but also the growth of the phase domains on thermal annealing in the melt was significantly reduced. The presence of the graft polymer in the interphase of the blend was shown directly by electron microscopy. Improvements in mech. properties of I-II blends contg. compatibilizers were noted.
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    Embree, K. DOW’s Breakthrough Barrier Film Technology Makes Stand-Up Pouches Recyclable. Plastics Today , June 21, 2016; https://www.plasticstoday.com/packaging/dows-breakthrough-barrier-film-technology-makes-stand-pouches-recyclable.
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    Charoensirisomboon, P.; Inoue, T.; Weber, M. Pull-out of Copolymer in situ-Formed during Reactive Blending: Effect of the Copolymer Architecture. Polymer 2000, 41 (18), 6907– 6912,  DOI: 10.1016/S0032-3861(00)00025-2
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    Pull-out of copolymer in situ-formed during reactive blending: effect of the copolymer architecture
    Charoensirisomboon, P.; Inoue, T.; Weber, M.
    Polymer (2000), 41 (18), 6907-6912CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
    Reactive melt blending of polyamide 6 (PA) and polysulfone (PSU) was carried out and the effect of the copolymer architecture on the pull-out of the copolymer in situ-formed during reactive blending was studied. To create various block and graft copolymers by reactive blending, three types of reactive PSU were prepd. and used; maleic anhydride-grafted PSU, carboxylic-grafted PSU, and phthalic anhydride-terminated PSU. Polymer blend morphol. was obsd. by transmission electron microscopy (TEM). The TEM results suggested that the block copolymers with linear chain structures are more easily pulled out to form micelles in the matrix than the graft copolymers having branch structure with trunk chains locating in the dispersed phase. Such graft copolymers stayed at the interface and played the role of emulsifiers. By contrast, the in situ-formed graft copolymers having trunk chains locating in the matrix were easily pulled out. The micelle formation via the pull-out of copolymers took place even in the rather sym. block or graft copolymer system. Such interfacial behavior is against the current theories on polymer-polymer interface, which deal with the chain statistics under quiescent state; implying that the hydrodynamic contribution plays an important role of the pull-out.
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    Thurber, C. M.; Xu, Y.; Myers, J. C.; Lodge, T. P.; Macosko, C. W. Accelerating Reactive Compatibilization of PE/PLA Blends by an Interfacially Localized Catalyst. ACS Macro Lett. 2015, 4 (1), 30– 33,  DOI: 10.1021/mz500770y
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    Accelerating Reactive Compatibilization of PE/PLA Blends by an Interfacially Localized Catalyst
    Thurber, Christopher M.; Xu, Yuewen; Myers, Jason C.; Lodge, Timothy P.; Macosko, Christopher W.
    ACS Macro Letters (2015), 4 (1), 30-33CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    We show catalyst localized at the interface can compatibilize polyethylene (PE) and polylactide (PLA) blends. Telechelic hydroxyl functional PE was synthesized by ring opening metathesis polymn., which reacted with PLA in melt mixing (shown by adhesion and droplet size redn.). Lewis acid tin catalysts were examd. as interfacial reaction promoters, with the goal of interfacial localization. Stannous octoate was shown to localize at the interface by transmission electron microscopy with energy dispersive X-ray spectroscopy and improved dispersion of PLA in PE as compared to uncatalyzed materials and a nonlocalized tin chloride dihydrate.
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    Graziano, A.; Jaffer, S.; Sain, M. Review on Modification Strategies of Polyethylene/Polypropylene Immiscible Thermoplastic Polymer Blends for Enhancing Their Mechanical Behavior. J. Elastomers Plast. 2019, 51 (4), 291– 336,  DOI: 10.1177/0095244318783806
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    Review on modification strategies of polyethylene/polypropylene immiscible thermoplastic polymer blends for enhancing their mechanical behavior
    Graziano, Antimo; Jaffer, Shaffiq; Sain, Mohini
    Journal of Elastomers & Plastics (2019), 51 (4), 291-336CODEN: JEPLAX; ISSN:0095-2443. (Sage Publications Ltd.)
    A review . Blends of polyethylene (PE) and polypropylene (PP) have always been the subject of intense reasearch for encouraging polymer waste recycling while producing new materials for specific applications in a sustainable way. However, being thermodynamically immiscible, these polyolefins form a binary system usually exhibiting lower performances compared with those of the homopolymers. Many studies have been carried out to better understand the PE/PP blend compatibilization for developing a high-performance and cost-effective product. Both nonreactive and reactive compatibilization promote the brittle to ductile transition for a PE/PP blend. However, the final product usually does not meet the requirements for high demanding com. applications. Therefore, further PE/PP modification with a reinforcing filler, being either synthetic or natural, proved to be a good method for manufg. high-performance reinforcend polymer blend composites, with superior and tailored properties. This review summarizes the recent progress in compatibilization techniques applied for enhancing the interfacial adhesion between PE and PP. Moreover, future perspectives on better understanding the influence of themodynamics on PE/PP synergy are discussed to introduce more effective compatibilization strategies, which will allow this blend to be used for innovative industrial applications.
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    Song, J.; Ewoldt, R. H.; Hu, W.; Craig Silvis, H.; Macosko, C. W. Flow Accelerates Adhesion between Functional Polyethylene and Polyurethane. AIChE J. 2011, 57 (12), 3496– 3506,  DOI: 10.1002/aic.12551
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    Flow accelerates adhesion between functional polyethylene and polyurethane
    Song, Jie; Ewoldt, Randy H.; Hu, Wanli; Craig Silvis, H.; Macosko, Christopher W.
    AIChE Journal (2011), 57 (12), 3496-3506CODEN: AICEAC; ISSN:0001-1541. (John Wiley & Sons, Inc.)
    Polyethylene (PE) has relatively poor adhesion with polar polymeric materials. In an effort to improve the adhesion between PE and thermoplastic polyurethane (TPU), maleic anhydride (MA), hydroxyl (OH), and secondary amine (NHR) functionalized PEs were blended into nonmodified PE. These functional groups will react with urethane linkages in TPU at the temp. of melt processing. We bonded these PEs to TPU via lamination and coextrusion. To compare the two processes, we detd. the interfacial copolymer d. Σ considering both advection and interfacial area generation. We found that the development of adhesion in coextrusion was much faster in comparison with lamination at the same temp. This difference was attributed to the extensional and compressive flow in coextrusion overcoming the diffusion barrier at the interface and forcing reactive species to penetrate the interface. The effects of functional group reactivity and processing variables on adhesion were correlated with interfacial copolymer coverage. Amine functionalized PE showed dramatic adhesion improvement even at 1%. © 2011 American Institute of Chem. Engineers AIChE J, 2011.
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    Dogan, S. K.; Reyes, E. A.; Rastogi, S.; Ozkoc, G. Reactive Compatibilization of PLA/TPU Blends with a Diisocyanate. J. Appl. Polym. Sci. 2014, 131 (10), 40251,  DOI: 10.1002/app.40251
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    Reactive compatibilization of PLA/TPU blends with a diisocyanate
    Dogan, Sebnem Kemaloglu; Reyes, Efren Andablo; Rastogi, Sanjay; Ozkoc, Guralp
    Journal of Applied Polymer Science (2014), 131 (10), 40251/1-40251/10CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    This study focuses on the compatibilization of poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blends by using 1,4 phenylene diisocyanate (PDI) for the first time, as the compatibilizer. Because of the potential interactions of diisocyanates with -OH/-COOH, they are useful for reactive processing of PLA/TPU blends in the melt processing. To have insight on the reactively compatibilized structure of PLA/TPU blends, phase morphologies are obsd. by means of SEM. The mech., thermal, and rheol. responses of the blends are investigated. The observations are that the brittle behavior of PLA changes to ductile with the addn. of TPUs. The addn. of PDI improves the tensile properties of the blends. The compatibilization action of PDI is monitored with DMA and rheol. expts. Cross-over in the G' and G'' curves of compatibilized blends indicates the relaxation of branches formed in the presence of PDI. The dispersed phase size of TPU decreases in PLA in the presence of PDI due to the improved compatibility. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40251.
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    Lu, Q.-W.; Hoye, T. R.; Macosko, C. W. Reactivity of Common Functional Groups with Urethanes: Models for Reactive Compatibilization of Thermoplastic Polyurethane Blends. J. Polym. Sci. Part A Polym. Chem. 2002, 40 (14), 2310– 2328,  DOI: 10.1002/pola.10310
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    Reactivity of common functional groups with urethanes: models for reactive compatibilization of thermoplastic polyurethane blends
    Lu, Qi-Wei; Hoye, Thomas R.; Macosko, Christopher W.
    Journal of Polymer Science, Part A: Polymer Chemistry (2002), 40 (14), 2310-2328CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    Two model urethane compds., di-Bu 4,4'-methylenebis(Ph carbamate) (BMB) and dioctyl 4,4'-methylenebis(Ph carbamate) (OMO) were prepd. by capping 4,4'-methylenebis(Ph isocyanate) with n-butanol and n-octanol, resp. The reactions of the two model urethane compds. with several small monofunctional compds. as well as two model poly(ethylene glycols) were carried out with neat mixts. at elevated temps. The ranking of reactivity of the functional groups with the urethanes was detd. as follows-primary amine > secondary amine » hydroxyl ∼ acid ∼ anhydride » epoxide. NMR spectroscopy (NMR) was used for the quant. anal. Fourier transform IR spectroscopy was used to complement the NMR anal. Conversions of carbamate in each reaction were monitored over time at const. temp. (200°). The reactions between OMO and primary amine were conducted at 170°, 180°, 190°, and 200° and best described with a second-order bimol. reaction model. The rate const. was estd. to be 1.8 × 10-3 L·mol-1·s-1 and activation energy 115 kJ·mol-1.
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    Abdul Razak, N. C.; Inuwa, I. M.; Hassan, A.; Samsudin, S. A. Effects of Compatibilizers on Mechanical Properties of PET/PP Blend. Compos. Interfaces 2013, 20 (7), 507– 515,  DOI: 10.1080/15685543.2013.811176
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    Effects of compatibilizers on mechanical properties of PET/PP blend
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    Composite Interfaces (2013), 20 (7), 507-515CODEN: CMNTEU; ISSN:1568-5543. (Taylor & Francis Ltd.)
    Polyethylene terephthalate (PET) and polypropylene (PP) are incompatible thermoplastics due to differences in chem. structure and polarity hence their blends posses inferior mech. properties. Compatibilization with a suitable block/graft copolymer is one way to improve the mech. properties esp. impact strength of such a blend. In this work, the effects of two compatibilizers, maleic anhydride grafted polypropylene (PP-g-MAH) and maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH), were investigated for compatibilization of PET/PP blends and the results were compared. PET, PP, and compatibilizers were melt blended in a single step using a counter-rotating twin screw extruder with compatibilizer concns. 0, 2, 4, 6, 8, and 10 phr, resp. Std. test samples were prepd. by injection molding process. The resulting compatibilized blends were characterized by tensile, flexural, and impact tests. The results showed improvements in mech. properties of the blends due to the in-situ polymn. reaction between the ester groups of PET and the maleic anhydride (MAH) during melt extrusion. The incorporation of 4 phr PP-g-MAH in the blends resulted in the highest tensile and flexural strength, while no significant improvements in Young's modulus were obsd. for both compatibilized blends. The max. impact strength of the blends was obtained at 8 phr of SEBS-g-MAH. Improvement of impact strength of the blends may be attributed to the elastomeric nature of the SEBS-g-MAH while greater improvement recorded for tensile and flexural strength is likely to be due to the affinity between PP-g-MAH with PP of the blend. SEM shows the addn. of PP-g-MAH and SEBS-g-MAH compatibilizers into the blends promote a better dispersion of PP into PET matrix.
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    Papadopoulou, C. P.; Kalfoglou, N. K. Comparison of Compatibilizer Effectiveness for PET/PP Blends: Their Mechanical, Thermal and Morphology Characterization. Polymer 2000, 41 (7), 2543– 2555,  DOI: 10.1016/S0032-3861(99)00442-5
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    Holsti-Miettinen, R.; Seppala, J.; Ikkala, O. T.
    Polymer Engineering and Science (1992), 32 (13), 868-7CODEN: PYESAZ; ISSN:0032-3888.
    Compatibilization of polyamide 6 (I)/isotactic polypropylene (II) blends was investigated by mech., morphol., thermal, and rheometrical methods. Four compatibilizers including maleic anhydride, fumaric acid, or glycidyl functionalities were applied at 5 and 10% concns. Maleated hydrogenated triblock SBR gave excellent mech. properties, esp. at high I/II ratios. The correlation between morphol. and mech. and rheol. properties was discussed, and the interesting effect of blending on the kinetics of crystn. was noted.
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    Shi, D.; Ke, Z.; Yang, J.; Gao, Y.; Wu, J.; Yin, J. Rheology and Morphology of Reactively Compatibilized PP/PA6 Blends. Macromolecules 2002, 35 (21), 8005– 8012,  DOI: 10.1021/ma020595d
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    Macromolecules (2002), 35 (21), 8005-8012CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    This work aims to use the Palierne emulsion type model to describe the relationship between the rheol. response to small amplitude oscillatory deformation and morphol. of polypropylene/polyamide 6 (PP/PA6) blends compatibilized with maleic anhydride grafted polypropylene (PP-g-MAH). It was found that the Palierne emulsion type model could describe very well the linear viscoelastic responses of binary uncompatibilized PP/PA6 blends and failed to describe the ternary compatibilized PP/PP-g-MAH/PA6 blends. These features could be attributed to the fact that the morphol. of the ternary blends was not of the emulsion type with the PA6 particles dispersed in the PP matrix but of an emulsion-in-emulsion type, i.e., PA6 particles dispersed in the PP matrix themselves contained PP or PP-g-MAH inclusions. By consideration of PP-in-PA6 particles as pure PA6 particles, where the vol. fraction of the PA6 phase was increased accordingly, the Palierne emulsion type model could work very well for a ternary blending system. Preshear at low frequencies modified the morphol. of both binary and ternary blends. The particles of the dispersed phase (PA6) became more uniform. These results suggested that the Palierne emulsion type model could be used to ext. information on rheol. properties and interfacial tension of polymer blends from known morphol. and vice versa.
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    Eriksen, M. K.; Pivnenko, K.; Faraca, G.; Boldrin, A.; Astrup, T. F. Dynamic Material Flow Analysis of PET, PE, and PP Flows in Europe: Evaluation of the Potential for Circular Economy. Environ. Sci. Technol. 2020, 54 (24), 16166– 16175,  DOI: 10.1021/acs.est.0c03435
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    Dynamic material flow analysis of PET, PE, and PP flows in Europe: Evaluation of the potential for circular economy
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    Environmental Science & Technology (2020), 54 (24), 16166-16175CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    This study evaluates the potential circularity of PET, PE, and PP flows in Europe based on dynamic material flow anal. (MFA), considering product lifetimes, demand growth rates, and quality redns. of recycled plastic (downcycling). The circularity was evaluated on a baseline scenario, representing 2016 conditions, and on prospective scenarios representing key circularity enhancing initiatives, including maintaining const. plastic consumption, managing waste plastic exports in the EU, design-for-recycling initiatives, improved collection, and improved recovery and reprocessing. Low recycling rates (RR, 13-20%) and dependence on virgin plastic, representing 85-90% of the annual plastic demand, were demonstrated after 50 years in the baseline. Limited improvements were related to the individual scenarios, insufficient to meet existing recycling targets. However, by combining initiatives, RRs above 55%, where 75-90% was recycled in a closed loop, were demonstrated. Moreover, 40-65% of the annual demand could potentially be covered by recycled plastic. Maintaining a const. plastic demand over time was crucial in order to reduce the abs. dependence on virgin plastic, which was not reflected by the RR. Thus, focusing strictly on RRs and even whether and to which extent virgin material is substituted, is insufficient for evaluating the transition toward circularity, which cannot be achieved by technol. improvements alone-the demand must also be stabilized.
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    Wang, D.; Li, Y.; Xie, X. M.; Guo, B. H. Compatibilization and Morphology Development of Immiscible Ternary Polymer Blends. Polymer 2011, 52 (1), 191– 200,  DOI: 10.1016/j.polymer.2010.11.019
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    Wang, Dong; Li, Yan; Xie, Xu-Ming; Guo, Bao-Hua
    Polymer (2011), 52 (1), 191-200CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    We report a novel and effective strategy that compatibilizes three immiscible polymers, polyolefins, styrene polymers, and engineering plastics, achieved by using a polyolefin-based multi-phase compatibilizer. Compatibilizing effect and morphol. development are investigated in a model ternary immiscible polymer blends consisting of polypropylene (PP)/polystyrene(PS)/polyamide(PA6) and a multi-phase compatibilizer (PP-g-(MAH-co-St)) as prepd. by maleic anhydride (MAH) and styrene (St) dual monomers melt grafting PP. SEM results indicate that, as a multi-phase compatibilizer, PP-g-(MAH-co-St) shows effective compatibilization in the PP/PS/PA6 blends. The particle size of both PS and PA6 is greatly decreased due to the addn. of multi-phase compatibilizer, while the interfacial adhesion in immiscible pairs is increased. This good compatibilizing effect is promising for developing a new, technol. attractive method for achieving compatibilization of immiscible multi-component polymer blends as well as for recycling and reusing of such blends. For phase morphol. development, the morphol. of PP/PS/PA6 (70/15/15) uncompatibilized blend reveals that the blend is constituted from PP matrix in which are dispersed composite droplets of PA6 core encapsulated by PS phase. Whereas, the compatibilized blend shows the three components strongly interact with each other, i.e. multi-phase compatibilizer has good compatibilization between the various immiscible pairs. For the 40/30/30 blend, the morphol. changed from a three-phase co-continuous morphol. (uncompatibilized) to the dispersed droplets of PA6 and PS in the PP matrix (compatibilized).
  102. 102
    Li, H.; Xie, X. M. Morphology Development and Superior Mechanical Properties of PP/PA6/SEBS Ternary Blends Compatibilized by Using a Highly Efficient Multi-Phase Compatibilizer. Polymer 2017, 108, 1– 10,  DOI: 10.1016/j.polymer.2016.11.044
    Google Scholar
    102
    Morphology development and superior mechanical properties of PP/PA6/SEBS ternary blends compatibilized by using a highly efficient multi-phase compatibilizer
    Li, Huanmin; Xie, Xu-Ming
    Polymer (2017), 108 (), 1-10CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    Multi-phase compatibilizers are potentially attractive, not only for the prepn. of ternary or multi-phase immiscible polymer blends with high performance, but also for recycling and reuse of waste plastics mixt. In this study, the maleic anhydride (MAH) and styrene (St) dual monomers grafted PP, PP-g-(MAH-co-St) is prepd. as a multi-phase compatibilizer, which exhibits highly effective compatibility on the PP/PA6/SEBS (70/15/15) ternary blends. SEM (SEM) reveals that, with increasing the compatibilizer, the morphol. evolves from the individual PA6 particle encapsulated by SEBS to several smaller-size PA6 particles partially encapsulated by SEBS phase, then to the tiny PA6 particles and some larger-size SEBS agglomerates predominantly dispersed sep. in PP matrix. The morphol. development predicted by spreading coeffs. shows a consummate consistency with that obsd. by SEM. Moreover, the good compatibilization and corresponding morphologies result in superior enhancement of mech. properties. Compared to the uncompatibilized blend, adding 15 wt% multi-phase compatibilizer to the blend leads to the best mech. properties with the yield stress, stress at break, strain at break and impact failure energy improved significantly by 23%, 132%, 647% and 220%, resp. The results verify that the domains with small-size PA6 particles (0.3-0.4 μm) partially encapsulated by SEBS (0.5-0.7 μm) in PP matrix are very effective to enhance the mech. properties of the blends. The morphologies of large-size PA6 particles encapsulated by SEBS or tiny PA6 particles and some larger-size SEBS agglomerates dispersed sep. in PP matrix for the enhancement in mech. properties of the blends are very limited. Consequently, the enhanced interfacial interactions and the morphol. with the rigid particles partially encapsulated by a rubber-like phase in matrix are crucial for the ternary polymer blends.

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  • Abstract

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    Figure 1

    Figure 1. Structures, names, and recycling codes for common polymers discussed in this perspective.

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    Figure 2

    Figure 2. Illustration of a polymer–polymer interface being stabilized with a (i) diblock copolymer, (ii) triblock copolymer, and (iii) grafted copolymer.

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    Figure 3

    Figure 3. Diverse range of possible copolymer architectures using only two distinct blocks.

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    Figure 4

    Figure 4. Depiction of several MBCPs (n > 2) stabilizing a polymer–polymer interface, highlighting the increased number of interface crossings per molecule with an increased number of blocks.

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    Figure 5

    Figure 5. Uniaxial tensile elongation of PE/iPP materials and blends. Materials were melt-blended at 190 °C without BCPs (black) or with 1 wt % diblock (green), 1 wt % tetrablock (orange), or 5 wt % tetrablock copolymers (purple). These materials were then compression molded into tensile specimens at 180 °C and tensile tested at a rate of 100%/min (Adapted with permission from the work of Eagan et al. (35) Copyright 2017 AAAS).

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    Figure 6

    Figure 6. Schematics of lMBCP forming trapped entanglements and cocrystallizing with homopolymers.

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    Figure 7

    Figure 7. Schematic of reactively formed graft copolymers. Reactive groups must both be present at the interface to form the compatibilizer.

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    Figure 8

    Figure 8. Interplay between phases and compatibilizer in preliminary ternary system studies (Adapted with permission from ref (101). Copyright 2011 Elsevier Ltd.).

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      A review with 21 refs. Introduction of a compatibilizing agent, i.e. block or graft copolymers having segments of similar structure or soly. parameter, permitted the blending of incompatible polymers and enhanced the dispersion of fillers and reinforcing agents.
    20. 20
      Macosko, C. W.; Guégan, P.; Khandpur, A. K.; Nakayama, A.; Marechal, P.; Inoue, T. Compatibilizers for Melt Blending: Premade Block Copolymers. Macromolecules 1996, 29 (17), 5590– 5598,  DOI: 10.1021/ma9602482
      20
      Compatibilizers for Melt Blending: Premade Block Copolymers
      Macosko, C. W.; Guegan, Philippe; Khandpur, Ashish K.; Nakayama, Akinari; Marechal, Philippe; Inoue, Takashi
      Macromolecules (1996), 29 (17), 5590-5598CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Poly(Me methacrylate) (PMMA) was melt mixed 30:70 into polystyrene (PS) with and without sym. P(S-b-MMA) diblock copolymers. The mol. wt. of the components was varied. After 5 min of shear mixing, the PMMA was dispersed into roughly spherical, submicron particles. Particle size was measured by light scattering and transmission electron microscopy. As little as 1% copolymer led to a significant redn. in PMMA particle size, although larger amts. were needed to make the particles stable to annealing (180° for 15 min). The main role of block copolymers in controlling morphol. appears to be in preventing coalescence. Preventing dynamic coalescence leads to size redn., while preventing static coalescence results in stability or compatibilization. We est. that less than 5% of the interface needs to be covered to prevent dynamic coalescence while ∼20% is necessary to impart static stability. Mobility, crit. micelle concn., and mol. wt. of the block copolymer also appear to be important. Lowering the mol. wt. of the PMMA phase from 43,000 to 11,000 resulted in dramatically lower particle size (700 vs 60 nm). These variables are discussed in terms of a qual. balance between rate of diffusion and rate of area generation during blending.
    21. 21
      Noolandi, J.; Hong, K. M. Interfacial Properties of Immiscible Homopolymer Blends in the Presence of Block Copolymers. Macromolecules 1982, 15 (2), 482– 492,  DOI: 10.1021/ma00230a054
      21
      Interfacial properties of immiscible homopolymer blends in the presence of block copolymers
      Noolandi, J.; Hong, K. M.
      Macromolecules (1982), 15 (2), 482-92CODEN: MAMOBX; ISSN:0024-9297.
      The emulsifying effect of block copolymers in immiscible homopolymer blends was studied using a formalism for inhomogeneous, multicomponent polymer systems previously developed. The redn. in interfacial tension with increasing block polymer concn. was calcd. for a range of copolymer and homopolymer mol. wt. and compared with the data of G. Riess et al. (1980) for polystyrene [9003-53-6]-polybutadiene [9003-17-2]-butadiene-styrene block polymer [9003-55-8] blends. The calcd. interfacial d. profiles show increasing exclusion of homopolymers from the interphase region with increasing block polymer mol. wt. The crit. concn. of block polymer for micellar aggregation in the bulk of the homopolymer was detd.
    22. 22
      Galloway, J. A.; Jeon, H. K.; Bell, J. R.; Macosko, C. W. Block Copolymer Compatibilization of Cocontinuous Polymer Blends. Polymer 2005, 46 (1), 183– 191,  DOI: 10.1016/j.polymer.2004.10.061
      22
      Block copolymer compatibilization of cocontinuous polymer blends
      Galloway, Jeffrey A.; Jeon, Hyun K.; Bell, Joel R.; Macosko, Christopher W.
      Polymer (2005), 46 (1), 183-191CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      The effect of block copolymers on the cocontinuous morphol. of 50/50 (wt./wt.) polystyrene (PS)/high d. polyethylene (HDPE) blends was investigated using sym. polystyrene-polyethylene block copolymers (PS-PE) with mol. wts. varying from 6 to 200 kg/mol. The coarsening rate during annealing was compared to the Doi-Ohta theory. An intermediate mol. wt. PS-PE, 40 kg/mol, showed remarkable results in reducing the phase size and stabilizing the blend morphol. during annealing. Mixing small amts. of 6, 100 or 200 kg/mol PS-PE in the blend did not reduce the phase size significantly, but did decrease the coarsening rate during annealing. In stabilizing the morphol., 6 kg/mol PS-PE was inferior to 100 and 200 kg/mol. The existence of an optimal mol. wt. block copolymer is due to a balance between the ability of the block copolymer to reach the interface and its relative stabilization effect at the interface.
    23. 23
      Chang, K.; Macosko, C. W.; Morse, D. C. Interfacial Tension Measurement and Micellization in a Polymer Blend with Copolymer Surfactant: A False Critical Micelle Concentration. Macromolecules 2015, 48 (22), 8154– 8168,  DOI: 10.1021/acs.macromol.5b01268
      23
      Interfacial Tension Measurement and Micellization in a Polymer Blend with Copolymer Surfactant: A False Critical Micelle Concentration
      Chang, Kwanho; Macosko, Christopher W.; Morse, David C.
      Macromolecules (Washington, DC, United States) (2015), 48 (22), 8154-8168CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The interfacial tension between polystyrene (PS) and polybutadiene (PB) homopolymers is measured in the presence of a nearly sym. poly(styrene-b-butadiene) (SB) copolymer and compared to independent measurements of the crit. micelle concn. (CMC) by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), and to SCF theory (SCFT) predictions. Interfacial tension is measured with a spinning drop tensiometer (SDT) contg. a drop of PB in a PS matrix, using samples in which varying concns. of SB copolymer were initially added to either PS or PB. When SB is premixed with PS, the dependence of the interfacial tension γ upon copolymer concn. c is qual. similar to that expected in equil., showing a decrease of γ with increasing c for c less than an apparent CMC and then satg. at higher concns. TEM and SAXS studies of a binary mixt. of the same copolymer and PS homopolymer show, however, that the true CMC in PS is much lower than the apparent CMC inferred from these SDT expts. We analyze the role of transport limitations in this expt. and propose that this discrepancy may be a result of a suppressed copolymer chem. potential near the interface due to continual diffusion of copolymer into the PB drop.
    24. 24
      Willis, J. M.; Favis, B. D. Processing-morphology Relationships of Compatibilized Polyolefin/Polyamide Blends. Part I: The Effect of an Lonomer Compatibilizer on Blend Morphology. Polym. Eng. Sci. 1988, 28 (21), 1416– 1426,  DOI: 10.1002/pen.760282111
      24
      Processing-morphology relationships of compatibilized polyolefin/polyamide blends. Part I. The effect of an ionomer compatibilizer on blend morphology
      Willis, J. M.; Favis, B. D.
      Polymer Engineering and Science (1988), 28 (21), 1416-26CODEN: PYESAZ; ISSN:0032-3888.
      The addn. of Surlyn 9020 (I) compatibilizer to HDPE- and isotactic polypropylene-nylon 6 blends increased the dispersion and decreased the particle size of the dispersed phase as shown by SEM of the fracture-surface morphol. For a dispersed phase content of 10%, a max. redn. in phase size was obsd. when only 0.5% I was added to the blend. Mol. interaction between I and nylon 6 resulted in a greater redn. in the phase size of dispersed nylon compared to that of dispersed polyolefin. Flocculation of the nylon dispersed phase was obsd. at high I concns. The blend morphol. was also dependent on the mode of addn. of I. In comparison to 1-step mixing, blends prepd. by 2-step or batch mixing exhibited a smaller dispersed phase when nylon was the matrix and a larger particle size when nylon was the minor phase.
    25. 25
      Zhang, C. L.; Feng, L. F.; Gu, X. P.; Hoppe, S.; Hu, G. H. Efficiency of Graft Copolymers as Compatibilizers for Immiscible Polymer Blends. Polymer 2007, 48 (20), 5940– 5949,  DOI: 10.1016/j.polymer.2007.07.042
      25
      Efficiency of graft copolymers as compatibilizers for immiscible polymer blends
      Zhang, Cai-Liang; Feng, Lian-Fang; Gu, Xue-Ping; Hoppe, Sandrine; Hu, Guo-Hua
      Polymer (2007), 48 (20), 5940-5949CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      This work was aimed at studying the emulsification efficiency of graft copolymers and the effect of feeding mode on the emulsification efficiency using the emulsification curve approach. The blends were composed of polystyrene (PS) and polyamide 6 (PA6). PS was always the matrix and PA6 the dispersed phase. A series of graft copolymers of PS and PA6, denoted as PS-g-PA6, with different mol. structures were used as emulsifiers. Feeding mode had a very significant effect on the size of the dispersed phase domains at short mixing time and its effect decreased or became negligible at long mixing time. This indicates that feeding mode affected mostly the time necessary for the PS-g-PA6 emulsifier to reach and emulsify the PS/PA6 interfaces. The mol. structure of the PS-g-PA6 graft copolymer also had a profound effect on its emulsification efficiency. The longer the PA6 grafts (from 1.7 to 5.1 kg/mol), the higher the emulsification efficiency. On the other hand, the no. of PA6 grafts had little effect on the emulsification efficiency when the PA6 grafts were short (1.6-1.7 kg/mol). The effect of the blend compn. was also investigated.
    26. 26
      Lee, M. S.; Lodge, T. P.; Macosko, C. W. Can Random Copolymers Serve as Effective Polymeric Compatibilizers?. J. Polym. Sci., Part B: Polym. Phys. 1997, 35 (17), 2835– 2842,  DOI: 10.1002/(SICI)1099-0488(199712)35:17<2835::AID-POLB8>3.0.CO;2-P
      26
      Can random copolymers serve as effective polymeric compatibilizers?
      Lee, M. S.; Lodge, T. P.; Macosko, C. W.
      Journal of Polymer Science, Part B: Polymer Physics (1997), 35 (17), 2835-2842CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
      We investigate the compatibilizing performance of a random copolymer in the melt state, using transmission electron microscopy. Blends of polystyrene (PS) and poly(Me methacrylate) (PMMA) are chosen as a model system, and a random copolymer of styrene and Me methacrylate (SMMA) with 70 wt% styrene is used as a compatibilizer. From TEM photographs it is clear that SMMA moves to the interface between PS and PMMA domains during melt mixing, and forms encapsulating layers. However, the characteristic size of the dispersed phase increases gradually with annealing time for all blend systems studied. This demonstrates that the encapsulating layer of SMMA does not provide stability against static coalescence, which calls into question the effectiveness of random copolymers as practical compatibilizers. We interpret the encapsulation by random copolymers in terms of a simple model for ternary polymer blends.
    27. 27
      Sundararaj, U.; Macosko, C. W. Drop Breakup and Coalescence in Polymer Blends: The Effects of Concentration and Compatibilization. Macromolecules 1995, 28 (8), 2647– 2657,  DOI: 10.1021/ma00112a009
      27
      Drop Breakup and Coalescence in Polymer Blends: The Effects of Concentration and Compatibilization
      Sundararaj, Uttandaraman; Macosko, C. W.
      Macromolecules (1995), 28 (8), 2647-57CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A limiting dispersed phase particle size exists at low concns. for polymer blends mixed in an internal batch mixer and 2 types of twin-screw extruders. The Taylor limit for breakup of a single drop in a matrix under-predicts the limiting particle size; this discrepancy is attributed to viscoelastic effects. For uncompatibilized blends, the final particle size increases with the dispersed phase concn. due to increased coalescence. The particle size distribution also broadens at higher concns. Using in-situ reaction during blending or adding pre-made diblock copolymers suppresses coalescence resulting in smaller particle size and narrower particle size distribution. Using pre-made block copolymers is not as efficient in stabilizing morphol. as using reactive polymers. The main advantage of using compatibilizers in polymer blends is the suppression of coalescence achieved through stabilizing the interface, not a redn. in the interfacial tension. There is a crit. shear rate in polymer systems where a min. particle size is achieved. A qual. explanation of why this occurs is given based on droplet elasticity.
    28. 28
      Fayt, R.; Jerome, R.; Teyssié, P. Molecular Design of Multicomponent Polymer Systems, 13. Control of the Morphology of Polyethylene/Polystyrene Blends by Block Copolymers. Die Makromol. Chemie 1986, 187 (4), 837– 852,  DOI: 10.1002/macp.1986.021870414
      There is no corresponding record for this reference.
    29. 29
      Lefebvre, M. D.; Dettmer, C. M.; McSwain, R. L.; Xu, C.; Davila, J. R.; Composto, R. J.; Nguyen, S. T.; Shull, K. R. Effect of Sequence Distribution on Copolymer Interfacial Activity. Macromolecules 2005, 38 (25), 10494– 10502,  DOI: 10.1021/ma0509762
      29
      Effect of Sequence Distribution on Copolymer Interfacial Activity
      Lefebvre, Michelle D.; Dettmer, Christine M.; McSwain, Rachel L.; Xu, Chen; Davila, Jonathan R.; Composto, Russell J.; Nguyen, SonBinh T.; Shull, Kenneth R.
      Macromolecules (2005), 38 (25), 10494-10502CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Interfacial segregation of diblock, gradient, and random copolymers was measured using forward recoil spectrometry. The polymers were synthesized by a ring-opening metathesis polymn., allowing a high degree of control over the sequence distribution. The norbornene-based monomers have reactivity ratios close to unity, which makes them ideal for facile tailoring of different gradient copolymer profiles. The copolymers form a good weakly segregating model system for which we can obtain an est. of the interaction parameter χ. Mean-field theory was used to describe the interfacial segregation results and to relate the measured quantities to the detailed mol. structure of the interface. The diblock copolymer forms a monolayer at the interface and significantly reduces the interfacial tension, while the random copolymer forms an interfacial wetting layer. The gradient copolymer exhibits intermediate behavior, forming a monolayer with a larger interfacial width than that of the diblock copolymer.
    30. 30
      Lefebvre, M. D.; Olvera de la Cruz, M.; Shull, K. R. Phase Segregation in Gradient Copolymer Melts. Macromolecules 2004, 37 (3), 1118– 1123,  DOI: 10.1021/ma035141a
      30
      Phase Segregation in Gradient Copolymer Melts
      Lefebvre, Michelle D.; Olvera de la Cruz, Monica; Shull, Kenneth R.
      Macromolecules (2004), 37 (3), 1118-1123CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Local segregation in melts of copolymers with compn. gradients along their backbones is analyzed. The transition to a lamellar periodic structure as the effective degree of incompatibility χN increases is studied for sym. copolymers with various compn. gradients. A numerical self-consistent mean-field (SCMF) technique is used to characterize the ordered lamellar state in the weak and strong segregation regimes, and the RPA is used to calc. the scattering function anal. and find the location of the crit. order-disorder transition for each melt. The crit. point increases from (χN)c = 10.495 for block copolymers to (χN)c = 29.25 for a fully tapered linear gradient copolymer. For broad compn. gradients the equil. lamellar repeat length is shorter for a given value of χN, and the unit cell compn. profile is more sinusoidal. The dependence of the equil. repeat distance on χN is nearly universal when renormalized by the crit. point of each copolymer.
    31. 31
      Shull, K. R. Interfacial Activity of Gradient Copolymers. Macromolecules 2002, 35 (22), 8631– 8639,  DOI: 10.1021/ma020698w
      31
      Interfacial Activity of Gradient Copolymers
      Shull, Kenneth R.
      Macromolecules (2002), 35 (22), 8631-8639CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Numerical SCF theory is used to study the equil. segregation of A/B gradient copolymers to the interface between immiscible A and B homopolymers. A generalized SCF theory is developed that allows arbitrary compn. gradients to be investigated. The focus of this paper is on sym. copolymers consisting of equal amts. of A and B repeat units, with a linear or hyperbolic tangent compn. gradient. A gradient parameter, λ, is introduced that describes the length of the compn. gradient relative to the length of the entire copolymer mol. Crit. values of the copolymer chem. potential corresponding to the formation of copolymer micelles, or to a vanishing interfacial free energy between A and B homopolymer phases, decrease with λ, and are about 1.6kBT lower for λ = 1 than for λ = 0. The width of the concn. profile of A or B repeat units within a lamellar copolymer phase, or across an emulsified interface, increases with λ, and is equal to about twice the copolymer radius of gyration for λ = 1.
    32. 32
      Levine, W. G.; Seo, Y.; Brown, J. R.; Hall, L. M. Effect of Sequence Dispersity on Morphology of Tapered Diblock Copolymers from Molecular Dynamics Simulations. J. Chem. Phys. 2016, 145 (23), 234907,  DOI: 10.1063/1.4972141
      32
      Effect of sequence dispersity on morphology of tapered diblock copolymers from molecular dynamics simulations
      Levine, William G.; Seo, Youngmi; Brown, Jonathan R.; Hall, Lisa M.
      Journal of Chemical Physics (2016), 145 (23), 234907/1-234907/8CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Tapered diblock copolymers are similar to typical AB diblock copolymers but have an added transition region between the two blocks which changes gradually in compn. from pure A to pure B. This tapered region can be varied from 0% (true diblock) to 100% (gradient copolymer) of the polymer length, and this allows some control over the microphase sepd. domain spacing and other material properties. We perform mol. dynamics simulations of linearly tapered block copolymers with tapers of various lengths, initialized from fluids d. functional theory predictions. To investigate the effect of sequence dispersity, we compare systems composed of identical polymers, whose taper has a fixed sequence that most closely approximates a linear gradient, with sequentially disperse polymers, whose sequences are created statistically to yield the appropriate ensemble av. linear gradient. Esp. at high segregation strength, we find clear differences in polymer conformations and microstructures between these systems. Importantly, the statistical polymers are able to find more favorable conformations given their sequence, for instance, a statistical polymer with a larger fraction of A than the median will tend towards the A lamellae. The conformations of the statistically different polymers can thus be less stretched, and these systems have higher overall d. Consequently, the lamellae formed by statistical polymers have smaller domain spacing with sharper interfaces. (c) 2016 American Institute of Physics.
    33. 33
      Von Tiedemann, P.; Blankenburg, J.; Maciol, K.; Johann, T.; Müller, A. H. E.; Frey, H. Copolymerization of Isoprene with P-Alkylstyrene Monomers: Disparate Reactivity Ratios and the Shape of the Gradient. Macromolecules 2019, 52 (3), 796– 806,  DOI: 10.1021/acs.macromol.8b02280
      33
      Copolymerization of Isoprene with p-Alkylstyrene Monomers: Disparate Reactivity Ratios and the Shape of the Gradient
      von Tiedemann, Philipp; Blankenburg, Jan; Maciol, Kamil; Johann, Tobias; Mueller, Axel H. E.; Frey, Holger
      Macromolecules (Washington, DC, United States) (2019), 52 (3), 796-806CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The statistical copolymn. of isoprene with p-ethyl- (p-ES), p-isopropyl- (p-iPS), and p-tert-butylstyrene (p-tBS) initiated by sec-butyllithium in cyclohexane was studied with respect to kinetics, reactivity ratios, and formation of tapered block copolymers with pronounced monomer gradient. An efficient synthetic route to the monomers was developed on a multigram scale, relying on the pptn. of the side-product triphenylphosphine oxide at low temp. The copolymn. kinetics and resulting mol. wt. distributions were analyzed. The dispersity, D, of the copolymers depends on the p-alkyl substituent, the d.p. Pn and the comonomer mole fraction, X. In situ1H NMR kinetics characterization revealed a strong gradient structure for all three copolymer systems (rI = 21.9, rp-ES = 0.022; rI = 19.7, rp-iPS = 0.027; rI = 19.8, rp-tBS = 0.022). The rate of crossover from a polyisoprenyllithium chain end (I) to a p-alkylstyrene (S) unit relative to the alkylstyrene homopolymn., kIS/kSS (in 10-3 (L mol-1)-1/4), decreases in the order p-MS (19.1) > p-ES (11.3) > p-iPS (5.71) ≈ p-tBS (5.63), supporting the obsd., increasingly bimodal character of the mol. wt. distributions and the higher dispersity. Thermogravimetric anal. revealed that all poly(p-alkylstyrene) homopolymers are stable up to 300°C.
    34. 34
      Fayt, R.; Jérôme, R.; Teyssié, P. Interface Modification in Polymer Blends. Multiphase Polymers: Blends and Ionomers 1989, 58, 38– 66,  DOI: 10.1021/bk-1989-0395.ch002
      There is no corresponding record for this reference.
    35. 35
      Eagan, J. M.; Xu, J.; Di Girolamo, R.; Thurber, C. M.; Macosko, C. W.; LaPointe, A. M.; Bates, F. S.; Coates, G. W. Combining Polyethylene and Polypropylene: Enhanced Performance with PE/ i PP Multiblock Polymers. Science 2017, 355 (6327), 814– 816,  DOI: 10.1126/science.aah5744
      35
      Combining polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers
      Eagan, James M.; Xu, Jun; Di Girolamo, Rocco; Thurber, Christopher M.; Macosko, Christopher W.; La Pointe, Anne M.; Bates, Frank S.; Coates, Geoffrey W.
      Science (Washington, DC, United States) (2017), 355 (6327), 814-816CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Polyethylene (PE) and isotactic polypropylene (iPP) constitute nearly two-thirds of the world's plastic. Despite their similar hydrocarbon makeup, the polymers are immiscible with one another. Thus, common grades of PE and iPP do not adhere or blend, creating challenges for recycling these materials. We synthesized PE/iPP multiblock copolymers using an isoselective alkene polymn. initiator. These polymers can weld common grades of com. PE and iPP together, depending on the mol. wts. and architecture of the block copolymers. Interfacial compatibilization of phase-sepd. PE and iPP with tetrablock copolymers enables morphol. control, transforming brittle materials into mech. tough blends.
    36. 36
      Nomura, K.; Peng, X.; Kim, H.; Jin, K.; Kim, H. J.; Bratton, A. F.; Bond, C. R.; Broman, A. E.; Miller, K. M.; Ellison, C. J. Multiblock Copolymers for Recycling Polyethylene-Poly(Ethylene Terephthalate) Mixed Waste. ACS Appl. Mater. Interfaces 2020, 12 (8), 9726– 9735,  DOI: 10.1021/acsami.9b20242
      36
      Multiblock Copolymers for Recycling Polyethylene-Poly(ethylene terephthalate) Mixed Waste
      Nomura, Keiichiro; Peng, Xiayu; Kim, Hanim; Jin, Kailong; Kim, Hee Joong; Bratton, Abigail F.; Bond, Christopher R.; Broman, Amelia E.; Miller, Kevin M.; Ellison, Christopher J.
      ACS Applied Materials & Interfaces (2020), 12 (8), 9726-9735CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Plastic pollution is one of the most pressing global environmental issues we face today, in part due to the continued rise in prodn. and use of disposable plastic products. Polyolefins and polyesters are two of the most prevalent polymers in the world accounting for ∼80% of total nonfiber plastic prodn. Recycling, despite being intrinsically environmentally friendly and sometimes economically viable, remains at a surprisingly low level (<9% in the U.S.) with most plastic waste ending up in landfills. One reason for this low rate of recycling stems from the challenge of recycling mixed waste streams and multicomponent plastics. In mixed waste streams, phys. presorting of components prior to recycling requires significant effort, which translates to added cost. For multicomponent plastics (e.g., multilayer films such as food wrappers), the individual plastic components cannot be efficiently phys. sepd., and they are immiscible with poor interfacial adhesion when melt reprocessed. Thus, direct recycling of mixed plastics by melt reprocessing results in products that lack desired end-use properties. In this study, we describe the synthesis of novel poly(ethylene terephthalate)-polyethylene multiblock copolymers (PET-PE MBCPs) and evaluate their utility as adhesive tie layers in multilayer films and compatibilizer additives for melt reprocessed blends. PET and PE are targeted because they are two of the most prevalent com. polymers in the world and are high vol. waste streams. The work described here demonstrates two key findings. First, the PET-PE MBCPs serve as effective adhesive tie layers between neat PET/PE films with adhesive strength comparable to that of com. available adhesives. Second, PET/PE (80/20 wt %) blends contg. ∼0.5 wt % PET-PE MBCP were melt mixed to mimic recycling mixed plastic waste, and they were found to exhibit mech. properties better than neat PET. Overall, this study demonstrates that PET-PE MBCPs could significantly enhance the ability to recycle PET/PE mixed waste streams by serving the role as both an adhesive promoting layer and a compatibilizer additive.
    37. 37
      Klimovica, K.; Pan, S.; Lin, T. W.; Peng, X.; Ellison, C. J.; Lapointe, A. M.; Bates, F. S.; Coates, G. W. Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers. ACS Macro Lett. 2020, 9 (8), 1161– 1166,  DOI: 10.1021/acsmacrolett.0c00339
      37
      Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers
      Klimovica, Kristine; Pan, Sanshui; Lin, Ting-Wei; Peng, Xiayu; Ellison, Christopher J.; LaPointe, Anne M.; Bates, Frank S.; Coates, Geoffrey W.
      ACS Macro Letters (2020), 9 (8), 1161-1166CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges assocd. with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepd. using a grafting-through strategy by copolymn. of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (Mn = 6-28 kg/mol), graft nos., and graft spacings were prepd. These graft copolymers were melt-blended with high-d. polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 wt./wt.) and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt. % loading, with higher tensile strength obsd. for larger block nos. and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.
    38. 38
      Macosko, C. W.; Jeon, H. K.; Hoye, T. R. Reactions at Polymer-Polymer Interfaces for Blend Compatibilization. Prog. Polym. Sci. 2005, 30 (8–9), 939– 947,  DOI: 10.1016/j.progpolymsci.2005.06.003
      38
      Reactions at polymer-polymer interfaces for blend compatibilization
      Macosko, Christopher W.; Jeon, Hyun K.; Hoye, Thomas R.
      Progress in Polymer Science (2005), 30 (8-9), 939-947CODEN: PRPSB8; ISSN:0079-6700. (Elsevier B.V.)
      This review focuses on our research that has investigated the major factors influencing the interfacial reaction such as the inherent reactivity of functional polymers, thermodn. interaction between polymers, functional group location along a chain, and the effect of processing flows.
    39. 39
      Majumdar, B.; Keskkula, H.; Paul, D. R. Effect of the Nature of the Polyamide on the Properties and Morphology of Compatibilized Nylon/Acrylonitrile-Butadiene-Styrene Blends. Polymer 1994, 35 (25), 5468– 5477,  DOI: 10.1016/S0032-3861(05)80010-2
      39
      Effect of the nature of the polyamide on the properties and morphology of compatibilized nylon/acrylonitrile-butadiene-styrene blends
      Majumdar, B.; Keskkula, H.; Paul, D. R.
      Polymer (1994), 35 (25), 5468-77CODEN: POLMAG; ISSN:0032-3861. (Elsevier)
      The mech. properties and phase morphol. of compatibilized blends of acrylonitrile-butadiene-styrene (ABS) with a wide range of polyamide materials having different phys. and chem. characteristics were explored. The most efficient dispersion of the ABS phase and the best combination of mech. properties occur within an optimum range of the nylon/ABS viscosity ratio. It is significantly more difficult to disperse the ABS and to generate toughened blends when the polyamide material is difunctional in character, i.e. a fraction of the chains having 2 amine end-groups. Increasing the inherent ductility of the polyamide leads to improved toughness of these blends.
    40. 40
      Borggreve, R. J. M.; Gaymans, R. J. Impact Behaviour of Nylon-Rubber Blends: 4. Effect of the Coupling Agent, Maleic Anhydride. Polymer 1989, 30 (1), 63– 70,  DOI: 10.1016/0032-3861(89)90384-4
      40
      Impact behavior of nylon-rubber blends. 4. Effect of the coupling agent, maleic anhydride
      Borggreve, R. J. M.; Gaymans, R. J.
      Polymer (1989), 30 (1), 63-70CODEN: POLMAG; ISSN:0032-3861.
      Blends of 90% nylon-6 and 10% EPDM rubber were prepd. The rubber was grafted with various amts. of maleic anhydride (I) with the aid of a peroxide. The initial moduli and the melt viscosities of the rubbers were affected slightly by the I and peroxide concns. The effect of I concn. on the blending process and the impact behavior was studied. The interfacial layer was investigated using IR spectroscopy and elemental anal. The I grafted onto the rubber reacted with the nylon during the blending process. With the I-grafted rubbers, a much finer dispersion could be obtained. However, the concn. of the coupling agent, within the range 0.13 to 0.89% grafted onto the rubber, had hardly any influence on either the dispersion process or the impact behavior of the blends.
    41. 41
      Xanthos, M.; Dagli, S. S. Compatibilization of Polymer Blends by Reactive Processing. Polym. Eng. Sci. 1991, 31 (13), 929– 935,  DOI: 10.1002/pen.760311302
      41
      Compatibilization of polymer blends by reactive processing
      Xanthos, M.; Dagli, S. S.
      Polymer Engineering and Science (1991), 31 (13), 929-35CODEN: PYESAZ; ISSN:0032-3888.
      A review with 91 refs. on some recent developments in the field of reactive compatibilization of plastic blends by melt processing in extruders and intensive batch mixers is presented, discussing 3 routes to reactive compatibilization, i.e., (1) the use of suitably functionalized blend constituents, (2) the incorporation of polymeric compatibilizers, and (3) the addn. of low-mol.-wt. compds. A variety of plastic blends are discussed, including impact-modified thermoplastics, polymer-modified engineering thermoplastics, dynamically vulcanized thermoplastic elastomers, and co-crosslinked rubber/rubber blends.
    42. 42
      DOW. Polymer Compatibilizer for Recycling. https://corporate.dow.com/en-us/news/press-releases/polymer-compatibilizer-for-recycling.html (accessed Jan 4, 2022).
      There is no corresponding record for this reference.
    43. 43
      Utracki, L. A. Reactive Compatibilization. In Comercial Polymer Blends; Chapman & Hall, 1998; pp 94– 97.
      There is no corresponding record for this reference.
    44. 44
      Quirk, R. P. Compatibilization of Polymer Blends. US Patent 5264491, November 23, 1993.
      There is no corresponding record for this reference.
    45. 45
      Orr, C. A.; Cernohous, J. J.; Guegan, P.; Hirao, A.; Jeon, H. K.; Macosko, C. W. Homogeneous Reactive Coupling of Terminally Functional Polymers. Polymer 2001, 42 (19), 8171– 8178,  DOI: 10.1016/S0032-3861(01)00329-9
      45
      Homogeneous reactive coupling of terminally functional polymers
      Orr, C. A.; Cernohous, J. J.; Guegan, P.; Hirao, A.; Jeon, H. K.; Macosko, C. W.
      Polymer (2001), 42 (19), 8171-8178CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
      The rates of nine melt coupling reactions were measured by reacting terminally functional polymer chains. The functional groups are carboxylic acid, oxazoline, epoxy, arom. primary amine, aliph. primary amine, hydroxyl and cyclic anhydride. The functional groups were attached to the end of polystyrene (PS) and poly(Me methacrylate) (PMMA) chains with most expts. performed at mol. wts. of about 25,000 g/mol and temp. of 180°. Reactions were performed homogeneously by blending stoichiometric amts. of the same type of polymer contg. complementary functional groups. Reaction rates were detd. from the amt. of coupled chains via gel permeation chromatog. The functional group pairs, in order of increasing reactivity, are acid/amine, hydroxyl/(anhydride or acid), arom. amine/epoxy, aliph. amine/epoxy, acid/oxazoline, acid/epoxy, arom. amine/anhydride, aliph. amine/anhydride. This is in general agreement with results for very dil. small mol. analogs. Some expts. performed at higher mol. wts. gave similar results. Coupling between aliph. amine terminal and cyclic anhydride terminal chains was found to be extremely fast; complete conversion occurred in <30 s. Diln. studies and comparison to theory indicate that this reaction was not diffusion controlled. Mixing and diffusion are rapid enough to bring every chain end in contact within 15 s.
    46. 46
      Jeon, H. K.; Macosko, C. W.; Moon, B.; Hoye, T. R.; Yin, Z. Coupling Reactions of End- vs Mid-Functional Polymers. Macromolecules 2004, 37 (7), 2563– 2571,  DOI: 10.1021/ma030581n
      46
      Coupling Reactions of End- vs Mid-Functional Polymers
      Jeon, Hyun K.; Macosko, Christopher W.; Moon, Bongjin; Hoye, Thomas R.; Yin, Zhihui
      Macromolecules (2004), 37 (7), 2563-2571CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Reactive compatibilization of immiscible polymer blends is typically accomplished by grafting reactions between functional groups distributed randomly on one polymer and end-functional groups on the other polymer. A no. of model studies have focused on end coupling in polymer melts. In this work we compare directly reaction rate consts. for an end-functional chain reacting with an end-functional chain, kE, vs reacting with a mid-functional chain, kM, using competitive reaction of phthalic anhydride end- and mid-functional poly(Me methacrylate) (PMMA-eAn and PMMA-mAn) with amine terminal PMMA and polystyrene (PMMA-NH2 and PS-NH2). PMMA-eAn was labeled with 7-nitrobenz-2-oxa-1,3-diazole (NBD) while PMMA-mAn was labeled with anthracene. We measured the extent of coupling to block and graft copolymers selectively at the characteristic excitation and emission wavelengths of NBD and anthracene using a fluorescence detector coupled with GPC. We found that coupling with the mid-functional PMMA was slower under all reaction conditions studied and had the increasing order of kE/kM: homogeneous melt (1.7), soln. (2.8), heterogeneous blend prepd. in the mixer (2.6-3.2), and static flat interface (>10). The kinetic excluded-vol. effect and steric hindrance due to the polymer chain are considered to be the reasons for kE/kM > 1 in the homogeneous case. kE/kM in soln. was in agreement with the value (2.1) predicted by the kinetic excluded-vol. theory. The large value of kE/kM in the static flat interface was attributed to end-group segregation at the interface. Interestingly, we found that flow affected the interfacial reaction tremendously, resulting in over 1000 times higher rate const. in heterogeneous melt blending than that in the static bilayer film.
    47. 47
      Kim, S.; Kim, J. K.; Park, C. E. Effect of Molecular Architecture of in situ Reactive Compatibilizer on the Morphology and Interfacial Activity of an Immiscible. Polyolefin/Polystyrene Blend 1997, 38 (8), 1809– 1815,  DOI: 10.1016/S0032-3861(96)00714-8
      There is no corresponding record for this reference.
    48. 48
      Yin, Z.; Koulic, C.; Pagnoulle, C.; Jé Rô Me, R. Reactive Blending of Functional PS and PMMA: Interfacial Behavior of in situ Formed Graft Copolymers. Macromolecules 2001, 34, 5132– 5139,  DOI: 10.1021/ma001798+
      48
      Reactive Blending of Functional PS and PMMA: Interfacial Behavior of in situ Formed Graft Copolymers
      Yin, Z.; Koulic, C.; Pagnoulle, C.; Jerome, R.
      Macromolecules (2001), 34 (15), 5132-5139CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      An ω-Isocyanate PMMA, an α-anhydride PMMA, and a styrene-styrylamine copolymer (PS-co-PSNH2) were prepd. by atom transfer radical polymn. (ATRP) with controlled mol. wt. (104 and 3.5 × 104) and low polydispersity (1.2). The functionalized compds. were used as precursors of PS-g-PMMA copolymers via reaction in the melt (170°, for 10 min) under moderate shear rate. The well-controlled mol. characteristics of the precursors allow for study of the effect of interfacial reaction kinetics on phase morphol. When the grafting reaction is fast (NH2/anhydride pair) and low mol. wt. chains are used, the interfacial reaction is quasi-complete and a nanophase morphol. is obsd., whereas limited reaction and formation of microphases are obsd. in all the other cases. A high reaction yield requires that the functional groups are highly reactive and that the interface is available to the functional polymers for the reaction to progress. Then, the nanophase morphol. is that of the copolymer formed by the interfacial reaction. A low reaction yield is dictated by either a slow interfacial reaction or a slow diffusion of the copolymer away from the interface. In the latter case, the phases formed by the unreacted precursors are stabilized by the copolymer which resides at the interface.
    49. 49
      Szwarc, M. ‘Living’ Polymers. Nature 1956, 178 (4543), 1168– 1169,  DOI: 10.1038/1781168a0
      49
      "Living" polymers
      Szwarc, M.
      Nature (London, United Kingdom) (1956), 178 (), 1168-9CODEN: NATUAS; ISSN:0028-0836.
      The polymerization of styrene (I) in tetrahydrofuran (II) initiated by Na naphthyl (III) with the exclusion of air and H2O constitutes a "living" polymer system. The propagating anion chain (IV) has the structure Ph-CH-CH2-CH2CH-Ph. No proton is available from II for chain termination, nor is electron transfer from IV to II energetically feasible. IV, therefore, continues to grow until I is exhausted without ever losing its anion centers. This is proved by the immediate conversion of the green color of III to red when I is added in the described system. The red color (that of neg. benzyl ions) persists for days in the absence of air and moisture. The addn. of I and II to IV results in further polymerization as shown by viscosity changes and gives further evidence of the existence of "living" ends in IV. Block polymers were prepd. by the addn. of isoprene to IV. H2O provides protons that terminate IV with no increase in viscosity. O terminates IV by radical formation followed by dimerization and a viscosity increase.
    50. 50
      Whelan, D. Thermoplastic Elastomers. In Brydson’s Plastics Materials; Elsevier, 2017; Vol. 26, pp 653– 703.  DOI: 10.1016/B978-0-323-35824-8.00024-4 .
      There is no corresponding record for this reference.
    51. 51
      Bates, F. S.; Hillmyer, M. A.; Lodge, T. P.; Bates, C. M.; Delaney, K. T.; Fredrickson, G. H. Multiblock Polymers: Panacea or Pandora’s Box?. Science 2012, 336 (6080), 434– 440,  DOI: 10.1126/science.1215368
      51
      Multiblock Polymers: Panacea or Pandora's Box?
      Bates, Frank S.; Hillmyer, Marc A.; Lodge, Timothy P.; Bates, Christopher M.; Delaney, Kris T.; Fredrickson, Glenn H.
      Science (Washington, DC, United States) (2012), 336 (6080), 434-440CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      A review. Advances in synthetic polymer chem. have unleashed seemingly unlimited strategies for producing block polymers with arbitrary nos. (n) and types (k) of unique sequences of repeating units. Increasing (k,n) leads to a geometric expansion of possible mol. architectures, beyond conventional ABA-type triblock copolymers (k = 2, n = 3), offering alluring opportunities to generate exquisitely tailored materials with unparalleled control over nanoscale-domain geometry, packing symmetry, and chem. compn. Transforming this potential into targeted structures endowed with useful properties hinges on imaginative mol. designs guided by predictive theory and computer simulation. Here, we review recent developments in the field of block polymers.
    52. 52
      Wang, W.; Lu, W.; Goodwin, A.; Wang, H.; Yin, P.; Kang, N.-G.; Hong, K.; Mays, J. W. Recent Advances in Thermoplastic Elastomers from Living Polymerizations: Macromolecular Architectures and Supramolecular Chemistry. Prog. Polym. Sci. 2019, 95, 1– 31,  DOI: 10.1016/j.progpolymsci.2019.04.002
      52
      Recent advances in thermoplastic elastomers from living polymerizations: Macromolecular architectures and supramolecular chemistry
      Wang, Weiyu; Lu, Wei; Goodwin, Andrew; Wang, Huiqun; Yin, Panchao; Kang, Nam-Goo; Hong, Kunlun; Mays, Jimmy W.
      Progress in Polymer Science (2019), 95 (), 1-31CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. Thermoplastic elastomers (TPEs) have found use in a wide range of applications, such as adhesives, elastomers, coatings, fibers, and in additive manufg. techniques such as 3D printing. Despite their omnipresence, the need for advanced TPEs with adaptive properties is continuously growing. Along with a brief historical introduction, this review presents an overview of typical structure-property relationships for various TPEs and discusses the design principles of TPEs from a synthetic chem. perspective. Recent advances in TPEs with different macromol. architectures, including linear ABA triblock copolymers, ABC triblock terpolymers, multiblock copolymers, star copolymers, graft copolymers, bottlebrush polymers, and hyperbranched polymers are reviewed. Service temps. and mech. properties of the different materials are compared in each section. Incorporating various supramol. interactions into different macromol. architectures as a means to further extend the range of TPE applications is also discussed. Future opportunities for TPE research in both academia and industry are addressed as perspectives.
    53. 53
      Chen, Y.; Zhang, L.; Jin, Y.; Lin, X.; Chen, M. Recent Advances in Living Cationic Polymerization with Emerging Initiation/Controlling Systems. Macromol. Rapid Commun. 2021, 42 (13), 2100148,  DOI: 10.1002/marc.202100148
      53
      Recent Advances in Living Cationic Polymerization with Emerging Initiation/Controlling Systems
      Chen, Yinan; Zhang, Lu; Jin, Yi; Lin, Xinrong; Chen, Mao
      Macromolecular Rapid Communications (2021), 42 (13), 2100148CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. While the conventional living cationic polymn. (LCP) provided opportunities to synthesizing well-defined polymers with predetd. mol. wts., desirable chem. structures and narrow dispersity, it is still important to continuously innovate new synthetic methods to meet the increasing requirements in advanced material engineering. Consequently, a variety of novel initiation/controlling systems have be demonstrated recently, which have enabled LCP with spatiotemporal control, broadened scopes of monomers and terminals, more user-friendly operations and reaction conditions, as well as improved thermomech. properties for obtained polymers. In this work, recent advances in LCP is summarized with emerging initiation/controlling systems, including chem.-initiated/controlled cationic reversible addn.-fragmentation chain transfer (RAFT) polymn., photoinitiated/controlled LCP, electrochem.-controlled LCP, thionyl/selenium halide-initiated LCP, org. acid-assisted LCP, and stereoselective LCP. It is hoped that this summary will provide useful knowledge to people in related fields and stimulate new ideas to promote the development and application of LCP in both academia and industry.
    54. 54
      Grubbs, R. B.; Grubbs, R. H. 50th Anniversary Perspective: Living Polymerization - Emphasizing the Molecule in Macromolecules. Macromolecules 2017, 50 (18), 6979– 6997,  DOI: 10.1021/acs.macromol.7b01440
      54
      50th Anniversary Perspective: Living Polymerization-Emphasizing the Molecule in Macromolecules
      Grubbs, Robert B.; Grubbs, Robert H.
      Macromolecules (Washington, DC, United States) (2017), 50 (18), 6979-6997CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A review. The ideal of living polymn. has defined research in polymer chem. over the past 50 years. In this Perspective, we present the case that this concept has enabled the treatment of polymers as org. mols., rather than impure mixts. of species, and allowed the translation of methods developed by synthetic org. chemists into ever more accessible living and/or controlled polymn. methods. The concurrent development of rapid anal. methods for screening new polymn. methods for living characteristics, chiefly size exclusion chromatog., has greatly aided in the expansion of living polymn. methods.
    55. 55
      Beyer, V. P.; Kim, J.; Remzi Becer, C. Synthetic Approaches for Multiblock Copolymers. Polymer Chemistry 2020, 11, 1271– 1291,  DOI: 10.1039/C9PY01571J
      55
      Synthetic approaches for multiblock copolymers
      Beyer, Valentin P.; Kim, Jungyeon; Becer, C. Remzi
      Polymer Chemistry (2020), 11 (7), 1271-1291CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A review. Multiblock copolymers (MBCs) are an emerging class of synthetic polymers that exhibit different macromol. architectures and behaviors to those of homopolymers or di/triblock copolymers. Owing to the rapidly expanding field of synthetic methodologies applied in the field of polymer chem., sequenced controlled MBCs are becoming the new functional materials of this decade. MBCs can now be synthesized with precision and control unlike before and yet some of the synthetic limitations remain a challenge. In this review article, we summarise the various synthetic methodologies that have been reported to date with recent advances in different polymn. techniques and applications.
    56. 56
      Hu, L.; Vuillaume, P. Y. Reactive Compatibilization of Polymer Blends by Coupling Agents and Interchange Catalysts. Compat. Polym. Blends Micro Nano Scale Phase Morphol. Interphase Charact. Prop. 2020, 205– 248,  DOI: 10.1016/B978-0-12-816006-0.00007-4
      There is no corresponding record for this reference.
    57. 57
      Geng, Z.; Shin, J. J.; Xi, Y.; Hawker, C. J. Click Chemistry Strategies for the Accelerated Synthesis of Functional Macromolecules. J. Polym. Sci. 2021, 59, 963– 1042,  DOI: 10.1002/pol.20210126
      57
      Click chemistry strategies for the accelerated synthesis of functional macromolecules
      Geng, Zhishuai; Shin, Jaeman J.; Xi, Yumeng; Hawker, Craig J.
      Journal of Polymer Science (Hoboken, NJ, United States) (2021), 59 (11), 963-1042CODEN: JPSHBC; ISSN:2642-4169. (John Wiley & Sons, Inc.)
      A review. Click chem. is one of the most powerful strategies for constructing polymeric soft materials with precise control over architecture and functionality. In this review, we provide a comprehensive summary of the state-of-the art for synthesizing functional polymers and their expanding range of applications. The synthetic and mechanistic aspects are discussed for key reactions that fulfill "click" requirements and their applications in construction of macromols. with linear, branched, and other complex architectures are described.
    58. 58
      Lee, I.; Panthani, T. R.; Bates, F. S. Sustainable Poly(Lactide- b -Butadiene) Multiblock Copolymers with Enhanced Mechanical Properties. Macromolecules 2013, 46 (18), 7387– 7398,  DOI: 10.1021/ma401508b
      58
      Sustainable Poly(lactide-b-butadiene) Multiblock Copolymers with Enhanced Mechanical Properties
      Lee, Intaek; Panthani, Tessie R.; Bates, Frank S.
      Macromolecules (Washington, DC, United States) (2013), 46 (18), 7387-7398CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      To develop mech. improved polylactide (PLA)-based sustainable polymers, a series of poly-(lactide-b-butadiene) (PLA-PB) multiblock copolymers were synthesized in a two-step procedure: PLA-PB-PLA (LBL) triblock copolymers were prepd. using ring-opening polymn. of D,L-lactide, followed by chain extension of LBL triblock polymers with toluene-2,4-diisocyanate (TDI) and terephthaloyl chloride (TCl). Mol. characterization revealed that the synthetic procedures yielded the desired triblock and multiblock copolymers with a compn. range of 0.5 ≤ fPLA ≤ 0.9. Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) demonstrated nearly identical, well-ordered, morphologies in the homologous triblock and multiblock copolymer materials, in sharp contrast with the findings of a recent study involving poly-(styrene-b-butadiene) (PS-PB) multiblock polymers. These results indicate a transition from classically ordered morphologies to a state of bicontinuous disorder for multiblocks contg. 〈n'〉 ≥ 10, where 〈n'〉 is the av. total no. of blocks. Lamellae (fPLA = 0.6) and cylinder (fPLA = 0.7 and 0.8) forming PLA-PB multiblock copolymers exhibited dramatically enhanced mech. properties compared to the corresponding LBL triblock copolymers. However, this toughening effect was not evident in samples contg. a spherical morphol. (fPLA = 0.9). These findings demonstrate a com. viable approach to prepg. sustainable plastics with competitive mech. properties.
    59. 59
      Pawlak, A.; Morawiec, J.; Pazzagli, F.; Pracella, M.; Galeski, A. Recycling of Postconsumer Poly(Ethylene Terephthalate) and High-Density Polyethylene by Compatibilized Blending. J. Appl. Polym. Sci. 2002, 86 (6), 1473– 1485,  DOI: 10.1002/app.11307
      59
      Recycling of postconsumer poly(ethylene terephthalate) and high-density polyethylene by compatibilized blending
      Pawlak, A.; Morawiec, J.; Pazzagli, F.; Pracella, M.; Galeski, A.
      Journal of Applied Polymer Science (2002), 86 (6), 1473-1485CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      Two methods for recycling scrap PET and HDPE were analyzed: blending incompletely segregated polymers with a compatibilizer or blending nonsegregated polymers with a small amt. of another compatibilizer. The advancement of the compatibilization reaction in a twin-screw extruder depended on the residence time and intensity of mixing according to melt viscosity measurements and SEM observations. The acceptable mech. properties for systems with various PET contents were obtained in blends compatibilized with ethylene-glycidyl methacrylate copolymer (EGMA) and maleated SEBS rubber. For a blend contg. 75% PET and 25% HDPE, the optimum content of EGMA was ∼4 pph, and a film was produced with this compn. Admixts. present in recycled HDPE migrated to PET during blending and accelerated the hydrolysis of PET. As a result of migration, differences in the mech. properties of the blends were obsd., depending on the brand of recycled HDPE used. EGMA also was successfully used for the improvement of the mech. properties of a nonsegregated mixt. based on PET. Tensile properties of two compatibilized PET-rich and HDPE-rich commingled scraps indicated the possibility of using these blends for film extrusion, with potential applications in the packaging of tech. products.
    60. 60
      Zhang, Y.; Zhang, H.; Guo, W.; Wu, C. Effects of Different Types of Polyethylene on the Morphology and Properties of Recycled Poly(Ethylene Terephthalate)/Polyethylene Compatibilized Blends. Polym. Adv. Technol. 2011, 22 (12), 1851– 1858,  DOI: 10.1002/pat.1683
      60
      Effects of different types of polyethylene on the morphology and properties of recycled poly(ethylene terephthalate)/polyethylene compatibilized blends
      Zhang, Yue; Zhang, Hongsheng; Guo, Weihong; Wu, Chifei
      Polymers for Advanced Technologies (2011), 22 (12), 1851-1858CODEN: PADTE5; ISSN:1042-7147. (John Wiley & Sons Ltd.)
      Recycled poly(ethylene terephthalate) (R-PET) was blended with four types of polyethylene (PE), linear low d. polyethylene (LLDPE; LL0209AA, Fs150), low d. polyethylene (LDPE; F101-1), and metallocene-LLDPE (m-LLDPE; Fv203) by co-rotating twin-screw extruder. Maleic anhydride-grafted poly(styrene-ethylene/butyldiene-styrene) (SEBS-g-MA) was added as compatibilizer. R-PET/PE/SEBS-g-MA blends were examd. by SEM, differential scanning calorimeter (DSC), dynamic mech. anal. (DMA), and mech. property testing. The results indicated that the morphol. and properties of the blends depended to a great extent on the miscibility between the olefin segments of SEBS-g-MA and PE. Due to the proper interaction between SEBS-g-MA and LDPE (F101-1), most SEBS-g-MA, located at the interface between two phases of PET and LDPE to increase the interfacial adhesion, lead to better mech. properties of R-PET/LDPE (F101-1) blend. However, both the poor miscibility of SEBS-g-MA with LLDPE (LL0209AA) and the excessive miscibility of SEBS-g-MA with LLDPE (Fs150) and m-LLDPE (Fv203) reduced the compatibilization effect of SEBS-g-MA. DSC results showed that the interaction between SEBS-g-MA and PE obviously affected the crystn. of PET and PE. DMA results indicated that PE had more influence on the movement of SEBS-g-MA than PE did. Copyright © 2010 John Wiley & Sons, Ltd.
    61. 61
      Todd, A. D.; McEneany, R. J.; Topolkaraev, V. A.; Macosko, C. W.; Hillmyer, M. A. Reactive Compatibilization of Poly(Ethylene Terephthalate) and High-Density Polyethylene Using Amino-Telechelic Polyethylene. Macromolecules 2016, 49 (23), 8988– 8994,  DOI: 10.1021/acs.macromol.6b02080
      61
      Reactive Compatibilization of Poly(ethylene terephthalate) and High-Density Polyethylene Using Amino-Telechelic Polyethylene
      Todd, Alexander D.; McEneany, Ryan J.; Topolkaraev, Vasily A.; Macosko, Christopher W.; Hillmyer, Marc A.
      Macromolecules (Washington, DC, United States) (2016), 49 (23), 8988-8994CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Low molar mass (3-17 kg/mol) amino-telechelic polyethylene (ATPE) was used to reactively compatibilize polyethylene terephthalate (PET) and high d. polyethylene (HDPE) via ester aminolysis of PET. A tert-butyl-oxycarbonyl (Boc)-protected polyethylene precursor was thermolytically deprotected during the melt-blending process to render the reactive amine termini. Spectroscopic anal. of a model reaction confirmed the presence of amide functionality in the resultant material. Through blending studies, we found that low loadings of ATPE (0.5 wt %) significantly reduced the vol. of the dispersed HDPE phase particles by a factor of 8 when compared to a binary PET/HDPE blend as assessed by SEM. Mech. anal. of the ATPE-compatibilized blends showed a 12-fold increase in the elongation at break over the unmodified PET/HDPE blend. Ultimately, the results here offer a new approach to reactively compatibilize and toughen PET/HDPE blends and opens the door for other uses of amino-telechelic polyethylene.
    62. 62
      Wang, H.; Onbulak, S.; Weigand, S.; Bates, F. S.; Hillmyer, M. A. Polyolefin Graft Copolymers through a Ring-Opening Metathesis Grafting through Approach. Polym. Chem. 2021, 12 (14), 2075– 2083,  DOI: 10.1039/D0PY01728K
      62
      Polyolefin graft copolymers through a ring-opening metathesis grafting through approach
      Wang, Huiqun; Onbulak, Sebla; Weigand, Steven; Bates, Frank S.; Hillmyer, Marc A.
      Polymer Chemistry (2021), 12 (14), 2075-2083CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A series of polyethylene-graft-atactic polypropylene (PE-g-aPP) graft copolymers were synthesized by grafting through copolymn. of a cyclooctene terminated aPP macromonomer and cyclooctene using ring opening metathesis polymn. (ROMP) and subsequent hydrogenation. The macromonomer was prepd. by a facile alkoxycarbonylation reaction between 1,5-cyclooctadiene, hydroxyl terminated aPP and carbon monoxide. Near complete monomer conversion, a near random graft distribution, and relatively low dispersity were achieved. Thermal anal. of the graft polymers indicates decreasing Tm and Tg as the wt. percentage of aPP increases. The percent Xc of PE decreases as aPP content increases, confirmed by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS) characterization. The normalized percent crystallinity (Xc,norm) indicates that changing side chain nos. and/or length of aPP do not have a significant impact on PE Xc. Small angle X-ray scattering indicates the PE lamellae crystals in the graft copolymers have similar interlamellar spacing but decreased thickness as aPP content increases. In addn., the linear viscoelastic behavior shows that the PE-g-aPP graft copolymers exhibit greatly enhanced dynamic modulus and complex viscosity compared to the linear PE, and the effect increases as side chain no. and/or length increases. This work is important for further development of graft polymers for direct recycling of ubiquitous polyolefins from mixed polyolefin waste.
    63. 63
      Rose, J. M.; Mourey, T. H.; Slater, L. A.; Keresztes, I.; Fetters, L. J.; Coates, G. W. Poly(Ethylene-Co-Propylene Macromonomer)s: Synthesis and Evidence for Starlike Conformations in Dilute Solution. Macromolecules 2008, 41 (3), 559– 567,  DOI: 10.1021/ma702190c
      63
      Poly(ethylene-co-propylene macromonomer)s: Synthesis and Evidence for Starlike Conformations in Dilute Solution
      Rose, Jeffrey M.; Mourey, Thomas H.; Slater, Lisa A.; Keresztes, Ivan; Fetters, Lewis J.; Coates, Geoffrey W.
      Macromolecules (Washington, DC, United States) (2008), 41 (3), 559-567CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      By use of two sequential coordination-insertion polymns., a series of ethylene-co-propylene-based comb polymers was synthesized. First, poly(ethylene-co-propylene) macromonomers featuring one unsatd. chain end were synthesized using a titanium bis(phenoxyimine) catalyst. The macromonomers were then homopolymd. using a living nickel α-diimine catalyst. The mol. wt. and corresponding no. of arms for each poly(macromonomer) were detd. using size-exclusion chromatog. with viscometry detection and universal calibration. Viscosity-mol. wt. conformation plots for the poly(macromonomer)s revealed compact soln. structures. The viscometric radius for each poly(macromonomer) (Rv) and corresponding linear macromonomer (Rv)a was detd. and the ratio (Rv)/(Rv)a for each pair was compared to those of a variety of polyisoprene-based star polymers with similar functionality. The comparison revealed that despite the obvious comb topol. of the poly(macromonomer)s their dil. soln. conformations correspond reasonably well to the bona fide polyisoprene stars.
    64. 64
      Klimovica, K.; Pan, S.; Lin, T. W.; Peng, X.; Ellison, C. J.; Lapointe, A. M.; Bates, F. S.; Coates, G. W. Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers. ACS Macro Lett. 2020, 9 (8), 1161– 1166,  DOI: 10.1021/acsmacrolett.0c00339
      64
      Compatibilization of iPP/HDPE Blends with PE-g-iPP Graft Copolymers
      Klimovica, Kristine; Pan, Sanshui; Lin, Ting-Wei; Peng, Xiayu; Ellison, Christopher J.; LaPointe, Anne M.; Bates, Frank S.; Coates, Geoffrey W.
      ACS Macro Letters (2020), 9 (8), 1161-1166CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges assocd. with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepd. using a grafting-through strategy by copolymn. of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (Mn = 6-28 kg/mol), graft nos., and graft spacings were prepd. These graft copolymers were melt-blended with high-d. polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 wt./wt.) and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt. % loading, with higher tensile strength obsd. for larger block nos. and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.
    65. 65
      Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. Catalytic Production of Olefin Block Copolymers via Chain Shuttling Polymerization. Science 2006, 312 (5774), 714– 719,  DOI: 10.1126/science.1125268
      65
      Catalytic Production of Olefin Block Copolymers via Chain Shuttling Polymerization
      Arriola, Daniel J.; Carnahan, Edmund M.; Hustad, Phillip D.; Kuhlman, Roger L.; Wenzel, Timothy T.
      Science (Washington, DC, United States) (2006), 312 (5774), 714-719CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      We report a catalytic system that produces olefin block copolymers with alternating semicryst. and amorphous segments, achieved by varying the ratio of α-olefin to ethylene in the two types of blocks. The system uses a chain shuttling agent to transfer growing chains between two distinct catalysts with different monomer selectivities in a single polymn. reactor. The block copolymers simultaneously have high melting temps. and low glass transition temps., and therefore they maintain excellent elastomeric properties at high temps. Furthermore, the materials are effectively produced in economically favorable, continuous polymn. processes.
    66. 66
      Shan, C. L. P.; Walton, K. L.; Marchand, G. R.; Carnahan, E. M.; Karjala, T. Crystalline Block Composites as Compatibilizers. US Patent US8822599B2, 2014.
      There is no corresponding record for this reference.
    67. 67
      Hu, Y.; Conley, B.; Walton, K. L.; Shan, C. L. P.; Marchand, G. R.; Patel, R. M.; Kupsch, E.-M.; Walther, B. W. Multilayered Polyolefin-Based Films. US Patent US9511567B2, 2013.
      There is no corresponding record for this reference.
    68. 68
      Listak, J.; Jakubowski, W.; Mueller, L.; Plichta, A.; Matyjaszewski, K.; Bockstaller, M. R. Effect of Symmetry of Molecular Weight Distribution in Block Copolymers on Formation of “Metastable” Morphologies. Macromolecules 2008, 41 (15), 5919– 5927,  DOI: 10.1021/ma800816j
      68
      Effect of Symmetry of Molecular Weight Distribution in Block Copolymers on Formation of "Metastable" Morphologies
      Listak, Jessica; Jakubowski, Wojciech; Mueller, Laura; Plichta, Andrzej; Matyjaszewski, Krzysztof; Bockstaller, Michael R.
      Macromolecules (Washington, DC, United States) (2008), 41 (15), 5919-5927CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Polystyrene-b-poly(Me acrylate) (PS-PMA) copolymers were synthesized using activators regenerated by electron transfer (ARGET) for atom transfer radical polymn. (ATRP). Polydispersity of the PMA block was varied by adjusting the amt. of copper catalyst in ARGET ATRP, and the resulting mol. wt. distributions were approx. sym. At a compn. of 35 vol. % of PMA, the formation of a hexagonally perforated lamellar (HPL) morphol. was obsd. for a polydisperse PS-PMA copolymer for short- and long-term solvent-casting conditions. No order-order transitions were obsd. at elevated temps. or after prolonged thermal annealing. The obsd. stabilization of the HPL morphol.-that is considered to be metastable in narrow-disperse diblock copolymers and diblock copolymers with selective block polydispersity given by a Schulz-Zimm distribution-suggests that the skewness of the distribution of block mol. wts. is an important parameter for the structure selection during the microphase sepn. process. In particular, near-sym. block mol. wt. distributions (as realized by the ARGET ATRP technique) facilitate the stabilization of microdomain morphologies with increased std. deviation of mean curvature. The results point to the relevance of controlling both the width and symmetry of mol. wt. distribution as a potential route toward the tailored synthesis of non-regular microstructures with particular topol. properties that might be of future technol. interest.
    69. 69
      Lynd, N. A.; Meuler, A. J.; Hillmyer, M. A. Polydispersity and Block Copolymer Self-Assembly. Prog. Polym. Sci. 2008, 33 (9), 875– 893,  DOI: 10.1016/j.progpolymsci.2008.07.003
      69
      Polydispersity and block copolymer self-assembly
      Lynd, Nathaniel A.; Meuler, Adam J.; Hillmyer, Marc A.
      Progress in Polymer Science (2008), 33 (9), 875-893CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
      A review. Block copolymers consist of two or more chem. distinct polymers that are covalently bound. These materials self-assemble into fascinating mesostructures with features on the nanometer length scale and have been the subject of intense research interest for about four decades. These efforts have generally focused on model block copolymer systems where the mol. wt. distributions of all blocks are very narrow. Traditionally, many block copolymer systems have been prepd. by living anionic polymn. and thus usually exhibit narrow mol. wt. distributions in all blocks. Therefore, the assumption of monodisperse blocks that greatly simplifies theor. work is on solid exptl. ground. Prepn. of block copolymers with relatively broad mol. wt. distributions in one or more block has become increasingly common, however, as use of synthetic techniques such as controlled radical polymn. has proliferated. A review. Advances in these techniques have increased the no. of monomers readily incorporated into block copolymers and potentially will drive com. costs down. These polymn. strategies often, however, result in broader mol. wt. distributions than are typically obtained using living anionic, cationic, or metal-catalyzed techniques; understanding polydispersity effects should aid deployment of these block copolymers in advanced materials applications. This review describes both theor. and exptl. investigations of the effects of polydispersity on the melt-phase morphol. behavior of block copolymers. The summary includes research efforts focused on both continuous mol. wt. distributions and multicomponent blends. The review concludes with a summary and outlook on the potential utility of polydispersity as a tool to tune the morphol. behavior of block copolymers.
    70. 70
      Hillmyer, M. A. Polydisperse Block Copolymers: Don’t Throw Them Away. J. Polym. Sci., Part B: Polym. Phys. 2007, 45 (24), 3249– 3251,  DOI: 10.1002/polb.21323
      70
      Polydisperse block copolymers: don't throw them away
      Hillmyer, Marc A.
      Journal of Polymer Science, Part B: Polymer Physics (2007), 45 (24), 3249-3251CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
      A review. The relevance of block copolymers with continuous distribution of mol. wt. and block compns. is discussed with focus on applicability of these properties to new materials. Organized microstructures upon self assembly; phase behavior; processing; and reproducibility of polymn. procedures are also discussed.
    71. 71
      Chen, H.; Ginzburg, V. Reaction: Size Distribution in Olefin Block Copolymers: Not Bad at All. Chem. 2019, 5 (3), 491– 492,  DOI: 10.1016/j.chempr.2019.02.018
      71
      Reaction: Size Distribution in Olefin Block Copolymers: Not Bad at All
      Chen, Hongyu; Ginzburg, Valeriy
      Chem (2019), 5 (3), 491-492CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
      Hongyu Chen completed his PhD in macromol. science at Case Western Reserve University in 2010. He is a fellow of the Dow Chem. Company, where he focuses on developing new products. He is also a fellow of the American Phys. Society and American Chem. Society. Valeriy Ginzburg completed his PhD in polymer physics at the Moscow Institute of Physics and Technol. in 1992. He is a senior scientist at the Dow Chem. Company and a fellow of the American Phys. Society.
    72. 72
      Creton, C.; Kramer, E. J.; Brown, H. R.; Hui, C.-Y. Adhesion and Fracture of Interfaces Between Immiscible Polymers: From the Molecular to the Continuum Scal. Adv. Polym. Sci. 2001, 156, 53– 136,  DOI: 10.1007/3-540-45141-2_2
      There is no corresponding record for this reference.
    73. 73
      Eastwood, E. A.; Dadmun, M. D. Multiblock Copolymers in the Compatibilization of Polystyrene and Poly(Methyl Methacrylate) Blends: Role of Polymer Architecture. Macromolecules 2002, 35 (13), 5069– 5077,  DOI: 10.1021/ma011701z
      73
      Multiblock copolymers in the compatibilization of polystyrene and poly(methyl methacrylate) blends: role of polymer architecture
      Eastwood, E. A.; Dadmun, M. D.
      Macromolecules (2002), 35 (13), 5069-5077CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      An asym. double cantilever beam (ADCB) was utilized to det. the ability of a series of styrene and Me methacrylate copolymers with varying architectures to compatibilize the polystyrene/poly(Me methacrylate) interface. Diblock, triblock, pentablock, and heptablock multiblock copolymers with similar mol. wts. were compared to a random copolymer. When the surface is satd. with copolymer, PS/PMMA interfaces compatibilized with pentablock copolymers [S-M-S-M-S(30) and M-S-M-S-M(30)] were the strongest, followed by triblock [S-M-S(50) and M-S-M(50)] and then diblock [S-M(100)]. The least blocky structures, heptablocks [S-M-S-M-S-M-S(21) and M-S-M-S-M-S(21)] and random, provided the weakest interfaces under similar conditions. The ability of the multiblock copolymers to strengthen the PS/PMMA interfaces was attributed to multiple interface crossings and blocks of monomers that are able to anchor into the homopolymers. The results suggest that block lengths with mol. wt. greater than 21 000 are required for adequate anchoring into the PS/PMMA homopolymer phases. Surprisingly, a dependence of the interfacial fracture toughness on copolymer compn. was not obsd. for the multiblock copolymers studied. Both styrene-centered and Me methacrylate-centered multiblock copolymers gave comparable results even though the compns. of the comparable copolymers differed greatly, as much as 70/30 to 30/70. In addn., increasing block lengths in multiblock copolymers of a given architecture increased interfacial adhesion.
    74. 74
      Gersappe, D.; Harm, P. K.; Irvine, D.; Balazs, A. C. Contrasting the Compatibilizing Activity of Comb and Linear Copolymers. Macromolecules 1994, 27 (3), 720– 724,  DOI: 10.1021/ma00081a015
      74
      Contrasting the compatibilizing activity of comb and linear copolymers
      Gersappe, Dilip; Harm, Paul K.; Irvine, Darrell; Balazs, Anna C.
      Macromolecules (1994), 27 (3), 720-4CODEN: MAMOBX; ISSN:0024-9297.
      Using Monte Carlo computer simulations, the authors compared the interfacial behavior of various comb and linear copolymers at a penetrable interface, which represented the boundary between two incompatible homopolymers, A and B. The backbone of the combs was composed of A sites (the majority of the species in the comb), while the teeth were composed of B sites. The authors varied the no. and length of the teeth and found that combs with fewer, longer teeth could more readily localize at the interface than combs with multiple, short teeth. In addn., combs would more readily localize at the interface than comparable linear multiblocks. The findings highlighted the importance of mol. architecture in detg. the interfacial activity of copolymers. The results also provided guidelines for fabricating copolymers that acted as optimal compatibilizers between immiscible polymers.
    75. 75
      Alamo, R. G.; Glaser, R. H.; Mandelkern, L. The Cocrystallization of Polymers: Polyethylene and Its Copolymers. J. Polym. Sci., Part B: Polym. Phys. 1988, 26 (10), 2169– 2195,  DOI: 10.1002/polb.1988.090261011
      75
      The cocrystallization of polymers: polyethylene and its copolymers
      Alamo, R. G.; Glaser, R. H.; Mandelkern, L.
      Journal of Polymer Science, Part B: Polymer Physics (1988), 26 (10), 2169-95CODEN: JPBPEM; ISSN:0887-6266.
      The cocrystn. of both homopolymer-copolymer mixts. and copolymer mixts. of polyethylene were studied. Mol. wt. and compn. fractions were used exclusively. Mol. wts. of the components were matched so that attention is given to the influence of chain structure. DSC and selective extn. techniques were used to assess whether cocrystn. occurs. Linear polyethylene, and random copolymers which contained ≤2 mol% of either Et or acetate branches, cocrystd. upon rapid crystn. from the melt. When the branching content became ≥3 mol%, cocrystn. did not occur. Copolymers contg. ∼1-2 mol% cocrystd. with one another. However, copolymers contg. higher counit contents did not cocrystallize with one another or with samples contg. a smaller amt. of counit. These results were explained on the basis of the concn. of eligible sequences that were available for crystn.
    76. 76
      Yuan, B.-L.; Wool, R. P. Strength Development at Incompatible Semicrystalline Polymer Interfaces. Polym. Eng. Sci. 1990, 30 (22), 1454– 1464,  DOI: 10.1002/pen.760302206
      76
      Strength development at incompatible semicrystalline polymer interfaces
      Yuan, B. L.; Wool, Richard P.
      Polymer Engineering and Science (1990), 30 (22), 1454-64CODEN: PYESAZ; ISSN:0032-3888.
      The structure of an interface that develops from laminating isotactic polypropylene (I)-polyethylene (II) by hot compression-molding was analyzed by optical and electron microscopy. The interface strength (S) was measured by means of a butt-joint specimen. For the laminate formed by isothermal crystn. above the II m.p., S increased with time due to the formation of II influxes between the I spherulites. The interspherulitic influxes broke up the sharp I-II interface plane and provided considerable strength by mech. interlocking. Intraspherulitic entanglements were also noted for I spherulites nucleated near the interface. Fast crystn. prevented the formation of influxes and resulted in a weak interface. For the nonisothermal crystn. case during cooling at 10°/min, the morphol. of a I-HDPE interface was different from that of a I-linear LDPE interface. The difference in crystn. temps. and growth rates between I and HDPE during rapid cooling permitted the HDPE to crystallize first, which prevented the formation of influxes. With I-linear LDPE, the I crystd. first, allowing some influxes to develop. To obtain good mech. properties for a given I-II couple, one can control the processing thermal history to optimize the development of influxes and mech. strength at the interface.
    77. 77
      Schnell, R.; Stamm, M.; Rauch, F. Segregation of Diblock Copolymers to the Interface between Weakly Incompatible Polymers. Macromol. Chem. Phys. 1999, 200 (7), 1806– 1812,  DOI: 10.1002/(SICI)1521-3935(19990701)200:7<1806::AID-MACP1806>3.0.CO;2-9
      77
      Segregation of diblock copolymers to the interface between weakly incompatible polymers
      Schnell, Ralf; Stamm, Manfred; Rauch, Friedrich
      Macromolecular Chemistry and Physics (1999), 200 (7), 1806-1812CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH)
      The interface between thin films of polystyrene (PS) and poly(p-methylstyrene) (PpMS) was investigated in the presence of the diblock copolymer P(S-b-pMS). The use of neutron reflectivity and 15N nuclear reaction anal. in combination with suitable deuteration of the components provides information on the interface width and the distribution of the diblock copolymer at the interface. By variation of the mol. wt. of the homopolymers, compatibility can be changed from compatible to incompatible. Depending on mol. wt. the diblock copolymers segregate to the interface between the incompatible phases, while in weakly incompatible systems (χN = 3) copolymers are dissolved to a considerable amt. in the homopolymer phases. At large copolymer concn. even full compatibility of components can be achieved, which is in good agreement with mean field predictions.
    78. 78
      Shull, K. R.; Kramer, E. J.; Hadziioannou, G.; Tang, W. Segregation of Block Copolymers to Interfaces between Immiscible Homopolymers. Macromolecules 1990, 23 (22), 4780– 4787,  DOI: 10.1021/ma00224a006
      78
      Segregation of block copolymers to interfaces between immiscible homopolymers
      Shull, Kenneth R.; Kramer, Edward J.; Hadziioannou, Georges; Tang, Wing
      Macromolecules (1990), 23 (22), 4780-7CODEN: MAMOBX; ISSN:0024-9297.
      Predictions from a mean-field theory for the dependence of the segregation of perdeuterostyrene-2-vinylpyridine diblock copolymer (I) to the interface in polystyrene (II)-poly(2-vinylpyridine) immiscible blends on the equil. I concn. in the II phase were quant. accurate for values of I chem. potential which were below the limiting value assocd. with the formation of I micelles. Segregation behavior in the regime where micelles were present was complicated by a strong tendency for micelles to segregate to the free II surface and by a weaker tendency for micelles to segregate to the interfacial region. I chem. potentials at the micelle transition were detd.
    79. 79
      Semenov, A. N. Theory of Diblock-Copolymer Segregation to the Interface and Free Surface of a Homopolymer Layer. Macromolecules 1992, 25 (19), 4967– 4977,  DOI: 10.1021/ma00045a024
      79
      Theory of diblock-copolymer segregation to the interface and free surface of a homopolymer layer
      Semenov, A. N.
      Macromolecules (1992), 25 (19), 4967-77CODEN: MAMOBX; ISSN:0024-9297.
      Equil. and dynamics of block copolymer chains in a homopolymer layer (between the interface with another homopolymer and the free surface) are considered. An anal. mean-field theory for equil. copolymer segregation to the interface is presented, the results being in good agreement with those of another theor. approach and with exptl. data. The dynamics of an interface copolymer excess are also considered. The situation above the crit. micelle concn. (CMC) is also analyzed. Copolymer micelles usually strongly attract each other, tending to form a sep. micellar macrophase. Primings of the copolymer phase are attracted to the free surface and (somewhat weaker) to the interface; the superwetting of the free surface by the micellar phase is expected for copolymer mol. wts. exceeding some crit. value. The formation of micelles is an activation process usually with a high energy of activation; the apparent CMC might be appreciably greater than the equil. CMC. For high enough copolymer mol. wts., the micellar geometry should be dynamically controlled; in that case the formation of spherical micelles dominates over other geometries in a wide range of copolymer compns. including sym. copolymers (provided that the copolymer vol. fraction is small). The micellar contribution to the free surface and interface excesses is due to higher rate of the micelles' formation at the surfaces.
    80. 80
      Kim, S. H.; Jo, W. H. A Monte Carlo Simulation of Polymer/Polymer Interface in the Presence of Block Copolymer. I. Effects of the Chain Length of Block Copolymer and Interaction Energy. J. Chem. Phys. 1999, 110 (24), 12193– 12201,  DOI: 10.1063/1.479156
      80
      A Monte Carlo simulation of polymer/polymer interface in the presence of block copolymer. I. Effects of the chain length of block copolymer and interaction energy
      Kim, Seung Hyun; Jo, Won Ho
      Journal of Chemical Physics (1999), 110 (24), 12193-12201CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      A Monte Carlo simulation for the segregation behavior of sym. diblock copolymer at the interface between immiscible homopolymers was performed on a simplified lattice model. The simulation results show that the segregation behavior of block copolymer is significantly dependent on the mol. parameters, such as the chain length Nc of block copolymer and the interaction energy εAB between A and B segments. In a weakly repulsive system with εAB=0.1, the block copolymers are more strongly segregated at the interface with increasing the chain length when the block length is shorter than and comparable to the homopolymer length. However, when the block length becomes longer than the homopolymer length, the concn. of copolymer segments at the interface rather decreases and its distribution becomes broadened. In a strongly repulsive system with εAB=0.5, the distribution of copolymer segments at the interface becomes broader as the chain length of block copolymer increases. This behavior is closely related to the stretching and orientation of block copolymer chains at the interface and to the extent of penetration of homopolymers into the copolymer layer. These simulation results are in excellent agreement with the numerical predictions by the self-consistent mean field theory.
    81. 81
      Cho, D.; Hu, W.; Koberstein, J. T.; Lingelser, J. P.; Gallot, Y. Segregation Dynamics of Block Copolymers to Immiscible Polymer Blend Interfaces. Macromolecules 2000, 33 (14), 5245– 5251,  DOI: 10.1021/ma981699k
      81
      Segregation Dynamics of Block Copolymers to Immiscible Polymer Blend Interfaces
      Cho, Dongman; Hu, Wenchun; Koberstein, Jeffrey T.; Lingelser, J. P.; Gallot, Y.
      Macromolecules (2000), 33 (14), 5245-5251CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Dynamic interfacial tension measurements were used to characterize segregation rates of diblock copolymers to a polymer-polymer interface. The system studied is a poly(styrene-b-dimethylsiloxane) [P(S-b-DMS); Mn = 13 000] sym. diblock copolymer added to a molten blend of the corresponding immiscible homopolymers. Interfacial tension was measured by the pendant drop technique with poly(styrene) [PS; Mn = 4000] as the pendant drop phase and a mixt. of poly(dimethylsiloxane) [PDMS; Mn = 1600] with silane-terminated P(S-b-DMS) as the surrounding phase. The pendant drop technique is found to suffer from two intrinsic limitations in this application: short time data are inaccessible due to the finite time required for the drop shape to equilibrate, and long time data may not be readily analyzed as a result of the finite drop size. Intermediate time data were compared to the predictions of diffusion-limited segregation models proposed by A.Budkowski, A. Losch, and J. Klein (BLK, (1995)) and by A. Semenov (1992) that were modified to treat interfacial tension data. The apparent block copolymer diffusion coeff. obtained from the two analyses fall in the range of 10-5-10-6 cm2/s, in agreement with the estd. self-diffusion coeff. of the PDMS homopolymer matrix.
    82. 82
      Balazs, A. C.; Siemasko, C. P.; Lantman, C. W. Monte Carlo Simulations for the Behavior of Multiblock Copolymers at a Penetrable Interface. J. Chem. Phys. 1991, 94 (2), 1653– 1663,  DOI: 10.1063/1.460715
      82
      Monte Carlo simulations for the behavior of multiblock copolymers at a penetrable interface
      Balazs, A. C.; Siemasko, C. P.; Lantman, C. W.
      Journal of Chemical Physics (1991), 94 (2), 1653-63CODEN: JCPSA6; ISSN:0021-9606.
      Monte Carlo simulations were used to examine the behavior of a single multiblock AB copolymer near the penetrable interface between two immiscible fluids, A and B. The values of χAB, the interaction energy between comonomer and fluid, necessary to localize the chain at the fluid-fluid boundary were detd. and the dependence of this value on the block length was investigated. Once localized at the interface, how the conformation of the multiblock copolymer was perturbed from its random coil dimensions was calcd. The interfacial behavior of the multiblock chain for a range of χAB values and for different block length was then compared. These results were compared with the properties of various diblocks at such an interface. The behavior of several multiblocks at the fluid-fluid surface was examd. The findings of the simulations were helpful in contrasting the compatibilizing activity of diblock and multiblock copolymers.
    83. 83
      Liu, D.; Gong, K.; Lin, Y.; Bo, H.; Liu, T.; Duan, X. Effects of Repulsion Parameter and Chain Length of Homopolymers on Interfacial Properties of An/Ax/2BxAx/2/Bm Blends: A DPD Simulation Study. Polymers (Basel) 2021, 13 (14), 2333,  DOI: 10.3390/polym13142333
      83
      Effects of Repulsion Parameter and Chain Length of Homopolymers on Interfacial Properties of An/Ax/2BxAx/2/Bm Blends: A DPD Simulation Study
      Liu, Dongmei; Gong, Kai; Lin, Ye; Bo, Huifeng; Liu, Tao; Duan, Xiaozheng
      Polymers (Basel, Switzerland) (2021), 13 (14), 2333CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
      We explored the effects of the repulsion parameter (aAB) and chain length (NHA or NHB) of homopolymers on the interfacial properties of An/Ax/2BxAx/2/Bm ternary polymeric blends using dissipative particle dynamics (DPD) simulations. Our simulations show that: (i) The ternary blends exhibit the significant segregation at the repulsion parameter (aAB = 40). (ii) Both the interfacial tension and the d. of triblock copolymer at the center of the interface increase to a plateau with increasing the homopolymer chain length, which indicates that the triblock copolymers with shorter chain length exhibit better performance as the compatibilizers for stabilizing the blends. (iii) For the case of NHA = 4 (chain length of homopolymers An) and NHB (chain length of homopolymers Bm) ranging from 16 to 64, the blends exhibit larger interfacial widths with a weakened correlation between bead An and Bm of homopolymers, which indicates that the triblock copolymer compatibilizers (Ax/2BxAx/2) show better performance in reducing the interfacial tension. The effectiveness of triblock copolymer compatibilizers is, thus, controlled by the regulation of repulsion parameters and the homopolymer chain length. This work raises important considerations concerning the use of the triblock copolymer as compatibilizers in the immiscible homopolymer blend systems.
    84. 84
      Liu, D.; Gong, K.; Lin, Y.; Liu, T.; Liu, Y.; Duan, X. Dissipative Particle Dynamics Study on Interfacial Properties of Symmetric Ternary Polymeric Blends. Polymers (Basel) 2021, 13 (9), 1516,  DOI: 10.3390/polym13091516
      84
      Dissipative particle dynamics study on interfacial properties of symmetric ternary polymeric blends
      Liu, Dongmei; Gong, Kai; Lin, Ye; Liu, Tao; Liu, Yu.; Duan, Xiaozheng
      Polymers (Basel, Switzerland) (2021), 13 (9), 1516CODEN: POLYCK; ISSN:2073-4360. (MDPI AG)
      We investigated the interfacial properties of sym. ternary An/AmBm/Bn and An/Am/2BmAm/2/Bn polymeric blends by means of dissipative particle dynamics (DPD) simulations. We systematically analyzed the effects of compn., chain length, and concn. of the copolymers on the interfacial tensions, interfacial widths, and the structures of each polymer component in the blends. Our simulations show that: (i) the efficiency of the copolymers in reducing the interfacial tension is highly dependent on their compns. The triblock copolymers are more effective in reducing the interfacial tension compared to that of the diblock copolymers at the same chain length and concn.; (ii) the interfacial tension of the blends increases with increases in the triblock copolymer chain length, which indicates that the triblock copolymers with a shorter chain length exhibit a better performance as the compatibilizers compared to that of their counterparts with longer chain lengths; and (iii) elevating the triblock copolymer concn. can promote copolymer enrichment at the center of the interface, which enlarges the width of the phase interfaces and reduces the interfacial tension. These findings illustrate the correlations between the efficiency of copolymer compatibilizers and their detailed mol. parameters.
    85. 85
      Gindy, M. E.; Prud’homme, R. K.; Panagiotopoulos, A. Z. Phase Behavior and Structure Formation in Linear Multiblock Copolymer Solutions by Monte Carlo Simulation. J. Chem. Phys. 2008, 128, 164906,  DOI: 10.1063/1.2905231
      85
      Phase behavior and structure formation in linear multiblock copolymer solutions by Monte Carlo simulation
      Gindy, Marian E.; Prud'homme, Robert K.; Panagiotopoulos, Athanassios Z.
      Journal of Chemical Physics (2008), 128 (16), 164906/1-164906/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The soln. phase behavior of short, strictly alternating multiblock copolymers of type (AnBn)m was studied using lattice Monte Carlo simulations. The polymer mols. were modeled as flexible chains in a monomeric solvent selective for block type A. The degree of block polymn. n and the no. of diblock units per chain m were treated as variables. The authors show that within the regime of parameters accessible to this study, the thermodn. phase transition type is dependent on the ratio of m/n. The simulations show microscopic phase sepn. into roughly spherical aggregates for m/n ratios less than a crit. value and first-order macroscopic pptn. otherwise. In general, increasing m at fixed n, or n at fixed m, promotes the tendency toward macroscopic phase pptn. The enthalpic driving force of phase change is found to universally scale with chain length for all multiblock systems considered and is independent of the existence of a true phase transition. For aggregate forming systems at low amphiphile concns., multiblock chains are shown to self-assemble into intramol., multichain clusters. Predictions for microstructural dimensions, including crit. micelle concn., equil. size, shape, aggregation parameters, and d. distributions, are provided. At increasing amphiphile d., interaggregate bridging is shown to result in the formation of networked structures, leading to an eventual soln.-gel transition. The gel is swollen and consists of highly interconnected aggregates of approx. spherical morphol. Qual. agreement is found between exptl. obsd. phys. property changes and phase transitions predicted by simulations. Thus, a potential application of the simulations is the design of multiblock copolymer systems which can be optimized with regard to soln. phase behavior and ultimately phys. and mech. properties. (c) 2008 American Institute of Physics.
    86. 86
      Halperin, A. On the Collapse of Multiblock Copolymers. Macromolecules 1991, 24 (6), 1418– 1419,  DOI: 10.1021/ma00006a033
      86
      On the collapse of multiblock copolymers
      Halperin, A.
      Macromolecules (1991), 24 (6), 1418-19CODEN: MAMOBX; ISSN:0024-9297.
      The formation of intramol. micelles in (AB)n multiblock polymers immersed in a highly selective solvent was considered. For flexible chains comprising sol. A blocks and insol. B blocks consisting of NA and NB monomer units such that NA » NB » 1, 2 simple limits emerged: (1) for n ≈ NB4/5, a single starlike mol. micelle is formed, and (2) for n » NB4/5, a string of starlike micelles is expected. In case (1), the chain dimensions scaled as n1/5NA3/5, while in case (2), a n3/5NA3/5NB-8/25 behavior is expected.
    87. 87
      López-Barrón, C. R.; Tsou, A. H. Strain Hardening of Polyethylene/Polypropylene Blends via Interfacial Reinforcement with Poly(Ethylene- Cb -Propylene) Comb Block Copolymers. Macromolecules 2017, 50 (7), 2986– 2995,  DOI: 10.1021/acs.macromol.7b00264
      87
      Strain Hardening of Polyethylene/Polypropylene Blends via Interfacial Reinforcement with Poly(ethylene-cb-propylene) Comb Block Copolymers
      Lopez-Barron, Carlos R.; Tsou, Andy H.
      Macromolecules (Washington, DC, United States) (2017), 50 (7), 2986-2995CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      A poly(ethylene-cb-propylene) comb block copolymer (P(E-cb-P)), prepd. by copolymn. of vinyl-terminated atactic polypropylene and ethylene, was used to compatibilize immiscible blends of high-d. polyethylene (HDPE) and isotactic polypropylene (iPP). Addn. of 5 wt % P(E-cb-P) resulted in 5-fold microdomain size redns. and the concomitant increase in the elastic modulus, as typically obsd. in immiscible blends compatibilized with linear block copolymers. We report an unexpected phenomenon, namely, the development of extensional flow hardening by the addn. of P(E-cb-P) to the HDPE/iPP blends. This unprecedented effect is stronger in blends with cocontinuous morphol. (50/50 HDPE/iPP) than in blends with matrix-droplet morphol. (75/25 or 25/75 HDPE/iPP). We postulate that the melt strength enhancement and extensional strain hardening obsd. in the compatibilized blends may arise from the interfacial stiffening as a result of the interfacial stitching by the P(E-cb-P) comb block copolymer. This interfacial stitched network acts as an elastic membrane that resists interfacial deformations. Entanglements of the PP comb arms with iPP generates interfacial stitches which, in turn, could lead to the stretching of the PE backbone of the P(E-cb-P) comb block at large interfacial deformations and, hence, extensional flow hardening.
    88. 88
      Datta, S.; Lohse, D. J. Graft Copolymer Compatibilizers for Blends of Isotactic Polypropylene and Ethene-Propene Copolymers. 2. Functional Polymers Approach. Macromolecules 1993, 26 (8), 2064– 2076,  DOI: 10.1021/ma00060a040
      88
      Graft copolymer compatibilizers for blends of isotactic polypropylene and ethene-propene copolymers. 2. Functional polymers approach
      Datta, Sudhin; Lohse, David J.
      Macromolecules (1993), 26 (8), 2064-76CODEN: MAMOBX; ISSN:0024-9297.
      A graft polymer with isotactic polypropylene (I) arms pendent from an ethene-propene copolymer (II) backbone was made and it effectively compatibilized I-II blends. The graft copolymer was made by treatment of maleated I with II contg. 5-(methylamino)-2-norbornene groups, either in soln. or in the melt state. The addn. of <10% of this graft polymer to a I-II blend had a large effect on its morphol. and properties. Not only did the size of dispersed II phase domains shrink by a factor of 4 when the compatibilizer is added, but also the growth of the phase domains on thermal annealing in the melt was significantly reduced. The presence of the graft polymer in the interphase of the blend was shown directly by electron microscopy. Improvements in mech. properties of I-II blends contg. compatibilizers were noted.
    89. 89
      Embree, K. DOW’s Breakthrough Barrier Film Technology Makes Stand-Up Pouches Recyclable. Plastics Today , June 21, 2016; https://www.plasticstoday.com/packaging/dows-breakthrough-barrier-film-technology-makes-stand-pouches-recyclable.
      There is no corresponding record for this reference.
    90. 90
      Charoensirisomboon, P.; Inoue, T.; Weber, M. Pull-out of Copolymer in situ-Formed during Reactive Blending: Effect of the Copolymer Architecture. Polymer 2000, 41 (18), 6907– 6912,  DOI: 10.1016/S0032-3861(00)00025-2
      90
      Pull-out of copolymer in situ-formed during reactive blending: effect of the copolymer architecture
      Charoensirisomboon, P.; Inoue, T.; Weber, M.
      Polymer (2000), 41 (18), 6907-6912CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
      Reactive melt blending of polyamide 6 (PA) and polysulfone (PSU) was carried out and the effect of the copolymer architecture on the pull-out of the copolymer in situ-formed during reactive blending was studied. To create various block and graft copolymers by reactive blending, three types of reactive PSU were prepd. and used; maleic anhydride-grafted PSU, carboxylic-grafted PSU, and phthalic anhydride-terminated PSU. Polymer blend morphol. was obsd. by transmission electron microscopy (TEM). The TEM results suggested that the block copolymers with linear chain structures are more easily pulled out to form micelles in the matrix than the graft copolymers having branch structure with trunk chains locating in the dispersed phase. Such graft copolymers stayed at the interface and played the role of emulsifiers. By contrast, the in situ-formed graft copolymers having trunk chains locating in the matrix were easily pulled out. The micelle formation via the pull-out of copolymers took place even in the rather sym. block or graft copolymer system. Such interfacial behavior is against the current theories on polymer-polymer interface, which deal with the chain statistics under quiescent state; implying that the hydrodynamic contribution plays an important role of the pull-out.
    91. 91
      Thurber, C. M.; Xu, Y.; Myers, J. C.; Lodge, T. P.; Macosko, C. W. Accelerating Reactive Compatibilization of PE/PLA Blends by an Interfacially Localized Catalyst. ACS Macro Lett. 2015, 4 (1), 30– 33,  DOI: 10.1021/mz500770y
      91
      Accelerating Reactive Compatibilization of PE/PLA Blends by an Interfacially Localized Catalyst
      Thurber, Christopher M.; Xu, Yuewen; Myers, Jason C.; Lodge, Timothy P.; Macosko, Christopher W.
      ACS Macro Letters (2015), 4 (1), 30-33CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      We show catalyst localized at the interface can compatibilize polyethylene (PE) and polylactide (PLA) blends. Telechelic hydroxyl functional PE was synthesized by ring opening metathesis polymn., which reacted with PLA in melt mixing (shown by adhesion and droplet size redn.). Lewis acid tin catalysts were examd. as interfacial reaction promoters, with the goal of interfacial localization. Stannous octoate was shown to localize at the interface by transmission electron microscopy with energy dispersive X-ray spectroscopy and improved dispersion of PLA in PE as compared to uncatalyzed materials and a nonlocalized tin chloride dihydrate.
    92. 92
      Graziano, A.; Jaffer, S.; Sain, M. Review on Modification Strategies of Polyethylene/Polypropylene Immiscible Thermoplastic Polymer Blends for Enhancing Their Mechanical Behavior. J. Elastomers Plast. 2019, 51 (4), 291– 336,  DOI: 10.1177/0095244318783806
      92
      Review on modification strategies of polyethylene/polypropylene immiscible thermoplastic polymer blends for enhancing their mechanical behavior
      Graziano, Antimo; Jaffer, Shaffiq; Sain, Mohini
      Journal of Elastomers & Plastics (2019), 51 (4), 291-336CODEN: JEPLAX; ISSN:0095-2443. (Sage Publications Ltd.)
      A review . Blends of polyethylene (PE) and polypropylene (PP) have always been the subject of intense reasearch for encouraging polymer waste recycling while producing new materials for specific applications in a sustainable way. However, being thermodynamically immiscible, these polyolefins form a binary system usually exhibiting lower performances compared with those of the homopolymers. Many studies have been carried out to better understand the PE/PP blend compatibilization for developing a high-performance and cost-effective product. Both nonreactive and reactive compatibilization promote the brittle to ductile transition for a PE/PP blend. However, the final product usually does not meet the requirements for high demanding com. applications. Therefore, further PE/PP modification with a reinforcing filler, being either synthetic or natural, proved to be a good method for manufg. high-performance reinforcend polymer blend composites, with superior and tailored properties. This review summarizes the recent progress in compatibilization techniques applied for enhancing the interfacial adhesion between PE and PP. Moreover, future perspectives on better understanding the influence of themodynamics on PE/PP synergy are discussed to introduce more effective compatibilization strategies, which will allow this blend to be used for innovative industrial applications.
    93. 93
      Song, J.; Ewoldt, R. H.; Hu, W.; Craig Silvis, H.; Macosko, C. W. Flow Accelerates Adhesion between Functional Polyethylene and Polyurethane. AIChE J. 2011, 57 (12), 3496– 3506,  DOI: 10.1002/aic.12551
      93
      Flow accelerates adhesion between functional polyethylene and polyurethane
      Song, Jie; Ewoldt, Randy H.; Hu, Wanli; Craig Silvis, H.; Macosko, Christopher W.
      AIChE Journal (2011), 57 (12), 3496-3506CODEN: AICEAC; ISSN:0001-1541. (John Wiley & Sons, Inc.)
      Polyethylene (PE) has relatively poor adhesion with polar polymeric materials. In an effort to improve the adhesion between PE and thermoplastic polyurethane (TPU), maleic anhydride (MA), hydroxyl (OH), and secondary amine (NHR) functionalized PEs were blended into nonmodified PE. These functional groups will react with urethane linkages in TPU at the temp. of melt processing. We bonded these PEs to TPU via lamination and coextrusion. To compare the two processes, we detd. the interfacial copolymer d. Σ considering both advection and interfacial area generation. We found that the development of adhesion in coextrusion was much faster in comparison with lamination at the same temp. This difference was attributed to the extensional and compressive flow in coextrusion overcoming the diffusion barrier at the interface and forcing reactive species to penetrate the interface. The effects of functional group reactivity and processing variables on adhesion were correlated with interfacial copolymer coverage. Amine functionalized PE showed dramatic adhesion improvement even at 1%. © 2011 American Institute of Chem. Engineers AIChE J, 2011.
    94. 94
      Dogan, S. K.; Reyes, E. A.; Rastogi, S.; Ozkoc, G. Reactive Compatibilization of PLA/TPU Blends with a Diisocyanate. J. Appl. Polym. Sci. 2014, 131 (10), 40251,  DOI: 10.1002/app.40251
      94
      Reactive compatibilization of PLA/TPU blends with a diisocyanate
      Dogan, Sebnem Kemaloglu; Reyes, Efren Andablo; Rastogi, Sanjay; Ozkoc, Guralp
      Journal of Applied Polymer Science (2014), 131 (10), 40251/1-40251/10CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      This study focuses on the compatibilization of poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blends by using 1,4 phenylene diisocyanate (PDI) for the first time, as the compatibilizer. Because of the potential interactions of diisocyanates with -OH/-COOH, they are useful for reactive processing of PLA/TPU blends in the melt processing. To have insight on the reactively compatibilized structure of PLA/TPU blends, phase morphologies are obsd. by means of SEM. The mech., thermal, and rheol. responses of the blends are investigated. The observations are that the brittle behavior of PLA changes to ductile with the addn. of TPUs. The addn. of PDI improves the tensile properties of the blends. The compatibilization action of PDI is monitored with DMA and rheol. expts. Cross-over in the G' and G'' curves of compatibilized blends indicates the relaxation of branches formed in the presence of PDI. The dispersed phase size of TPU decreases in PLA in the presence of PDI due to the improved compatibility. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40251.
    95. 95
      Lu, Q.-W.; Hoye, T. R.; Macosko, C. W. Reactivity of Common Functional Groups with Urethanes: Models for Reactive Compatibilization of Thermoplastic Polyurethane Blends. J. Polym. Sci. Part A Polym. Chem. 2002, 40 (14), 2310– 2328,  DOI: 10.1002/pola.10310
      95
      Reactivity of common functional groups with urethanes: models for reactive compatibilization of thermoplastic polyurethane blends
      Lu, Qi-Wei; Hoye, Thomas R.; Macosko, Christopher W.
      Journal of Polymer Science, Part A: Polymer Chemistry (2002), 40 (14), 2310-2328CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      Two model urethane compds., di-Bu 4,4'-methylenebis(Ph carbamate) (BMB) and dioctyl 4,4'-methylenebis(Ph carbamate) (OMO) were prepd. by capping 4,4'-methylenebis(Ph isocyanate) with n-butanol and n-octanol, resp. The reactions of the two model urethane compds. with several small monofunctional compds. as well as two model poly(ethylene glycols) were carried out with neat mixts. at elevated temps. The ranking of reactivity of the functional groups with the urethanes was detd. as follows-primary amine > secondary amine » hydroxyl ∼ acid ∼ anhydride » epoxide. NMR spectroscopy (NMR) was used for the quant. anal. Fourier transform IR spectroscopy was used to complement the NMR anal. Conversions of carbamate in each reaction were monitored over time at const. temp. (200°). The reactions between OMO and primary amine were conducted at 170°, 180°, 190°, and 200° and best described with a second-order bimol. reaction model. The rate const. was estd. to be 1.8 × 10-3 L·mol-1·s-1 and activation energy 115 kJ·mol-1.
    96. 96
      Abdul Razak, N. C.; Inuwa, I. M.; Hassan, A.; Samsudin, S. A. Effects of Compatibilizers on Mechanical Properties of PET/PP Blend. Compos. Interfaces 2013, 20 (7), 507– 515,  DOI: 10.1080/15685543.2013.811176
      96
      Effects of compatibilizers on mechanical properties of PET/PP blend
      Abdul Razak, N. C.; Inuwa, I. M.; Hassan, A.; Samsudin, S. A.
      Composite Interfaces (2013), 20 (7), 507-515CODEN: CMNTEU; ISSN:1568-5543. (Taylor & Francis Ltd.)
      Polyethylene terephthalate (PET) and polypropylene (PP) are incompatible thermoplastics due to differences in chem. structure and polarity hence their blends posses inferior mech. properties. Compatibilization with a suitable block/graft copolymer is one way to improve the mech. properties esp. impact strength of such a blend. In this work, the effects of two compatibilizers, maleic anhydride grafted polypropylene (PP-g-MAH) and maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH), were investigated for compatibilization of PET/PP blends and the results were compared. PET, PP, and compatibilizers were melt blended in a single step using a counter-rotating twin screw extruder with compatibilizer concns. 0, 2, 4, 6, 8, and 10 phr, resp. Std. test samples were prepd. by injection molding process. The resulting compatibilized blends were characterized by tensile, flexural, and impact tests. The results showed improvements in mech. properties of the blends due to the in-situ polymn. reaction between the ester groups of PET and the maleic anhydride (MAH) during melt extrusion. The incorporation of 4 phr PP-g-MAH in the blends resulted in the highest tensile and flexural strength, while no significant improvements in Young's modulus were obsd. for both compatibilized blends. The max. impact strength of the blends was obtained at 8 phr of SEBS-g-MAH. Improvement of impact strength of the blends may be attributed to the elastomeric nature of the SEBS-g-MAH while greater improvement recorded for tensile and flexural strength is likely to be due to the affinity between PP-g-MAH with PP of the blend. SEM shows the addn. of PP-g-MAH and SEBS-g-MAH compatibilizers into the blends promote a better dispersion of PP into PET matrix.
    97. 97
      Papadopoulou, C. P.; Kalfoglou, N. K. Comparison of Compatibilizer Effectiveness for PET/PP Blends: Their Mechanical, Thermal and Morphology Characterization. Polymer 2000, 41 (7), 2543– 2555,  DOI: 10.1016/S0032-3861(99)00442-5
      There is no corresponding record for this reference.
    98. 98
      Holsti-Miettinen, R.; Seppälä, J.; Ikkala, O. T. Effects of Compatibilizers on the Properties of Polyamide/Polypropylene Blends. Polym. Eng. Sci. 1992, 32 (13), 868– 877,  DOI: 10.1002/pen.760321306
      98
      Effects of compatibilizers on the properties of polyamide/polypropylene blends
      Holsti-Miettinen, R.; Seppala, J.; Ikkala, O. T.
      Polymer Engineering and Science (1992), 32 (13), 868-7CODEN: PYESAZ; ISSN:0032-3888.
      Compatibilization of polyamide 6 (I)/isotactic polypropylene (II) blends was investigated by mech., morphol., thermal, and rheometrical methods. Four compatibilizers including maleic anhydride, fumaric acid, or glycidyl functionalities were applied at 5 and 10% concns. Maleated hydrogenated triblock SBR gave excellent mech. properties, esp. at high I/II ratios. The correlation between morphol. and mech. and rheol. properties was discussed, and the interesting effect of blending on the kinetics of crystn. was noted.
    99. 99
      Shi, D.; Ke, Z.; Yang, J.; Gao, Y.; Wu, J.; Yin, J. Rheology and Morphology of Reactively Compatibilized PP/PA6 Blends. Macromolecules 2002, 35 (21), 8005– 8012,  DOI: 10.1021/ma020595d
      99
      Rheology and Morphology of Reactively Compatibilized PP/PA6 Blends
      Shi, Dean; Ke, Zhuo; Yang, Jinghui; Gao, Ying; Wu, Jing; Yin, Jinghua
      Macromolecules (2002), 35 (21), 8005-8012CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      This work aims to use the Palierne emulsion type model to describe the relationship between the rheol. response to small amplitude oscillatory deformation and morphol. of polypropylene/polyamide 6 (PP/PA6) blends compatibilized with maleic anhydride grafted polypropylene (PP-g-MAH). It was found that the Palierne emulsion type model could describe very well the linear viscoelastic responses of binary uncompatibilized PP/PA6 blends and failed to describe the ternary compatibilized PP/PP-g-MAH/PA6 blends. These features could be attributed to the fact that the morphol. of the ternary blends was not of the emulsion type with the PA6 particles dispersed in the PP matrix but of an emulsion-in-emulsion type, i.e., PA6 particles dispersed in the PP matrix themselves contained PP or PP-g-MAH inclusions. By consideration of PP-in-PA6 particles as pure PA6 particles, where the vol. fraction of the PA6 phase was increased accordingly, the Palierne emulsion type model could work very well for a ternary blending system. Preshear at low frequencies modified the morphol. of both binary and ternary blends. The particles of the dispersed phase (PA6) became more uniform. These results suggested that the Palierne emulsion type model could be used to ext. information on rheol. properties and interfacial tension of polymer blends from known morphol. and vice versa.
    100. 100
      Eriksen, M. K.; Pivnenko, K.; Faraca, G.; Boldrin, A.; Astrup, T. F. Dynamic Material Flow Analysis of PET, PE, and PP Flows in Europe: Evaluation of the Potential for Circular Economy. Environ. Sci. Technol. 2020, 54 (24), 16166– 16175,  DOI: 10.1021/acs.est.0c03435
      100
      Dynamic material flow analysis of PET, PE, and PP flows in Europe: Evaluation of the potential for circular economy
      Eriksen, Marie Kampmann; Pivnenko, Kostyantyn; Faraca, Giorgia; Boldrin, Alessio; Astrup, Thomas Fruergaard
      Environmental Science & Technology (2020), 54 (24), 16166-16175CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      This study evaluates the potential circularity of PET, PE, and PP flows in Europe based on dynamic material flow anal. (MFA), considering product lifetimes, demand growth rates, and quality redns. of recycled plastic (downcycling). The circularity was evaluated on a baseline scenario, representing 2016 conditions, and on prospective scenarios representing key circularity enhancing initiatives, including maintaining const. plastic consumption, managing waste plastic exports in the EU, design-for-recycling initiatives, improved collection, and improved recovery and reprocessing. Low recycling rates (RR, 13-20%) and dependence on virgin plastic, representing 85-90% of the annual plastic demand, were demonstrated after 50 years in the baseline. Limited improvements were related to the individual scenarios, insufficient to meet existing recycling targets. However, by combining initiatives, RRs above 55%, where 75-90% was recycled in a closed loop, were demonstrated. Moreover, 40-65% of the annual demand could potentially be covered by recycled plastic. Maintaining a const. plastic demand over time was crucial in order to reduce the abs. dependence on virgin plastic, which was not reflected by the RR. Thus, focusing strictly on RRs and even whether and to which extent virgin material is substituted, is insufficient for evaluating the transition toward circularity, which cannot be achieved by technol. improvements alone-the demand must also be stabilized.
    101. 101
      Wang, D.; Li, Y.; Xie, X. M.; Guo, B. H. Compatibilization and Morphology Development of Immiscible Ternary Polymer Blends. Polymer 2011, 52 (1), 191– 200,  DOI: 10.1016/j.polymer.2010.11.019
      101
      Compatibilization and morphology development of immiscible ternary polymer blends
      Wang, Dong; Li, Yan; Xie, Xu-Ming; Guo, Bao-Hua
      Polymer (2011), 52 (1), 191-200CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      We report a novel and effective strategy that compatibilizes three immiscible polymers, polyolefins, styrene polymers, and engineering plastics, achieved by using a polyolefin-based multi-phase compatibilizer. Compatibilizing effect and morphol. development are investigated in a model ternary immiscible polymer blends consisting of polypropylene (PP)/polystyrene(PS)/polyamide(PA6) and a multi-phase compatibilizer (PP-g-(MAH-co-St)) as prepd. by maleic anhydride (MAH) and styrene (St) dual monomers melt grafting PP. SEM results indicate that, as a multi-phase compatibilizer, PP-g-(MAH-co-St) shows effective compatibilization in the PP/PS/PA6 blends. The particle size of both PS and PA6 is greatly decreased due to the addn. of multi-phase compatibilizer, while the interfacial adhesion in immiscible pairs is increased. This good compatibilizing effect is promising for developing a new, technol. attractive method for achieving compatibilization of immiscible multi-component polymer blends as well as for recycling and reusing of such blends. For phase morphol. development, the morphol. of PP/PS/PA6 (70/15/15) uncompatibilized blend reveals that the blend is constituted from PP matrix in which are dispersed composite droplets of PA6 core encapsulated by PS phase. Whereas, the compatibilized blend shows the three components strongly interact with each other, i.e. multi-phase compatibilizer has good compatibilization between the various immiscible pairs. For the 40/30/30 blend, the morphol. changed from a three-phase co-continuous morphol. (uncompatibilized) to the dispersed droplets of PA6 and PS in the PP matrix (compatibilized).
    102. 102
      Li, H.; Xie, X. M. Morphology Development and Superior Mechanical Properties of PP/PA6/SEBS Ternary Blends Compatibilized by Using a Highly Efficient Multi-Phase Compatibilizer. Polymer 2017, 108, 1– 10,  DOI: 10.1016/j.polymer.2016.11.044
      102
      Morphology development and superior mechanical properties of PP/PA6/SEBS ternary blends compatibilized by using a highly efficient multi-phase compatibilizer
      Li, Huanmin; Xie, Xu-Ming
      Polymer (2017), 108 (), 1-10CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      Multi-phase compatibilizers are potentially attractive, not only for the prepn. of ternary or multi-phase immiscible polymer blends with high performance, but also for recycling and reuse of waste plastics mixt. In this study, the maleic anhydride (MAH) and styrene (St) dual monomers grafted PP, PP-g-(MAH-co-St) is prepd. as a multi-phase compatibilizer, which exhibits highly effective compatibility on the PP/PA6/SEBS (70/15/15) ternary blends. SEM (SEM) reveals that, with increasing the compatibilizer, the morphol. evolves from the individual PA6 particle encapsulated by SEBS to several smaller-size PA6 particles partially encapsulated by SEBS phase, then to the tiny PA6 particles and some larger-size SEBS agglomerates predominantly dispersed sep. in PP matrix. The morphol. development predicted by spreading coeffs. shows a consummate consistency with that obsd. by SEM. Moreover, the good compatibilization and corresponding morphologies result in superior enhancement of mech. properties. Compared to the uncompatibilized blend, adding 15 wt% multi-phase compatibilizer to the blend leads to the best mech. properties with the yield stress, stress at break, strain at break and impact failure energy improved significantly by 23%, 132%, 647% and 220%, resp. The results verify that the domains with small-size PA6 particles (0.3-0.4 μm) partially encapsulated by SEBS (0.5-0.7 μm) in PP matrix are very effective to enhance the mech. properties of the blends. The morphologies of large-size PA6 particles encapsulated by SEBS or tiny PA6 particles and some larger-size SEBS agglomerates dispersed sep. in PP matrix for the enhancement in mech. properties of the blends are very limited. Consequently, the enhanced interfacial interactions and the morphol. with the rigid particles partially encapsulated by a rubber-like phase in matrix are crucial for the ternary polymer blends.