The Beauty of Branching in Polymer ScienceClick to copy article linkArticle link copied!
- Soyoung E. Seo
- Craig J. Hawker*
This publication is licensed for personal use by The American Chemical Society.
A number of major research themes have emerged during the 100 years following Staudinger’s landmark 1920 paper (1) “Über Polymerization” and the establishment of polymer science as a discipline. Concepts such as block copolymers, living polymerizations, biodegradable materials, and dendritic macromolecules are now central to the next macromolecular century. It is therefore valuable to use this anniversary to personally look back at the genesis of these scientific directions. For ourselves, two pivotal papers in Macromolecules—(i) Tomalia et al. (2) “Dendritic Macromolecules: Synthesis of Starburst Dendrimers” (1986) and (ii) Kim and Webster (3) “Hyperbranched Polyphenylenes” (1992)— illustrate the emergence of branching as an important and tunable structural feature for the control of polymer properties.
Branching can range from hard to detect side reactions during the growth of linear polymers to perfectly branched, fractal-like dendrimers. As synthetic materials, dendrimers come closest to resembling proteins in their three-dimensional structure and discrete molecular weight. In fact, branched/fractal structures are widely found in nature and have attracted significant attention throughout history for their beauty and geometric complexity. Today a multitude of molecular-based systems are known to have fractal features including the actin cytoskeleton, hyperbranched glycogen, or amylopectin. Building on these natural systems, Paul Flory calculated in the 1950s the molecular weight distribution of ABx polycondensation products and demonstrated that no cross-linking can occur in such systems, in contrast to A2 + B3 systems. (4) However, it was not until the late 1970s that synthetic chemists developed the first strategies for the deliberate preparation of well-defined, branched molecules. (5) In doing so, they significantly extended macromolecular architectures beyond traditional linear or cross-linked materials. These were given a variety of names, such as arborols, starburst polymers, or cascade molecules; however, it is now generally accepted that dendritic macromolecules broadly cover all highly branched systems with dendrimers encompassing regular, near monodisperse materials and hyperbranched macromolecules comprising less regular, polydisperse structures (Figure 1).
For the synthesis of high molecular weight dendrimers, a major move away from traditional one-step polymerization processes to repetitive, multistep strategies was required. More akin to small molecule synthesis, a key insight is the acceleration in molecular weight buildup that is provided through the symmetrical nature of dendrimers. This shift in synthetic design was followed by an increase in focus on the preparation of monodisperse macromolecules and introduction of concepts such as generation number, focal point group, and degree of branching—all of which had to be adapted to fit these new materials. This marriage of organic chemistry and polymer synthesis caused an explosion of interest which has resulted in more than 10000 scientific papers and patents published in the area of dendritic macromolecules over the past 35 years. The overall impact of this rapid evolution in thinking has given polymer researchers another “knob to turn” in their continual search for new and/or improved properties.
In this Editorial, we have the distinct honor of discussing these two seminal Macromolecules papers, (2,3) both instrumental in defining dendritic polymers and bringing the community’s attention to the unique properties and potential for highly branched systems. In turn, these studies focused awareness on the role of controlled branching in developing structure–function relationships across polymer science, inspiring the postulation of fascinating questions, such as “when does a branched polymer become a particle?”, (6) and building on the development of other macromolecular architectures including brush or cyclic polymers.
In helping to develop dendrimers as a new macromolecular architecture, Don Tomalia took advantage of the research culture at Dow Chemical coupled with his passion as an amateur horticulturist. Mimicking the branching structure of trees (dendra, the Greek word for tree), Tomalia and his team pursued the idea of directing molecular growth in a stepwise manner by adding branch after branch to a central core molecule. On the basis of the combination of efficient Michael addition chemistry with transamidation, Tomalia reported the preparation of high molecular weight dendrimers using a divergent approach where ammonia is initially reacted with methyl acrylate to give a first-generation dendrimer with three terminal ester groups followed by a second amidation step with an excess of ethylenediamine (Figure 2). This leads to the regeneration of reactive primary N–H units and doubling of the number of N–H units, from three for ammonia to six for the first-generation dendrimer. Repetition of this two-step process then allows the molecular weight of the dendrimer to essentially double for each generation and the number of reactive terminal groups to increase in a geometric fashion—3 to 6 to 12 to 24 and upward. By use of this strategy, PAMAM dendrimers have been grown up to generation 11 with molecular weights of over 1000000 Da. Because of the close packing of end groups in higher generation dendritic structures, simple geometrical considerations dictate incomplete growth with an increasing number of failure sequences and associated dispersity. (2,5,7) Additional challenges are associated with the very large excess of ethylenediamine employed at higher generation numbers leading to purification issues.
A consequence of this stepwise approach is that dendrimers have a unique set of features making them distinct from conventional polymers. This includes precise control over shape, size, and molecular weight as well as three distinguishing architectural features: a core, internal layers defined as generations, and a multitude of chain end or terminal functionalities. Significantly, each of these can be finely tuned to give a myriad of possible structures which allow more rigorous characterization when compared to traditional polymers. Various analytical methods such as 1H and 13C NMR spectroscopies have proven to be especially useful, in combination with size exclusion chromatography and mass spectroscopy, for illustrating the near-monodisperse and discrete nature of dendritic structures.
Other notable contributions around this time, including the synthesis of cascade polyols (arborols) by Newkome and co-workers (8) at Louisiana State University and the synthesis of dendritic poly(lysine) derivatives by Denkewalter at AlliedSignal, (9) clearly demonstrated the wide variety of building blocks and associated chemistries that could be used for the preparation of dendrimers. An explosion of other dendritic structures based on alternative building blocks and growth chemistries was then subsequently published in Macromolecules, (10−14) illustrating the ability to tune the reactivity and stability. Stability is an important consideration for these highly functional materials with stability studies being facilitated by the monodisperse nature of dendrimers. (15)
These initial studies also foresaw the potential of these branched systems as unique, three-dimensional microenvironments having a well-defined outer surface. A pivotal example is the development of the “dendritic box” by Bert Meijer and co-workers in 1994. (16) This seminal study was a powerful illustration of the potential of dendrimers, taking advantage of their highly branched nature to achieve a dense packed outer shell that acts as a molecular barrier to diffusion. Notably, this phenomenon was predicted by Pierre de Gennes as a fundamental property of dendrimers driven by their highly branched structure with this surface congestion now referred to as “de Gennes dense packing”. (17) In the Meijer system, modification of a fifth-generation poly(propyleneimine) dendrimer with N-BOC-l-phenylalanine groups leads to supramolecular encapsulation of guest molecules in the internal cavities of the dendrimer driven by preferred interactions of guests with the inner atoms of the dendrimer (Figure 3). Remarkably, the diffusion of guest molecules out of the “dendritic box” into solution was unmeasurably slow because of the close packing of the shell, even though the overall diameter of the dendrimer was ∼4.5 nm, with the shell being <1 nm thick. Theory and simulations of these systems by Ballauff (18) and Goddard (19) have provided key insights into the question of the dynamic nature of chain end back-folding and how the shape and inner structure of dendrimers depend on the generation number as well as the effective interactions that exist between dendrimers in solution. Molecular encapsulation has subsequently evolved to include a number of other polymer architectures including single-chain nanoparticles. (20)
In expanding the impact of dendrimers prepared by the divergent growth approach, a number of disadvantages, driven primarily by the increasing number of reactions required for full functionalization, became apparent. In addressing this challenge, Hawker and Fréchet introduced the convergent growth approach to dendrimers. (21,22) Instead of growing the dendrimer from a central core through an ever-increasing number of peripheral coupling steps, the convergent growth approach starts at what will become the periphery of the molecule and requires only a limited number of coupling steps for all generations, resulting in increased purity for higher generation materials. Larger and larger dendritic fragments can therefore be prepared in a stepwise fashion with the final reaction being coupling with a central core or focal point group. In a similar fashion to divergently grown dendrimers, a wide selection of building blocks and associated chemistries is available with the convergent growth approach allowing unparalleled control over functionality at specified locations within the dendrimeric framework. This strategy also provides easy access to numerous novel architectures such as hybrid dendritic–linear diblock copolymers where a single, linear polymer chain is attached to the focal point of a dendritic fragment (Figure 4). (23)
The excitement surrounding dendrimers drove research in many different directions from fundamental studies concerning shape and chain end location (24) to applications as drug delivery agents. (25) However, an underlying issue was, and still is, synthetic availability. Obtaining a large amount of a fifth-generation dendrimer is challenging. Recognizing this as an opportunity to bridge the gap between discrete, highly branched dendrimers and traditional linear polymers, DuPont scientists Young Kim and Owen Webster reported the one-step preparation of soluble, branched polyphenylene derivatives from AB2 monomers, coining the term “hyperbranched macromolecules” in 1990 (Figure 5). (26) This was a surprising and unexpected result since linear polyphenylenes are known for their insolubility at even low molecular weights. The impact on the community of a procedure for preparing high molecular weight polyphenylenes that were not only soluble but also soluble in water cannot be overstated.
In 1992, Kim and Webster published a key follow-up paper in Macromolecules, “Hyperbranched Polyphenylenes”, which detailed the characterization and postsynthetic modification of these hyperbranched polyphenylenes to alter mechanical and solubility characteristics. (3) In a single step and on a large scale, they were able to prepare soluble derivatives with molecular weights in the range 5000–35000 and dispersities <1.5 while still maintaining thermal stability up to 550 °C.
The commercial potential of this work can be seen in the range of scalable systems that have been subsequently developed in academic and industrial laboratories from readily available ABx monomers through both condensation and addition chemistries. (27,28) This includes hyperbranched poly(ethylenimines), first commercialized by BASF in the 1970s as Lupasol, (29) polyethers, (30) Boltorn hyperbranched polyesters which are available with hydroxyl, amino, fatty acid, and nonionic peripheral functionality, (31) and Hybrane hyperbranched polyesteramide developed by DSM. (32) A distinguishing feature of these systems is the concept of degree of branching, (33) where the percentage of linear, dendritic, and terminal units within the structure is mathematically analyzed. For the majority of hyperbranched polymers, this value is ∼0.5, which places them between linear polymers and dendrimers in terms of branching. This level of branching is borne out in the physical and mechanical properties of hyperbranched polymers which are intermediate between entangled linear polymers and nonentangled dendrimers.
In 30+ years since the first experimental manifestations of dendrimers and hyperbranched polymers, the impact on broader fields within polymer science is readily apparent. The concepts have permeated neighboring scientific disciplines and driven new research in exploring different branched architectures and the powerful interplay between structure, properties, and function. While the acceptance of dendritic structures in polymer science was initially slow, Paul Flory in the 1980s summed up the potential succinctly: “architecture is a consequence of special atom relationships and just as observed for small molecules, different properties should be expected for new polymeric architectures”. (5) The availability of branched architectures opened up new possibilities in polymer research, and their applications in fields ranging from viral vectors to rheology modifiers and porogens have continued to expand. (34,35) We owe much to the pioneering Macromolecules publications from Tomalia and co-workers in 1986 and Kim and Webster in 1992.
Acknowledgments
Primary support by the National Science Foundation (NSF) through the Materials Research Science and Engineering Center at UC Santa Barbara (DMR-1720256) is gratefully acknowledged.
References
This article references 35 other publications.
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- 2Tomalia, D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.; Ryder, J.; Smith, P. Dendritic Macromolecules: Synthesis of Starburst Dendrimers. Macromolecules 1986, 19, 2466– 2468, DOI: 10.1021/ma00163a029Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XltlCnsbc%253D&md5=62363ccdd423754a28613ee93ce823c5Dendritic macromolecules: synthesis of starburst dendrimersTomalia, Donald A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.; Ryder, J.; Smith, P.Macromolecules (1986), 19 (9), 2466-8CODEN: MAMOBX; ISSN:0024-9297.The synthesis of a class of topol. macromols. referred to as starburst dendrimers is described. These dendrimers possessed three distinguishing architectural features, i.e., an initiator core, interior layers (generations) composed of repeating units radially attached to the initiator core, and an exterior or surface of terminal functionality attached to the outermost generation. Using a time-sequenced propagation synthon consisting of Michael addn. of α,β-unsatd. esters to amine cores and amidation of the resulting polyesters with large excesses of ethylenediamine, produced these mol. entities which grew in a geometrically progressive fashion. These mol. arrays which possessed both convergent and divergent binding sites had important implications in the synthesis of certain biocatalytic mimics. Surface modification of a dendrimer, (generation = 4.5), with Group I metal carboxylate moieties allowed direct observation of individual dendrimer mols. by electron microscopy. Covalently bridging these fundamental building blocks gave new, higher ordered matrixes referred to as starburst polymers.
- 3Kim, Y. H.; Webster, O. W. Hyperbranched Polyphenylenes. Macromolecules 1992, 25, 5561– 5572, DOI: 10.1021/ma00047a001Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38Xlslahtrs%253D&md5=e233a809990e74955d058d300afe4630Hyperbranched polyphenylenesKim, Young H.; Webster, Owen W.Macromolecules (1992), 25 (21), 5561-72CODEN: MAMOBX; ISSN:0024-9297.Highly branched polyphenylenes were synthesized from AB2 type monomers, e.g., (3,5-dibromophenyl)boronic acid and 3,5-dihalophenyl Grignard reagents. These monomers were polymd. by Pd(0) and Ni(II)-catalyzed aryl-aryl coupling reactions, resp. Polymers with mol. wts. 5,000-35,000 and polydispersities <1.5 were obtained. They were thermally stable to 550° and sol. in many org. solvents. 13C NMR indicated ∼70% branching efficiency. A Tg at 236° was obsd., but the polymer was brittle and did not form films. The melt flow viscosity of polystyrene was reduced, and the modulus was improved as a bromo functional hyperbranched polymer was added. The bromo polymer was metalated with butyllithium. The resulting lithio polymer reacted with various electrophiles to provide polymers with other end groups which control soly. as well as thermal properties. Some of these derivs. were used as multifunctional initiators to prep. star polymers, for example, via ring-opening polymn. of propiolactone and anionic polymn. of Me methacrylate.
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- 5Tomalia, D. A.; Fréchet, J. M. J. Discovery of Dendrimers and Dendritic Polymers: A Brief Historical Perspective. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2719– 2728, DOI: 10.1002/pola.10301Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XlslWgt78%253D&md5=e38484be491990f270209b62eae14146Discovery of dendrimers and dendritic polymers: a brief historical perspectiveTomalia, Donald A.; Frechet, Jean M. J.Journal of Polymer Science, Part A: Polymer Chemistry (2002), 40 (16), 2719-2728CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)A brief review on the discovery of dendrimers and other dendritic polymers is presented. Dendritic polymers are recognized as the fourth major class of macromol. architecture consisting of four subclasses, namely (1) random hyperbranched, (2) dendrigrafts, (3) dendrons, and (4) dendrimers. The previous literature is reviewed with anecdotal events leading to implications for dendrimers in the emerging science of nanotechnol.
- 6Chremos, A.; Douglas, J. F. When Does a Branched Polymer Become a Particle?. J. Chem. Phys. 2015, 143, 111104, DOI: 10.1063/1.4931483Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFWrtL%252FP&md5=750c0998440bc9ed18b486f1f73f896aCommunication: When does a branched polymer become a particle?Chremos, Alexandros; Douglas, Jack F.Journal of Chemical Physics (2015), 143 (11), 111104/1-111104/5CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)Polymer melts with topol. distinct mol. structures, namely, linear chain, ring, and star polymers, are investigated by mol. dynamics simulation. In particular, we det. the mean polymer size and shape, and glass transition temp. for each mol. topol. Both in terms of structure and dynamics, unknotted ring polymers behave similarly to star polymers with f ≈ 5-6 star arms, close to a configurational transition point between anisotropic chains to spherically sym. particle-like structures. These counter-intuitive findings raise fundamental questions regarding the importance of free chain-ends and chain topol. in the packing and dynamics of polymeric materials. (c) 2015 American Institute of Physics.
- 7Tomalia, D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.; Ryder, J.; Smith, P. A New Class of Polymers: Starburst-Dendritic Macromolecules. Polym. J. 1985, 17, 117– 132, DOI: 10.1295/polymj.17.117Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXhsV2ru70%253D&md5=895258598349ce237cc337df0cca089bA new class of polymers: starburst-dendritic macromoleculesTomalia, D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.; Ryder, J.; Smith, P.Polymer Journal (Tokyo, Japan) (1985), 17 (1), 117-32CODEN: POLJB8; ISSN:0032-3896.This paper describes the first synthesis of a new class of topol. macromols. referred to as starburst polymers. The building blocks to this polymer class are referred to as dendrimers. These dendrimers differ from classical monomers or oligomers by their extraordinary symmetry, high branching, and maximized (telechelic) terminal functionality d. The dendrimers possess reactive end groups which allow (a) controlled mol. wt. building (monodispersity), (b) controlled branching (topol.), and (c) versatility in design and modification of the terminal end groups. Dendrimer synthesis is accomplished by a variety of strategies involving time-sequenced propagation techniques. The resulting dendrimers grow in a geometrically progressive fashion. Chem. bridging these dendrimers leads to the starburst polymers. Dendrimers consist of an initiator core, interior layers (composed of repeating units radially attached to the interior core, and exterior layers (i.e., terminal functionality) attached to the outermost interior layer. Thus, the title macromol. was prepd. by amidation and Michael reactions involving ethylenediamine [107-15-3] and Me acrylate [96-33-3].
- 8Newkome, G. R.; Yao, Z.; Baker, G. R.; Gupta, V. K. Micelles. Part 1. Cascade Molecules: a New Approach to Micelles. A [27]-Arborol. J. Org. Chem. 1985, 50, 2003– 2004, DOI: 10.1021/jo00211a052Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXit1Snsrc%253D&md5=8f6beff29cfdcda3c4883b3dfae3b6f3Micelles. Part 1. Cascade molecules: a new approach to micelles. A [27]-arborolNewkome, George R.; Yao, Zhongqi; Baker, Gregory R.; Gupta, Vinod K.Journal of Organic Chemistry (1985), 50 (11), 2003-4CODEN: JOCEAH; ISSN:0022-3263.The preliminary synthesis and spectral characterization of monocascade spheres (Arborols) which possess a three-dimensional microenvironment having the outer surface covered with polar functional groups is described. Thus, the [27]-arborol I was prepd. in 6 steps from Me(CH2)5CHO and HCHO via Me(CH2)4C(CH2OCH2CH2OH)3.
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- 10Newkome, G. R.; Lin, X. Symmetrical, Four-directional, Poly(ether-amide) Cascade Polymers. Macromolecules 1991, 24, 1443– 1444, DOI: 10.1021/ma00006a042Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXht1eiurg%253D&md5=b29bcc0d0031f5a711511098ba1fe20bSymmetrical, four-directional, poly(ether-amide) cascade polymersNewkome, George R.; Lin, XiaofengMacromolecules (1991), 24 (6), 1443-4CODEN: MAMOBX; ISSN:0024-9297.Sym., 4-directional, highly branched, and alternating ether-amide-linked spherical cascade polymers with distinct mol. wt. are described; new building blocks and cascade cores are reported.
- 11Gauthier, M.; Moeller, M. Uniform Highly Branched Polymers by Anionic Grafting: Arborescent Graft Polymers. Macromolecules 1991, 24, 4548– 4553, DOI: 10.1021/ma00016a011Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXkslagsbo%253D&md5=c8068bc99a1b444ee2b03dfe8e9ab6bbUniform highly branched polymers by anionic grafting: arborescent graft polymersGauthier, Mario; Moeller, MartinMacromolecules (1991), 24 (16), 4548-53CODEN: MAMOBX; ISSN:0024-9297.Branched polystyrenes were prepd. by treating Ph2C:CH2-terminated polystyrene with chloromethylated polystyrene. The polymers had a very compact structure, but a low d., indicative of a hollow structure.
- 12Miller, T. M.; Kwock, E. W.; Neenan, T. X. Synthesis of Four Generations of Monodisperse Aryl Ester Dendrimers Based on 1,3,5-benzenetricarboxylic Acid. Macromolecules 1992, 25, 3143– 3148, DOI: 10.1021/ma00038a019Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XisFKitb0%253D&md5=32286de3fecd5db6ef4b10865044de7dSynthesis of four generations of monodisperse aryl ester dendrimers based on 1,3,5-benzenetricarboxylic acidMiller, Timothy M.; Kwock, Elizabeth W.; Neenan, Thomas X.Macromolecules (1992), 25 (12), 3143-8CODEN: MAMOBX; ISSN:0024-9297.The convergent synthesis of a series of monodisperse dendrimers based on sym. substituted benzenetricarboxylic acid esters is described. These materials consist of 4, 10, 22, and 46 benzene rings connected sym. and have mol. diams. of ≤45 Å. The synthesis proceeds in a stepwise convergent manner, building dendritic arms, 3 of which are subsequently attached to a mol. core. The crit. intermediate for the dendrimer arm synthesis is 5-(tert-butyldimethylsiloxy)isophthaloyl dichloride (I), obtainable in 3 steps from 5-hydroxyisophthalic acid. Reaction of the diacid chloride with phenol, followed by removal of the silyl protecting group, gives a new substituted phenol. Two moles of the latter are further reacted with I. This process is repeated several times. The dendrimer arms formed by these reactions are coupled to 1,3,5-benzenetricarbonyl trichloride yielding dendrimers. Kinetic results suggest that the rate of reaction of the 1st dendrimer arm with the core is independent of the size of the dendrimer arm. These materials are stable at ≤500° under N and are highly sol. in typical org. solvents. Possible applications for these materials include mol. wt. stds., polymer rheol. modifiers, or mol. inclusion hosts.
- 13Percec, V.; Kawasumi, M. Synthesis and Characterization of a Thermotropic Nematic Liquid Crystalline Dendrimeric Polymer. Macromolecules 1992, 25, 3843– 3850, DOI: 10.1021/ma00041a004Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XksV2gt7c%253D&md5=f36d6bb1eb937b19f6bf644ff0c74954Synthesis and characterization of a thermotropic nematic liquid crystalline dendrimeric polymerPercec, Virgil; Kawasumi, MasayaMacromolecules (1992), 25 (15), 3843-50CODEN: MAMOBX; ISSN:0024-9297.The prepn. and characterization of 1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)decane (I) and of 10-bromo-1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)decane (II) are described. Polyetherification of I with α,ω-dibromoalkanes contg. 6-10 methylene units leads to the model polyethers I-x (x = 6-10). Polyethers I-x, where x = 6, 8, and 10, exhibit an enantiotropic nematic mesophase, while those with x = 7 and 9 are glassy. Homopolymn. of II followed by in situ alkylation of the phenol chain-ends leads to dendritic polymers II-x (x is the structure of the alkylated phenol chain ends, i.e., Bz = benzyl, 4 = Bu, 6 = hexyl, 8 = octyl). Dendritic polymers II-x, where x = Bz, 6, and 8, represent the 1st examples of dendritic polymers which exhibit a thermotropic enantiotropic nematic mesophase. The isotropization temp. of the dendritic polymer II-x is lower than that of the model linear polyether I-8.
- 14Morikawa, A.; Kakimoto, M.; Imai, Y. Convergent Synthesis of Starburst Poly(ether ketone) Dendrons. Macromolecules 1993, 26, 6324– 6329, DOI: 10.1021/ma00076a003Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXmsFSltrc%253D&md5=7f767f4b350c2e0af5395223e4086478Convergent synthesis of starburst poly(ether ketone) dendronsMorikawa, Atsushi; Kakimoto, Masaaki; Imai, YoshioMacromolecules (1993), 26 (24), 6324-9CODEN: MAMOBX; ISSN:0024-9297.New highly branched starburst poly(ether ketone) dendrons were synthesized by the convergent approach through arom. nucleophilic substitution reactions. 3,5-Bis(4-fluorobenzoyl)anisole was used as the building block, where the methoxy group was a protected form of the hydroxy group. The reaction of the building block with phenol gave the first-generation dendron (G1). Next, after the methoxy group was converted to a hydroxy group by reaction with aluminum chloride, the resulting phenol functionality of G1-OH was allowed to react with the building block to yield the second-generation dendron (G2). By repeating these procedures G3 and G4 generation dendrons possessing 8 and 16 phenoxy groups, resp., at the periphery position were obtained. The 1H- and 13C-NMR spectra were consistent with the structure of these dendrons. The mol. wt. and mol.-wt. distribution detd. by gel permeation chromatog. indicated that after purifn. by silica gel column chromatog., the dendrons possessed remarkably narrow mol.-wt. distribution.
- 15Lloyd, J. R.; Jayasekaraab, P. S.; Jacobson, K. A. Characterization of Polyamidoamino (PAMAM) Dendrimers using In-line Reversed Phase LC Electrospray Ionization Mass Spectrometry. Anal. Methods 2016, 8, 263– 269, DOI: 10.1039/C5AY01995HGoogle Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVSks73F&md5=7858275ad0c4f003fc13996e3ad4d48aCharacterization of polyamidoamino (PAMAM) dendrimers using in-line reversed phase LC electrospray ionization mass spectrometryLloyd, John R.; Jayasekara, P. Suresh; Jacobson, Kenneth A.Analytical Methods (2016), 8 (2), 263-269CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)Generation 3 (G3) PAMAM dendrimers are sym., highly branched polymers widely reported in the scientific literature as therapeutic agents themselves or as carrier scaffolds for various therapeutic agents. A large no. of anal. techniques have been applied to study PAMAM dendrimers, but one that has been missing is in-line reversed phase LC electrospray ionization mass spectrometry (RP/LC/ESI/MS). To translate PAMAM dendrimers into therapeutic agents, a better understanding of their purity, stability and structure is required, and in-line RP/LC/ESI/MS is widely applied to all three of these anal. questions. In this study, we developed a robust in-line RP/LC/ESI/MS method for assessing stability, purity and structure of the G3 PAMAM dendrimers, and we also examd. the reasons why previous attempts at method development failed. Using the RP/LC/ESI/MS method we uncovered several unique aspects of the chem. of G3 PAMAM dendrimers. They are interconverted between two isomeric forms by dialysis, and under higher concn. levels there is an inter-mol. displacement reaction resulting, which degrades PAMAM dendrimers. Purifn. of G3 dendrimers by RP/LC was also previously unreported; so we slightly modified the LC/MS method for isolating individual components from a complex dendrimer mixt. Thus, we have developed a robust, comprehensive method for characterizing PAMAM dendrimers and their degrdn.
- 16Jansen, J. F. G. A.; de Brabander-van den Berg, E. M. M.; Meijer, E. W. Encapsulation of Guest Molecules into a Dendritic Box. Science 1994, 266, 1226– 1229, DOI: 10.1126/science.266.5188.1226Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXit1GrtLg%253D&md5=84f24d561d127b77b91c5a76e8683b98Encapsulation of guest molecules into a dendritic boxJansen, Johan F. G. A.; de Brabander van den Berg, Ellen M. M.; Meijer, E. W.Science (Washington, D. C.) (1994), 266 (5188), 1226-9CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Dendrimers are well-defined, highly branched macromols. that emanate from a central core and are synthesized through a stepwise, repetitive reaction sequence. The synthesis and characterization of dendritic boxes, based on the construction of a chiral shell of protected amino acids onto poly(propyleneimine) dendrimers with 64 amine end groups, is reported here. NMR-relaxation and optical data show that a dense shell with solid-phase character is formed. Guest mols. were captured within the internal cavities of the boxes when these boxes were constructed in the presence of guest mols. The diffusion of guest mols. out of the boxes into soln. was unmeasurably slow because of the close packing of the shell. These monomol. dendritic containers of 5-nm dimensions with phys. locked-in guest mols. were characterized spectroscopically. Guest mols. were captured within the internal cavities of the boxes when these boxes were constructed in the presence of guest mols. The diffusion of guest mols. out of the boxes into soln. was unmeasurably slow because of the close packing of the shell. These monomol. dendritic containers of 5-nm dimensions with phys. locked-in guest mols. were characterized spectroscopically.
- 17de Gennes, P. G.; Hervet, H. Statistics of Starburst Polymers. J. Phys., Lett. 1983, 44, 351– 360, DOI: 10.1051/jphyslet:01983004409035100Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXktVKhtbo%253D&md5=667658bcec21a46d41f5a7bc5ee5f2d7Statistics of "starburst" polymersDe Gennes, P. G.; Hervet, H.Journal de Physique, Lettres (1983), 44 (9), 351-60CODEN: JPSLBO; ISSN:0302-072X.The growth of completely branched polymers, based on tertiary amine branch points connected by flexible linear portions (spacers) of each P monomers, was discussed. The method was a modified version of the Edwards self-consistent fields (1965). The ideal starburst growth (without any residual second amine functions) was found to be restricted to a no. of generations m ≤ m1, where m1 ≃ 2.88 (lnP + 1.5). This corresponded in space to a limiting radius (R1), which increased linearly with P. Well below this limit, the polymer radius R(M), plotted as a function of mol. rate (M), was predicted to increase as M0.2, while above the limit (R > R1) compact structures were predicted (R ∼ M0.33).
- 18Ballauff, M.; Likos, C. N. Dendrimers in Solution: Insight from Theory and Simulation. Angew. Chem., Int. Ed. 2004, 43, 2998– 3020, DOI: 10.1002/anie.200300602Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltFWhs7s%253D&md5=b84d5c00fe26d5fdf7ff367e799ff8dbDendrimers in solution: insight from theory and simulationBallauff, Matthias; Likos, Christos N.Angewandte Chemie, International Edition (2004), 43 (23), 2998-3020CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. A variety of exptl. and theor. approaches show that, akin the to linear polymers, dendrimers in good solvent conditions are best described as flexible macromol. aggregates with a dense core and fluctuating monomer groups. We present theor. and simulation evidence of how the shape and inner structure of dendrimers depends on the generation no. and the effective interactions that exist between dendrimers in soln. These approaches based on simplified dendritic structures show there is a tunable and ultrasoft interaction between the centers of the solubilized dendrimers. Results from small-angle neutron scattering data confirm the theory and indicate that dendrimers are model systems of ultrasoft colloids that bridge the gap between polymers and hard spheres. Dendrimers can form a class of materials analogous to the related systems of star polymers and block copolymer micelles which-exhibit special properties.
- 19Miklis, P.; Çaǧin, T.; Goddard, W. A., III Dynamics of Bengal Rose Encapsulated in the Meijer Dendrimer Box. J. Am. Chem. Soc. 1997, 119, 7458– 7462, DOI: 10.1021/ja964230iGoogle Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXkvVens74%253D&md5=048c7303e13db030d779a1270e4aa956Dynamics of Bengal Rose Encapsulated in the Meijer Dendrimer BoxMiklis, Paul; Cagin, Tahir; Goddard, William A., IIIJournal of the American Chemical Society (1997), 119 (32), 7458-7462CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Mol. dynamics (MD) techniques were used to study the encapsulation of Bengal Rose (BR) mols. in the Meijer dendrimer box (DBox) formed by the addn. of tert-butyloxycarbonyl-L-Phe (tBOC-L-Phe) cap mols. to the 64 terminal primary amines of a fifth generation poly(propyleneimine) (PPI-5) dendrimer. Using a large periodic box (including DBox, four to six BR, and CH2Cl2 solvent, totaling ∼25 000 atoms), the MD of these systems was examd. periods of ∼0.5 ns. Without the cap, BR mols. establish a concn. dependent equil. between the interior and surface regions of PPI-5 and the solvent region outside the dendrimer. The no. of BR mols. calcd. to assoc. with the interior of the PPI-5 dendrimer agrees exactly with expt. (at the same BR/PPI concn.). MD simulations on the DBox in CH2Cl2 show that the tBOC-L-Phe surface is completely impermeable to encapsulated BR mols., even when an excess is forced inside the box. The close correspondence of the theory with expt. suggests that these methods can be used to design such systems in advance of expt. The encapsulation of mols. is of interest in development of materials which can be selectively carried and released into another environment.
- 20Seo, M.; Beck, B. J.; Paulusse, J. M. J.; Hawker, C. J.; Kim, S. Y. Polymeric Nanoparticles via Noncovalent Cross-linking of Linear Chains. Macromolecules 2008, 41, 6413– 6418, DOI: 10.1021/ma8009678Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXpvVakur4%253D&md5=cd985390f617f4a24d2f88f56c051d0dPolymeric Nanoparticles via Noncovalent Cross-Linking of Linear ChainsSeo, Myungeun; Beck, Benjamin J.; Paulusse, Jos M. J.; Hawker, Craig J.; Kim, Sang YoulMacromolecules (Washington, DC, United States) (2008), 41 (17), 6413-6418CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Novel polymeric nanoparticles were prepd. through the chain collapse of linear polymers driven by noncovalent crosslinking of dendritic self-complementary hydrogen-bonding units (SHB). Random copolymers contg. SHB units, poly[(Me methacrylate)-r-2-((3,5-bis(4-carbamoyl-3-(trifluoromethyl)phenoxy)benzyloxy)carbonylamino)ethyl methacrylate] (A1, A2), were synthesized with various incorporation ratios by reversible addn.-fragmentation chain transfer (RAFT) polymn. Dramatically different behavior was obsd. depending on the level of incorporation of the supramol. units. At high loadings of A2 (6% SHB incorporation), intramol. chain collapse is favored, resulting in the formation of well-defined polymer nanoparticles, which were characterized by scanning force microscopy (SFM), dynamic light scattering (DLS), and viscosity studies. In contrast, anal. of copolymer A1 (1% SHB incorporation) revealed that chain collapse occurred primarily through intermol. interactions leading to large aggregates.
- 21Hawker, C. J.; Fréchet, J. M. J. Preparation of Polymers with Controlled Molecular Architecture. A New Convergent Approach to Dendritic Macromolecules. J. Am. Chem. Soc. 1990, 112, 7638– 7647, DOI: 10.1021/ja00177a027Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXmtFaktLY%253D&md5=ce32a188723646f08702123d51ee5426Preparation of polymers with controlled molecular architecture. A new convergent approach to dendritic macromoleculesHawker, Craig J.; Frechet, Jean M. J.Journal of the American Chemical Society (1990), 112 (21), 7638-47CODEN: JACSAT; ISSN:0002-7863.The condensation of 3,5-bis(benzyloxy)benzyl bromide (I) with 3,5-(HO)2C6H4CH2OH gave bis[3,5-bis[(3,5-benzyloxy)benzyloxy]]benzyl alc (II) which was converted to the resp. benzyl bromide deriv. The latter was again treated with monomer I in a repeated sequence to give a dendritic oligomer. The oligomer was added to (4-HOC4H4)3CMe to give a dendritic starburst polyether of low polydispersity.
- 22Wooley, K. L.; Hawker, C. J.; Fréchet, J. M. J. A “Branched-Monomer Approach” for the Rapid Synthesis of Dendimers. Angew. Chem., Int. Ed. Engl. 1994, 33, 82– 85, DOI: 10.1002/anie.199400821Google ScholarThere is no corresponding record for this reference.
- 23Malkoch, M.; Malmström, E.; Hult, A. Rapid and Efficient Synthesis of Aliphatic Ester Dendrons and Dendrimers. Macromolecules 2002, 35, 8307– 8314, DOI: 10.1021/ma0205360Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XntV2rurk%253D&md5=d7f8e535265f91952d9b9feec04091dfRapid and Efficient Synthesis of Aliphatic Ester Dendrons and DendrimersMalkoch, Michael; Malmstroem, Eva; Hult, AndersMacromolecules (2002), 35 (22), 8307-8314CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A divergent approach to synthesize dendritic aliph. polyester structures based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) is described. The key building block is the anhydride of isopropylidene-2,2-bis(methoxy)propionic acid which is synthesized in high yields through self-dehydration, utilizing N,N'-dicyclohexylcarbodiimide (DCC) as reagent. The high reactivity of the anhydride toward hydroxyl groups makes the divergent synthesis of dendrimers and dendrons viable. Dendritic growth occurs in the presence of protecting groups sensitive toward hydrogenolysis, such as benzyl esters and ethers. The acetonide-protecting group is easily removed under acidic conditions using DOWEX 50W-X2 resin in methanol. Fourth-generation dendrons and dendrimers were successfully synthesized in high yields utilizing 1.3-1.5 equiv of anhydride per hydroxyl group. Common characteristics of the esterification reaction were short reaction time, mild reaction conditions, easy monitoring by NMR anal., and simple workup. This synthetic approach opens up the possibility to utilize orthogonal protecting groups of acetonide-protected 2,2-bis(hydroxymethyl)propionic anhydride as a novel building block.
- 24Wooley, K. L.; Klug, C. A.; Tasaki, K.; Schaefer, J. Shapes of Dendrimers from Rotational-Echo Double-Resonance NMR. J. Am. Chem. Soc. 1997, 119, 53– 58, DOI: 10.1021/ja962285eGoogle Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XnsVemurk%253D&md5=4607abec025c52a1b7a77d9721571b2dShapes of Dendrimers from Rotational-Echo Double-Resonance NMRWooley, Karen L.; Klug, Christopher A.; Tasaki, Kenzabu; Schaefer, JacobJournal of the American Chemical Society (1997), 119 (1), 53-58CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The solid-state shape, size, and intermol. packing of a fifth-generation dendritic macromol. were detd. by a combination of site-specific stable-isotope-labeling, rotational-echo double-resonance (REDOR) NMR and distance-constrained mol. dynamics simulations. REDOR expts. measured dipolar couplings between 13C atoms located near the chain ends and an 19F label placed at the core of benzyl ether dendrimers (generations 1-5) based on 3,5-dihydroxybenzyl alc. as the monomeric repeat unit. Intramol. 13C-19F coupling was distinguished from intermol. coupling by diln. with nonlabeled dendrimer. The av. intramol. 13C-19F distances for generations 3-5 were each approx. 12 Å, which indicates inward-folding of chain ends with increasing generation no. The av. intermol. 13C-19F dipolar coupling decreased with increasing generation no., consistent with decreased interpenetration for larger dendrimers. The measured intra- and intermol. distances for the fifth-generation dendrimer were used as constraints on energy minimizations and mol. dynamics simulations, which resulted in visualizations of the dendrimer packing and an est. of d. in the solid state.
- 25Liu, M.; Kono, K.; Fréchet, J. M. J. Water-Soluble Dendrimer-Poly(ethylene glycol) Starlike Conjugates as Potential Drug Carriers. J. Polym. Sci., Part A: Polym. Chem. 1999, 37, 3492– 3503, DOI: 10.1002/(SICI)1099-0518(19990901)37:17<3492::AID-POLA7>3.0.CO;2-0Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlsV2jt7Y%253D&md5=7507382cf0f277d4f7cea6305eb1a5deWater-soluble dendrimer-poly(ethylene glycol) starlike conjugates as potential drug carriersLiu, Mingjun; Kono, Kenji; Frechet, Jean M. J.Journal of Polymer Science, Part A: Polymer Chemistry (1999), 37 (17), 3492-3503CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)The design and synthesis of a new dendrimer-polyethylene glycol (PEG) conjugate that may be used as a model drug carrier are described. The starting material is a polyether dendrimer with two different types of chain end functionalities. The dendritic assembly is made water sol. through attachment of short PEG chains to the dendrimer via one type of functionality. The remaining chain end functionalities then were used to incorporate model drug mols. of varying polarity into the modified dendrimer. Cholesterol and two amino acid derivs. were selected as model drugs for attachment through their resp. hydroxyl, carboxylic acid, and amino functional groups to the dendrimer via carbonate, ester, and carbamate linkages. The resulting water-sol. dendrimer-model drug conjugates were characterized by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry.
- 26Kim, Y. H.; Webster, O. W. Water-Soluble Hyperbranched Polyphenylene: “A Unimolecular Micelle”?. J. Am. Chem. Soc. 1990, 112, 4592– 4593, DOI: 10.1021/ja00167a094Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXitFOltro%253D&md5=3c9a84f4d68a76abf4dbf0af16a8736bWater soluble hyperbranched polyphenylene: "a unimolecular micelle?"Kim, Young H.; Webster, Owen W.Journal of the American Chemical Society (1990), 112 (11), 4592-3CODEN: JACSAT; ISSN:0002-7863.Hyperbranched polyphenylene with bromo functional groups was prepd. by homocoupling of 3,5-dibromophenylboronic acid with Pd(PPH3)4 as a catalyst. The mol. wt. of the polymer was 4000-8000. Reaction of the polymer with BuLi, followed by CO2, resulted in a water-sol. carboxylated polymer Li salt. This polymer showed properties resembling those of micelles. Upfield shifts of the NMR chem. signals of p-toluidine of ≤0.8 ppm in water occurred when the carboxylated hyperbranched polymer was added.
- 27Jikei, M.; Kakimoto, M. Hyperbranched Polymers: A Promising New Class of Materials. Prog. Polym. Sci. 2001, 26, 1233– 1285, DOI: 10.1016/S0079-6700(01)00018-1Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXptFCisro%253D&md5=8b93877f60df7a56b9ab9174bbc0c327Hyperbranched polymers: a promising new class of materialsJikei, Mitsutoshi; Kakimoto, Masa-akiProgress in Polymer Science (2001), 26 (8), 1233-1285CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)A review. The general concepts, syntheses and the properties of hyperbranched polymers are reviewed with refs. The polymn. reactions are classified into three categories: (1) step-growth polycondensation of ABx monomers; and (2) self-condensing vinyl polymn. of AB* monomers; (3) multibranching ring-opening polymn. of latent ABx monomers. Hyperbranched polymers are generally composed of dendritic, linear and terminal units and a degree of branching (DB) helps to describe their structures. Most of the hyperbranched polymers possess some of the unique properties exhibit dendritic macromols., such as low viscosity, good soly., and multi-functionality. Owing to multi-functionality, phys. properties such as soly. in solvents and the glass transition temp. can be controlled by the chem. modification of the end functional groups (endcapping reactions). Applications of designed hyperbranched polymers to specific fields are also described.
- 28Hawker, C. J.; Fréchet, J. M. J.; Grubbs, R. B.; Dao, J. Preparation of Hyperbranched and Star Polymers by a” Living”, Self-Condensing Free Radical Polymerization. J. Am. Chem. Soc. 1995, 117, 10763– 10764, DOI: 10.1021/ja00148a027Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXosF2jsbc%253D&md5=84d480a54fb075717dc981dce4b94ba2Preparation of Hyperbranched and Star Polymers by a "Living", Self-Condensing Free Radical PolymerizationHawker, Craig J.; Frechet, Jean M. J.; Grubbs, Robert B.; Dao, JulianJournal of the American Chemical Society (1995), 117 (43), 10763-4CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The prepn. of hyperbranched and novel hyperbranched-star macromols. based on the combined concepts of "living" free radical and "self-condensing" polymn. techniques is reported for the first time. A unimol. monomer, 4-[2-(phenyl)-2-(1-2,2,6,6-tetramethylpiperidinyloxy)ethyloxy]methylstyrene (I), contg. both a polymerizable double bond and a reactive styrene-TEMPO (2,2,6,6-tetramethylpiperidinyloxy) group has been shown to afford highly branched irregular dendritic structures on polymn. These hyperbranched macromols. which contain numerous initiating functionalities at the chain ends are also capable of initiating the polymn. of vinyl monomers to give multi-arm stars. Copolymn. of I with vinyl monomers, such as styrene, is also shown to afford branched polymers with a controlled branch d. and length.
- 29Voit, B. I.; Lederer, A. Hyperbranched and Highly Branched Polymer Architectures—Synthetic Strategies and Major Characterization Aspects. Chem. Rev. 2009, 109, 5924– 5973, DOI: 10.1021/cr900068qGoogle Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtF2lurjP&md5=146b9182a7d6dd3d3f172fbe61606ca4Hyperbranched and Highly Branched Polymer Architectures-Synthetic Strategies and Major Characterization AspectsVoit, Brigitte I.; Lederer, AlbenaChemical Reviews (Washington, DC, United States) (2009), 109 (11), 5924-5973CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. This review has covered the principle synthetic approaches toward hyperbranched polymers as well as various other highly branched polymer architectures developed over the last 20 years.
- 30Stiriba, S. E.; Kautz, H.; Frey, H. Hyperbranched Molecular Nanocapsules: Comparison of the Hyperbranched Architecture with the Perfect Linear Analogue. J. Am. Chem. Soc. 2002, 124, 9698– 9699, DOI: 10.1021/ja026835mGoogle Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XlsFygu7o%253D&md5=38f827bc7169d03ffffce8ae4911aeeeHyperbranched Molecular Nanocapsules: Comparison of the Hyperbranched Architecture with the Perfect Linear AnalogueStiriba, Salah-Eddine; Kautz, Holger; Frey, HolgerJournal of the American Chemical Society (2002), 124 (33), 9698-9699CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Two hyperbranched polyglycerol samples with mol. wt. of 3000 and 8000 g/mol (Mw/Mn = 1.3), resp., were partially esterified using palmitoyl chloride. The same modification was applied to the structurally analogous linear polyglycerol (3000 g/mol). A detailed UV-vis study correlated with viscosity expts. demonstrated that only the hyperbranched core-shell structures form nanocapsules, leading to the encapsulation of polar guest mols. (Congo Red). The results underline the crucial role of the hyperbranched topol. and the resulting soln. conformation for supramol. guest encapsulation and phase transfer. The unusually compact (collapsed) structure assumed by the hyperbranched core-shell amphiphiles in apolar media is responsible for the formation of a hydrophilic compartment, capable of irreversibly taking up guest mols.
- 31Malmstroem, E.; Johansson, M.; Hult, A. Hyperbranched Aliphatic Polyesters. Macromolecules 1995, 28, 1698– 1703, DOI: 10.1021/ma00109a049Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXjs1Cgu7o%253D&md5=feb7da904b5119ab3242b8e432a32ddcHyperbranched Aliphatic PolyestersMalmstroem, E.; Johansson, M.; Hult, A.Macromolecules (1995), 28 (5), 1698-703CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Hyperbranched, aliph. polyesters of theor. calcd. molar mass 1200-44,300 were prepd. in the molten state from 2,2-bis(hydroxymethyl)propionic acid (repeating unit of ABx type) and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (core mol.) using acid catalysis. The procedure is a pseudo-1-step reaction where stoichiometric amts. corresponding to each generation were added successively. The resulting polymers were glassy, slightly yellow solids at room temp. with terminal hydroxy groups. The degree of branching, detd. with model compds. using 13C-NMR, was ∼80%. The materials exhibited good thermal stability as analyzed with TGA. Glass transition temps., detd. using DSC, were ∼40° and were relatively insensitive to variations in molar mass.
- 32Froehling, P. Development of DSM’s Hybrane® Hyperbranched Polyesteramides. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 3110– 3115, DOI: 10.1002/pola.20113Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltlGktrs%253D&md5=b41b77166d4b21eb7dd3dbff057d07edDevelopment of DSM's Hybrane hyperbranched polyesteramidesFroehling, PeerJournal of Polymer Science, Part A: Polymer Chemistry (2004), 42 (13), 3110-3115CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)A review. The development of DSM's Hybrane hyperbranched poly(ester amides) is described. The monomer for the hyperbranched polyester is obtained from the reaction of a cyclic anhydride with diisopropanol amine, yielding a tertiary amide with one COOH and two OH groups. Polycondensation takes place via an oxazolinium intermediate in bulk at relatively mild conditions in the absence of catalyst. The reaction was scaled up to ton scale. By varying and combining anhydrides, and modification with several types of end groups, a large variety of structures with concomitant properties and industrial applications was realized.
- 33Hawker, C. J.; Lee, R.; Fréchet, J. M. J. One-Step Synthesis of Hyperbranched Dendritic Polyesters. J. Am. Chem. Soc. 1991, 113, 4583– 4588, DOI: 10.1021/ja00012a030Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXisVOru78%253D&md5=cbbc28df7dbd7a658501dc741567ebddOne-step synthesis of hyperbranched dendritic polyestersHawker, C. J.; Lee, R.; Frechet, J. M. J.Journal of the American Chemical Society (1991), 113 (12), 4583-8CODEN: JACSAT; ISSN:0002-7863.The 1-step prepn. of a hyperbranched polyester possessing a dendritic structure was achieved by thermal self-condensation of 3,5-bis(trimethylsiloxy)benzoyl chloride. The hyperbranched polymers were obtained in yields ≥80% and with polystyrene-equiv. wt.-av. mol. wts. 30,000-200,00. The polydispersity and the mol. wts. of the polyesters varied greatly with the temp. of the polymn. Characterization of the polymers was readily accomplished by NMR spectroscopy with the help of model compds. The degree of branching of the polyesters as detd. from NMR expts. was 55-60%. The polyesters, which contained reactive functional groups at all chain extremities, were glassy materials that showed a very high thermal stability comparable to that of analogous linear materials. In contrast, the excellent soly. properties of the hyperbranched polyesters influenced by their shape and functionalization were at variance with those of their linear polyester analogs.
- 34Hudde, T.; Rayner, S.; Comer, R.; Weber, M.; Isaacs, J. D.; Waldmann, H.; Larkin, D. F. P.; George, A. J. T. Activated Polyamidoamine Dendrimers, a Non-Viral Vector for Gene Transfer to the Corneal Dndothelium. Gene Ther. 1999, 6, 939– 943, DOI: 10.1038/sj.gt.3300886Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjtVKgtLY%253D&md5=56578b77f619dd23b3ca4a4dbab35381Activated polyamidoamine dendrimers, a non-viral vector for gene transfer to the corneal endotheliumHudde, T.; Rayner, S. A.; Comer, R. M.; Weber, M.; Isaacs, J. D.; Waldmann, H.; Larkin, D. F. P.; George, A. J. T.Gene Therapy (1999), 6 (5), 939-943CODEN: GETHEC; ISSN:0969-7128. (Stockton Press)We investigated the efficiency of activated polyamidoamine dendrimers, a new class of nonviral vectors, to transfect rabbit and human corneas in ex vivo culture. In addn. to assessing the expression of a marker gene we have demonstrated that this approach can be used to induce the prodn. of TNF receptor fusion protein (TNFR-Ig), a protein with therapeutic potential. Whole thickness rabbit or human corneas were transfected ex vivo with complexes consisting of dendrimers and plasmids contg. lacZ or TNFR-Ig genes. Following optimization 6-10% of the corneal endothelial cells expressed the marker gene. Expression was restricted to the endothelium and was maximal after transfection with 18:1 (wt./wt.) activated dendrimer:plasmid DNA ratio and culture for 3 days. The supernatant of corneas transfected with TNFR-Ig plasmid contained TNFR-Ig protein which was able to inhibit TNF-mediated cytotoxicity in a bioassay. We have therefore shown that activated dendrimers are an efficient nonviral vector capable of transducing corneal endothelial cells ex vivo. They may have applications in gene-based approaches aimed at prevention of corneal allograft rejection or in treatment of other disorders of corneal endothelium.
- 35Nguyen, C.; Hawker, C. J.; Miller, R. D.; Huang, E.; Hedrick, J. L.; Gauderon, R.; Hilborn, J. G. Hyperbranched Polyesters as Nanoporosity Templating Agents for Organosilicates. Macromolecules 2000, 33, 4281– 4284, DOI: 10.1021/ma991407vGoogle Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXivVaisLw%253D&md5=f7c59393df36626d0722c5813de3c1dbHyperbranched Polyesters as Nanoporosity Templating Agents for OrganosilicatesNguyen, C.; Hawker, C. J.; Miller, R. D.; Huang, E.; Hedrick, J. L.; Gauderon, R.; Hilborn, J. G.Macromolecules (2000), 33 (11), 4281-4284CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Hyperbranched polyesters based on copolymers of ε-caprolactone and bis(hydroxymethyl)-substituted ε-caprolactone were used as templates for prepn. of nanoporous silica ultralow dielec. materials for advanced microelectronic devices. The 1:4 copolymer having mol. wt. of 8000 g/mol and polydispersity of 2.81 (degree of branching = 0.15) was used to form the nanoscopically phase-sepd. hybrid morphol. with Me silsesquioxane (MSSQ); MSSQ softened at 40° and network formation onset was just below 200°, vitrification increased with temp. to over 400°, which coincided with the decompn. temp. of the polyester. Formation of porous thin films was accomplished by spin-coating a soln. of MSSQ and the polyester dissolved in propylene glycol Me ether acetate (PM-acetate) and heating to 430° (5°/min). The polyester content in the hybrids was 10-30%. It is crit. that phase sepn. between polyester and MSSQ occur during vitrification and that the size scale of kinetic phase sepn. be limited. This is accomplished by kinetically quenching the film structure prior to coarsening of the morphol., via nucleation and growth mechanisms. Porosity in the organosilicate films is generated upon curing the hybrids to 430°; the polyester undergoes quant. degrdn., leaving pores with size and shape of the original hybrid morphol. The porosity was verified by IR, refractive index, dielec. const., and TEM measurements.
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- 1Staudinger, H. Über Polymerisation. Ber. Dtsch. Chem. Ges. B 1920, 53, 1073– 1085, DOI: 10.1002/cber.192005306271https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaB3cXhvVarsQ%253D%253D&md5=e85c424244476944145c0c1b8946d255PolymerizationStaudinger, H.Berichte der Deutschen Chemischen Gesellschaft [Abteilung] B: Abhandlungen (1920), 53B (), 1073-85CODEN: BDCBAD; ISSN:0365-9488.cf. Schroeter, C. A. 11, 2776. S. believes the most varied polymerization products can be satisfactorily represented by formulas with normal valences without the necessity of assuming that they are mol. compds. in which the components are held together by subsidiary valences. Polymerization processes in the wider sense are all processes in which two or more mols. combine to a product of the same compn. but of higher mol. wt. They can be divided into two groups: (1) True polymerization processes in which the atoms in the product are united in the same way as in the monomol. product; and (2) "condensing" polymerization processes in which there is more or less of a shifting of the atoms. Only processes of the first kind are discussed. These may occur with mols. having an unsatd. atom (Ph3C) or with compds. having a double bond (these are by far the most important cases); finally, unstable ring systems have a tendency to change over into stable products of higher mol. wt. The true polymerization processes of substances with double bonds may lead to ring systems with 4-, 6- or 8-membered rings or to products with very high mol. wts. As to what conditions det. whether the polymerization will proceed in one or the other of these two ways the data at present available are not sufficient to make clear; slight differences in constitution often change the course of the polymerization (e. g., cinnamic acid polymerizes to truxillic acid while its esters give products of high mol. wt.). On the other hand some quite general conclusions as to the stability and tendency to depolymerization of the polymers can be drawn. Four- are in general less stable than 6-membered rings; the tendency to break down depends on the nature of the members of the ring; heterocyclic 4-membered rings, especially when they contain several hetero atoms, are in general not as stable as cyclobutane derivs.; the stability, especially of cyclobutane derivs., is greatly modified by substituents and the ring may be greatly weakened, as, e. g., by the introduction of several Ph or CO groups. Six-membered ring derivs., especially isocyclic, are stable. In polymerization products of high mol. wt., also, the stability varies greatly with the compn. and the substituents. Whether smooth depolymerization to monomol. compds. will occur depends in all cases not only on the decompn. temp. of the polymerization product but also on the stability of the monomol. compd.
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- 3Kim, Y. H.; Webster, O. W. Hyperbranched Polyphenylenes. Macromolecules 1992, 25, 5561– 5572, DOI: 10.1021/ma00047a0013https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38Xlslahtrs%253D&md5=e233a809990e74955d058d300afe4630Hyperbranched polyphenylenesKim, Young H.; Webster, Owen W.Macromolecules (1992), 25 (21), 5561-72CODEN: MAMOBX; ISSN:0024-9297.Highly branched polyphenylenes were synthesized from AB2 type monomers, e.g., (3,5-dibromophenyl)boronic acid and 3,5-dihalophenyl Grignard reagents. These monomers were polymd. by Pd(0) and Ni(II)-catalyzed aryl-aryl coupling reactions, resp. Polymers with mol. wts. 5,000-35,000 and polydispersities <1.5 were obtained. They were thermally stable to 550° and sol. in many org. solvents. 13C NMR indicated ∼70% branching efficiency. A Tg at 236° was obsd., but the polymer was brittle and did not form films. The melt flow viscosity of polystyrene was reduced, and the modulus was improved as a bromo functional hyperbranched polymer was added. The bromo polymer was metalated with butyllithium. The resulting lithio polymer reacted with various electrophiles to provide polymers with other end groups which control soly. as well as thermal properties. Some of these derivs. were used as multifunctional initiators to prep. star polymers, for example, via ring-opening polymn. of propiolactone and anionic polymn. of Me methacrylate.
- 4Flory, P. J. Principles of Polymer Chemistry; Cornell University Press: Ithaca, NY, 1953.There is no corresponding record for this reference.
- 5Tomalia, D. A.; Fréchet, J. M. J. Discovery of Dendrimers and Dendritic Polymers: A Brief Historical Perspective. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2719– 2728, DOI: 10.1002/pola.103015https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XlslWgt78%253D&md5=e38484be491990f270209b62eae14146Discovery of dendrimers and dendritic polymers: a brief historical perspectiveTomalia, Donald A.; Frechet, Jean M. J.Journal of Polymer Science, Part A: Polymer Chemistry (2002), 40 (16), 2719-2728CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)A brief review on the discovery of dendrimers and other dendritic polymers is presented. Dendritic polymers are recognized as the fourth major class of macromol. architecture consisting of four subclasses, namely (1) random hyperbranched, (2) dendrigrafts, (3) dendrons, and (4) dendrimers. The previous literature is reviewed with anecdotal events leading to implications for dendrimers in the emerging science of nanotechnol.
- 6Chremos, A.; Douglas, J. F. When Does a Branched Polymer Become a Particle?. J. Chem. Phys. 2015, 143, 111104, DOI: 10.1063/1.49314836https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFWrtL%252FP&md5=750c0998440bc9ed18b486f1f73f896aCommunication: When does a branched polymer become a particle?Chremos, Alexandros; Douglas, Jack F.Journal of Chemical Physics (2015), 143 (11), 111104/1-111104/5CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)Polymer melts with topol. distinct mol. structures, namely, linear chain, ring, and star polymers, are investigated by mol. dynamics simulation. In particular, we det. the mean polymer size and shape, and glass transition temp. for each mol. topol. Both in terms of structure and dynamics, unknotted ring polymers behave similarly to star polymers with f ≈ 5-6 star arms, close to a configurational transition point between anisotropic chains to spherically sym. particle-like structures. These counter-intuitive findings raise fundamental questions regarding the importance of free chain-ends and chain topol. in the packing and dynamics of polymeric materials. (c) 2015 American Institute of Physics.
- 7Tomalia, D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.; Ryder, J.; Smith, P. A New Class of Polymers: Starburst-Dendritic Macromolecules. Polym. J. 1985, 17, 117– 132, DOI: 10.1295/polymj.17.1177https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXhsV2ru70%253D&md5=895258598349ce237cc337df0cca089bA new class of polymers: starburst-dendritic macromoleculesTomalia, D. A.; Baker, H.; Dewald, J.; Hall, M.; Kallos, G.; Martin, S.; Roeck, J.; Ryder, J.; Smith, P.Polymer Journal (Tokyo, Japan) (1985), 17 (1), 117-32CODEN: POLJB8; ISSN:0032-3896.This paper describes the first synthesis of a new class of topol. macromols. referred to as starburst polymers. The building blocks to this polymer class are referred to as dendrimers. These dendrimers differ from classical monomers or oligomers by their extraordinary symmetry, high branching, and maximized (telechelic) terminal functionality d. The dendrimers possess reactive end groups which allow (a) controlled mol. wt. building (monodispersity), (b) controlled branching (topol.), and (c) versatility in design and modification of the terminal end groups. Dendrimer synthesis is accomplished by a variety of strategies involving time-sequenced propagation techniques. The resulting dendrimers grow in a geometrically progressive fashion. Chem. bridging these dendrimers leads to the starburst polymers. Dendrimers consist of an initiator core, interior layers (composed of repeating units radially attached to the interior core, and exterior layers (i.e., terminal functionality) attached to the outermost interior layer. Thus, the title macromol. was prepd. by amidation and Michael reactions involving ethylenediamine [107-15-3] and Me acrylate [96-33-3].
- 8Newkome, G. R.; Yao, Z.; Baker, G. R.; Gupta, V. K. Micelles. Part 1. Cascade Molecules: a New Approach to Micelles. A [27]-Arborol. J. Org. Chem. 1985, 50, 2003– 2004, DOI: 10.1021/jo00211a0528https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2MXit1Snsrc%253D&md5=8f6beff29cfdcda3c4883b3dfae3b6f3Micelles. Part 1. Cascade molecules: a new approach to micelles. A [27]-arborolNewkome, George R.; Yao, Zhongqi; Baker, Gregory R.; Gupta, Vinod K.Journal of Organic Chemistry (1985), 50 (11), 2003-4CODEN: JOCEAH; ISSN:0022-3263.The preliminary synthesis and spectral characterization of monocascade spheres (Arborols) which possess a three-dimensional microenvironment having the outer surface covered with polar functional groups is described. Thus, the [27]-arborol I was prepd. in 6 steps from Me(CH2)5CHO and HCHO via Me(CH2)4C(CH2OCH2CH2OH)3.
- 9Denkewalter, R. G.; Kolc, J. F.; Lukasavage, W. J. Macromolecular Highly Branched Homogeneous Compound. US Patent 4410688A.There is no corresponding record for this reference.
- 10Newkome, G. R.; Lin, X. Symmetrical, Four-directional, Poly(ether-amide) Cascade Polymers. Macromolecules 1991, 24, 1443– 1444, DOI: 10.1021/ma00006a04210https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXht1eiurg%253D&md5=b29bcc0d0031f5a711511098ba1fe20bSymmetrical, four-directional, poly(ether-amide) cascade polymersNewkome, George R.; Lin, XiaofengMacromolecules (1991), 24 (6), 1443-4CODEN: MAMOBX; ISSN:0024-9297.Sym., 4-directional, highly branched, and alternating ether-amide-linked spherical cascade polymers with distinct mol. wt. are described; new building blocks and cascade cores are reported.
- 11Gauthier, M.; Moeller, M. Uniform Highly Branched Polymers by Anionic Grafting: Arborescent Graft Polymers. Macromolecules 1991, 24, 4548– 4553, DOI: 10.1021/ma00016a01111https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXkslagsbo%253D&md5=c8068bc99a1b444ee2b03dfe8e9ab6bbUniform highly branched polymers by anionic grafting: arborescent graft polymersGauthier, Mario; Moeller, MartinMacromolecules (1991), 24 (16), 4548-53CODEN: MAMOBX; ISSN:0024-9297.Branched polystyrenes were prepd. by treating Ph2C:CH2-terminated polystyrene with chloromethylated polystyrene. The polymers had a very compact structure, but a low d., indicative of a hollow structure.
- 12Miller, T. M.; Kwock, E. W.; Neenan, T. X. Synthesis of Four Generations of Monodisperse Aryl Ester Dendrimers Based on 1,3,5-benzenetricarboxylic Acid. Macromolecules 1992, 25, 3143– 3148, DOI: 10.1021/ma00038a01912https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XisFKitb0%253D&md5=32286de3fecd5db6ef4b10865044de7dSynthesis of four generations of monodisperse aryl ester dendrimers based on 1,3,5-benzenetricarboxylic acidMiller, Timothy M.; Kwock, Elizabeth W.; Neenan, Thomas X.Macromolecules (1992), 25 (12), 3143-8CODEN: MAMOBX; ISSN:0024-9297.The convergent synthesis of a series of monodisperse dendrimers based on sym. substituted benzenetricarboxylic acid esters is described. These materials consist of 4, 10, 22, and 46 benzene rings connected sym. and have mol. diams. of ≤45 Å. The synthesis proceeds in a stepwise convergent manner, building dendritic arms, 3 of which are subsequently attached to a mol. core. The crit. intermediate for the dendrimer arm synthesis is 5-(tert-butyldimethylsiloxy)isophthaloyl dichloride (I), obtainable in 3 steps from 5-hydroxyisophthalic acid. Reaction of the diacid chloride with phenol, followed by removal of the silyl protecting group, gives a new substituted phenol. Two moles of the latter are further reacted with I. This process is repeated several times. The dendrimer arms formed by these reactions are coupled to 1,3,5-benzenetricarbonyl trichloride yielding dendrimers. Kinetic results suggest that the rate of reaction of the 1st dendrimer arm with the core is independent of the size of the dendrimer arm. These materials are stable at ≤500° under N and are highly sol. in typical org. solvents. Possible applications for these materials include mol. wt. stds., polymer rheol. modifiers, or mol. inclusion hosts.
- 13Percec, V.; Kawasumi, M. Synthesis and Characterization of a Thermotropic Nematic Liquid Crystalline Dendrimeric Polymer. Macromolecules 1992, 25, 3843– 3850, DOI: 10.1021/ma00041a00413https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XksV2gt7c%253D&md5=f36d6bb1eb937b19f6bf644ff0c74954Synthesis and characterization of a thermotropic nematic liquid crystalline dendrimeric polymerPercec, Virgil; Kawasumi, MasayaMacromolecules (1992), 25 (15), 3843-50CODEN: MAMOBX; ISSN:0024-9297.The prepn. and characterization of 1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)decane (I) and of 10-bromo-1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)decane (II) are described. Polyetherification of I with α,ω-dibromoalkanes contg. 6-10 methylene units leads to the model polyethers I-x (x = 6-10). Polyethers I-x, where x = 6, 8, and 10, exhibit an enantiotropic nematic mesophase, while those with x = 7 and 9 are glassy. Homopolymn. of II followed by in situ alkylation of the phenol chain-ends leads to dendritic polymers II-x (x is the structure of the alkylated phenol chain ends, i.e., Bz = benzyl, 4 = Bu, 6 = hexyl, 8 = octyl). Dendritic polymers II-x, where x = Bz, 6, and 8, represent the 1st examples of dendritic polymers which exhibit a thermotropic enantiotropic nematic mesophase. The isotropization temp. of the dendritic polymer II-x is lower than that of the model linear polyether I-8.
- 14Morikawa, A.; Kakimoto, M.; Imai, Y. Convergent Synthesis of Starburst Poly(ether ketone) Dendrons. Macromolecules 1993, 26, 6324– 6329, DOI: 10.1021/ma00076a00314https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXmsFSltrc%253D&md5=7f767f4b350c2e0af5395223e4086478Convergent synthesis of starburst poly(ether ketone) dendronsMorikawa, Atsushi; Kakimoto, Masaaki; Imai, YoshioMacromolecules (1993), 26 (24), 6324-9CODEN: MAMOBX; ISSN:0024-9297.New highly branched starburst poly(ether ketone) dendrons were synthesized by the convergent approach through arom. nucleophilic substitution reactions. 3,5-Bis(4-fluorobenzoyl)anisole was used as the building block, where the methoxy group was a protected form of the hydroxy group. The reaction of the building block with phenol gave the first-generation dendron (G1). Next, after the methoxy group was converted to a hydroxy group by reaction with aluminum chloride, the resulting phenol functionality of G1-OH was allowed to react with the building block to yield the second-generation dendron (G2). By repeating these procedures G3 and G4 generation dendrons possessing 8 and 16 phenoxy groups, resp., at the periphery position were obtained. The 1H- and 13C-NMR spectra were consistent with the structure of these dendrons. The mol. wt. and mol.-wt. distribution detd. by gel permeation chromatog. indicated that after purifn. by silica gel column chromatog., the dendrons possessed remarkably narrow mol.-wt. distribution.
- 15Lloyd, J. R.; Jayasekaraab, P. S.; Jacobson, K. A. Characterization of Polyamidoamino (PAMAM) Dendrimers using In-line Reversed Phase LC Electrospray Ionization Mass Spectrometry. Anal. Methods 2016, 8, 263– 269, DOI: 10.1039/C5AY01995H15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXitVSks73F&md5=7858275ad0c4f003fc13996e3ad4d48aCharacterization of polyamidoamino (PAMAM) dendrimers using in-line reversed phase LC electrospray ionization mass spectrometryLloyd, John R.; Jayasekara, P. Suresh; Jacobson, Kenneth A.Analytical Methods (2016), 8 (2), 263-269CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)Generation 3 (G3) PAMAM dendrimers are sym., highly branched polymers widely reported in the scientific literature as therapeutic agents themselves or as carrier scaffolds for various therapeutic agents. A large no. of anal. techniques have been applied to study PAMAM dendrimers, but one that has been missing is in-line reversed phase LC electrospray ionization mass spectrometry (RP/LC/ESI/MS). To translate PAMAM dendrimers into therapeutic agents, a better understanding of their purity, stability and structure is required, and in-line RP/LC/ESI/MS is widely applied to all three of these anal. questions. In this study, we developed a robust in-line RP/LC/ESI/MS method for assessing stability, purity and structure of the G3 PAMAM dendrimers, and we also examd. the reasons why previous attempts at method development failed. Using the RP/LC/ESI/MS method we uncovered several unique aspects of the chem. of G3 PAMAM dendrimers. They are interconverted between two isomeric forms by dialysis, and under higher concn. levels there is an inter-mol. displacement reaction resulting, which degrades PAMAM dendrimers. Purifn. of G3 dendrimers by RP/LC was also previously unreported; so we slightly modified the LC/MS method for isolating individual components from a complex dendrimer mixt. Thus, we have developed a robust, comprehensive method for characterizing PAMAM dendrimers and their degrdn.
- 16Jansen, J. F. G. A.; de Brabander-van den Berg, E. M. M.; Meijer, E. W. Encapsulation of Guest Molecules into a Dendritic Box. Science 1994, 266, 1226– 1229, DOI: 10.1126/science.266.5188.122616https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXit1GrtLg%253D&md5=84f24d561d127b77b91c5a76e8683b98Encapsulation of guest molecules into a dendritic boxJansen, Johan F. G. A.; de Brabander van den Berg, Ellen M. M.; Meijer, E. W.Science (Washington, D. C.) (1994), 266 (5188), 1226-9CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Dendrimers are well-defined, highly branched macromols. that emanate from a central core and are synthesized through a stepwise, repetitive reaction sequence. The synthesis and characterization of dendritic boxes, based on the construction of a chiral shell of protected amino acids onto poly(propyleneimine) dendrimers with 64 amine end groups, is reported here. NMR-relaxation and optical data show that a dense shell with solid-phase character is formed. Guest mols. were captured within the internal cavities of the boxes when these boxes were constructed in the presence of guest mols. The diffusion of guest mols. out of the boxes into soln. was unmeasurably slow because of the close packing of the shell. These monomol. dendritic containers of 5-nm dimensions with phys. locked-in guest mols. were characterized spectroscopically. Guest mols. were captured within the internal cavities of the boxes when these boxes were constructed in the presence of guest mols. The diffusion of guest mols. out of the boxes into soln. was unmeasurably slow because of the close packing of the shell. These monomol. dendritic containers of 5-nm dimensions with phys. locked-in guest mols. were characterized spectroscopically.
- 17de Gennes, P. G.; Hervet, H. Statistics of Starburst Polymers. J. Phys., Lett. 1983, 44, 351– 360, DOI: 10.1051/jphyslet:0198300440903510017https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXktVKhtbo%253D&md5=667658bcec21a46d41f5a7bc5ee5f2d7Statistics of "starburst" polymersDe Gennes, P. G.; Hervet, H.Journal de Physique, Lettres (1983), 44 (9), 351-60CODEN: JPSLBO; ISSN:0302-072X.The growth of completely branched polymers, based on tertiary amine branch points connected by flexible linear portions (spacers) of each P monomers, was discussed. The method was a modified version of the Edwards self-consistent fields (1965). The ideal starburst growth (without any residual second amine functions) was found to be restricted to a no. of generations m ≤ m1, where m1 ≃ 2.88 (lnP + 1.5). This corresponded in space to a limiting radius (R1), which increased linearly with P. Well below this limit, the polymer radius R(M), plotted as a function of mol. rate (M), was predicted to increase as M0.2, while above the limit (R > R1) compact structures were predicted (R ∼ M0.33).
- 18Ballauff, M.; Likos, C. N. Dendrimers in Solution: Insight from Theory and Simulation. Angew. Chem., Int. Ed. 2004, 43, 2998– 3020, DOI: 10.1002/anie.20030060218https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltFWhs7s%253D&md5=b84d5c00fe26d5fdf7ff367e799ff8dbDendrimers in solution: insight from theory and simulationBallauff, Matthias; Likos, Christos N.Angewandte Chemie, International Edition (2004), 43 (23), 2998-3020CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. A variety of exptl. and theor. approaches show that, akin the to linear polymers, dendrimers in good solvent conditions are best described as flexible macromol. aggregates with a dense core and fluctuating monomer groups. We present theor. and simulation evidence of how the shape and inner structure of dendrimers depends on the generation no. and the effective interactions that exist between dendrimers in soln. These approaches based on simplified dendritic structures show there is a tunable and ultrasoft interaction between the centers of the solubilized dendrimers. Results from small-angle neutron scattering data confirm the theory and indicate that dendrimers are model systems of ultrasoft colloids that bridge the gap between polymers and hard spheres. Dendrimers can form a class of materials analogous to the related systems of star polymers and block copolymer micelles which-exhibit special properties.
- 19Miklis, P.; Çaǧin, T.; Goddard, W. A., III Dynamics of Bengal Rose Encapsulated in the Meijer Dendrimer Box. J. Am. Chem. Soc. 1997, 119, 7458– 7462, DOI: 10.1021/ja964230i19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXkvVens74%253D&md5=048c7303e13db030d779a1270e4aa956Dynamics of Bengal Rose Encapsulated in the Meijer Dendrimer BoxMiklis, Paul; Cagin, Tahir; Goddard, William A., IIIJournal of the American Chemical Society (1997), 119 (32), 7458-7462CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Mol. dynamics (MD) techniques were used to study the encapsulation of Bengal Rose (BR) mols. in the Meijer dendrimer box (DBox) formed by the addn. of tert-butyloxycarbonyl-L-Phe (tBOC-L-Phe) cap mols. to the 64 terminal primary amines of a fifth generation poly(propyleneimine) (PPI-5) dendrimer. Using a large periodic box (including DBox, four to six BR, and CH2Cl2 solvent, totaling ∼25 000 atoms), the MD of these systems was examd. periods of ∼0.5 ns. Without the cap, BR mols. establish a concn. dependent equil. between the interior and surface regions of PPI-5 and the solvent region outside the dendrimer. The no. of BR mols. calcd. to assoc. with the interior of the PPI-5 dendrimer agrees exactly with expt. (at the same BR/PPI concn.). MD simulations on the DBox in CH2Cl2 show that the tBOC-L-Phe surface is completely impermeable to encapsulated BR mols., even when an excess is forced inside the box. The close correspondence of the theory with expt. suggests that these methods can be used to design such systems in advance of expt. The encapsulation of mols. is of interest in development of materials which can be selectively carried and released into another environment.
- 20Seo, M.; Beck, B. J.; Paulusse, J. M. J.; Hawker, C. J.; Kim, S. Y. Polymeric Nanoparticles via Noncovalent Cross-linking of Linear Chains. Macromolecules 2008, 41, 6413– 6418, DOI: 10.1021/ma800967820https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXpvVakur4%253D&md5=cd985390f617f4a24d2f88f56c051d0dPolymeric Nanoparticles via Noncovalent Cross-Linking of Linear ChainsSeo, Myungeun; Beck, Benjamin J.; Paulusse, Jos M. J.; Hawker, Craig J.; Kim, Sang YoulMacromolecules (Washington, DC, United States) (2008), 41 (17), 6413-6418CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Novel polymeric nanoparticles were prepd. through the chain collapse of linear polymers driven by noncovalent crosslinking of dendritic self-complementary hydrogen-bonding units (SHB). Random copolymers contg. SHB units, poly[(Me methacrylate)-r-2-((3,5-bis(4-carbamoyl-3-(trifluoromethyl)phenoxy)benzyloxy)carbonylamino)ethyl methacrylate] (A1, A2), were synthesized with various incorporation ratios by reversible addn.-fragmentation chain transfer (RAFT) polymn. Dramatically different behavior was obsd. depending on the level of incorporation of the supramol. units. At high loadings of A2 (6% SHB incorporation), intramol. chain collapse is favored, resulting in the formation of well-defined polymer nanoparticles, which were characterized by scanning force microscopy (SFM), dynamic light scattering (DLS), and viscosity studies. In contrast, anal. of copolymer A1 (1% SHB incorporation) revealed that chain collapse occurred primarily through intermol. interactions leading to large aggregates.
- 21Hawker, C. J.; Fréchet, J. M. J. Preparation of Polymers with Controlled Molecular Architecture. A New Convergent Approach to Dendritic Macromolecules. J. Am. Chem. Soc. 1990, 112, 7638– 7647, DOI: 10.1021/ja00177a02721https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXmtFaktLY%253D&md5=ce32a188723646f08702123d51ee5426Preparation of polymers with controlled molecular architecture. A new convergent approach to dendritic macromoleculesHawker, Craig J.; Frechet, Jean M. J.Journal of the American Chemical Society (1990), 112 (21), 7638-47CODEN: JACSAT; ISSN:0002-7863.The condensation of 3,5-bis(benzyloxy)benzyl bromide (I) with 3,5-(HO)2C6H4CH2OH gave bis[3,5-bis[(3,5-benzyloxy)benzyloxy]]benzyl alc (II) which was converted to the resp. benzyl bromide deriv. The latter was again treated with monomer I in a repeated sequence to give a dendritic oligomer. The oligomer was added to (4-HOC4H4)3CMe to give a dendritic starburst polyether of low polydispersity.
- 22Wooley, K. L.; Hawker, C. J.; Fréchet, J. M. J. A “Branched-Monomer Approach” for the Rapid Synthesis of Dendimers. Angew. Chem., Int. Ed. Engl. 1994, 33, 82– 85, DOI: 10.1002/anie.199400821There is no corresponding record for this reference.
- 23Malkoch, M.; Malmström, E.; Hult, A. Rapid and Efficient Synthesis of Aliphatic Ester Dendrons and Dendrimers. Macromolecules 2002, 35, 8307– 8314, DOI: 10.1021/ma020536023https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XntV2rurk%253D&md5=d7f8e535265f91952d9b9feec04091dfRapid and Efficient Synthesis of Aliphatic Ester Dendrons and DendrimersMalkoch, Michael; Malmstroem, Eva; Hult, AndersMacromolecules (2002), 35 (22), 8307-8314CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)A divergent approach to synthesize dendritic aliph. polyester structures based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) is described. The key building block is the anhydride of isopropylidene-2,2-bis(methoxy)propionic acid which is synthesized in high yields through self-dehydration, utilizing N,N'-dicyclohexylcarbodiimide (DCC) as reagent. The high reactivity of the anhydride toward hydroxyl groups makes the divergent synthesis of dendrimers and dendrons viable. Dendritic growth occurs in the presence of protecting groups sensitive toward hydrogenolysis, such as benzyl esters and ethers. The acetonide-protecting group is easily removed under acidic conditions using DOWEX 50W-X2 resin in methanol. Fourth-generation dendrons and dendrimers were successfully synthesized in high yields utilizing 1.3-1.5 equiv of anhydride per hydroxyl group. Common characteristics of the esterification reaction were short reaction time, mild reaction conditions, easy monitoring by NMR anal., and simple workup. This synthetic approach opens up the possibility to utilize orthogonal protecting groups of acetonide-protected 2,2-bis(hydroxymethyl)propionic anhydride as a novel building block.
- 24Wooley, K. L.; Klug, C. A.; Tasaki, K.; Schaefer, J. Shapes of Dendrimers from Rotational-Echo Double-Resonance NMR. J. Am. Chem. Soc. 1997, 119, 53– 58, DOI: 10.1021/ja962285e24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XnsVemurk%253D&md5=4607abec025c52a1b7a77d9721571b2dShapes of Dendrimers from Rotational-Echo Double-Resonance NMRWooley, Karen L.; Klug, Christopher A.; Tasaki, Kenzabu; Schaefer, JacobJournal of the American Chemical Society (1997), 119 (1), 53-58CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The solid-state shape, size, and intermol. packing of a fifth-generation dendritic macromol. were detd. by a combination of site-specific stable-isotope-labeling, rotational-echo double-resonance (REDOR) NMR and distance-constrained mol. dynamics simulations. REDOR expts. measured dipolar couplings between 13C atoms located near the chain ends and an 19F label placed at the core of benzyl ether dendrimers (generations 1-5) based on 3,5-dihydroxybenzyl alc. as the monomeric repeat unit. Intramol. 13C-19F coupling was distinguished from intermol. coupling by diln. with nonlabeled dendrimer. The av. intramol. 13C-19F distances for generations 3-5 were each approx. 12 Å, which indicates inward-folding of chain ends with increasing generation no. The av. intermol. 13C-19F dipolar coupling decreased with increasing generation no., consistent with decreased interpenetration for larger dendrimers. The measured intra- and intermol. distances for the fifth-generation dendrimer were used as constraints on energy minimizations and mol. dynamics simulations, which resulted in visualizations of the dendrimer packing and an est. of d. in the solid state.
- 25Liu, M.; Kono, K.; Fréchet, J. M. J. Water-Soluble Dendrimer-Poly(ethylene glycol) Starlike Conjugates as Potential Drug Carriers. J. Polym. Sci., Part A: Polym. Chem. 1999, 37, 3492– 3503, DOI: 10.1002/(SICI)1099-0518(19990901)37:17<3492::AID-POLA7>3.0.CO;2-025https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlsV2jt7Y%253D&md5=7507382cf0f277d4f7cea6305eb1a5deWater-soluble dendrimer-poly(ethylene glycol) starlike conjugates as potential drug carriersLiu, Mingjun; Kono, Kenji; Frechet, Jean M. J.Journal of Polymer Science, Part A: Polymer Chemistry (1999), 37 (17), 3492-3503CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)The design and synthesis of a new dendrimer-polyethylene glycol (PEG) conjugate that may be used as a model drug carrier are described. The starting material is a polyether dendrimer with two different types of chain end functionalities. The dendritic assembly is made water sol. through attachment of short PEG chains to the dendrimer via one type of functionality. The remaining chain end functionalities then were used to incorporate model drug mols. of varying polarity into the modified dendrimer. Cholesterol and two amino acid derivs. were selected as model drugs for attachment through their resp. hydroxyl, carboxylic acid, and amino functional groups to the dendrimer via carbonate, ester, and carbamate linkages. The resulting water-sol. dendrimer-model drug conjugates were characterized by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry.
- 26Kim, Y. H.; Webster, O. W. Water-Soluble Hyperbranched Polyphenylene: “A Unimolecular Micelle”?. J. Am. Chem. Soc. 1990, 112, 4592– 4593, DOI: 10.1021/ja00167a09426https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXitFOltro%253D&md5=3c9a84f4d68a76abf4dbf0af16a8736bWater soluble hyperbranched polyphenylene: "a unimolecular micelle?"Kim, Young H.; Webster, Owen W.Journal of the American Chemical Society (1990), 112 (11), 4592-3CODEN: JACSAT; ISSN:0002-7863.Hyperbranched polyphenylene with bromo functional groups was prepd. by homocoupling of 3,5-dibromophenylboronic acid with Pd(PPH3)4 as a catalyst. The mol. wt. of the polymer was 4000-8000. Reaction of the polymer with BuLi, followed by CO2, resulted in a water-sol. carboxylated polymer Li salt. This polymer showed properties resembling those of micelles. Upfield shifts of the NMR chem. signals of p-toluidine of ≤0.8 ppm in water occurred when the carboxylated hyperbranched polymer was added.
- 27Jikei, M.; Kakimoto, M. Hyperbranched Polymers: A Promising New Class of Materials. Prog. Polym. Sci. 2001, 26, 1233– 1285, DOI: 10.1016/S0079-6700(01)00018-127https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXptFCisro%253D&md5=8b93877f60df7a56b9ab9174bbc0c327Hyperbranched polymers: a promising new class of materialsJikei, Mitsutoshi; Kakimoto, Masa-akiProgress in Polymer Science (2001), 26 (8), 1233-1285CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)A review. The general concepts, syntheses and the properties of hyperbranched polymers are reviewed with refs. The polymn. reactions are classified into three categories: (1) step-growth polycondensation of ABx monomers; and (2) self-condensing vinyl polymn. of AB* monomers; (3) multibranching ring-opening polymn. of latent ABx monomers. Hyperbranched polymers are generally composed of dendritic, linear and terminal units and a degree of branching (DB) helps to describe their structures. Most of the hyperbranched polymers possess some of the unique properties exhibit dendritic macromols., such as low viscosity, good soly., and multi-functionality. Owing to multi-functionality, phys. properties such as soly. in solvents and the glass transition temp. can be controlled by the chem. modification of the end functional groups (endcapping reactions). Applications of designed hyperbranched polymers to specific fields are also described.
- 28Hawker, C. J.; Fréchet, J. M. J.; Grubbs, R. B.; Dao, J. Preparation of Hyperbranched and Star Polymers by a” Living”, Self-Condensing Free Radical Polymerization. J. Am. Chem. Soc. 1995, 117, 10763– 10764, DOI: 10.1021/ja00148a02728https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXosF2jsbc%253D&md5=84d480a54fb075717dc981dce4b94ba2Preparation of Hyperbranched and Star Polymers by a "Living", Self-Condensing Free Radical PolymerizationHawker, Craig J.; Frechet, Jean M. J.; Grubbs, Robert B.; Dao, JulianJournal of the American Chemical Society (1995), 117 (43), 10763-4CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The prepn. of hyperbranched and novel hyperbranched-star macromols. based on the combined concepts of "living" free radical and "self-condensing" polymn. techniques is reported for the first time. A unimol. monomer, 4-[2-(phenyl)-2-(1-2,2,6,6-tetramethylpiperidinyloxy)ethyloxy]methylstyrene (I), contg. both a polymerizable double bond and a reactive styrene-TEMPO (2,2,6,6-tetramethylpiperidinyloxy) group has been shown to afford highly branched irregular dendritic structures on polymn. These hyperbranched macromols. which contain numerous initiating functionalities at the chain ends are also capable of initiating the polymn. of vinyl monomers to give multi-arm stars. Copolymn. of I with vinyl monomers, such as styrene, is also shown to afford branched polymers with a controlled branch d. and length.
- 29Voit, B. I.; Lederer, A. Hyperbranched and Highly Branched Polymer Architectures—Synthetic Strategies and Major Characterization Aspects. Chem. Rev. 2009, 109, 5924– 5973, DOI: 10.1021/cr900068q29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtF2lurjP&md5=146b9182a7d6dd3d3f172fbe61606ca4Hyperbranched and Highly Branched Polymer Architectures-Synthetic Strategies and Major Characterization AspectsVoit, Brigitte I.; Lederer, AlbenaChemical Reviews (Washington, DC, United States) (2009), 109 (11), 5924-5973CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. This review has covered the principle synthetic approaches toward hyperbranched polymers as well as various other highly branched polymer architectures developed over the last 20 years.
- 30Stiriba, S. E.; Kautz, H.; Frey, H. Hyperbranched Molecular Nanocapsules: Comparison of the Hyperbranched Architecture with the Perfect Linear Analogue. J. Am. Chem. Soc. 2002, 124, 9698– 9699, DOI: 10.1021/ja026835m30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XlsFygu7o%253D&md5=38f827bc7169d03ffffce8ae4911aeeeHyperbranched Molecular Nanocapsules: Comparison of the Hyperbranched Architecture with the Perfect Linear AnalogueStiriba, Salah-Eddine; Kautz, Holger; Frey, HolgerJournal of the American Chemical Society (2002), 124 (33), 9698-9699CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Two hyperbranched polyglycerol samples with mol. wt. of 3000 and 8000 g/mol (Mw/Mn = 1.3), resp., were partially esterified using palmitoyl chloride. The same modification was applied to the structurally analogous linear polyglycerol (3000 g/mol). A detailed UV-vis study correlated with viscosity expts. demonstrated that only the hyperbranched core-shell structures form nanocapsules, leading to the encapsulation of polar guest mols. (Congo Red). The results underline the crucial role of the hyperbranched topol. and the resulting soln. conformation for supramol. guest encapsulation and phase transfer. The unusually compact (collapsed) structure assumed by the hyperbranched core-shell amphiphiles in apolar media is responsible for the formation of a hydrophilic compartment, capable of irreversibly taking up guest mols.
- 31Malmstroem, E.; Johansson, M.; Hult, A. Hyperbranched Aliphatic Polyesters. Macromolecules 1995, 28, 1698– 1703, DOI: 10.1021/ma00109a04931https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXjs1Cgu7o%253D&md5=feb7da904b5119ab3242b8e432a32ddcHyperbranched Aliphatic PolyestersMalmstroem, E.; Johansson, M.; Hult, A.Macromolecules (1995), 28 (5), 1698-703CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Hyperbranched, aliph. polyesters of theor. calcd. molar mass 1200-44,300 were prepd. in the molten state from 2,2-bis(hydroxymethyl)propionic acid (repeating unit of ABx type) and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (core mol.) using acid catalysis. The procedure is a pseudo-1-step reaction where stoichiometric amts. corresponding to each generation were added successively. The resulting polymers were glassy, slightly yellow solids at room temp. with terminal hydroxy groups. The degree of branching, detd. with model compds. using 13C-NMR, was ∼80%. The materials exhibited good thermal stability as analyzed with TGA. Glass transition temps., detd. using DSC, were ∼40° and were relatively insensitive to variations in molar mass.
- 32Froehling, P. Development of DSM’s Hybrane® Hyperbranched Polyesteramides. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 3110– 3115, DOI: 10.1002/pola.2011332https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXltlGktrs%253D&md5=b41b77166d4b21eb7dd3dbff057d07edDevelopment of DSM's Hybrane hyperbranched polyesteramidesFroehling, PeerJournal of Polymer Science, Part A: Polymer Chemistry (2004), 42 (13), 3110-3115CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)A review. The development of DSM's Hybrane hyperbranched poly(ester amides) is described. The monomer for the hyperbranched polyester is obtained from the reaction of a cyclic anhydride with diisopropanol amine, yielding a tertiary amide with one COOH and two OH groups. Polycondensation takes place via an oxazolinium intermediate in bulk at relatively mild conditions in the absence of catalyst. The reaction was scaled up to ton scale. By varying and combining anhydrides, and modification with several types of end groups, a large variety of structures with concomitant properties and industrial applications was realized.
- 33Hawker, C. J.; Lee, R.; Fréchet, J. M. J. One-Step Synthesis of Hyperbranched Dendritic Polyesters. J. Am. Chem. Soc. 1991, 113, 4583– 4588, DOI: 10.1021/ja00012a03033https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3MXisVOru78%253D&md5=cbbc28df7dbd7a658501dc741567ebddOne-step synthesis of hyperbranched dendritic polyestersHawker, C. J.; Lee, R.; Frechet, J. M. J.Journal of the American Chemical Society (1991), 113 (12), 4583-8CODEN: JACSAT; ISSN:0002-7863.The 1-step prepn. of a hyperbranched polyester possessing a dendritic structure was achieved by thermal self-condensation of 3,5-bis(trimethylsiloxy)benzoyl chloride. The hyperbranched polymers were obtained in yields ≥80% and with polystyrene-equiv. wt.-av. mol. wts. 30,000-200,00. The polydispersity and the mol. wts. of the polyesters varied greatly with the temp. of the polymn. Characterization of the polymers was readily accomplished by NMR spectroscopy with the help of model compds. The degree of branching of the polyesters as detd. from NMR expts. was 55-60%. The polyesters, which contained reactive functional groups at all chain extremities, were glassy materials that showed a very high thermal stability comparable to that of analogous linear materials. In contrast, the excellent soly. properties of the hyperbranched polyesters influenced by their shape and functionalization were at variance with those of their linear polyester analogs.
- 34Hudde, T.; Rayner, S.; Comer, R.; Weber, M.; Isaacs, J. D.; Waldmann, H.; Larkin, D. F. P.; George, A. J. T. Activated Polyamidoamine Dendrimers, a Non-Viral Vector for Gene Transfer to the Corneal Dndothelium. Gene Ther. 1999, 6, 939– 943, DOI: 10.1038/sj.gt.330088634https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjtVKgtLY%253D&md5=56578b77f619dd23b3ca4a4dbab35381Activated polyamidoamine dendrimers, a non-viral vector for gene transfer to the corneal endotheliumHudde, T.; Rayner, S. A.; Comer, R. M.; Weber, M.; Isaacs, J. D.; Waldmann, H.; Larkin, D. F. P.; George, A. J. T.Gene Therapy (1999), 6 (5), 939-943CODEN: GETHEC; ISSN:0969-7128. (Stockton Press)We investigated the efficiency of activated polyamidoamine dendrimers, a new class of nonviral vectors, to transfect rabbit and human corneas in ex vivo culture. In addn. to assessing the expression of a marker gene we have demonstrated that this approach can be used to induce the prodn. of TNF receptor fusion protein (TNFR-Ig), a protein with therapeutic potential. Whole thickness rabbit or human corneas were transfected ex vivo with complexes consisting of dendrimers and plasmids contg. lacZ or TNFR-Ig genes. Following optimization 6-10% of the corneal endothelial cells expressed the marker gene. Expression was restricted to the endothelium and was maximal after transfection with 18:1 (wt./wt.) activated dendrimer:plasmid DNA ratio and culture for 3 days. The supernatant of corneas transfected with TNFR-Ig plasmid contained TNFR-Ig protein which was able to inhibit TNF-mediated cytotoxicity in a bioassay. We have therefore shown that activated dendrimers are an efficient nonviral vector capable of transducing corneal endothelial cells ex vivo. They may have applications in gene-based approaches aimed at prevention of corneal allograft rejection or in treatment of other disorders of corneal endothelium.
- 35Nguyen, C.; Hawker, C. J.; Miller, R. D.; Huang, E.; Hedrick, J. L.; Gauderon, R.; Hilborn, J. G. Hyperbranched Polyesters as Nanoporosity Templating Agents for Organosilicates. Macromolecules 2000, 33, 4281– 4284, DOI: 10.1021/ma991407v35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXivVaisLw%253D&md5=f7c59393df36626d0722c5813de3c1dbHyperbranched Polyesters as Nanoporosity Templating Agents for OrganosilicatesNguyen, C.; Hawker, C. J.; Miller, R. D.; Huang, E.; Hedrick, J. L.; Gauderon, R.; Hilborn, J. G.Macromolecules (2000), 33 (11), 4281-4284CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)Hyperbranched polyesters based on copolymers of ε-caprolactone and bis(hydroxymethyl)-substituted ε-caprolactone were used as templates for prepn. of nanoporous silica ultralow dielec. materials for advanced microelectronic devices. The 1:4 copolymer having mol. wt. of 8000 g/mol and polydispersity of 2.81 (degree of branching = 0.15) was used to form the nanoscopically phase-sepd. hybrid morphol. with Me silsesquioxane (MSSQ); MSSQ softened at 40° and network formation onset was just below 200°, vitrification increased with temp. to over 400°, which coincided with the decompn. temp. of the polyester. Formation of porous thin films was accomplished by spin-coating a soln. of MSSQ and the polyester dissolved in propylene glycol Me ether acetate (PM-acetate) and heating to 430° (5°/min). The polyester content in the hybrids was 10-30%. It is crit. that phase sepn. between polyester and MSSQ occur during vitrification and that the size scale of kinetic phase sepn. be limited. This is accomplished by kinetically quenching the film structure prior to coarsening of the morphol., via nucleation and growth mechanisms. Porosity in the organosilicate films is generated upon curing the hybrids to 430°; the polyester undergoes quant. degrdn., leaving pores with size and shape of the original hybrid morphol. The porosity was verified by IR, refractive index, dielec. const., and TEM measurements.