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Thiol–Ene Linear Step-Growth Photopolymerization in Miniemulsion: Fast Rates, Redox-Responsive Particles, and Semicrystalline Films

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† †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France
§ Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France
∥ Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France
⊥ Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
*E-mail [email protected]; Fax +33 389 60 87 99; Tel +33 389 60 88 04 (A.C.).
Cite this: Macromolecules 2016, 49, 4, 1143–1153
Publication Date (Web):February 2, 2016
https://doi.org/10.1021/acs.macromol.5b02512

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Abstract

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Radical step-growth photopolymerization of dithiol–diene monomer miniemulsion is shown to be a highly efficient, robust, and versatile route to generate film-forming linear poly(thioether) latexes. At extremely fast rates, the process results in high-molecular-weight polysulfide products, exhibiting both semicrystalline and oxidation-responsive properties. Four key issues are addressed as regards the practical implementation of this novel UV-driven waterborne technology: the preparation of a photolatent and colloidally stable thiol–ene monomer miniemulsion, the identification of key experimental parameters controlling reaction kinetics and polymer microstructure, the characterization of film semicrystallinity, and the application of poly(thioether ester) latexes as dual-stimuli-responsive nanocarriers sensitive to both oxidation and hydrolysis.

Introduction

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Waterborne heterogeneous polymerization encompasses a number of processes; common to all of them is a polymer dispersion product used as coating vehicle or recovered as dry resin. (1, 2) When the usage of water is permitted, it is usually the preferred industrial method due to distinctive advantages. (3) First, high molecular weight (MW) polymers can be produced in reasonable reaction times. Second, monomer can be added throughout the polymerization in semibatch operations to maintain copolymer composition. The other key features include a lower price production process over alternative methods (solution, bulk), easy-to-handle low viscous product, and an aqueous continuous phase improving the green credential of the process.
However, this eco-efficient technology has flourished almost exclusively on the ground of a single polymerization mechanism: radical chain-growth polymerization. In recent years, great efforts have been made to expand to more water-sensitive polymerizations: ionic (4) and catalytic (5) chain-growth polymerizations, even step-growth polymerizations. (6) Despite these efforts, commercial processes based on nonradical alternatives are still scarce, and free radical polymerization has now been widely accepted as an inherent limitation of large-scale waterborne heterogeneous polymerization. This strongly impacts the versatility in terms of copolymer composition and final properties for the material made from aqueous dispersions. To achieve new film properties, the main response has been an improved control of polymer architecture (7, 8) or hybrid colloids (9) prepared with preformed non-vinyl polymers. Additionally, the chemical industry addressed the lack of diversity with the addition of auxiliary monomers. (10) Used in a small proportion (<5%) and often based on functional acrylates, their role is to impart film with specific cross-linking, adhesion, or hydrophobic properties.
Following the seminal work of Marvel et al. in the 1940s, (11) we have focused our attention on thiol–ene step-growth polymerization as a novel route to polymer dispersions. Of primary importance is the water tolerance of the active species exploited for a wide range of purposes, (12) including the synthesis of hydrogels. (13) Both propagation and transfer reactions governing polymer evolution rely indeed on thiyl and carbo radicals, respectively (see detailed mechanism in Scheme S1 of the Supporting Information). This is in sharp contrast with previous investigations on nonradical polymerization processes where the main challenge has been to overcome water sensitivity. In 2012, Shipp et al. have revived the subject’s interest, (14) and several groups have since experienced the unique advantages of thiol–ene polymerization in dispersed medium: fast rates in the matter of seconds, (15) easy thiol or alkene particle functionalization, (16, 17) ambient temperature reaction, (18) semicrystallinity of the resulting poly(thioether), (15) etc. Suspension polymerization (17-19) and microfluidic techniques were implemented to synthesize microparticles, while miniemulsion polymerization (15, 16) resulted in nanosized particles. The success of this approach gave birth to variant click chemistry approaches based on thiol–acrylate Michael addition (20, 21) and thiol–yne (22) or thiol–isocyanate (23) chemistry. Additionally, most of these studies employed a UV photochemical initiation providing spatiotemporal control and energy-saving process. Nevertheless, monomers with more than two functional groups per molecule were present, resulting with the formation of polymer network. The main caveat is that highly cross-linked polymer particles have far fewer uses than linear analogues because film forming ability or processability are generally more limited. Their niche applications cover chromatographic columns, ion exchangers, functional beads for medical diagnostics, support materials, calibration standards, and drug delivery carriers.
To fully tap the potential of thiol–ene emulsion photopolymerization, bifunctional monomers are needed as precursors of linear polymer particles having film-forming ability after water evaporation or flow properties after latex coagulation. Such polymers could be used as thermoplastic resins but also in all the conventional applications of emulsion polymer dispersions, including adhesives, paints, binders for nonwoven fabrics, additives for paper, textiles and construction materials, and impact modifiers for plastic. (2) However, the successful synthesis of high-MW linear polymers using any step-growth polymerization reaction is more challenging than the corresponding small molecule or cross-linking reaction, since high MW values can be achieved only at very high conversions (>98–99%). The need for very high conversions places several stringent requirements on any coupling reaction to be used for step-growth polymerization. This has been achieved by only handful of commercially important polymers (polyester, polycarbonate, or polyamide) under conditions not easily transposable in water because of high activation energy and often equilibrium condensation processes. In a recent letter, we have proved that these stringent conditions could be fulfilled during the photopolymerization of dithiol–diene monomer miniemulsion. (15) In this new contribution, we present a detailed study of this system. Starting with two pairs of thiol–ene bifunctional monomers given in Scheme 1, we present extensive characterization, including real-time Fourier transform near-infrared (RT-FTNIR) spectroscopy, nuclear magnetic resonance (NMR), cryo-transmission electron microscopy (cryo-TEM), X-ray diffraction (XRD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), which provides insight into four key issues for the practical implementation of this novel UV emulsion technology: (i) the preparation of a monomer miniemulsion combining chemical and colloidal stability, (ii) the review of the main experimental parameters (irradiance, solid contents, etc.) controlling reaction kinetics and polymer microstructure, (iii) the characterization of polymer semicrystallinity, and (iv) the assessment of poly(thioether ester) particles as dual oxidation- and hydrolysis-responsive nanomaterials.

Scheme 1

Scheme 1. Two Couples of Thiol–Ene Bifunctional Monomers (EDDT-DAP: 1; EDDT-DAA: 2) and the Corresponding Poly(thioether) Structure (P1 and P2) Formed by Step-Growth Linear Polymerization
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Experimental Section

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Chemicals

2,2-(Ethylenedioxy)diethanethiol (EDDT, TCI Chemicals, 95%), diallyl phthalate (DAP, TCI Chemicals, 98%), and diallyl adipate (DAA, TCI Chemicals, 98%) were used as monomers. The two couples EDDT-DAP (1) and EDDT-DAA (2) gave birth to two poly(thioether ester) P1 and P2, as shown in Scheme 1. Distilled water was used for the preparation of the continuous phase of the miniemulsion. Hexadecane (HD, Aldrich, 98%) and sodium dodecyl sulfate (SDS, Aldrich, 98%) were respectively used as costabilizer and surfactant. Type I photoinitiators (PI), 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (I2959, BASF, 98%) and 2,2-dimethoxy-2-phenylacetophenone (I651, BASF, 99%), ensured the generation of initiating radicals. 2,5-Di-tert-butylhydroquinone (DBHQ, Aldrich, 99%) was used as radical inhibitor. A 10 wt % hydrogen peroxide solution (Aldrich) and a hydrochloric acid solution (pH = 2) (Fluka) were prepared for experiments on polysulfide latex degradation. In the latter, a commercial poly(acrylate-b-styrene) latex (UCAR poly(ester-b-acrylate) latex, Dow Chemicals) was used as a benchmark dispersion (Dp ≈ 150 nm). Dimethyl sulfoxide (DMSO, Aldrich) was used as solvent for bulk polymerization and tetrahydrofuran (THF, Aldrich) as the solvent for size exclusion chromatography (SEC). All aforementioned chemicals were used without further purification.

Thiol–Ene Monomer Miniemulsion Preparation

Dithiol (EDDT) and diallyl (DAP or DAA) compounds were mixed together to obtain the monomer phase (4 g, Cmonomer = 20 wt %). Mixtures were prepared so as to obtain a 1:1 stoichiometry in thiol and ene functions, taking into account the purity of the chemicals. HD was added to the monomer phase (0.16 g, 4 wt %/Cmonomer). In certain experiments, 6 drops (0.3 mL) of a DBHQ solution in acetone (600 ppm, 6 × 10–4 g/L) were added to the mixture. The continuous phase consists of distilled water (16 g), SDS (0.14 g, 3.5 wt %/Cmonomer), and the water-soluble PI, I2959 (0.08 g, 2 wt %/Cmonomer). Both monomer and aqueous phases were stirred together for 10 min at 600 rpm. The miniemulsion was prepared subsequently by homogenizing the resultant coarse emulsion for 5 min using ultrasonication (Branson Sonifier 450 W, amplitude 90%) while maintaining stirring.

Thiol–Ene Miniemulsion Photopolymerization

The thiol–ene monomer miniemulsion was placed in a dismountable spectroscopic quartz cell of 1 mm optical path (volume 0.34 mL, no stirring). Photopolymerization was triggered using the polychromatic UV–vis light of a medium pressure Hg–Xe arc lamp (Hamamatsu L8252, 200 W). The quartz cell was irradiated vertically using a flexible light guide ensuring a homogeneous irradiation. A semielliptical mirror or reflector at 365 nm was used to enhance irradiance at this corresponding wavelength. Additionally, UV light below 310 nm was filtered using a long pass filter in order to avoid thiol self-initiation. Control experiments were undergone to check that there was no self-initiated polymerization with the filtered irradiation. In the 310–600 nm wavelength emission range, an output irradiance of 590 mW cm–2 was measured by radiometry (Ocean Optics HR4000 spectrometer). Note that this irradiation setup was also coupled with RT-FTNIR spectroscopy to assess the photopolymerization kinetics.

Poly(thioether ester) Latex Degradation

After polymerization, P1 and P2 latexes (20 wt % of polysulfide) were diluted 20 times in a hydroperoxide aqueous solution (10 wt %) or hydrochloric solution (pH = 2) depending on the degradation route considered. A similar procedure was performed with polystyrene-based latex (UCAR) to provide benchmark experiments. Diluted latexes samples were continuously stirred then taken at different time, inserted in a 1 cm optical path quartz cuvette, and analyzed by UV–vis spectroscopy.

Methods

Monomer conversion was followed in situ by RT-FTNIR in rapid scan mode (temporal resolution: 0.5 s; spectral resolution: 4 cm2). The spectroscopic cell containing the miniemulsion was irradiated simultaneously by a NIR probe beam and a UV exciting beam (see Scheme S2 in the Supporting Information). The NIR region (970–1940 nm, 9000–4000 cm–1) is well suited to aqueous miniemulsions because high water concentrations can be accommodated without detector saturation. Ene conversion relied on an specific absorption band at 4484 cm–1, which is assumed to be a combination of two C–H stretching bands. (24) By contrast, the measurement of thiol conversion was not found to be possible because of the absence of well-defined vibrational modes in the NIR region. Polymerization kinetics were assessed in situ by integrating the attenuance of the ene band and monitoring its decrease during irradiation. The limited signal-to-noise ratio, especially at high conversion, provided motivation to fit the conversion–time plots using a sigmoidal function described in ref 25. A typical experimental conversion–time plot and its fitted homologue are shown in Figure S1 of the Supporting Information.
Thiol–ene miniemulsion stability was assessed using multiple-light scattering (Turbiscan LAB, Formulaction). In a typical measurement, 20 mL of freshly prepared miniemulsion was placed in a vial and placed in the instrument. The temporal evolution of the backscattered light intensity (reflectance) normalized with respect to a nonabsorbing standard reflector was assessed during 3.5 h at 25 °C. The evolution of the backscattered light (at 45° from the incident beam) was determined by scanning the entire volume of the miniemulsion from the bottom to the cap of the cell. (26) Measurements were taken at the middle of the vial (≈20 mm). Droplet and particles diameters, respectively labeled as Dd and Dp, were determined through dynamic light scattering (DLS) using a Zetasizer Nano ZS (Malvern Instrument). Thiol–ene miniemulsion and polymerized latex were diluted 125 times in filtered and distilled water before analysis.
UV–vis attenuance spectra of thiol–ene miniemulsions, solutions in DMSO, and diluted latexes used in degradation experiments were all recorded with a double-beam SPECORD 210 BU UV–vis spectrometer (Analytic Jena AG).
Molecular weights were determined by SEC. Prior to analysis, 1–2 drops of the polymer latex was directly dissolved in 1 mL of THF to avoid the onset of insoluble crystalline parts. The analysis was performed on a Shimadzu LC-20AD liquid chromatograph equipped with two Varian PL gel 5 μm MIXED-C columns (column, injection, and refractometer temperature: 30 °C; injection volume: 100 μL) and a refractive index detector (Shimadzu RID-10A). THF was used as the eluent at a flow rate of 1.0 mL/min. The and Đ = / values were determined relative to linear polystyrene calibration standards.
The DSC experiments (DSC Q200, TA Instruments) were performed under a nitrogen atmosphere (50 mL/min) using either dry latex or as-synthesized liquid latexes. In both cases, the sample (8 mg) was placed within an aluminum hermetic pan, which was heated/cooled at 10 °C/min. Thermogravimetric analysis (TGA) (TGA Q500, TA Instruments) was carried out under a nitrogen atmosphere (20 mL/min). 9 mg of the dry polysulfide film was placed in an open aluminum pan and heated from ambient conditions to 1000 °C at 10 °C/min.
In POM analysis, the polysulfide latexes were coated using a 1 μm calibration bar at ambient temperature on glass plates and left drying at ambient temperature for 24 h. Resultant polysulfide films were then analyzed by POM with an Olympus Statif BX51 microscope. Glass plates were placed in a heating cell (Linkam LTS350) coupled with the microscope, and the cell temperature was controlled (Linkam TP94). Polysulfide films were heated at 10 °C/min from 15 to 130 °C. Images were taken using the acquisition software Cell^A.
XRD patterns were recorded on a X’Pert Pro diffractometer (PANalytical) equipped with a copper tube (Kα1–2 = 0.154 18 nm, 45 kV, and 40 mA) and a linear detector X’Celerator (active length = 2.122° 2θ). Dried polysulfide latex samples were coated on zero background plates (silicon) and then fixed in a specific sample holder with modeling clay. Diffractograms were recorded at high angles at ambient temperature for angle ranging from 3° to 50° 2θ with 0.017° 2θ path and time per path of 220 s (wide-angle XRD). Total analysis time was 1.5 h. In order to visualize reflexions lower than 3° 2θ, small-angle recording were realized from 0.5° to 10° 2θ (path and time per path identical to high angles). On the X-ray beam path was mounted as primary optics: Soller slits of 0.04 rad, a divergent slit of 1/16 (1/32 for small angles), a mask of 10 mm, and an antiscattering slit of 1/8 (1/16 for small-angle). As secondary optics: a receptor slit of 5 mm, Soller slits of 0.04 rad, and a nickel filter. All samples were put under rotation (1 rps) during spectrum acquisition.
For NMR analysis, the as-synthesized polysulfide latexes (0.05 mL) were directly added to an NMR tube without deuterated solvent for NMR analysis to hinder crystallization. 1H (400 MHz) was obtained on a Bruker Advance 400 at 295 K using tetramethylsilane (TMS) as internal standard.
For cryo-TEM analysis, a 400 carbon lacey film (Ted Pella) was rendered hydrophilic with a glow discharge treatment (Elmo Cordouan), a 5 μL drop was deposited onto the grid, and the film was blotted and plunged-freezed with a homemade freezing machine. The humidity and T are controlled at >80% and 23 °C, respectively. Subsequently, the grid was then transferred onto a Gatan 626 cryoholder and observed under low dose conditions in a Tecnai G2 under 200 kV. Images were recorded with an Eagle 2k2k ssCCD camera (FEI).

Results and Discussion

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The starting monomer miniemulsion (20 wt % monomer content) is based on a stoichiometric amount of bifunctional A–A (thiol) and B–B (ene) monomers. 2,2-(Ethylenedioxy)diethanethiol (EDDT) was chosen as dithiol while diallyl adipate (DAA) or phthalate (DAP) forms the two possible dialkene comonomers (chemical structures shown in Scheme 1). The analysis, in parallel, of these two miniemulsions (M1: EDDT-DAP; M2: EDDT-DAA) enables a critical approach. The choice of allyl ether functions is dictated by their inability to homopolymerize because a stable allylic radical is formed. This suppresses the risk of stoichiometric imbalance of reactants that may drastically lower the polymer MW. In addition to monomers, HD and SDS serve as stabilizers against Ostwald ripening and coalescence, respectively, as conventionally reported for a miniemulsion formulation. (27) A water-soluble α-hydroxy ketone type I PI (I2959) is also introduced in the aqueous phase.

Thiol–Ene Monomer Miniemulsion: Chemical and Colloidal Stability

Prior to photopolymerization, there are two important aspects with thiol–ene monomer miniemulsion with regard to chemical and colloidal stability.

Chemical Stability

Premature reaction, i.e., before UV exposure, is generally managed in free radical photopolymerization of acrylate or styrene monomers by avoiding exposure to light or heat. By contrast, this is a significant issue in thiol–ene chemistry because of the relatively high rates of polymerization. Obviously, the main reason for thiol–ene reaction efficiency also accounts for the adventitious initiation, mostly induced by radical traces. (28, 29) As shown in Table 1, both organic mixtures EDDT-DAP (1) and EDDT-DAA (2) prepared without PI significantly suffer from premature polymerization, with respectively 24% and 45% ene conversion (FTIR data) after 1 h storage at ambient temperature without exposure to light. Both dienes have similar functional groups (electron-rich allyl propionate) and only differ from the bridging group: phenyl (DAP) or butylene (DAA). Lower or more difficult solubility of the higher-molecular-weight reactants produced in the DAP-EDDT system may be responsible for the observed, apparent lower reactivity. The formation of miniemulsion from these two organic monomer phases further increases the consumption (56% in M1 and 73% in M2 after 1 h). The PI present in the aqueous phase of the miniemulsion is not responsible for this drift, as checked by control experiments performed without this component. More probably, a supplement of initiating radicals may be produced by ultrasonic cavitation through decomposition of water, monomer, surfactant, or impurities as reported in the literature. (30) While this limited shelf life undermines temporal control of the reaction, the long-term photolatency in our miniemulsion thiol–ene photopolymerization is less crucial than in a conventional UV-curable formulation. The main reason is that step-growth polymerization of bifunctional monomers is manifested by a slow increase of molecular weight evolution with impossibility of gelation. (16)
Despite these considerations, the improvement of chemical stability remains important to avoid run-to-run irreproducibility. In fact, a gradual increase in MW of the monomer phase to be emulsified, although proceeding slowly, changes composition and viscosity. The consequences are large discrepancies of several tens of nanometers in average droplet size when changing the time between organic phase preparation and emulsification (data not given) and notably a tendency to obtain larger droplet diameters and broader size distributions when this time is lengthened. These latter results were assigned to a poorer efficiency of droplet breakup when the organic monomer phase becomes more viscous. (31) Based on the recent findings of Liska et al., (28) a possible solution to improve chemical stability, and indirectly repeatability and reproducibility, is the addition of a conventional phenolic radical stabilizer (DBHQ).
Table 1 shows that DBHQ (ca. 40 ppm) behaves as an efficient stabilizer for the less reactive EDDT-DAP system, either in bulk or in miniemulsion form, with ene conversions limited to 5% and 15% after 1 h, respectively. In addition, the resulting miniemulsion M1 containing the radical inhibitor exhibited a smaller average droplet diameter (155 nm) compared to the analogue without stabilizer (190 nm), and an acceptable level of repeatability was found (standard deviation of 7 nm calculated from five replicates; see the collection of data in Table S1 of the Supporting Information). By contrast, the addition of DBHQ to the more reactive EDDT-DAA couple showed no improvement of shelf life stability for the bulk and the miniemulsion because of the difficulty to manage its higher reactivity. Accordingly, the preparation of the miniemulsion M2, repeated five times, led to Dd values ranging from 150 to 200 nm (standard deviation = 16 nm). Although this poor repeatability does not prevent the photopolymerization of M2, caution must be taken in the interpretation of the results.
Table 1. Data on Chemical and Colloidal Stability of Thiol–Ene Pairs 1: EDDT-DAP and 2: EDDT-DAA in Bulk and Miniemulsion Form
thiol–ene pairformene conv (after 1 h)a (%)Dd (nm)Dd (after 1 h)a (nm)
EDDT-DAPbulk 124  
 M1b56190205
 bulk 1 + 40 ppm DBHQ5  
 M1b + 40 ppm DBHQ15155160
EDDT-DAAbulk 245  
 M2b73190170
 bulk 2 + 40 ppm DBHQ47  
 M2b + 40 ppm DBHQ77170170
a

Data determined 1 h after the emulsification. Conversion values were given by FTIR and droplet size by DLS.

b

The aqueous phase of the miniemulsion contains the PI.

Colloidal Stability

Figure 1 is a plot of the average droplet diameter Dd (y right ordinate) and reflectance R (y left coordinate) as a function of storage time (4 h) for the two miniemulsions M1 and M2 containing DBHQ. The temporal variation of these two values, obtained independently by DLS (Dd) and backscattering measurements (R), can be linked to the colloidal stability. In both instances, the evolution of the miniemulsion’s average droplet size given by DLS measurement is not very significant within 4 h, but larger variations are found with the chemically instable sample (M2) compared to the photolatent one (M1) within 1 h after emulsification. Because dilution is not necessary, the reflectance data seem more accurate to detect droplet size change and/or local concentration variation because of sample colloidal destabilization. Once again, both backscattering profiles are in line with an acceptable stability of the two samples. However, we note that the reflectance profile of M2 remains almost unchanged within 4 h, indicating a superior colloidal stability compared to M1. As previously mentioned, premature polymerization of M2 causes a significant consumption of monomer and consequently a depletion of the primary vector for Ostwald ripening. (32) Because it combines a reasonable chemical and colloidal stability, M1 has been selected in the following part, where the influence of various experimental parameters was examined. Note that all miniemulsions were photopolymerized within 5 min after preparation in the rest of the study.

Figure 1

Figure 1. Reflectance values determined at the middle of the vial (left y axis, line) and droplet average diameter values (right y axis, dot) as a function of storage time for the two thiol–ene miniemulsions: M1 (red) and M2 (black). Cmonomer = 20 wt %; both miniemulsions contain DBHQ inhibitor.

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Influence of Different Parameters on Miniemulsion Photopolymerization

Comparison between Bulk, Solution, and Miniemulsion Conditions

Miniemulsion features a droplet size (50–500 nm) substantially smaller than a conventional macroemulsion (0.1–20 μm). While the resultant decrease in scattering is desirable to mitigate nonuniform irradiation within the sample, the average droplet size reached by M1 (Dd = 155 nm) for example makes monomer miniemulsion nonetheless opaque to the naked eye. To investigate more quantitatively the extent of scattering and its effect on light depth, Figure 2A shows the attenuance spectrum of M1 at three different optical paths (0.1, 0.5, and 1 mm) as well as a comparison with a solution analogue S1 in which water was replaced by DMSO. In the visible range, M1 shows high attenuance values assigned only to scattering, whereas S1 is transparent. In the UV region, there is a superimposition of scattering and absorption (due to monomer and PI), leading to much higher attenuance values in M1 with respect to S1. Attenuance is even too high to be detected for the thickest samples (≥0.5 mm). At 350 nm corresponding to the threshold value below which the acetophenone-derivative PI absorbs, less than 1% of the incident photons are transmitted beyond 0.1 mm of the optical path (versus 80% in solution). As a result, at the beginning of the irradiation, only a minority of the actinically relevant UV photons are transmitted beyond a few tens of micrometers of the optical path. To improve significantly light penetration (without changing PI concentration), sub-100 nm monomer droplets exhibiting a narrow enough size distribution would be necessary. However, the control of these two parameters is very challenging during emulsification.
Using a 1 mm thick spectroscopic cell as photoreactor, M1 and S1 were photopolymerized at room temperature, without stirring, and under continuous UV irradiation of a conventional medium-pressure Hg arc lamp for only 20 s. Figure 2B shows the reaction kinetics monitored in situ by RT-FTNIR spectroscopy through the decay of the ene absorption band at 4484 cm–1 over time (see the inset). Remarkably, there are no noticeable differences of polymerization rates between these two systems. Additionally, a control experiment in bulk (B1) did not alter the kinetic profiles, confirming the minor role played by the organic solvent. Therefore, the miniemulsion photopolymerization may be not diffusion limited, suggesting that the rates of diffusion of monomer droplets to the irradiated areas are faster than the rate of reaction of the two functional groups. This indicates that an efficient mass transfer may overcome the limited depth of light penetration. Nevertheless, the equivalence between M1, S1, and B1 was obtained in specific conditions that thicker optical path reactors, larger droplets, or higher concentration could jeopardize. Another key feature is the very high conversion rates: a full conversion was accomplished in less than 15 s. As a result, thiol–ene chemistry holds a high potential for fast polymerization under mild conditions, which is a notable exception in linear step-growth polymerization. Of paramount importance is that high kinetic coefficients in the range of 105–106 L mol–1 s–1 are found for a broad classes of terminal thiol and ene monomers regardless of their other structural features. (33) This is not true for chain radical polymerization where very high values of propagation rate coefficient (kp) are found only with some specific monomers such as acrylates (e.g., butyl acrylate kp = 13 000 L/(mol s) at 50 °C) versus much lower values for methacrylates (methyl methacrylate: 648 L/(mol s) at 50 °C) or styrene (160 L/(mol s) at 40 °C). (34)

Figure 2

Figure 2. (A) Attenuance spectra of miniemulsion M1 (full symbols) and solution homologue S1 in DMSO (empty symbols) with Cmonomer = 20 wt % at different optical paths: 1 mm (triangle), 0.5 mm (circle), and 0.1 mm (square). (B) Conversion–times curves profiles for M1 (full symbols), S1 (open symbols), and bulk system B1 (solid line). All photopolymerizations were performed in a 1 mm thick spectroscopic cell under UV light provided by a filtered mercury–xenon arc lamp (λ > 310 nm, I = 590 mW cm–2). The inset shows a series of NIR spectra of M1 during photopolymerization.

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Table 2 summarizes the results of the three polymerizations M1, S1, and B1 as regards with conversion, molecular weight (, , and Đ), and colloidal properties when it is relevant. 1H NMR spectroscopy (see spectrum in Figure S2) of the obtained polymers unambiguously confirmed the formation of the desired poly(thioether) and the very high ene conversion in agreement with the FTIR data. In addition, SEC data show polydispersity index between 2 and 3 as well as values higher than 10 kDa regardless of the method (see SEC traces in Figure S3). This result shows that thiol–ene chemistry using AA and BB monomers is well-suited for step-growth polymerization, even without monomer purification. Significantly higher MW values were realized in M1 ( = 20.3 kDa) in comparison with S1 (11.0 kDa) and B1 (11.6 kDa). It is suggested that a radical compartmentalization (or segregation) effect may take place, similarly as chain polymerization. A propagating radical in a polymer particle isolates it from other propagating radicals and allows growth to higher MW than might be achieved in solution or bulk polymerization (provided that the rate of entry of another radical from the aqueous phase is sufficiently slow). (35-37) However, achieving high MW in a step reaction with AA and BB monomers may seem more complex in dispersed medium because of the strong difference in water solubility between EDDT (15 g/L) and DAP (0.15 g/L). Therefore, each individual droplet is likely to deviate compositionally from the exact stoichiometric balance. The fact that high MW polymers are created in the miniemulsion polymerization provides indirect evidence that the thiol reactant can diffuse from the aqueous phase to the particle and undergoes polymerization. It also reflects that oxidation of thiols to disulfides (also resulting in stoichiometric imbalance) plays a minor role. The resultant high monomer conversion drives high MW but also ensures a minimal amount of residual monomers, which is another positive effect of a step-growth polymerization. By contrast, in a chain mechanism, the unconverted reactive functionality necessarily derives from monomer molecules; therefore, a certain amount of monomer remains in the final material (several thousand parts per million typically in a conventional emulsion polymerization), raising toxicity concern, and requiring postpolymerization operations for their removal. (3) In our step-growth process, the residual thiol or allyl groups are retained as end groups of nonvolatile polymer or oligomer chains, thereby reducing toxicity.
Table 2. Effect of Polymerization Method (Miniemulsion, Solution, and Bulk) on Kinetic, Colloidal, and Polymer Properties for the EDDT-DAP System
entryene conva (%)Ddb (nm)Dpb (nm)Np/Ndcd (kDa)d (kDa)Đe
B1 (bulk)>99   11.636.03.1
S1 (solution)>99   11.023.62.1
M1 (miniemulsion)>991601531.0720.354.32.7
a

Conversion of alkene function determined by FTIR data.

b

Droplet (Dd) and particle (Dp) z-average diameters as determined by DLS.

c

Calculated by the equation Np/Nd = (ρmonomers × Dd3)(ρpolymer × Dp3)ρmonomers is the density of EDDT-DAP (1.06). ρpolymer is the resulting poly(thioether–ester) density (1.13) and was measured by pycnometry.

d

Number-average () and weight-average () molar mass as determined by size exclusion chromatography.

e

The breadth of molecular weight distribution also referred to as polydispersity index Đ = /.

As far as colloidal properties are concerned, droplet (Dd = 160 nm) and particle size (Dp = 155 nm) are very similar given the experimental error of DLS. From these data, a ratio of particle to droplet number was estimated to 1.07, fully in line with an effective droplet nucleation and also indicative of minor destabilization. As emphasized earlier, step-growth polymerizations are characterized by the disappearance of monomer early in the reaction and far before the production of high MW polymer. As small monomer molecules are the main drivers of Ostwald ripening, diffusional degradation is rapidly suppressed in this mechanism because low-MW species have weaker mass transfer ability through the aqueous phase. The exact opposite is the case for chain-growth polymerizations, where monomer species are still present even at high conversions. Therefore, Ostwald ripening is suppressed only when a sufficient concentration of polymer is formed (>30–40%). (38)

Effect of Various Experimental Parameters

Table 3 shows the effect of PI solubility, irradiance, and solids content on ene conversion and reaction rates as well as colloidal properties (Dd, Dp, Np/Nd). Additionally, all the kinetic curves are provided in Supporting Information (Figure S4). A unique advantage of miniemulsion over other heterogeneous methods is the ability to use PI of different solubility in water. We replaced hydroxyacetophenone (run A), fully soluble in the aqueous phase by dialkoxyacetophenone (2,2-dimethoxy-2-phenylacetophenone, run B), a widely used type I (α-cleavable) PI exhibiting an enhanced water-insolubility and dissolved in the monomer phase. (39) The difference between these two initiators involve not only solubility but also photochemical properties (quantum yield, triplet state lifetime, initiating radicals, absorption spectrum), making direct comparison of photopolymerization results difficult. However, it is surprising to note that the change of PI was not accompanied by any significant modification of polymerization rates and particle size, confirming the robustness of the present process. In addition, Table 3 emphasizes the effect of irradiance (60–590 mW/cm2) on thiol–ene miniemulsion kinetics (runs C–F). There is a net accelerating effect related to the increase in irradiance until a threshold value of 150 mW/cm2. The amount of absorbed photons determines the number of initiating radicals generated through PI cleavage. Upon decreasing irradiance, a lower number of initiating radicals is created; hydrogen abstraction on thiol functions decreases with fewer thiyl radicals generated. (40) Therefore, the addition rate on double bonds is diminished. As expected, the irradiance variation has a minimal effect on the nucleation mechanism because of limited destabilization process, and similar Dp and Np/Nd values were obtained. In a last series of experiments, the organic phase content was progressively increased from 20% to 50%. Runs G–J (Table 3) show the feasibility of conducting polymerization with organic phase contents up to 50%, which is a remarkable feature. High solid content latexes are highly desired industrially. The principal advantages are an increased space-time yield of the reactor, more efficient product transport, and faster drying times during film application. (41) In this series, the Np/Nd ratio remains close to unity, regardless the organic phase content. Additionally, there are no drastic changes on photopolymerization kinetics upon increasing the monomer concentration. Although miniemulsions of somehow similar average droplet sizes are generated, they differ from optical properties. A higher droplet concentration enhances scattering without undermining the polymerization rates. Again, this result suggests a non-diffusion-limited photopolymerization mechanism in agreement with the previous experiments. However, these observations remain qualitative, and the main challenge is the development of mechanistic models describing the interplay among UV radiation transfer in a scattering medium, photoreactor hydraulics, and intrinsic reaction kinetics. In this respect, an analogy can be drawn with TiO2 heterogeneous photocatalytic systems into which significant modeling efforts have been deployed recently for optimization of UV disinfection and oxidation photoreactors. (42)
Table 3. Effect of the Polymerization System, Irradiance (250–600 nm), Type of PI, and Monomer Content on Colloidal (Dd, Dp, and Np/Nd) and Kinetics
entrymonomer content (wt %)irradiance (mW/cm2)PIaene conv (%, t = 20 s)Rp,maxb (s–1)Dd (nm)Dp (nm)Np/Nd
A20590water-soluble PI>99641601531.07
B20590oil-soluble PI>99991551481.18
C20295water-soluble PI>99441451371.11
D20235water-soluble PI95371451371.11
E20145water-soluble PI92261451381.08
F2060water-soluble PI7581451381.08
G25590water-soluble PI>99391471411.06
H30590water-soluble PI95471731541.32
I35590water-soluble PI>991621611541.07
J50590water-soluble PI>99511521490.99
a

The water-soluble PI is I2959, and the oil-soluble one is I651.

b

Rp,max were obtained by differentiation of the fitted conversion plot for each run.

Semicrystalline Poly(thioether) Film

The latexes derived from the polymerized miniemulsions M1 and M2 were good film forming at room temperature. One of the outstanding characteristics of the resultant poly(thioether) films P1 and P2 is the resistance to a wide range of solvents and chemicals at ambient temperature. The insolubility gives a first indication of their high crystallinity and melting point. The semicrystallinity of linear poly(thioether) is well documented in the literature, in particular as regards with poly(ethylene sulfide) and poly(propylene sulfide). (43) By contrast, the latex particles can be dissolved in a water-miscible solvent such as THF (making SEC analysis possible). This result suggests indirectly that the polymer particles do not contain a high fraction of crystalline domains as they are synthesized. This phenomenon was also observed with poly(vinylidene chloride) copolymers produced by radical emulsion polymerization, in which a crystallization takes place during film formation. (44) Another indirect proof of limited semicrystallinity in the latex form was given by cryo-TEM images (Figure 3) showing particles having a spherical and deformable shape in line with a prevalent fraction of amorphous phase. Conversely, highly semicrystalline polymer nanoparticles exhibit generally an anisotropic morphology. (45) Semicrystalline polymers generally crystallize through heterogeneous nucleation on impurities or foreign surfaces acting as nucleation seeds. In a nanoconfined miniemulsion environment, the number of particles is several orders of magnitude higher than the number of active heterogeneities. (46) Therefore, only homogeneous nucleation proceeds, resulting in a decrease of the degree of crystallinity and a significant decrease of the crystallization temperature (also known as supercooling effect).

Figure 3

Figure 3. Cryo-TEM image of a representative area of P1 latex. The round-shaped homogeneous particles (indicated by white arrows) have a diameter ranging from 50 to 400 nm. The black arrow shows the lacy carbon supporting film. The solvent areas are fully amorphous due to the high speed of freezing (10 000 K/s) (arrowhead).

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Figure 4 shows the wide-angle X-ray diffraction (WAXRD) patterns of the two poly(thioether) samples. Independent of the polymer, many sharp Bragg peaks are visible as well as a broad envelope around 20° assigned to amorphous fraction, indicating respectively the coexistence of crystalline and amorphous domains. At small angles (see the small-angle X-ray diffraction pattern in Figure S5), three discernible Bragg peaks at 2.4°, 4.7°, and 7.0° with associated d-spacings of 36.5, 18.8, and 12.6 Å, respectively, are observed in both cases. They can be readily indexed as the (001), (002), and (003) directions of a lamellar mesostructure, with the typical regular stacks of crystalline lamellae and amorphous interlayers found in semicrystalline polymers. P2 is characterized by a higher degree of crystallinity than P1 as reflected by a much smaller halo on the WAXD pattern. Also present in the film after water evaporation, SDS and HD can both crystallize, (47, 48) but their melting point is around 18 °C, well below the temperature of the XRD analysis (30 °C). Poly(thioether) crystallinity is mainly a consequence of linearity (no branching) and flexibility. Highly favorable for crystallization, chain linearity and structural regularity in a thiol–ene polymerization originate from the very low probability of transfer to polymer since transfer to monomer is an intrinsic step of the propagation mechanism having a much higher kinetic constant. Second, the flexibility of the poly(thioether) is conducive to chain packing and stems from the relatively large C–S bond length. Obviously, crystallization can be promoted by additional attractive forces involving thioether and ester functional groups, but their low magnitude makes this factor secondary. It should also be noted that crystallization occurs despite the chemical heterogeneity of the film still containing SDS and HD. As expected, the rigid aromatic groups of P1 reduce flexibility and packing ability, leading to a somewhat lessened degree of crystallinity.

Figure 4

Figure 4. WAXRD patterns of P1 and P2 films.

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To investigate the crystallization behavior of the two poly(thioether) films, the DSC and TGA thermograms are also shown in Figure 5. From the TGA curves, the first signs of thermal decomposition temperature are manifested as low as 200 °C in both polymers. On both DSC curves, P1 and P2 show two distinct glass transition temperatures at −42 and −67 °C, respectively, indicative of highly flexible chains (see a magnification of the subambient temperature region in Figure S6). The supplement of rigidity provided by the phenyl group in P1 is sufficient to cause an increase of 25 °C of the Tg. However, no melting peak attributed to polymer can be observed although X-ray diffraction yielded a number of well-defined peaks. In contrast to what we have previously reported, (15) the two thermal transitions at 16 °C (melting) and 7 °C (crystallization) come from hexadecane and possibly sodium dodecyl sulfate (47, 49) rather than polysulfide chains. Their observation would not be possible in a fully miscible system and is indicative of a phase separation between poly(thioether), SDS, and hexadecane’s crystalline domains. (50) It is reasonable to deduce that the melting point is too high to be observed before the thermal decomposition which occurs as early as 200 °C. This hypothesis is supported by literature data indicating melting points of poly(methylene sulfide) and poly(ethylene sulfide) at 245 and 216 °C—values much higher than those of poly(methylene oxide) (180 °C) and poly(ethylene oxide) (68 °C). (51)

Figure 5

Figure 5. DSC (left y-axis) and TGA (right y-axis) thermograms of P1 (top) and P2 (bottom) films.

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The films were also analyzed with polarized optical microscopy (POM). The alternation of bright (crystallites) and dark (amorphous matrix) areas on Figure 6 in both samples give a first indication of crystalline domains. With P1, large spherulites are formed, indicating a slower crystallization process. In contrast, P2 displays a high number of small nuclei distributed in the film. In both instances, we observed no change of these crystalline macrostructures with temperature up to 130 °C (see Figure S7). This result shows again that the microcrystals do not result from SDS or hexadecane, both exhibiting a much lower melting temperature (ca. 18 °C). Although there is a lack of direct evidence, XRD and POM data are consistent with a semicrystallinity of the polysulfide films. Clearly, the deposition method is likely to have a strong influence on the crystallization process, and this important question needs to be addressed by future studies.

Figure 6

Figure 6. POM pictures in dark field mode of P1 (top) and P2 (bottom) films at ambient temperature.

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Dual Hydrolysis- and Oxidation-Responsive Poly(thioether ester) Nanoparticles

Poly(thioether)s such as poly(alkylene sulfide) have been recently proposed as redox-sensitive polymers. (52, 53) Hydrophobic thioether can be oxidized to more polar sulfoxide or sulfone depending on the oxidative conditions, thus driving a significant water solubility increase for the whole polymer chain. As a result, poly(thioether) nanoparticles dispersed in a hydrophilic solvent can act as oxidation-responsive nanocarriers because they are able to decompose by solubilization upon oxidative stress, thus causing the release of their encapsulated hydrophobic content (drug, gene, etc.). Besides other more popular stimuli (pH, light, etc.), oxidant is highly valuable for drug delivery because reactive oxygen species (ROS) possessing strong oxidizing capabilities play an important role in the progression of inflammatory disorders. (54) The design of poly(thioether) nanodispersions in water is especially relevant given that thioether are sensitive to a number of mild water-soluble oxidants such as H2O2 or NaOCl. (55) To date, the only single-step route to oxidation-responsive poly(thioether) nanoparticles relies on emulsion ring-opening polymerization of propylene sulfide. (56, 57) Although this method has been extensively investigated by Tirelli and Hubbell over the past 10 years as regards particle functionalization or encapsulation, (52) a novel and efficient method based on thiol–ene photochemistry could provide a simpler and more versatile alternative. In this fourth part, P1 and P2 polysulfide latexes derived from thiol–ene miniemulsion photopolymerization have been considered as dual-stimuli-responsive systems. (58) The combination of thioether and ester bonds in the same polymer backbone make these nanoparticles potentially sensitive to both oxidation and hydrolysis as sketched in Scheme 2.

Scheme 2

Scheme 2. Two Degradation Routes in Water of Poly(thioether ester) P1 Nanoparticles: Hydrogen Peroxide-Induced Oxidation of Thioether and HCl-Catalyzed Hydrolysis of Ester; Oxidation Leads Only to Sulfur(IV) with H2O2 (59)
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The nanoparticle response to these two stimuli was assessed by monitoring the attenuance decrease accompanying the loss of turbidity (scattering) as the polymer particles dissolves by oxidation or depolymerizes via hydrolysis. No precipitation was observed, and experiments were performed under constant stirring to eliminate the influence of sedimentation or creaming. Figure 7A shows a series of attenuance spectra of P1 for different characteristic times under oxidative conditions ([H2O2] = 10 wt %) or acid medium (pH = 2, HCl) (the corresponding curve for P2 is given in Figure S8). Although both routes seem effective for particle chemical modification, hydrolysis leads to faster and more effective decrease of attenuance in the case of P1. Further characterization of the resultant degradation products by SEC (for hydrolysis), FTIR, and NMR could validate the proposed particle degradation mechanisms. Additionally, Figure 7B shows the temporal variation of attenuance at a specific wavelength λ = 450 nm (A450) for the two latexes P1 and P2. Insensitive to oxidation and hydrolysis, a polystyrene-based latex of similar size (Dp = 130 nm) was also used for control experiments. P1 and P2 latexes show a gradual decrease of A450 under oxidative and acid stress leading to a medium becoming much less scattering or completely transparent. The high surface-to-volume ratio of nanoscale particles and low crystallinity in the particle form (vide supra) are both instrumental in the feasibility of the oxidation and hydrolysis reactions. However, the reaction rates between the two latexes are different depending on the degradation route. While the hydrolysis is faster and more effective than oxidation in the case of P1, the reverse process takes place with P2. In this latter case, a complete transparent solution was obtained in less than 1 day in the presence of oxidant. Based on two different mechanisms, both degradation processes may be influenced by polymer microstructure and the reactant solubility.

Figure 7

Figure 7. (A) Effect of oxidation (10 wt % H2O2 solution) and acid hydrolysis (pH = 2, HCl solution) on the absorption spectrum of diluted latex P1. (B) Normalized attenuance at 450 nm versus time of different latexes in oxidative medium (full symbols) and acid medium (open symbols): P1 (circle), P2 (square), and a reference polystyrene latex (triangle).

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Conclusion

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In summary, linear and film-forming poly(thioether) latexes were synthesized via the step-growth photopolymerization of dithiol–diallyl monomer miniemulsions (Cmonomer = 20 wt %). Radically mediated, the process retains the robustness of radical chain-growth polymerization while introducing new features: fast reaction kinetics and novel latex/film properties. The versatility of thiol–ene miniemulsion photopolymerization was demonstrated by the study, in parallel, of two thiol–ene monomer couples: EDDT-DAP (155 nm) and EDDT-DAA (170 nm). For the former, DBHQ turned out to be an efficient radical inhibitor to ensure a reliable preparation method of the monomer miniemulsion, which must be both photolatent and stable. A salient feature, revealed by real-time NIR spectroscopy techniques, is the very rapid polymerization rates accomplished in the matter of seconds (<15 s) and resulting in high-molecular-weight polymers ( = 20.3 kDa), without adverse effect related to the difference of water solubility between the two comonomers. Under our specific irradiation conditions (1 mm spectroscopic cell, I = 590 mW/cm2), a complete kinetic equivalence was noted between bulk, solution, and miniemulsion systems, indicative of a non-diffusion-limited process. Of high significance is the prospect that inherently fast thiol–ene photopolymerization can offset the limited penetration depth of turbid media, which is a major difference with chain-growth polymerization. However, dissipation of the exotherm will be a critical factor and would need to be addressed by appropriate photoreactors and operations.
Extensive characterization based on POM, DSC, XRD, and cryo-TEM revealed a film formation-induced crystallization of poly(thioether films) due to structural regularity and flexibility. In the form of nanoparticles, the polymer showed clear signs of degradation in oxidative media, thus opening avenue for the design of a new array of redox-responsive nanocarriers. Furthermore, a radical step-growth polymerization can create many other opportunities that need to be further explored: complete droplet nucleation, minimization of the residual monomer concentration, high solid contents (≥50 wt %) latexes, etc.

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b02512.

  • Thiol–ene polymerization mechanism (Scheme S1), RT-FTNIR setup (Scheme S2), size reproducibility data (Table S1), fitted polymerization kinetics (Figure S1), 1H NMR spectrum of P1 (Figure S2), SEC traces of P1 synthesized by miniemulsion (M1), solution (S1), and bulk (B1) (Figure S3), effect of irradiance, PI, and Cmonomer on reaction kinetics (Figure S4), small-angle XRD pattern (Figure S5), DSC thermogram (Figure S6), POM images upon heating (Figure S7), degradation experiments of P2 latex (Figure S8) (PDF)

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Author Information

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  • Corresponding Author
    • Abraham Chemtob - Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Email: [email protected]
  • Authors
    • Florent Jasinski - †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France;  Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France;  Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
    • Agnès Rannée - †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France;  Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France;  Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
    • Julie Schweitzer - †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France;  Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France;  Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
    • Diane Fischer - †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France;  Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France;  Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
    • Emeline Lobry - †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France;  Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France;  Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
    • Céline Croutxé-Barghorn - †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France;  Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France;  Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
    • Marc Schmutz - Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France
    • Didier Le Nouen - †Laboratory of Photochemistry and Macromolecular Engineering and ‡Laboratory of Organic and Bioorganic Chemistry, University of Haute-Alsace, 3 bis rue Alfred Werner, 68093 Mulhouse, Cedex, France;  Institut de Science des Matériaux de Mulhouse, CNRS UMR 7361, 15 rue Jean Starcky, 68057 Mulhouse, France;  Institut Charles Sadron, CNRS, UPR 22, University of Strasbourg, 23 Rue du Loess, BP 84047, 67034 Strasbourg, Cedex 2, France;  Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
    • Adrien Criqui - Mäder Research - MÄDER GROUP, 130 rue de la Mer Rouge, 68200 Mulhouse, France
  • Notes
    The authors declare no competing financial interest.

Acknowledgment

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The authors gratefully acknowledge the financial support of the French National Research Agency (ANR, Programme Chimie Durable-Industries-Innovation) under Contract ANR-2012-CDII-006-02. They express their gratitude to Dr. Cyrille Boyer (Associate Professor in the School of Chemical Engineering, University of New South Wales, Australia), who provided expertise and advice on analysis of the DSC thermograms.

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    Crespy, Daniel; Landfester, Katharina
    Beilstein Journal of Organic Chemistry (2010), 6 (), 1132-1148, No. 130CODEN: BJOCBH; ISSN:1860-5397. (Beilstein-Institut zur Foerderung der Chemischen Wissenschaften)
    A review. The miniemulsion technique is a particular case in the family of heterophase polymns., which allows the formation of functionalized polymers by polymn. or modification of polymers in stable nanodroplets. We present the different polymer syntheses within the miniemulsion droplets as reported in the literature, and of the current trends in the field.
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  7. 7
    Cunningham, M. F. Controlled/Living Radical Polymerization in Aqueous Dispersed Systems Prog. Polym. Sci. 2008, 33, 365– 398 DOI: 10.1016/j.progpolymsci.2007.11.002
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    7
    Controlled/living radical polymerization in aqueous dispersed systems
    Cunningham, Michael F.
    Progress in Polymer Science (2008), 33 (4), 365-398CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Recent advances in the understanding and application of living/controlled radical polymns. (L/CRP) to aq. dispersions, including miniemulsion, emulsion, and suspension, are reviewed. The advantages of aq. dispersions for commercializing L/CRP systems provide a powerful incentive for adapting L/CRP to dispersed systems, but there have been significant challenges posed by the inherent nature of operating in a heterogeneous environment and in confined reaction vols. Stable-free radical polymn. (SFRP), atom transfer radical polymn. (ATRP), and reversible-addn.-fragmentation-transfer (RAFT) polymn. in heterogeneous systems have all been the subject of active investigation. Developments in the chem. of each type of L/CRP have facilitated their successful adaptation to aq. dispersed systems. Newer types of L/CRP, including cobalt-mediated polymn. and reverse iodine transfer polymn. (RITP), have been rapidly adapted to enable their use in water-borne systems. The progress of each type of L/CRP in aq. dispersions is discussed, along with outstanding challenges, issues, and future opportunities.
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  8. 8
    Zetterlund, P. B.; Kagawa, Y.; Okubo, M. Controlled/Living Radical Polymerization in Dispersed Systems Chem. Rev. 2008, 108, 3747– 3794 DOI: 10.1021/cr800242x
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    8
    Controlled/Living Radical Polymerization in Dispersed Systems
    Zetterlund, Per B.; Kagawa, Yasuyuki; Okubo, Masayoshi
    Chemical Reviews (Washington, DC, United States) (2008), 108 (9), 3747-3794CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review on controlled living radical polymn. in dispersed systems, including: suspension polymn., emulsion polymn., dispersion polymn. and pptn. polymn.
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  9. 9
    Guyot, A.; Landfester, K.; Joseph Schork, F.; Wang, C. Hybrid Polymer Latexes Prog. Polym. Sci. 2007, 32, 1439– 1461 DOI: 10.1016/j.progpolymsci.2007.07.003
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    9
    Hybrid polymer latexes
    Guyot, Alain; Landfester, Katharina; Schork, F. Joseph; Wang, Chunpeng
    Progress in Polymer Science (2007), 32 (12), 1439-1461CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Ltd.)
    A review. Hybrid polymer latexes will be defined here as colloidal dispersions in which at least two distinct polymers exist within each particle. The two polymers may form a homogeneous blend within the particle or microphase sepn. may occur. There are two general routes for their prepn. The first involves the use of a mini-emulsion polymn. process, in which a first polymer, most often prepd. via polycondensation (or polyaddn.), is dissolved in an unsatd. monomer (or a mixt. of monomers). The soln. is first emulsified into small droplets under a high shear process and then polymd. through a radical polymn. process. A variation of this route involves the synthesis of the polycondensate directly in the mini-emulsion. The second route involves a seeded emulsion polymn. of unsatd. monomer(s), in which the polycondensate is modified for use as a seed in the emulsion polymn. Most often, styrenic and acrylic monomers are used, while the polycondensate may be alkyd resins, polyesters, epoxy resins, polyurethanes, or other polymers. The two routes are described in detail, as are the properties of the resulting materials (mostly as films). Up to now, there have been very few trials for the comparison of the two main routes. Most often the comparison is related to blends of the two kinds of emulsified polymers.
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    Schwartz, M.; Baumstark, R. Water-based Acrylates for Decorative Coatings; Vincentz: Hannover, 2001.
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    Marvel, C. S.; Chambers, R. R. Polyalkylene Sulfides from Diolefins and Dimercaptans J. Am. Chem. Soc. 1948, 70, 993– 998 DOI: 10.1021/ja01183a029
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    Dénès, F.; Pichowicz, M.; Povie, G.; Renaud, P. Thiyl Radicals in Organic Synthesis Chem. Rev. 2014, 114, 2587– 2693 DOI: 10.1021/cr400441m
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    12
    Thiyl radicals in organic synthesis
    Denes, Fabrice; Pichowicz, Mark; Povie, Guillaume; Renaud, Philippe
    Chemical Reviews (Washington, DC, United States) (2014), 114 (5), 2587-2693CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review was given on the chem. of thiyl radicals. Recently, some specific aspects of this chem. such as the thiol-ene coupling reaction, the thiol-yne reaction, and radical cyclizations were compiled. This review has the aim of covering in an extended manner the uses of thiyl radicals in org. synthesis and to provide sound mechanistic information to understand these processes and to design new synthetic applications.
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  13. 13
    Sawicki, L. A.; Kloxin, A. M. Design of Thiol-Ene Photoclick Hydrogels using Facile Techniques for Cell Culture Applications Biomater. Sci. 2014, 2, 1612– 1626 DOI: 10.1039/C4BM00187G
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    13
    Design of thiol-ene photoclick hydrogels using facile techniques for cell culture applications
    Sawicki, Lisa A.; Kloxin, April M.
    Biomaterials Science (2014), 2 (11), 1612-1626CODEN: BSICCH; ISSN:2047-4849. (Royal Society of Chemistry)
    Thiol-ene 'click' chemistries have been widely used in biomaterials applications, including drug delivery, tissue engineering, and controlled cell culture, owing to their rapid, cytocompatible, and often orthogonal reactivity. In particular, hydrogel-based biomaterials formed by photoinitiated thiol-ene reactions afford spatiotemporal control over the biochem. and biomech. properties of the network for creating synthetic materials that mimic the extracellular matrix or enable controlled drug release. However, the use of charged peptides functionalized with cysteines, which can form disulfides prior to reaction, and vinyl monomers that require multistep syntheses and contain ester bonds, may lead to undesired inhomogeneity or degrdn. under cell culture conditions. Here, we designed a thiol-ene hydrogel formed by the reaction of allyloxycarbonyl-functionalized peptides and thiol-functionalized poly(ethylene glycol). Hydrogels were polymd. by free radical initiation under cytocompatible doses of long wavelength UV light in the presence of water-sol. photoinitiators (lithium acylphosphinate, LAP, and 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, Irgacure 2959). Mech. properties of these hydrogels were controlled by varying the monomer concn. to mimic a range of soft tissue environments, and hydrogel stability in cell culture medium was obsd. over weeks. Patterns of biochem. cues were created within the hydrogels post-formation and confirmed through the incorporation of fluorescently-labeled peptides and Ellman's assay to detect free thiols. Human mesenchymal stem cells remained viable after encapsulation and subsequent photopatterning, demonstrating the utility of the monomers and hydrogels for three-dimensional cell culture. This facile approach enables the formation and characterization of hydrogels with well-defined, spatially-specific properties and expands the suite of monomers available for three-dimensional cell culture and other biol. applications.
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  14. 14
    Durham, O. Z.; Krishnan, S.; Shipp, D. A. Polymer Microspheres Prepared by Water-Borne Thiol–Ene Suspension Photopolymerization ACS Macro Lett. 2012, 1, 1134– 1137 DOI: 10.1021/mz300358j
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    14
    Polymer Microspheres Prepared by Water-Borne Thiol-Ene Suspension Photopolymerization
    Durham, Olivia Z.; Krishnan, Sitaraman; Shipp, Devon A.
    ACS Macro Letters (2012), 1 (9), 1134-1137CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Thiol-ene polymns. are possible in a water-borne suspension-like photopolymn. and yield spherical particles that have diams. in the range of submicrometers to hundreds of micrometers. This is the first report of such colloidal thiol-ene polymns. Thiol-ene polymn. offers unique conditions not commonly assocd. with a water-borne polymn. including a step-growth polymn. mechanism along with photoinitiation under ambient conditions. Example polymns. of a triene, 3,5-triallyl-1,3,5-triazine-2,4,6 (1N,3H,5H)-trione (TTT), and a tetrathiol, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), with the photoinitiator 1-hydroxycyclohexyl Ph ketone, surfactant sodium dodecyl sulfate (SDS), and a cosolvent (chloroform or toluene) are discussed. Various exptl. parameters were examd. such as surfactant concn., homogenization energy, cosolvent species, and cosolvent amt. to develop an understanding of the mechanism of microsphere formation. Particle size is dependent on homogenization energy, with greater mech. shear yielding smaller particles. In addn., higher concns. of surfactant or solvent also produced smaller spherical particles. These observations lead to the conclusion that the particles are formed via a suspension-like polymn.
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  15. 15
    Jasinski, F.; Lobry, E.; Tarablsi, B.; Chemtob, A.; Croutxé-Barghorn, C.; Le Nouen, D.; Criqui, A. Light-Mediated Thiol–Ene Polymerization in Miniemulsion: A Fast Route to Semicrystalline Polysulfide Nanoparticles ACS Macro Lett. 2014, 3, 958– 962 DOI: 10.1021/mz500458s
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    15
    Light-Mediated Thiol-Ene Polymerization in Miniemulsion: A Fast Route to Semicrystalline Polysulfide Nanoparticles
    Jasinski, Florent; Lobry, Emeline; Tarablsi, Bassam; Chemtob, Abraham; Croutxe-Barghorn, Celine; Le Nouen, Didier; Criqui, Adrien
    ACS Macro Letters (2014), 3 (9), 958-962CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Historically, the synthesis of aq. polymer dispersions has focused on radical chain-growth polymn. of low-cost acrylate or styrene emulsions. Herein, we demonstrate the potential of UV-initiated thiol-ene step-growth radical polymn., departing from a nontransparent difunctional monomer miniemulsion based on ethylene glycol dithiol and diallyl adipate. Performed without solvent and at ambient conditions, the photopolymn. process is energy-effective, environmentally friendly, and ultrafast, leading to full monomer consumption in 2 s, upon irradiating a miniemulsion contained in a 1 mm thick quartz cell microreactor. The resultant linear poly(thioether ester) particles have an av. diam. of 130 nm. After water evapn., they yield a clear elastomeric film combining chem. resistance and high degree of crystallinity (55%).
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  16. 16
    Amato, D. V.; Amato, D. N.; Flynt, A. S.; Patton, D. L. Functional, Sub-100 nm Polymer Nanoparticles via Thiol-Ene Miniemulsion Photopolymerization Polym. Chem. 2015, 6, 5625– 5632 DOI: 10.1039/C4PY01449A
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    16
    Functional, sub-100 nm polymer nanoparticles via thiol-ene miniemulsion photopolymerization
    Amato, D. V.; Amato, D. N.; Flynt, A. S.; Patton, D. L.
    Polymer Chemistry (2015), 6 (31), 5625-5632CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    In this work, sub-100 nm crosslinked polythioether nanoparticles were synthesized via thiol-ene photopolymn. in miniemulsion using high-energy homogenization. The effects of the miniemulsion formulation and homogenization parameters - including inhibitor concn., surfactant concn., org. wt. fraction, ultrasonication time and amplitude - on nanoparticle size and size distribution were investigated. Thiol-ene nanoparticles with a mean particle diam. of 46 nm were obtained under optimized conditions for the current system at 2.5 wt% org. fraction and 20 mM surfactant concn. In an effort to demonstrate potential utility of thiol-ene nanoparticles, we exploit the step-growth radical mechanism of thiol-ene photopolymn. under non-stoichiometric conditions to fabricate functional nanoparticles that express excess thiol or alkene at the particle surface. We show that these excess functional groups can be utilized as reactive handles in thiol-Michael and radical-mediated thiol-ene reactions for immobilization of fluorescent moieties via postpolymn. modification.
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  17. 17
    Durham, O.; Shipp, D. Suspension “Click” Polymerizations: Thiol-Ene Polymer Particles Prepared with Natural Gum Stabilizers Colloid Polym. Sci. 2015, 293, 2385– 2394 DOI: 10.1007/s00396-015-3628-2
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    17
    Suspension "click" polymerizations: thiol-ene polymer particles prepared with natural gum stabilizers
    Durham, Olivia Z.; Shipp, Devon A.
    Colloid and Polymer Science (2015), 293 (8), 2385-2394CODEN: CPMSB6; ISSN:0303-402X. (Springer)
    The impact of different natural gum species employed as stabilizers in the suspension photopolymn. of water-borne thiol-ene polymer particles is reported. The focus of anal. was on how hydrocolloids impact the synthesis of polymer particles prepd. using a "click" thiol-ene polymn. approach. The use of renewable and naturally occurring gums as particle stabilizers provide a shift toward greener methods of polymer particle synthesis. The natural gum species examd. include gum Arabic, guar gum, and xanthan gum. In particular, gum Arabic was examd. in thiol-ene particle synthesis due to inherent colloidal stabilizing properties that allow it to be utilized at concns. comparable to synthetic stabilizers (1 wt% or greater). The use of these naturally occurring polysaccharides led to the development of spherical, crosslinked thiol-ene polymer particles in the size range of several micrometers to hundreds of micrometers. Polymer particle synthesis was completed within minutes via photopolymn. Parameters examd. include variation of natural gum species, natural gum concn., monomer content, and stabilizer soln. viscosity. Thiol-ene polymer particles can be successfully developed at very low stabilizer concns. (0.005-0.5 wt%) due to the unique viscosity-enhancing properties of natural gum solns. compared to reactions stabilized by synthetic surfactant stabilizers.
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  18. 18
    Durham, O. Z.; Shipp, D. A. Suspension Thiol-Ene Photopolymerization: Effect of Stabilizing Agents on Particle Size and Stability Polymer 2014, 55, 1674– 1680 DOI: 10.1016/j.polymer.2014.02.044
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    18
    Suspension thiol-ene photopolymerization: Effect of stabilizing agents on particle size and stability
    Durham, Olivia Z.; Shipp, Devon A.
    Polymer (2014), 55 (7), 1674-1680CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    The impact of several surfactant species employed in the suspension photopolymn. of water-borne thiol-ene polymer microspheres is reported. The focus of anal. was on how different surfactant species and the surfactant concns. affected particle size and particle size distributions. Surfactants used included sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), and hexadecyltrimethylammonium bromide (HTAB), Tween 20, Tween 40, Tween 60, Tween 80, Lutensol XL 70, Lutensol XP 70, Pluronic PE 6400, and Pluronic F108 Pastille. Using stabilizing agents or surfactants is necessary to prevent extensive aggregation and agglomeration of crosslinked thiol-ene polymer. All surfactants used in this study for particle stabilization and development produced spherical thiol-ene polymer particles. The chem. structure and concn. of the surfactants influenced the final particle size and size distribution of particles obtained. In general, smaller particles are obtained with higher concns. of stabilizing agent, esp. for ionic surfactants.
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    Tan, J.; Li, C.; Zhou, J.; Yin, C.; Zhang, B.; Gu, J.; Zhang, Q. Fast and Facile Fabrication of Porous Polymer Particles via Thiol-Ene Suspension Photopolymerization RSC Adv. 2014, 4, 13334– 13339 DOI: 10.1039/c4ra00203b
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    19
    Fast and facile fabrication of porous polymer particles via thiol-ene suspension photopolymerization
    Tan, Jiaojun; Li, Chunmei; Zhou, Jian; Yin, Changjie; Zhang, Baoliang; Gu, Junwei; Zhang, Qiuyu
    RSC Advances (2014), 4 (26), 13334-13339CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    A fast and facile method of prepg. porous polymer particles via thiol-ene suspension photopolymn. was studied. The porous particles were fabricated by adding the porogen to the click chem. system. In this paper, the photopolymn. of dipentaerythritol hexakis (3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptopropionate), 1,3,5-tri-2-propenyl-1,3,5-triazine- 2,4,6(1H,3H,5H)-trione, sodium dodecyl sulfate, chloroform and different amts. of linear polymer porogen (polymethyl methacrylate, PMMA) was discussed in detail. The two crucial factors, polymn. time and amt. of porogen, were investigated. It was demonstrated that the conversion of monomers could reach 80% within 15 s of irradn., which further verified the high efficiency of click chem. By varying the amt. of PMMA, we were able to tailor the particle size, pore diams. and morphol. of the porous particles. Results of the mercury porosimetry indicated that the median pore diam. of particles was about 12.39 μm and the surface area was 4.393 m2 g-1. Moreover, the Tg of the particles given by DSC was about 45 °C.
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    Wang, C.; Chatani, S.; Podgorski, M.; Bowman, C. N. Thiol-Michael Addition Miniemulsion Polymerizations:Functional Nanoparticles and Reactive Latex Films Polym. Chem. 2015, 6, 3758– 3763 DOI: 10.1039/C5PY00326A
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    20
    Thiol-Michael addition miniemulsion polymerizations: functional nanoparticles and reactive latex films
    Wang, Chen; Chatani, Shunsuke; Podgorski, Maciej; Bowman, Christopher N.
    Polymer Chemistry (2015), 6 (20), 3758-3763CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    Thiol-Michael addn. polymn. is successfully implemented in a miniemulsion polymn. system. By off-stoichiometric polymn. between thiols and acrylates, inherently functionalized particles are facilely prepd. in a single step. We demonstrate that the latex films from such particles are readily available for further modification and second-stage photo-curing.
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    Wang, C.; Podgorski, M.; Bowman, C. N. Monodisperse Functional Microspheres from Step-Growth “Click” Polymerizations: Preparation, Functionalization and Implementation Mater. Horiz. 2014, 1, 535– 539 DOI: 10.1039/C4MH00082J
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    21
    Monodisperse functional microspheres from step-growth 'click' polymerizations: preparation, functionalization and implementation
    Wang, Chen; Podgorski, Maciej; Bowman, Christopher N.
    Materials Horizons (2014), 1 (5), 535-539CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    The monodisperse cross-linked clickable microspheres are made via step-growth thiol-acrylate Michael addn. polymn. The diam. of the microsphere is varied from 1-10 μm, depending on the cross-link d. and the reaction conditions. The implementations of these microspheres including functionalized microspheres for click chem., polymeric composites, fluorescent labeling and polymer degrdn. are discussed and/or demonstrated.
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  22. 22
    Amato, D. N.; Amato, D. V.; Narayanan, J.; Donovan, B. R.; Douglas, J. R.; Walley, S. E.; Flynt, A. S.; Patton, D. L. Functional, Composite Polythioether Nanoparticles via Thiol-Alkyne Photopolymerization in Miniemulsion Chem. Commun. 2015, 51, 10910– 10913 DOI: 10.1039/C5CC03319E
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    22
    Functional, composite polythioether nanoparticles via thiol-alkyne photopolymerization in miniemulsion
    Amato, Dahlia N.; Amato, Douglas V.; Narayanan, Jananee; Donovan, Brian R.; Douglas, Jessica R.; Walley, Susan E.; Flynt, Alex S.; Patton, Derek L.
    Chemical Communications (Cambridge, United Kingdom) (2015), 51 (54), 10910-10913CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Thiol-yne photopolymn. in miniemulsion is demonstrated as a simple, rapid, and 1-pot synthetic approach to polythioether nanoparticles with tuneable particle size and clickable functionality. The strategy is also useful in the synthesis of composite polymer-inorg. nanoparticles.
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  23. 23
    Tan, J.; Li, C.; Li, H.; Zhang, H.; Gu, J.; Zhang, B.; Zhang, H.; Zhang, Q. Water-Borne Thiol-Isocyanate Click Chemistry in Microfluidics: Rapid and Energy-Efficient Preparation of Uniform Particles Polym. Chem. 2015, 6, 4366– 4373 DOI: 10.1039/C5PY00412H
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    23
    Water-borne thiol-isocyanate click chemistry in microfluidics: rapid and energy-efficient preparation of uniform particles
    Tan, Jiaojun; Li, Chunmei; Li, Hui; Zhang, Hao; Gu, Junwei; Zhang, Baoliang; Zhang, Hepeng; Zhang, Qiuyu
    Polymer Chemistry (2015), 6 (24), 4366-4373CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    A nucleophile-catalyzed thiol-isocyanate reaction was exploited as an efficient route to fabricate uniform particles in a water-borne system. Droplets were generated in a simple microfluidic setup from stoichiometric thiol and isocyanate monomers, thereby creating an oil-in-water emulsion, and polymer particles were obtained once the monomer droplets were exposed to a nucleophile. This is the first report of thiol-isocyanate polymn. in a water-borne system, which shows great promise in the manuf. of particles for its mild conditions, rapid rate and high conversion. Notably, heat, UV, anhyd. or oxygen-free conditions are not required. Particles with sizes ranging from 40 to 250 μm can be prepd. via adjusting the flow rate of continuous and disperse phases. In addn., the functionality of the thiol monomer has a profound effect on the morphol. of particles. This method opens up possibilities for nucleophile-catalyzed thiol-isocyanate click chem. in water-borne and heterogeneous polymn.
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    Workman, J.; Weyer, L. Practical Guide to Interpretive Near-infrared Spectroscopy; CRC Press: New York, 2007; p 346.
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    Ibrahim, A.; Maurin, V.; Ley, C.; Allonas, X.; Croutxe-Barghorn, C.; Jasinski, F. Investigation of Termination Reactions in Free Radical Photopolymerization of UV Powder Formulations Eur. Polym. J. 2012, 48, 1475– 1484 DOI: 10.1016/j.eurpolymj.2012.05.019
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    Investigation of termination reactions in free radical photopolymerization of UV powder formulations
    Ibrahim, A.; Maurin, V.; Ley, C.; Allonas, X.; Croutxe-Barghorn, C.; Jasinski, F.
    European Polymer Journal (2012), 48 (8), 1475-1484CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
    The termination mechanisms occurring in a UV powder coating system during photopolymn. process are investigated and compared to a conventional acrylate monomer system. The influence of the photoinitiator concn., viscosity and conversion percentage of the monomer are assessed leading to the study of curing kinetics of a UV powder urethane diacrylate based system. It is shown that termination occurs mainly by bimol. termination (PRT). This mechanism is related to low reactive double bonds concn. and high photoinitiator concn. in the UV powder system. Moreover, the effect of surrounding atm. points out the role of the oxygen on polymn. mechanisms.
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  26. 26
    Mengual, O.; Meunier, G.; Cayré, I.; Puech, K.; Snabre, P. TURBISCAN MA 2000: Multiple Light Scattering Measurement for Concentrated Emulsion and Suspension Instability Analysis Talanta 1999, 50, 445– 456 DOI: 10.1016/S0039-9140(99)00129-0
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    26
    TURBISCAN MA 2000: multiple light scattering measurement for concentrated emulsion and suspension instability analysis
    Mengual, O.; Meunier, G.; Cayre, I.; Puech, K.; Snabre, P.
    Talanta (1999), 50 (2), 445-456CODEN: TLNTA2; ISSN:0039-9140. (Elsevier Science B.V.)
    Emulsion or suspension destabilization often results from coalescence or particle aggregation (flocculation) leading to particle migration (creaming or sedimentation). Creaming and sedimentation are often considered as reversible, while coalescence and flocculation spell disaster for the formulator. Thus, it is of prime importance to detect coalescence or cluster formation at an early stage to shorten the ageing tests and to improve the formulations. This work mainly concerns the independent and anisotropic scattering of light from an emulsion or suspension in a cylindrical glass measurement cell, in relation with the optical analyzer TURBISCAN MA 2000. The propagation of light through a concd. dispersion can be used to characterize the system physico-chem. stability. Indeed, photons undergo many scattering events in an optically thick dispersion before escaping the medium and entering a receiver aperture. Multiple scattering thus contributes significantly to the transmitted and backscattered flux measured by TURBISCAN MA 2000. We present statistical models and numerical simulations for the radiative transfer in a suspension (plane or cylindrical measurement cells) only involving the photon mean path length, the asymmetry factor and the geometry of the light receivers. We further have developed an imaging method with high gray level resoln. for the visualization and the anal. of the surface flux in the backscattered spot light. We compare the results from phys. models and numerical simulations with the expts. performed with the imaging method and the optical analyzer TURBISCAN MA 2000 for latex beads suspensions (variable size and particle vol. fraction). We then present a few examples of concd. emulsion and suspension instability anal. with TURBISCAN 2000. It is shown that the instrument is able to characterize particle or aggregate size variation and particle/aggregate migration and to detect these phenomena much more earlier than the operator's naked eye, esp. for concd. and optically thick media.
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    Schork, F. J.; Luo, Y.; Smulders, W.; Russum, J. P.; Butté, A.; Fontenot, K. Miniemulsion Polymerization. In Polymer Particles; Okubo, M., Ed.; Springer-Verlag: Heidelberg, 2005; p 129.
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    Esfandiari, P.; Ligon, S. C.; Lagref, J. J.; Frantz, R.; Cherkaoui, Z.; Liska, R. Efficient Stabilization of Thiol-Ene Formulations in Radical Photopolymerization J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4261– 4266 DOI: 10.1002/pola.26848
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    Efficient stabilization of thiol-ene formulations in radical photopolymerization
    Esfandiari, Paricher; Ligon, Samuel Clark; Lagref, Jean Jacques; Frantz, Richard; Cherkaoui, Zoubair; Liska, Robert
    Journal of Polymer Science, Part A: Polymer Chemistry (2013), 51 (20), 4261-4266CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    An efficient stabilizer system is presented for thiol-ene polymn. formulations with no increase of viscosity at ambient temps. and a significantly improved stability at elevated temps. The combination of a free radical scavenger and an acid with an appropriate pKa value of about 2 displays a surprising synergistic effect.
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    Hoyle, C. E.; Lee, T. Y.; Roper, T. Thiol–Enes: Chemistry of the Past with Promise for the Future J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 5301– 5338 DOI: 10.1002/pola.20366
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    Thiol-enes: Chemistry of the past with promise for the future
    Hoyle, Charles E.; Lee, Tai Yeon; Roper, Todd
    Journal of Polymer Science, Part A: Polymer Chemistry (2004), 42 (21), 5301-5338CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    A review. The photopolymn. of mixts. of multifunctional thiols and enes is an efficient method for the rapid prodn. of films and thermoset plastics with unprecedented phys. and mech. properties. One of the major obstacles in traditional free-radical photopolymn. is essentially eliminated in thiol-ene polymns. because the polymn. occurs in air almost as rapidly as in an inert atm. Virtually any type of ene will participate in a free-radical polymn. process with a multifunctional thiol. Hence, it is possible to tailor materials with virtually any combination of properties required for a particular application.
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    Xia, H.; Wang, Q.; Liao, Y.; Xu, X.; Baxter, S. M.; Slone, R. V.; Wu, S.; Swift, G.; Westmoreland, D. G. Polymerization Rate and Mechanism of Ultrasonically Initiated Emulsion Polymerization of n-Butyl Acrylate Ultrason. Sonochem. 2002, 9, 151– 158 DOI: 10.1016/S1350-4177(01)00118-3
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    Polymerization rate and mechanism of ultrasonically initiated emulsion polymerization of n-butyl acrylate
    Xia, Hesheng; Wang, Qi; Liao, Yongqin; Xu, Xi; Baxter, Steven M.; Slone, Robert V.; Wu, Shuguang; Swift, Graham; Westmoreland, David G.
    Ultrasonics Sonochemistry (2002), 9 (3), 151-158CODEN: ULSOER; ISSN:1350-4177. (Elsevier Science B.V.)
    The factors affecting the induction period and polymn. rate in ultrasonically initiated emulsion polymn. of Bu acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymn. of BA without any added initiator by enhancing the N2 flow rate. Increasing temp., power output and SDS concn., decreasing the monomer concn. results in further decreasing induction period and enhanced polymn. rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymn. rate can be controlled by varying reaction parameters. The app. of ultrasonically initiated semi-continuous and continuous emulsion polymn. were set up and the feasibility was first studied. Based on the exptl. results, a free radical polymn. mechanism for ultrasonically initiated emulsion polymn. was proposed, including the sources of the radicals, the process of radical formation, the locus of polymn. and the polymn. process. Compared with conventional emulsion polymn., where the radicals come from thermal decompn. of a chem. initiator, ultrasonically initiated emulsion polymn. has attractive features such as no need for a chem. initiator, lower reaction temp., faster polymn. rate, and higher mol. wt. of the polymer prepd.
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    Manea, M.; Chemtob, A.; Paulis, M.; de la Cal, J. C.; Barandiaran, M. J.; Asua, J. M. Miniemulsification in High-Pressure Homogenizers AIChE J. 2008, 54, 289– 297 DOI: 10.1002/aic.11367
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    Miniemulsification in high-pressure homogenizers
    Manea, Mihaela; Chemtob, Abraham; Paulis, Maria; de la Cal, Jose C.; Barandiaran, Maria J.; Asua, Jose M.
    AIChE Journal (2008), 54 (1), 289-297CODEN: AICEAC; ISSN:0001-1541. (John Wiley & Sons, Inc.)
    The mechanisms involved in the formation of high solids content composite polymer-monomer waterborne miniemulsions in a high-pressure homogenizer were investigated combining exptl. results and a math. model for the process. It was found that the final droplet size was the result of two consecutive processes: droplet break-up and coagulation. The final droplet size was detd. by the mechanism giving the largest droplet size.
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    Jafari, S. M.; Assadpoor, E.; He, Y.; Bhandari, B. Re-Coalescence of Emulsion Droplets during High-Energy Emulsification Food Hydrocolloids 2008, 22, 1191– 1202 DOI: 10.1016/j.foodhyd.2007.09.006
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    Re-coalescence of emulsion droplets during high-energy emulsification
    Jafari, Seid Mahdi; Assadpoor, Elham; He, Yinghe; Bhandari, Bhesh
    Food Hydrocolloids (2008), 22 (7), 1191-1202CODEN: FOHYES; ISSN:0268-005X. (Elsevier Ltd.)
    A review. Emulsion droplet size plays a key role in many emulsion properties such as stability, color, appearance, texture, and rheol. Accordingly, different emulsions have been classified based on emulsion size including microemulsions and submicron (nano) emulsions. The aim of emulsification is usually to produce emulsion droplets as small as possible, and various emulsification techniques can be used in this regard. One of the main problems of producing very fine emulsions with high-energy emulsification techniques such as microfluidization is the occurrence of "over-processing", which is increase in emulsion size by supplying more energy due to a high rate of re-coalescence of new droplets. Different reasons have been mentioned for "over-processing", including low adsorption rate of the surface-active agent, low residence time of the emulsion in the emulsification zone, high rate of coalescence frequency, and extreme amt. of energy d. This review highlights re-coalescence of new droplets during high-energy emulsification along with some common and important emulsification techniques and different factors affecting emulsion droplet size, and thereby re-coalescence.
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    Hoyle, C. E.; Bowman, C. N. Thiol–Ene Click Chemistry Angew. Chem., Int. Ed. 2010, 49, 1540– 1573 DOI: 10.1002/anie.200903924
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    Thiol-Ene Click Chemistry
    Hoyle, Charles E.; Bowman, Christopher N.
    Angewandte Chemie, International Edition (2010), 49 (9), 1540-1573CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Following Sharpless' visionary characterization of several idealized reactions as click reactions, the materials science and synthetic chem. communities have pursued numerous routes toward the identification and implementation of these click reactions. Herein, the authors review the radical-mediated thiol-ene reaction as one such click reaction. This reaction has all the desirable features of a click reaction, being highly efficient, simple to execute with no side products and proceeding rapidly to high yield. Further, the thiol-ene reaction is most frequently photoinitiated, particularly for photopolymns. resulting in highly uniform polymer networks, promoting unique capabilities related to spatial and temporal control of the click reaction. The reaction mechanism and its implementation in various synthetic methodologies, biofunctionalization, surface and polymer modification, and polymn. are all reviewed.
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    Beuermann, S.; Buback, M. Rate Coefficients of Free-Radical Polymerization Deduced from Pulsed Laser Experiments Prog. Polym. Sci. 2002, 27, 191– 254 DOI: 10.1016/S0079-6700(01)00049-1
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    Rate coefficients of free-radical polymerization deduced from pulsed laser experiments
    Beuermann, Sabine; Buback, Michael
    Progress in Polymer Science (2002), 27 (2), 191-254CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
    A review. Pulsed laser techniques have enormously improved the quality by which rate coeffs. of individual steps in free-radical polymn. may be measured. Pulsed laser initiated polymn. (PLP) in conjunction with size-exclusion chromatog. (SEC) yields the propagation rate coeff., kp. The PLP-SEC-technique has been applied to a wide variety of homopolymns. and copolymns., either in bulk or in soln. In addn. to reporting kinetic data, exptl. details of PLP, of SEC, and of the limitations assocd. with the accurate detn. of the MWD are discussed. The single pulse (SP)-PLP method, which combines PLP with time-resolved NIR spectroscopy, allows for a very detailed insight into the termination rate coeff., kt, for homo- and copolymns. kt data are reported as a function of temp., pressure, monomer conversion, solvent concn., and partly also of chain length. This review considers literature up to Dec. 2000.
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    Nakamura, T.; Okubo, M. Mechanistic Investigation of Particle Size Effects in TEMPO- Mediated Radical Polymerization of Styrene in Aqueous Miniemulsion Macromolecules 2007, 40, 8663– 8672 DOI: 10.1021/ma0712403
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    Nakamura, T.; Zetterlund, P. B.; Okubo, M. Particle Size Effects in TEMPO-Mediated Radical Polymerization of Styrene in Aqueous Miniemulsion Macromol. Rapid Commun. 2006, 27, 2014– 2018 DOI: 10.1002/marc.200600542
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    Particle size effects in TEMPO-mediated radical polymerization of styrene in aqueous miniemulsion
    Nakamura, Tadashi; Zetterlund, Per B.; Okubo, Masayoshi
    Macromolecular Rapid Communications (2006), 27 (23), 2014-2018CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
    2,2,6,6-Tetra-Me piperidinyl-1-oxy (TEMPO)-mediated radical polymn. of styrene in aq. miniemulsion at 125 °C using sodium dodecylbenzenesulfonate and poly(vinyl alc.), resp., as colloidal stabilizers has been investigated. The particle size had a dramatic effect on the polymn. process. Decreasing particle size led to a markedly higher polymn. rate, but less control and a lower degree of livingness. For particles with diams. greater than approx. 170 nm, the polymn. behavior was essentially the same as in the corresponding bulk system. By varying the particle size within an appropriate range, it is possible to tune the polymn. such that the polymn. rate is increased while still maintaining reasonable control and livingness.
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    Bechthold, N.; Landfester, K. Kinetics of Miniemulsion Polymerization As Revealed by Calorimetry Macromolecules 2000, 33, 4682– 4689 DOI: 10.1021/ma000061h
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    Aizpurua, I.; Amalvy, J. I.; Barandiaran, M. J. Influence of the Polymeric Hydrophobe on the Kinetics of Vinyl Acetate Miniemulsion Polymerization Colloids Surf., A 2000, 166, 59– 66 DOI: 10.1016/S0927-7757(99)00293-9
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    Influence of the polymeric hydrophobe on the kinetics of vinyl acetate miniemulsion polymerization
    Aizpurua, I.; Amalvy, J. I.; Barandiaran, M. J.
    Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2000), 166 (1-3), 59-66CODEN: CPEAEH; ISSN:0927-7757. (Elsevier Science B.V.)
    The influence of polymeric hydrophobes on the stabilization and kinetics of vinyl acetate miniemulsion polymn. was investigated by conducting reactions in batch mode of miniemulsions prepd. with poly(vinyl acetate) or polystyrene as cosurfactants. The results were compared with a miniemulsion stabilized with hexadecane and with a conventional emulsion. Shelf life stability anal. showed that miniemulsions prepd. with polymer as the unique cosurfactant were not stable. However, the appearance of the sepd. phases was not similar to that of conventional emulsion, which was interpreted as the formation of small monomer-swollen particles in the case of the miniemulsion. The kinetic anal. confirmed the different nucleation mechanism of these unstable miniemulsions compared with the conventional emulsion.
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  39. 39

    Octanol–water partition coefficients (KOW) of I2959 and I651 are respectively 0.84 and 3.42 (Safety Data Sheet) at 25 °C. KOW (I2959) value is low enough to enable its dissolution in the aqueous phase (5 g/L); however, it suggests a partition between the monomer and aqueous phases.

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    Cramer, N. B.; Bowman, C. N. Kinetics of Thiol–Ene and Thiol–Acrylate Photopolymerizations with Real-Time Fourier Transform Infrared J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 3311– 3319 DOI: 10.1002/pola.1314
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    Kinetics of thiol-ene and thiol-acrylate photopolymerizations with real-time fourier transform infrared
    Cramer, Neil B.; Bowman, Christopher N.
    Journal of Polymer Science, Part A: Polymer Chemistry (2001), 39 (19), 3311-3319CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
    We used real-time Fourier transform IR to monitor the conversion of both thiol and ene (vinyl) functional groups independently during photoinduced thiol-ene photopolymns. From these results, the stoichiometry of various thiol-ene and thiol-acrylate polymns. was detd. For thiol-ene polymns., the conversion of ene functional groups was up to 15% greater than the conversion of thiol functional groups. For stoichiometric thiol-acrylate polymns., the conversion of the acrylate functional groups was roughly twice that of the thiol functional groups. With kinetic expressions for thiol-acrylate polymns., the acrylate propagation kinetic const. was 1.5 times greater than the rate const. for hydrogen abstraction from the thiol. Conversions of thiol-acrylate systems of various initial stoichiometries were successfully predicted with this ratio of propagation and chain-transfer kinetic consts. Thiol-acrylate systems with different initial stoichiometries exhibited diverse network properties. Thiol-ene systems were initiated with benzophenone and 2,2-dimethoxy-2-phenylacetophenone as initiators and were also polymd. without a photoinitiator.
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    Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F. High Solid Content Latexes Prog. Polym. Sci. 2002, 27, 1573– 1615 DOI: 10.1016/S0079-6700(02)00014-X
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    High solid content latexes
    Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F.
    Progress in Polymer Science (2002), 27 (8), 1573-1615CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
    This article is a review of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn. High solids content latexes are of growing interest for many reasons; however, making this type of product entails many difficulties. Increasing the solids content (fraction of polymer relative to the continuous phase) in a reproducible manner entails the strict control of a complex particle size distribution (PSD). The PSD must be either quite broad, or multimodal in order to obtain solids contents much above 55 or 60 vol.%. In addn., the viscosity of a latex is highly sensitive to the PSD near the upper limit of solids content, but it is still not possible to predict a priori how a complex PSD will effect the viscosity. This article presents an overview of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn.
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    Alfano, O. M.; Negro, A. C.; Cabrera, M. I.; Cassano, A. E. Scattering Effects Produced By Inert Particles In Photochemical Reactors. 1. Model And Experimental Verification Ind. Eng. Chem. Res. 1995, 34, 488– 499 DOI: 10.1021/ie00041a009
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    Takahashi, Y.; Tadokoro, H.; Chatani, Y. Structure of Polyethylene Sulfide J. Macromol. Sci., Part B: Phys. 1968, 2, 361– 367 DOI: 10.1080/00222346808212456
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    Vinas, J.; Dufils, P. E. Poly(Vinylidene Chloride). In Ullmann’s Encyclopedia of Industrial Chemistry; Wiley-VCH: Berlin, 2012.
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    Staff, R. H.; Lieberwirth, I.; Landfester, K.; Crespy, D. Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers Macromol. Chem. Phys. 2012, 213, 351– 358 DOI: 10.1002/macp.201100529
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    Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers
    Staff, Roland H.; Lieberwirth, Ingo; Landfester, Katharina; Crespy, Daniel
    Macromolecular Chemistry and Physics (2012), 213 (3), 351-358CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The synthesis of colloidally stable submicron particles of syndiotactic polystyrene (sPS) and isotactic polystyrene (iPS) is reported. Model particles based on poly-L-lactic acid (PLLA), atactic polystyrene (aPS), sPS, and iPS are prepd. by the evapn. of a solvent present in miniemulsion droplets. The degree of crystallinity of the particles is found to decrease with their size, as shown by DSC and WAXS measurements. Remarkably, nonspherical particlLs can be formed in the dispersed state with sPS and iPS, whereas PLLA and aPS particles always display spherical morphologies.
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    Michell, R. M.; Blaszczyk-Lezak, I.; Mijangos, C.; Müller, A. J. Confinement Effects on Polymer Crystallization: From Droplets to Alumina Nanopores Polymer 2013, 54, 4059– 4077 DOI: 10.1016/j.polymer.2013.05.029
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    Confinement effects on polymer crystallization: From droplets to alumina nanopores
    Michell, Rose Mary; Blaszczyk-Lezak, Iwona; Mijangos, Carmen; Muller, Alejandro J.
    Polymer (2013), 54 (16), 4059-4077CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    We review previous works on polymer confined crystn. employing strategies that allow confinement to go from the micron to the nanometer scale: droplets, blends, block copolymers and infiltration into alumina nanopores. We also present novel results, reporting homogeneous nucleation and first order crystn. kinetics, for the first time, in a homopolymer and a diblock copolymer infiltrated within alumina nanopores. Confinement can produce fractionated crystn. or exclusive crystn. at much higher supercooling as compared to bulk polymers, as the degree of confinement increases. For highly confined heterogeneity free micro or nano-domains, the overall crystn. kinetics was dominated by nucleation and therefore was first order. The nucleation mechanism changes from heterogeneous nucleation for the bulk polymer to surface or homogeneous nucleation for ensembles of confined and isolated heterogeneity free micro or nanodomains. Surface nucleation is more commonly found than homogeneous nucleation, although this fact is not frequently recognized in the literature.
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    Pereira, R. F. P.; Valente, A. J. M.; Burrows, H. D.; de Zea Bermudez, V.; Carvalho, R. A.; Castro, R. A. E. Structural Characterization of Solid Trivalent Metal Dodecyl Sulfates: From Aqueous Solution to Lamellar Superstructures RSC Adv. 2013, 3, 1420– 1433 DOI: 10.1039/C2RA21906A
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    Structural characterization of solid trivalent metal dodecyl sulfates: from aqueous solution to lamellar superstructures
    Pereira, Rui F. P.; Valente, Artur J. M.; Burrows, Hugh D.; de Zea Bermudez, Veronica; Carvalho, Rui A.; Castro, Ricardo A. E.
    RSC Advances (2013), 3 (5), 1420-1433CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    Metal dodecyl sulfates of trivalent aluminum, chromium, lanthanum and gadolinium were prepd. by addn. of the corresponding salts to aq. solns. of sodium dodecyl sulfate at the natural pH (∼6). Using x-ray diffraction, FTIR and NMR spectroscopy, DSC, TG and polarizing light thermomicroscopy metal dodecyl sulfates are formed with lamellar structures. These have different degrees of hydration, which depend upon the metal ion. In some cases there is evidence for coexistence of different lamellar phases. The metal is strongly bound electrostatically to the sulfate group, and although the alkyl chain is in an extended conformation, there are suggestions of local disordering of the methylene groups adjacent to the anionic head group. SEM with an EDS probe on the trivalent metal complexes shows a 1:3 ratio at the surface identical to the bulk structure. Studies by SEM and AFM provide evidence of periodicity, which is likely to be induced by the lamellar, layered structures. Differences are obsd. in the thermal behavior, which appear to reflect both the coordination behavior of the metal ion and the degree of hydration.
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    Emulsified n-hexadecane or confectionery coating fat (CCF) were repeatedly thermally cycled (40 to -10-40°C at 1.5 °C/min) in a differential scanning calorimeter. There is a single exotherm on cooling each emulsion (at 0.5 and 5°C, resp.) corresponding to lipid crystn. by homogeneous nucleation. However, on subsequent cooling cycles, an increasing proportion of the CCF crystn. enthalpy occurs at a higher temp. (15°C) corresponding to crystn. of non-emulsified fat. (The net enthalpy of crystn. is const.). The second peak is taken to be due to destabilized fat and increases with no. of cycles and dispersed phase vol. fraction. All n-hexadecane emulsions are stable to freeze-thaw. When the CCF emulsions are cooled more rapidly (5°C/min) there is no destabilization. Micrographs are presented and used to argue that the destabilization is due to a collapse of partially coalesced structures on reheating.
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    The thermal properties of n-hexadecane (HD) encapsulated in crosslinked capsule particles contg. a water and/or air domain were studied from the view-point of heat-storage applications. The capsule particles were prepd. by the microsuspension polymn. of divinylbenzene at 70° with the self-assembling of phase-sepd. polymer method that we developed. In the differential scanning calorimetric thermograms, pure HD had a single solidification temp. (Ts) peak at 15°, whereas the encapsulated HD contg. a water domain had two peaks at 6 and 1°. That is, the encapsulated HD contg. the water domain required a longer time and lower temp. to complete the solidification than pure HD, which was neg. for heat-storage applications. However, once the particles were dried and the water domain was replaced with air, the problem with the partially lowered Ts improved. The air domain was also found in the encapsulated HD core after solidification because of the shrinkage of HD. The presence of the air domain did not affect the thermal stability of the encapsulated HD.
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    A review. Glutathione has been regarded as a significant signal for distinguishing between tumor and normal tissue. Recently, reactive oxygen species have attracted much attention for their close connection with many diseases. Taking advantage of the physiol. signals, redox-responsive polymeric drug carriers constitute a significant research area in the various stimuli-responsive polymers for biomedical applications. During the rapid development of redox-responsive polymers, mol. design and related synthetic methodol. plays a crucial role. In this review, we discuss the redn.- and oxidn.-responsive polymeric drug carriers from the view of functional groups, as well as their applications in controlled release.
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    A review. Significance: Reactive oxygen species and reactive nitrogen species (ROS/RNS) play an important role in cell signaling pathways. However, the increased prodn. of these species may disrupt cellular homeostasis, giving rise to pathol. conditions. Biomaterials that are responsive to ROS/RNS can be strategically used to specifically release therapeutics and diagnostic agents to regions undergoing oxidative stress. Recent Advances: Many nanocarriers intended to exploit redox micro-environments as triggers for drug release, summarized and compared in this review, have recently been developed. We describe these carriers' chem. structures, strategies for payload protection and oxidn.-selective release, and ROS/RNS sensitivity as tested in initial studies. Crit. Issues: ROS/RNS are unstable, so reliable measures of their concns. in various conditions are scarce. Combined with the dearth of materials shown to respond to physiol. relevant levels of ROS/RNS, evaluations of their true sensitivity are difficult. Future Directions: Oxidn.-responsive nanocarriers developed thus far show tremendous potential for applicability in vivo; however, the sensitivity of these chemistries needs to be fine tuned to enable responses to physiol. levels of ROS and RNS. Antioxid. Redox Signal. 21, 730-754.
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    Polymer Chemistry (2014), 5 (4), 1393-1404CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
    REDOX responsive (nano)materials typically exhibit chem. changes in response to the presence and concn. of oxidants/reductants. Due to the complexity of biol. environments, it is crit. to ascertain whether the chem. response may depend on the chem. details of the stimulus, in addn. to its REDOX potential, and whether chem. different responses can det. a different overall performance of the material. Here, the authors used oxidn.-sensitive materials, although these considerations can be extended also to reducible ones. In particular, the authors used poly(propylene sulfide) (PPS) nanoparticles coated with a PEGylated emulsifier (Pluronic F127); inter alia, the authors here present also an improved preparative method. The nanoparticles were exposed to 2 Reactive O Species (ROS) typically encountered in inflammatory reactions, H2O2 (H2O2) and hypochlorite (ClO-); their response was evaluated with a variety of techniques, including diffusion NMR spectroscopy that allowed to sep. characterize the chem. different colloidal species produced. The 2 oxidants triggered a different chem. response: H2O2 converted sulfides to sulfoxides, while ClO- partially oxidized them further to sulfones. The different chem. correlated to a different material response: H2O2 increased the polarity of the nanoparticles, causing them to swell in H2O and to release the surface PEGylated emulsifier; the uncoated oxidized particles still exhibited very low toxicity. On the contrary, ClO- rapidly converted the nanoparticles into water-sol., depolymd. fragments with a significantly higher toxicity. The take-home message is that it is more correct to discuss smart materials in terms of an environmentally specific response to (REDOX) stimuli. Far from being a problem, this could open the way to more sophisticated and precisely targeted applications.
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    The anionic ring-opening polymn. of episulfides has been successfully applied in emulsion. The polymn. proceeded with a living mechanism but was characterized by a limiting conversion, presumably arising from the increase in viscosity in the polymer. To the knowledge of the authors, only two other cases of living anionic polymn. in emulsion are known (silicones and cyanoacrylates); the addnl. novelty presented by episulfides is the ease of end-functionalization. Furthermore, the emulsion polymn. allowed the prepn. of highly stable particles, which, due to their PEGylated surface and their appropriate diam., can be applied in the biomedical field as nanocarriers.
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    We have recently demonstrated the possible use of org. polysulfides for the design of oxidn.-sensitive colloidal carriers in the form of polymeric vesicles, which are particularly suitable for the encapsulation of hydrosol. drugs. In the present research we extend our efforts to carriers specifically suitable for hydrophobic mols. Exploiting the living emulsion polymn. of episulfides, we have produced new crosslinked polysulfide nanoparticles. Here we demonstrate how this process allows the prodn. of stable nanoparticles with a good control over their size and functionality. The nanoparticles showed negligible cytotoxicity on a fibroblast model; furthermore, they exhibited sensitivity to oxidative conditions, which first produce swelling and then solubilize the material.
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    Dual-Stimuli-Responsive Microparticles
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    ACS Applied Materials & Interfaces (2015), 7 (18), 9744-9751CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    The need for smart materials in the area of biotechnol. has fueled the development of numerous stimuli-responsive polymers. Many of these polymers are responsive to pH, light, temp., or oxidative stress, and yet very few are responsive toward multiple stimuli. Here we report on the synthesis of a novel dual-stimuli-responsive poly(ethylene glycol)-based polymer capable of changing its hydrophilic properties upon treatment with UV light (exogenous stimulus) and markers of oxidative stress (endogenous stimulus). From this polymer, smart microparticles and fibers were fabricated and their responses to either stimulus sep. and in conjunction were examd. Comparison of the degrdn. kinetics demonstrated that the polymer became water-sol. only after both oxidn. and irradn. with UV light, which resulted in selective degrdn. of the corresponding particles. Furthermore, in vitro expts. demonstrated successful uptake of these particles by Raw 264.7 cells. Such dual-stimuli-responsive particles could have potential applications in drug delivery, imaging, and tissue engineering.
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    Macromolecular Chemistry and Physics (2012), 213 (19), 2052-2061CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Poly(propylene sulfide) (PPS) is studied as an oxidn.-responsive macromol. building block, in the perspective of anti-inflammatory therapies. Here, we show that the nature of the oxidant has profound effects on the outcome of the oxidn. process. PPS was exposed to hydrogen peroxide (H2O2) and hypochlorite (OCl-), which are oxidizing species commonly encountered during inflammatory processes. It was found that the oxidn. with H2O2 converted thioethers into sulfoxides, producing water-sol. macromol. products with extremely low toxicity (L929 fibroblasts); on the contrary, the reaction with NaOCl produced sulfones in addn. to sulfoxides, and this was accompanied by depolymn., which appears to considerably affect the toxicity of the oxidn. products.
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  • Abstract

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    Scheme 1

    Scheme 1. Two Couples of Thiol–Ene Bifunctional Monomers (EDDT-DAP: 1; EDDT-DAA: 2) and the Corresponding Poly(thioether) Structure (P1 and P2) Formed by Step-Growth Linear Polymerization
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    Figure 1

    Figure 1. Reflectance values determined at the middle of the vial (left y axis, line) and droplet average diameter values (right y axis, dot) as a function of storage time for the two thiol–ene miniemulsions: M1 (red) and M2 (black). Cmonomer = 20 wt %; both miniemulsions contain DBHQ inhibitor.

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    Figure 2

    Figure 2. (A) Attenuance spectra of miniemulsion M1 (full symbols) and solution homologue S1 in DMSO (empty symbols) with Cmonomer = 20 wt % at different optical paths: 1 mm (triangle), 0.5 mm (circle), and 0.1 mm (square). (B) Conversion–times curves profiles for M1 (full symbols), S1 (open symbols), and bulk system B1 (solid line). All photopolymerizations were performed in a 1 mm thick spectroscopic cell under UV light provided by a filtered mercury–xenon arc lamp (λ > 310 nm, I = 590 mW cm–2). The inset shows a series of NIR spectra of M1 during photopolymerization.

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    Figure 3

    Figure 3. Cryo-TEM image of a representative area of P1 latex. The round-shaped homogeneous particles (indicated by white arrows) have a diameter ranging from 50 to 400 nm. The black arrow shows the lacy carbon supporting film. The solvent areas are fully amorphous due to the high speed of freezing (10 000 K/s) (arrowhead).

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    Figure 4

    Figure 4. WAXRD patterns of P1 and P2 films.

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    Figure 5

    Figure 5. DSC (left y-axis) and TGA (right y-axis) thermograms of P1 (top) and P2 (bottom) films.

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    Figure 6

    Figure 6. POM pictures in dark field mode of P1 (top) and P2 (bottom) films at ambient temperature.

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    Scheme 2

    Scheme 2. Two Degradation Routes in Water of Poly(thioether ester) P1 Nanoparticles: Hydrogen Peroxide-Induced Oxidation of Thioether and HCl-Catalyzed Hydrolysis of Ester; Oxidation Leads Only to Sulfur(IV) with H2O2 (59)
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    Figure 7

    Figure 7. (A) Effect of oxidation (10 wt % H2O2 solution) and acid hydrolysis (pH = 2, HCl solution) on the absorption spectrum of diluted latex P1. (B) Normalized attenuance at 450 nm versus time of different latexes in oxidative medium (full symbols) and acid medium (open symbols): P1 (circle), P2 (square), and a reference polystyrene latex (triangle).

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  • References

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      Thiol-ene polymns. are possible in a water-borne suspension-like photopolymn. and yield spherical particles that have diams. in the range of submicrometers to hundreds of micrometers. This is the first report of such colloidal thiol-ene polymns. Thiol-ene polymn. offers unique conditions not commonly assocd. with a water-borne polymn. including a step-growth polymn. mechanism along with photoinitiation under ambient conditions. Example polymns. of a triene, 3,5-triallyl-1,3,5-triazine-2,4,6 (1N,3H,5H)-trione (TTT), and a tetrathiol, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), with the photoinitiator 1-hydroxycyclohexyl Ph ketone, surfactant sodium dodecyl sulfate (SDS), and a cosolvent (chloroform or toluene) are discussed. Various exptl. parameters were examd. such as surfactant concn., homogenization energy, cosolvent species, and cosolvent amt. to develop an understanding of the mechanism of microsphere formation. Particle size is dependent on homogenization energy, with greater mech. shear yielding smaller particles. In addn., higher concns. of surfactant or solvent also produced smaller spherical particles. These observations lead to the conclusion that the particles are formed via a suspension-like polymn.
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    15. 15
      Jasinski, F.; Lobry, E.; Tarablsi, B.; Chemtob, A.; Croutxé-Barghorn, C.; Le Nouen, D.; Criqui, A. Light-Mediated Thiol–Ene Polymerization in Miniemulsion: A Fast Route to Semicrystalline Polysulfide Nanoparticles ACS Macro Lett. 2014, 3, 958– 962 DOI: 10.1021/mz500458s
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      15
      Light-Mediated Thiol-Ene Polymerization in Miniemulsion: A Fast Route to Semicrystalline Polysulfide Nanoparticles
      Jasinski, Florent; Lobry, Emeline; Tarablsi, Bassam; Chemtob, Abraham; Croutxe-Barghorn, Celine; Le Nouen, Didier; Criqui, Adrien
      ACS Macro Letters (2014), 3 (9), 958-962CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Historically, the synthesis of aq. polymer dispersions has focused on radical chain-growth polymn. of low-cost acrylate or styrene emulsions. Herein, we demonstrate the potential of UV-initiated thiol-ene step-growth radical polymn., departing from a nontransparent difunctional monomer miniemulsion based on ethylene glycol dithiol and diallyl adipate. Performed without solvent and at ambient conditions, the photopolymn. process is energy-effective, environmentally friendly, and ultrafast, leading to full monomer consumption in 2 s, upon irradiating a miniemulsion contained in a 1 mm thick quartz cell microreactor. The resultant linear poly(thioether ester) particles have an av. diam. of 130 nm. After water evapn., they yield a clear elastomeric film combining chem. resistance and high degree of crystallinity (55%).
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    16. 16
      Amato, D. V.; Amato, D. N.; Flynt, A. S.; Patton, D. L. Functional, Sub-100 nm Polymer Nanoparticles via Thiol-Ene Miniemulsion Photopolymerization Polym. Chem. 2015, 6, 5625– 5632 DOI: 10.1039/C4PY01449A
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      16
      Functional, sub-100 nm polymer nanoparticles via thiol-ene miniemulsion photopolymerization
      Amato, D. V.; Amato, D. N.; Flynt, A. S.; Patton, D. L.
      Polymer Chemistry (2015), 6 (31), 5625-5632CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      In this work, sub-100 nm crosslinked polythioether nanoparticles were synthesized via thiol-ene photopolymn. in miniemulsion using high-energy homogenization. The effects of the miniemulsion formulation and homogenization parameters - including inhibitor concn., surfactant concn., org. wt. fraction, ultrasonication time and amplitude - on nanoparticle size and size distribution were investigated. Thiol-ene nanoparticles with a mean particle diam. of 46 nm were obtained under optimized conditions for the current system at 2.5 wt% org. fraction and 20 mM surfactant concn. In an effort to demonstrate potential utility of thiol-ene nanoparticles, we exploit the step-growth radical mechanism of thiol-ene photopolymn. under non-stoichiometric conditions to fabricate functional nanoparticles that express excess thiol or alkene at the particle surface. We show that these excess functional groups can be utilized as reactive handles in thiol-Michael and radical-mediated thiol-ene reactions for immobilization of fluorescent moieties via postpolymn. modification.
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    17. 17
      Durham, O.; Shipp, D. Suspension “Click” Polymerizations: Thiol-Ene Polymer Particles Prepared with Natural Gum Stabilizers Colloid Polym. Sci. 2015, 293, 2385– 2394 DOI: 10.1007/s00396-015-3628-2
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      Suspension "click" polymerizations: thiol-ene polymer particles prepared with natural gum stabilizers
      Durham, Olivia Z.; Shipp, Devon A.
      Colloid and Polymer Science (2015), 293 (8), 2385-2394CODEN: CPMSB6; ISSN:0303-402X. (Springer)
      The impact of different natural gum species employed as stabilizers in the suspension photopolymn. of water-borne thiol-ene polymer particles is reported. The focus of anal. was on how hydrocolloids impact the synthesis of polymer particles prepd. using a "click" thiol-ene polymn. approach. The use of renewable and naturally occurring gums as particle stabilizers provide a shift toward greener methods of polymer particle synthesis. The natural gum species examd. include gum Arabic, guar gum, and xanthan gum. In particular, gum Arabic was examd. in thiol-ene particle synthesis due to inherent colloidal stabilizing properties that allow it to be utilized at concns. comparable to synthetic stabilizers (1 wt% or greater). The use of these naturally occurring polysaccharides led to the development of spherical, crosslinked thiol-ene polymer particles in the size range of several micrometers to hundreds of micrometers. Polymer particle synthesis was completed within minutes via photopolymn. Parameters examd. include variation of natural gum species, natural gum concn., monomer content, and stabilizer soln. viscosity. Thiol-ene polymer particles can be successfully developed at very low stabilizer concns. (0.005-0.5 wt%) due to the unique viscosity-enhancing properties of natural gum solns. compared to reactions stabilized by synthetic surfactant stabilizers.
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    18. 18
      Durham, O. Z.; Shipp, D. A. Suspension Thiol-Ene Photopolymerization: Effect of Stabilizing Agents on Particle Size and Stability Polymer 2014, 55, 1674– 1680 DOI: 10.1016/j.polymer.2014.02.044
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      18
      Suspension thiol-ene photopolymerization: Effect of stabilizing agents on particle size and stability
      Durham, Olivia Z.; Shipp, Devon A.
      Polymer (2014), 55 (7), 1674-1680CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      The impact of several surfactant species employed in the suspension photopolymn. of water-borne thiol-ene polymer microspheres is reported. The focus of anal. was on how different surfactant species and the surfactant concns. affected particle size and particle size distributions. Surfactants used included sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), and hexadecyltrimethylammonium bromide (HTAB), Tween 20, Tween 40, Tween 60, Tween 80, Lutensol XL 70, Lutensol XP 70, Pluronic PE 6400, and Pluronic F108 Pastille. Using stabilizing agents or surfactants is necessary to prevent extensive aggregation and agglomeration of crosslinked thiol-ene polymer. All surfactants used in this study for particle stabilization and development produced spherical thiol-ene polymer particles. The chem. structure and concn. of the surfactants influenced the final particle size and size distribution of particles obtained. In general, smaller particles are obtained with higher concns. of stabilizing agent, esp. for ionic surfactants.
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    19. 19
      Tan, J.; Li, C.; Zhou, J.; Yin, C.; Zhang, B.; Gu, J.; Zhang, Q. Fast and Facile Fabrication of Porous Polymer Particles via Thiol-Ene Suspension Photopolymerization RSC Adv. 2014, 4, 13334– 13339 DOI: 10.1039/c4ra00203b
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      Fast and facile fabrication of porous polymer particles via thiol-ene suspension photopolymerization
      Tan, Jiaojun; Li, Chunmei; Zhou, Jian; Yin, Changjie; Zhang, Baoliang; Gu, Junwei; Zhang, Qiuyu
      RSC Advances (2014), 4 (26), 13334-13339CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      A fast and facile method of prepg. porous polymer particles via thiol-ene suspension photopolymn. was studied. The porous particles were fabricated by adding the porogen to the click chem. system. In this paper, the photopolymn. of dipentaerythritol hexakis (3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptopropionate), 1,3,5-tri-2-propenyl-1,3,5-triazine- 2,4,6(1H,3H,5H)-trione, sodium dodecyl sulfate, chloroform and different amts. of linear polymer porogen (polymethyl methacrylate, PMMA) was discussed in detail. The two crucial factors, polymn. time and amt. of porogen, were investigated. It was demonstrated that the conversion of monomers could reach 80% within 15 s of irradn., which further verified the high efficiency of click chem. By varying the amt. of PMMA, we were able to tailor the particle size, pore diams. and morphol. of the porous particles. Results of the mercury porosimetry indicated that the median pore diam. of particles was about 12.39 μm and the surface area was 4.393 m2 g-1. Moreover, the Tg of the particles given by DSC was about 45 °C.
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      Wang, C.; Chatani, S.; Podgorski, M.; Bowman, C. N. Thiol-Michael Addition Miniemulsion Polymerizations:Functional Nanoparticles and Reactive Latex Films Polym. Chem. 2015, 6, 3758– 3763 DOI: 10.1039/C5PY00326A
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      Thiol-Michael addition miniemulsion polymerizations: functional nanoparticles and reactive latex films
      Wang, Chen; Chatani, Shunsuke; Podgorski, Maciej; Bowman, Christopher N.
      Polymer Chemistry (2015), 6 (20), 3758-3763CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      Thiol-Michael addn. polymn. is successfully implemented in a miniemulsion polymn. system. By off-stoichiometric polymn. between thiols and acrylates, inherently functionalized particles are facilely prepd. in a single step. We demonstrate that the latex films from such particles are readily available for further modification and second-stage photo-curing.
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      Wang, C.; Podgorski, M.; Bowman, C. N. Monodisperse Functional Microspheres from Step-Growth “Click” Polymerizations: Preparation, Functionalization and Implementation Mater. Horiz. 2014, 1, 535– 539 DOI: 10.1039/C4MH00082J
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      Monodisperse functional microspheres from step-growth 'click' polymerizations: preparation, functionalization and implementation
      Wang, Chen; Podgorski, Maciej; Bowman, Christopher N.
      Materials Horizons (2014), 1 (5), 535-539CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
      The monodisperse cross-linked clickable microspheres are made via step-growth thiol-acrylate Michael addn. polymn. The diam. of the microsphere is varied from 1-10 μm, depending on the cross-link d. and the reaction conditions. The implementations of these microspheres including functionalized microspheres for click chem., polymeric composites, fluorescent labeling and polymer degrdn. are discussed and/or demonstrated.
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      Amato, D. N.; Amato, D. V.; Narayanan, J.; Donovan, B. R.; Douglas, J. R.; Walley, S. E.; Flynt, A. S.; Patton, D. L. Functional, Composite Polythioether Nanoparticles via Thiol-Alkyne Photopolymerization in Miniemulsion Chem. Commun. 2015, 51, 10910– 10913 DOI: 10.1039/C5CC03319E
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      Functional, composite polythioether nanoparticles via thiol-alkyne photopolymerization in miniemulsion
      Amato, Dahlia N.; Amato, Douglas V.; Narayanan, Jananee; Donovan, Brian R.; Douglas, Jessica R.; Walley, Susan E.; Flynt, Alex S.; Patton, Derek L.
      Chemical Communications (Cambridge, United Kingdom) (2015), 51 (54), 10910-10913CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Thiol-yne photopolymn. in miniemulsion is demonstrated as a simple, rapid, and 1-pot synthetic approach to polythioether nanoparticles with tuneable particle size and clickable functionality. The strategy is also useful in the synthesis of composite polymer-inorg. nanoparticles.
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      Tan, J.; Li, C.; Li, H.; Zhang, H.; Gu, J.; Zhang, B.; Zhang, H.; Zhang, Q. Water-Borne Thiol-Isocyanate Click Chemistry in Microfluidics: Rapid and Energy-Efficient Preparation of Uniform Particles Polym. Chem. 2015, 6, 4366– 4373 DOI: 10.1039/C5PY00412H
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      Water-borne thiol-isocyanate click chemistry in microfluidics: rapid and energy-efficient preparation of uniform particles
      Tan, Jiaojun; Li, Chunmei; Li, Hui; Zhang, Hao; Gu, Junwei; Zhang, Baoliang; Zhang, Hepeng; Zhang, Qiuyu
      Polymer Chemistry (2015), 6 (24), 4366-4373CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A nucleophile-catalyzed thiol-isocyanate reaction was exploited as an efficient route to fabricate uniform particles in a water-borne system. Droplets were generated in a simple microfluidic setup from stoichiometric thiol and isocyanate monomers, thereby creating an oil-in-water emulsion, and polymer particles were obtained once the monomer droplets were exposed to a nucleophile. This is the first report of thiol-isocyanate polymn. in a water-borne system, which shows great promise in the manuf. of particles for its mild conditions, rapid rate and high conversion. Notably, heat, UV, anhyd. or oxygen-free conditions are not required. Particles with sizes ranging from 40 to 250 μm can be prepd. via adjusting the flow rate of continuous and disperse phases. In addn., the functionality of the thiol monomer has a profound effect on the morphol. of particles. This method opens up possibilities for nucleophile-catalyzed thiol-isocyanate click chem. in water-borne and heterogeneous polymn.
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      Workman, J.; Weyer, L. Practical Guide to Interpretive Near-infrared Spectroscopy; CRC Press: New York, 2007; p 346.
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      Ibrahim, A.; Maurin, V.; Ley, C.; Allonas, X.; Croutxe-Barghorn, C.; Jasinski, F. Investigation of Termination Reactions in Free Radical Photopolymerization of UV Powder Formulations Eur. Polym. J. 2012, 48, 1475– 1484 DOI: 10.1016/j.eurpolymj.2012.05.019
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      Investigation of termination reactions in free radical photopolymerization of UV powder formulations
      Ibrahim, A.; Maurin, V.; Ley, C.; Allonas, X.; Croutxe-Barghorn, C.; Jasinski, F.
      European Polymer Journal (2012), 48 (8), 1475-1484CODEN: EUPJAG; ISSN:0014-3057. (Elsevier Ltd.)
      The termination mechanisms occurring in a UV powder coating system during photopolymn. process are investigated and compared to a conventional acrylate monomer system. The influence of the photoinitiator concn., viscosity and conversion percentage of the monomer are assessed leading to the study of curing kinetics of a UV powder urethane diacrylate based system. It is shown that termination occurs mainly by bimol. termination (PRT). This mechanism is related to low reactive double bonds concn. and high photoinitiator concn. in the UV powder system. Moreover, the effect of surrounding atm. points out the role of the oxygen on polymn. mechanisms.
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      Mengual, O.; Meunier, G.; Cayré, I.; Puech, K.; Snabre, P. TURBISCAN MA 2000: Multiple Light Scattering Measurement for Concentrated Emulsion and Suspension Instability Analysis Talanta 1999, 50, 445– 456 DOI: 10.1016/S0039-9140(99)00129-0
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      TURBISCAN MA 2000: multiple light scattering measurement for concentrated emulsion and suspension instability analysis
      Mengual, O.; Meunier, G.; Cayre, I.; Puech, K.; Snabre, P.
      Talanta (1999), 50 (2), 445-456CODEN: TLNTA2; ISSN:0039-9140. (Elsevier Science B.V.)
      Emulsion or suspension destabilization often results from coalescence or particle aggregation (flocculation) leading to particle migration (creaming or sedimentation). Creaming and sedimentation are often considered as reversible, while coalescence and flocculation spell disaster for the formulator. Thus, it is of prime importance to detect coalescence or cluster formation at an early stage to shorten the ageing tests and to improve the formulations. This work mainly concerns the independent and anisotropic scattering of light from an emulsion or suspension in a cylindrical glass measurement cell, in relation with the optical analyzer TURBISCAN MA 2000. The propagation of light through a concd. dispersion can be used to characterize the system physico-chem. stability. Indeed, photons undergo many scattering events in an optically thick dispersion before escaping the medium and entering a receiver aperture. Multiple scattering thus contributes significantly to the transmitted and backscattered flux measured by TURBISCAN MA 2000. We present statistical models and numerical simulations for the radiative transfer in a suspension (plane or cylindrical measurement cells) only involving the photon mean path length, the asymmetry factor and the geometry of the light receivers. We further have developed an imaging method with high gray level resoln. for the visualization and the anal. of the surface flux in the backscattered spot light. We compare the results from phys. models and numerical simulations with the expts. performed with the imaging method and the optical analyzer TURBISCAN MA 2000 for latex beads suspensions (variable size and particle vol. fraction). We then present a few examples of concd. emulsion and suspension instability anal. with TURBISCAN 2000. It is shown that the instrument is able to characterize particle or aggregate size variation and particle/aggregate migration and to detect these phenomena much more earlier than the operator's naked eye, esp. for concd. and optically thick media.
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      Schork, F. J.; Luo, Y.; Smulders, W.; Russum, J. P.; Butté, A.; Fontenot, K. Miniemulsion Polymerization. In Polymer Particles; Okubo, M., Ed.; Springer-Verlag: Heidelberg, 2005; p 129.
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      Esfandiari, P.; Ligon, S. C.; Lagref, J. J.; Frantz, R.; Cherkaoui, Z.; Liska, R. Efficient Stabilization of Thiol-Ene Formulations in Radical Photopolymerization J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4261– 4266 DOI: 10.1002/pola.26848
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      Efficient stabilization of thiol-ene formulations in radical photopolymerization
      Esfandiari, Paricher; Ligon, Samuel Clark; Lagref, Jean Jacques; Frantz, Richard; Cherkaoui, Zoubair; Liska, Robert
      Journal of Polymer Science, Part A: Polymer Chemistry (2013), 51 (20), 4261-4266CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      An efficient stabilizer system is presented for thiol-ene polymn. formulations with no increase of viscosity at ambient temps. and a significantly improved stability at elevated temps. The combination of a free radical scavenger and an acid with an appropriate pKa value of about 2 displays a surprising synergistic effect.
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      Hoyle, C. E.; Lee, T. Y.; Roper, T. Thiol–Enes: Chemistry of the Past with Promise for the Future J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 5301– 5338 DOI: 10.1002/pola.20366
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      Thiol-enes: Chemistry of the past with promise for the future
      Hoyle, Charles E.; Lee, Tai Yeon; Roper, Todd
      Journal of Polymer Science, Part A: Polymer Chemistry (2004), 42 (21), 5301-5338CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      A review. The photopolymn. of mixts. of multifunctional thiols and enes is an efficient method for the rapid prodn. of films and thermoset plastics with unprecedented phys. and mech. properties. One of the major obstacles in traditional free-radical photopolymn. is essentially eliminated in thiol-ene polymns. because the polymn. occurs in air almost as rapidly as in an inert atm. Virtually any type of ene will participate in a free-radical polymn. process with a multifunctional thiol. Hence, it is possible to tailor materials with virtually any combination of properties required for a particular application.
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      Xia, H.; Wang, Q.; Liao, Y.; Xu, X.; Baxter, S. M.; Slone, R. V.; Wu, S.; Swift, G.; Westmoreland, D. G. Polymerization Rate and Mechanism of Ultrasonically Initiated Emulsion Polymerization of n-Butyl Acrylate Ultrason. Sonochem. 2002, 9, 151– 158 DOI: 10.1016/S1350-4177(01)00118-3
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      Polymerization rate and mechanism of ultrasonically initiated emulsion polymerization of n-butyl acrylate
      Xia, Hesheng; Wang, Qi; Liao, Yongqin; Xu, Xi; Baxter, Steven M.; Slone, Robert V.; Wu, Shuguang; Swift, Graham; Westmoreland, David G.
      Ultrasonics Sonochemistry (2002), 9 (3), 151-158CODEN: ULSOER; ISSN:1350-4177. (Elsevier Science B.V.)
      The factors affecting the induction period and polymn. rate in ultrasonically initiated emulsion polymn. of Bu acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymn. of BA without any added initiator by enhancing the N2 flow rate. Increasing temp., power output and SDS concn., decreasing the monomer concn. results in further decreasing induction period and enhanced polymn. rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymn. rate can be controlled by varying reaction parameters. The app. of ultrasonically initiated semi-continuous and continuous emulsion polymn. were set up and the feasibility was first studied. Based on the exptl. results, a free radical polymn. mechanism for ultrasonically initiated emulsion polymn. was proposed, including the sources of the radicals, the process of radical formation, the locus of polymn. and the polymn. process. Compared with conventional emulsion polymn., where the radicals come from thermal decompn. of a chem. initiator, ultrasonically initiated emulsion polymn. has attractive features such as no need for a chem. initiator, lower reaction temp., faster polymn. rate, and higher mol. wt. of the polymer prepd.
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      Manea, M.; Chemtob, A.; Paulis, M.; de la Cal, J. C.; Barandiaran, M. J.; Asua, J. M. Miniemulsification in High-Pressure Homogenizers AIChE J. 2008, 54, 289– 297 DOI: 10.1002/aic.11367
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      Miniemulsification in high-pressure homogenizers
      Manea, Mihaela; Chemtob, Abraham; Paulis, Maria; de la Cal, Jose C.; Barandiaran, Maria J.; Asua, Jose M.
      AIChE Journal (2008), 54 (1), 289-297CODEN: AICEAC; ISSN:0001-1541. (John Wiley & Sons, Inc.)
      The mechanisms involved in the formation of high solids content composite polymer-monomer waterborne miniemulsions in a high-pressure homogenizer were investigated combining exptl. results and a math. model for the process. It was found that the final droplet size was the result of two consecutive processes: droplet break-up and coagulation. The final droplet size was detd. by the mechanism giving the largest droplet size.
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      Jafari, S. M.; Assadpoor, E.; He, Y.; Bhandari, B. Re-Coalescence of Emulsion Droplets during High-Energy Emulsification Food Hydrocolloids 2008, 22, 1191– 1202 DOI: 10.1016/j.foodhyd.2007.09.006
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      Re-coalescence of emulsion droplets during high-energy emulsification
      Jafari, Seid Mahdi; Assadpoor, Elham; He, Yinghe; Bhandari, Bhesh
      Food Hydrocolloids (2008), 22 (7), 1191-1202CODEN: FOHYES; ISSN:0268-005X. (Elsevier Ltd.)
      A review. Emulsion droplet size plays a key role in many emulsion properties such as stability, color, appearance, texture, and rheol. Accordingly, different emulsions have been classified based on emulsion size including microemulsions and submicron (nano) emulsions. The aim of emulsification is usually to produce emulsion droplets as small as possible, and various emulsification techniques can be used in this regard. One of the main problems of producing very fine emulsions with high-energy emulsification techniques such as microfluidization is the occurrence of "over-processing", which is increase in emulsion size by supplying more energy due to a high rate of re-coalescence of new droplets. Different reasons have been mentioned for "over-processing", including low adsorption rate of the surface-active agent, low residence time of the emulsion in the emulsification zone, high rate of coalescence frequency, and extreme amt. of energy d. This review highlights re-coalescence of new droplets during high-energy emulsification along with some common and important emulsification techniques and different factors affecting emulsion droplet size, and thereby re-coalescence.
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      Hoyle, C. E.; Bowman, C. N. Thiol–Ene Click Chemistry Angew. Chem., Int. Ed. 2010, 49, 1540– 1573 DOI: 10.1002/anie.200903924
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      Thiol-Ene Click Chemistry
      Hoyle, Charles E.; Bowman, Christopher N.
      Angewandte Chemie, International Edition (2010), 49 (9), 1540-1573CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Following Sharpless' visionary characterization of several idealized reactions as click reactions, the materials science and synthetic chem. communities have pursued numerous routes toward the identification and implementation of these click reactions. Herein, the authors review the radical-mediated thiol-ene reaction as one such click reaction. This reaction has all the desirable features of a click reaction, being highly efficient, simple to execute with no side products and proceeding rapidly to high yield. Further, the thiol-ene reaction is most frequently photoinitiated, particularly for photopolymns. resulting in highly uniform polymer networks, promoting unique capabilities related to spatial and temporal control of the click reaction. The reaction mechanism and its implementation in various synthetic methodologies, biofunctionalization, surface and polymer modification, and polymn. are all reviewed.
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      Beuermann, S.; Buback, M. Rate Coefficients of Free-Radical Polymerization Deduced from Pulsed Laser Experiments Prog. Polym. Sci. 2002, 27, 191– 254 DOI: 10.1016/S0079-6700(01)00049-1
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      Rate coefficients of free-radical polymerization deduced from pulsed laser experiments
      Beuermann, Sabine; Buback, Michael
      Progress in Polymer Science (2002), 27 (2), 191-254CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
      A review. Pulsed laser techniques have enormously improved the quality by which rate coeffs. of individual steps in free-radical polymn. may be measured. Pulsed laser initiated polymn. (PLP) in conjunction with size-exclusion chromatog. (SEC) yields the propagation rate coeff., kp. The PLP-SEC-technique has been applied to a wide variety of homopolymns. and copolymns., either in bulk or in soln. In addn. to reporting kinetic data, exptl. details of PLP, of SEC, and of the limitations assocd. with the accurate detn. of the MWD are discussed. The single pulse (SP)-PLP method, which combines PLP with time-resolved NIR spectroscopy, allows for a very detailed insight into the termination rate coeff., kt, for homo- and copolymns. kt data are reported as a function of temp., pressure, monomer conversion, solvent concn., and partly also of chain length. This review considers literature up to Dec. 2000.
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      Nakamura, T.; Okubo, M. Mechanistic Investigation of Particle Size Effects in TEMPO- Mediated Radical Polymerization of Styrene in Aqueous Miniemulsion Macromolecules 2007, 40, 8663– 8672 DOI: 10.1021/ma0712403
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      Nakamura, T.; Zetterlund, P. B.; Okubo, M. Particle Size Effects in TEMPO-Mediated Radical Polymerization of Styrene in Aqueous Miniemulsion Macromol. Rapid Commun. 2006, 27, 2014– 2018 DOI: 10.1002/marc.200600542
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      Particle size effects in TEMPO-mediated radical polymerization of styrene in aqueous miniemulsion
      Nakamura, Tadashi; Zetterlund, Per B.; Okubo, Masayoshi
      Macromolecular Rapid Communications (2006), 27 (23), 2014-2018CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
      2,2,6,6-Tetra-Me piperidinyl-1-oxy (TEMPO)-mediated radical polymn. of styrene in aq. miniemulsion at 125 °C using sodium dodecylbenzenesulfonate and poly(vinyl alc.), resp., as colloidal stabilizers has been investigated. The particle size had a dramatic effect on the polymn. process. Decreasing particle size led to a markedly higher polymn. rate, but less control and a lower degree of livingness. For particles with diams. greater than approx. 170 nm, the polymn. behavior was essentially the same as in the corresponding bulk system. By varying the particle size within an appropriate range, it is possible to tune the polymn. such that the polymn. rate is increased while still maintaining reasonable control and livingness.
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      Bechthold, N.; Landfester, K. Kinetics of Miniemulsion Polymerization As Revealed by Calorimetry Macromolecules 2000, 33, 4682– 4689 DOI: 10.1021/ma000061h
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      Aizpurua, I.; Amalvy, J. I.; Barandiaran, M. J. Influence of the Polymeric Hydrophobe on the Kinetics of Vinyl Acetate Miniemulsion Polymerization Colloids Surf., A 2000, 166, 59– 66 DOI: 10.1016/S0927-7757(99)00293-9
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      Influence of the polymeric hydrophobe on the kinetics of vinyl acetate miniemulsion polymerization
      Aizpurua, I.; Amalvy, J. I.; Barandiaran, M. J.
      Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2000), 166 (1-3), 59-66CODEN: CPEAEH; ISSN:0927-7757. (Elsevier Science B.V.)
      The influence of polymeric hydrophobes on the stabilization and kinetics of vinyl acetate miniemulsion polymn. was investigated by conducting reactions in batch mode of miniemulsions prepd. with poly(vinyl acetate) or polystyrene as cosurfactants. The results were compared with a miniemulsion stabilized with hexadecane and with a conventional emulsion. Shelf life stability anal. showed that miniemulsions prepd. with polymer as the unique cosurfactant were not stable. However, the appearance of the sepd. phases was not similar to that of conventional emulsion, which was interpreted as the formation of small monomer-swollen particles in the case of the miniemulsion. The kinetic anal. confirmed the different nucleation mechanism of these unstable miniemulsions compared with the conventional emulsion.
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      Octanol–water partition coefficients (KOW) of I2959 and I651 are respectively 0.84 and 3.42 (Safety Data Sheet) at 25 °C. KOW (I2959) value is low enough to enable its dissolution in the aqueous phase (5 g/L); however, it suggests a partition between the monomer and aqueous phases.

      There is no corresponding record for this reference.
    40. 40
      Cramer, N. B.; Bowman, C. N. Kinetics of Thiol–Ene and Thiol–Acrylate Photopolymerizations with Real-Time Fourier Transform Infrared J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 3311– 3319 DOI: 10.1002/pola.1314
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      Kinetics of thiol-ene and thiol-acrylate photopolymerizations with real-time fourier transform infrared
      Cramer, Neil B.; Bowman, Christopher N.
      Journal of Polymer Science, Part A: Polymer Chemistry (2001), 39 (19), 3311-3319CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
      We used real-time Fourier transform IR to monitor the conversion of both thiol and ene (vinyl) functional groups independently during photoinduced thiol-ene photopolymns. From these results, the stoichiometry of various thiol-ene and thiol-acrylate polymns. was detd. For thiol-ene polymns., the conversion of ene functional groups was up to 15% greater than the conversion of thiol functional groups. For stoichiometric thiol-acrylate polymns., the conversion of the acrylate functional groups was roughly twice that of the thiol functional groups. With kinetic expressions for thiol-acrylate polymns., the acrylate propagation kinetic const. was 1.5 times greater than the rate const. for hydrogen abstraction from the thiol. Conversions of thiol-acrylate systems of various initial stoichiometries were successfully predicted with this ratio of propagation and chain-transfer kinetic consts. Thiol-acrylate systems with different initial stoichiometries exhibited diverse network properties. Thiol-ene systems were initiated with benzophenone and 2,2-dimethoxy-2-phenylacetophenone as initiators and were also polymd. without a photoinitiator.
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      Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F. High Solid Content Latexes Prog. Polym. Sci. 2002, 27, 1573– 1615 DOI: 10.1016/S0079-6700(02)00014-X
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      High solid content latexes
      Guyot, A.; Chu, F.; Schneider, M.; Graillat, C.; McKenna, T. F.
      Progress in Polymer Science (2002), 27 (8), 1573-1615CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
      This article is a review of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn. High solids content latexes are of growing interest for many reasons; however, making this type of product entails many difficulties. Increasing the solids content (fraction of polymer relative to the continuous phase) in a reproducible manner entails the strict control of a complex particle size distribution (PSD). The PSD must be either quite broad, or multimodal in order to obtain solids contents much above 55 or 60 vol.%. In addn., the viscosity of a latex is highly sensitive to the PSD near the upper limit of solids content, but it is still not possible to predict a priori how a complex PSD will effect the viscosity. This article presents an overview of the rheol. of concd. latexes, followed by a discussion of the state of the art in the area of high solids latex prodn.
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      Alfano, O. M.; Negro, A. C.; Cabrera, M. I.; Cassano, A. E. Scattering Effects Produced By Inert Particles In Photochemical Reactors. 1. Model And Experimental Verification Ind. Eng. Chem. Res. 1995, 34, 488– 499 DOI: 10.1021/ie00041a009
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      Takahashi, Y.; Tadokoro, H.; Chatani, Y. Structure of Polyethylene Sulfide J. Macromol. Sci., Part B: Phys. 1968, 2, 361– 367 DOI: 10.1080/00222346808212456
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      Vinas, J.; Dufils, P. E. Poly(Vinylidene Chloride). In Ullmann’s Encyclopedia of Industrial Chemistry; Wiley-VCH: Berlin, 2012.
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      Staff, R. H.; Lieberwirth, I.; Landfester, K.; Crespy, D. Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers Macromol. Chem. Phys. 2012, 213, 351– 358 DOI: 10.1002/macp.201100529
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      Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers
      Staff, Roland H.; Lieberwirth, Ingo; Landfester, Katharina; Crespy, Daniel
      Macromolecular Chemistry and Physics (2012), 213 (3), 351-358CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The synthesis of colloidally stable submicron particles of syndiotactic polystyrene (sPS) and isotactic polystyrene (iPS) is reported. Model particles based on poly-L-lactic acid (PLLA), atactic polystyrene (aPS), sPS, and iPS are prepd. by the evapn. of a solvent present in miniemulsion droplets. The degree of crystallinity of the particles is found to decrease with their size, as shown by DSC and WAXS measurements. Remarkably, nonspherical particlLs can be formed in the dispersed state with sPS and iPS, whereas PLLA and aPS particles always display spherical morphologies.
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      Michell, R. M.; Blaszczyk-Lezak, I.; Mijangos, C.; Müller, A. J. Confinement Effects on Polymer Crystallization: From Droplets to Alumina Nanopores Polymer 2013, 54, 4059– 4077 DOI: 10.1016/j.polymer.2013.05.029
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      Confinement effects on polymer crystallization: From droplets to alumina nanopores
      Michell, Rose Mary; Blaszczyk-Lezak, Iwona; Mijangos, Carmen; Muller, Alejandro J.
      Polymer (2013), 54 (16), 4059-4077CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      We review previous works on polymer confined crystn. employing strategies that allow confinement to go from the micron to the nanometer scale: droplets, blends, block copolymers and infiltration into alumina nanopores. We also present novel results, reporting homogeneous nucleation and first order crystn. kinetics, for the first time, in a homopolymer and a diblock copolymer infiltrated within alumina nanopores. Confinement can produce fractionated crystn. or exclusive crystn. at much higher supercooling as compared to bulk polymers, as the degree of confinement increases. For highly confined heterogeneity free micro or nano-domains, the overall crystn. kinetics was dominated by nucleation and therefore was first order. The nucleation mechanism changes from heterogeneous nucleation for the bulk polymer to surface or homogeneous nucleation for ensembles of confined and isolated heterogeneity free micro or nanodomains. Surface nucleation is more commonly found than homogeneous nucleation, although this fact is not frequently recognized in the literature.
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      Pereira, R. F. P.; Valente, A. J. M.; Burrows, H. D.; de Zea Bermudez, V.; Carvalho, R. A.; Castro, R. A. E. Structural Characterization of Solid Trivalent Metal Dodecyl Sulfates: From Aqueous Solution to Lamellar Superstructures RSC Adv. 2013, 3, 1420– 1433 DOI: 10.1039/C2RA21906A
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      Structural characterization of solid trivalent metal dodecyl sulfates: from aqueous solution to lamellar superstructures
      Pereira, Rui F. P.; Valente, Artur J. M.; Burrows, Hugh D.; de Zea Bermudez, Veronica; Carvalho, Rui A.; Castro, Ricardo A. E.
      RSC Advances (2013), 3 (5), 1420-1433CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      Metal dodecyl sulfates of trivalent aluminum, chromium, lanthanum and gadolinium were prepd. by addn. of the corresponding salts to aq. solns. of sodium dodecyl sulfate at the natural pH (∼6). Using x-ray diffraction, FTIR and NMR spectroscopy, DSC, TG and polarizing light thermomicroscopy metal dodecyl sulfates are formed with lamellar structures. These have different degrees of hydration, which depend upon the metal ion. In some cases there is evidence for coexistence of different lamellar phases. The metal is strongly bound electrostatically to the sulfate group, and although the alkyl chain is in an extended conformation, there are suggestions of local disordering of the methylene groups adjacent to the anionic head group. SEM with an EDS probe on the trivalent metal complexes shows a 1:3 ratio at the surface identical to the bulk structure. Studies by SEM and AFM provide evidence of periodicity, which is likely to be induced by the lamellar, layered structures. Differences are obsd. in the thermal behavior, which appear to reflect both the coordination behavior of the metal ion and the degree of hydration.
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      Smith, L. A.; Duncan, A.; Thomson, G. B.; Roberts, K. J.; Machin, D.; McLeod, G. Crystallisation of Sodium Dodecyl Sulphate from Aqueous Solution: Phase Identification, Crystal Morphology, Surface Chemistry and Kinetic Interface Roughening J. Cryst. Growth 2004, 263, 480– 490 DOI: 10.1016/j.jcrysgro.2003.11.025
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      Crystallisation of sodium dodecyl sulfate from aqueous solution: phase identification, crystal morphology, surface chemistry and kinetic interface roughening
      Smith, L. A.; Duncan, A.; Thomson, G. B.; Roberts, K. J.; Machin, D.; McLeod, G.
      Journal of Crystal Growth (2004), 263 (1-4), 480-490CODEN: JCRGAE; ISSN:0022-0248. (Elsevier)
      The crystn. of the surfactant Na dodecyl sulfate (SDS) from aq. soln., above the crit. micelle concn. was studied via in situ differential interference phase contrast microscopy under a range of soln. cooling rates. Variation in the cooling rate has little effect on the morphol. for the range applied, producing a plate-like habit dominated by the {100} form. Nucleation studies demonstrate little correlation between metastable zone width (MSZW) and surfactant concn. with the MSZW suggesting that the ease of nucleation of SDS lies between those commonly obsd. for org. and inorg. systems. Weak dependence of the MSZW on cooling rate is obsd. Crystal morphologies predicted using an atom-atom method implemented in the HABIT98 program (Comput. Phys. Commun. 64(1991) 311; J. Crystal Growth 166(1996) 78; HABIT95, Quantum Chem. Program Exchange, Program no. 670, Bloomington, IN 47405, USA, 1996) for the four known crystal structures are presented. Comparison between these and exptl. data reveal the crystg. species to be consistent with the formation of C12H25OSO3-Na+·1/8H2O with a plate-like morphol. dominated by {200} and complemented by minor {110}, {202} and {111} forms. Kinetic roughening, which occurs at higher soln. supersaturations and notably on the {202} forms, is discussed in terms of the comparative surface chem. of the SDS habit faces.
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      Vanapalli, S. A.; Palanuwech, J.; Coupland, J. N. Stability of Emulsions to Dispersed Phase Crystallization: Effect of Oil Type, Dispersed Phase Volume Fraction, and Cooling Rate Colloids Surf., A 2002, 204, 227– 237 DOI: 10.1016/S0927-7757(01)01135-9
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      Stability of emulsions to dispersed phase crystallization: effect of oil type, dispersed phase volume fraction, and cooling rate
      Vanapalli, Siva A.; Palanuwech, Jirin; Coupland, John N.
      Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2002), 204 (1-3), 227-237CODEN: CPEAEH; ISSN:0927-7757. (Elsevier Science B.V.)
      Emulsified n-hexadecane or confectionery coating fat (CCF) were repeatedly thermally cycled (40 to -10-40°C at 1.5 °C/min) in a differential scanning calorimeter. There is a single exotherm on cooling each emulsion (at 0.5 and 5°C, resp.) corresponding to lipid crystn. by homogeneous nucleation. However, on subsequent cooling cycles, an increasing proportion of the CCF crystn. enthalpy occurs at a higher temp. (15°C) corresponding to crystn. of non-emulsified fat. (The net enthalpy of crystn. is const.). The second peak is taken to be due to destabilized fat and increases with no. of cycles and dispersed phase vol. fraction. All n-hexadecane emulsions are stable to freeze-thaw. When the CCF emulsions are cooled more rapidly (5°C/min) there is no destabilization. Micrographs are presented and used to argue that the destabilization is due to a collapse of partially coalesced structures on reheating.
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      Chaiyasat, P.; Suzuki, T.; Minami, H.; Okubo, M. Thermal Properties of Hexadecane Encapsulated in Poly(divinylbenzene) Particles J. Appl. Polym. Sci. 2009, 112, 3257– 3266 DOI: 10.1002/app.29648
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      Thermal properties of hexadecane encapsulated in poly(divinylbenzene) particles
      Chaiyasat, Preeyaporn; Suzuki, Toyoko; Minami, Hideto; Okubo, Masayoshi
      Journal of Applied Polymer Science (2009), 112 (6), 3257-3266CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      The thermal properties of n-hexadecane (HD) encapsulated in crosslinked capsule particles contg. a water and/or air domain were studied from the view-point of heat-storage applications. The capsule particles were prepd. by the microsuspension polymn. of divinylbenzene at 70° with the self-assembling of phase-sepd. polymer method that we developed. In the differential scanning calorimetric thermograms, pure HD had a single solidification temp. (Ts) peak at 15°, whereas the encapsulated HD contg. a water domain had two peaks at 6 and 1°. That is, the encapsulated HD contg. the water domain required a longer time and lower temp. to complete the solidification than pure HD, which was neg. for heat-storage applications. However, once the particles were dried and the water domain was replaced with air, the problem with the partially lowered Ts improved. The air domain was also found in the encapsulated HD core after solidification because of the shrinkage of HD. The presence of the air domain did not affect the thermal stability of the encapsulated HD.
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      Sasanuma, Y.; Hayashi, Y.; Matoba, H.; Touma, I.; Ohta, H.; Sawanobori, M.; Kaito, A. Conformational Analysis of Poly(propylene sulfide) Macromolecules 2002, 35, 8216– 8226 DOI: 10.1021/ma020730m
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      Song, C.-C.; Du, F.-S.; Li, Z.-C. Oxidation-Responsive Polymers for Biomedical Applications J. Mater. Chem. B 2014, 2, 3413– 3426 DOI: 10.1039/c3tb21725f
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      Song, Cheng-Cheng; Du, Fu-Sheng; Li, Zi-Chen
      Journal of Materials Chemistry B: Materials for Biology and Medicine (2014), 2 (22), 3413-3426CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
      A review. Reactive oxygen species (ROS) play key roles in many physiol. processes, such as cell signaling and host innate immunity. However, when they are overproduced, ROS may damage biomols. in vivo and cause diseases such as cardiovascular or neurodegenerative diseases, cancer, and so forth. Oxidative stress is usually implicated in various inflammatory tissues, representing an important target for the development of various therapeutic strategies. Therefore, various probes for the in vitro detection of ROS or the in vivo diagnosis of the oxidative stress-relevant diseases have been developed. Oxidn.-responsive polymers have also attracted great interest due to their potential applications in biomedical fields. In this feature article, we summarize six types of oxidn.-responsive polymers based on different oxidn.-responsive motifs. Poly(propylene sulfide)s, selenium-based polymers, aryl oxalate- and phenylboronic ester-contg. polymers are discussed in detail, while poly(thioketal)s and proline-contg. polymeric scaffolds are briefly introduced.
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      Huo, M.; Yuan, J.; Tao, L.; Wei, Y. Redox-Responsive Polymers for Drug Delivery: From Molecular Design to Applications Polym. Chem. 2014, 5, 1519– 1528 DOI: 10.1039/C3PY01192E
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      Redox-responsive polymers for drug delivery: from molecular design to applications
      Huo, Meng; Yuan, Jinying; Tao, Lei; Wei, Yen
      Polymer Chemistry (2014), 5 (5), 1519-1528CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      A review. Glutathione has been regarded as a significant signal for distinguishing between tumor and normal tissue. Recently, reactive oxygen species have attracted much attention for their close connection with many diseases. Taking advantage of the physiol. signals, redox-responsive polymeric drug carriers constitute a significant research area in the various stimuli-responsive polymers for biomedical applications. During the rapid development of redox-responsive polymers, mol. design and related synthetic methodol. plays a crucial role. In this review, we discuss the redn.- and oxidn.-responsive polymeric drug carriers from the view of functional groups, as well as their applications in controlled release.
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      Joshi-Barr, S.; de Gracia Lux, C.; Mahmoud, E.; Almutairi, A. Exploiting Oxidative Microenvironments in the Body as Triggers for Drug Delivery Systems Antioxid. Redox Signaling 2014, 21, 730– 754 DOI: 10.1089/ars.2013.5754
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      Exploiting Oxidative Microenvironments in the Body as Triggers for Drug Delivery Systems
      Joshi-Barr, Shivanjali; de Gracia Lux, Caroline; Mahmoud, Enas; Almutairi, Adah
      Antioxidants & Redox Signaling (2014), 21 (5), 730-754CODEN: ARSIF2; ISSN:1523-0864. (Mary Ann Liebert, Inc.)
      A review. Significance: Reactive oxygen species and reactive nitrogen species (ROS/RNS) play an important role in cell signaling pathways. However, the increased prodn. of these species may disrupt cellular homeostasis, giving rise to pathol. conditions. Biomaterials that are responsive to ROS/RNS can be strategically used to specifically release therapeutics and diagnostic agents to regions undergoing oxidative stress. Recent Advances: Many nanocarriers intended to exploit redox micro-environments as triggers for drug release, summarized and compared in this review, have recently been developed. We describe these carriers' chem. structures, strategies for payload protection and oxidn.-selective release, and ROS/RNS sensitivity as tested in initial studies. Crit. Issues: ROS/RNS are unstable, so reliable measures of their concns. in various conditions are scarce. Combined with the dearth of materials shown to respond to physiol. relevant levels of ROS/RNS, evaluations of their true sensitivity are difficult. Future Directions: Oxidn.-responsive nanocarriers developed thus far show tremendous potential for applicability in vivo; however, the sensitivity of these chemistries needs to be fine tuned to enable responses to physiol. levels of ROS and RNS. Antioxid. Redox Signal. 21, 730-754.
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    55. 55
      Jeanmaire, D.; Laliturai, J.; Almalik, A.; Carampin, P.; Richard, d. A.; Lallana, E.; Evans, R.; Winpenny, R. E. P.; Tirelli, N. Chemical Specificity in REDOX-Responsive Materials: The Diverse Effects of Different Reactive Oxygen Species (ROS) on Polysulfide Nanoparticles Polym. Chem. 2014, 5, 1393– 1404 DOI: 10.1039/c3py01475d
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      Chemical specificity in REDOX-responsive materials: the diverse effects of different Reactive Oxygen Species (ROS) on polysulfide nanoparticles
      Jeanmaire, Damien; Laliturai, Jureerat; Almalik, Abdulaziz; Carampin, Paolo; Richard d'Arcy; Lallana, Enrique; Evans, Robert; Winpenny, Richard E. P.; Tirelli, Nicola
      Polymer Chemistry (2014), 5 (4), 1393-1404CODEN: PCOHC2; ISSN:1759-9962. (Royal Society of Chemistry)
      REDOX responsive (nano)materials typically exhibit chem. changes in response to the presence and concn. of oxidants/reductants. Due to the complexity of biol. environments, it is crit. to ascertain whether the chem. response may depend on the chem. details of the stimulus, in addn. to its REDOX potential, and whether chem. different responses can det. a different overall performance of the material. Here, the authors used oxidn.-sensitive materials, although these considerations can be extended also to reducible ones. In particular, the authors used poly(propylene sulfide) (PPS) nanoparticles coated with a PEGylated emulsifier (Pluronic F127); inter alia, the authors here present also an improved preparative method. The nanoparticles were exposed to 2 Reactive O Species (ROS) typically encountered in inflammatory reactions, H2O2 (H2O2) and hypochlorite (ClO-); their response was evaluated with a variety of techniques, including diffusion NMR spectroscopy that allowed to sep. characterize the chem. different colloidal species produced. The 2 oxidants triggered a different chem. response: H2O2 converted sulfides to sulfoxides, while ClO- partially oxidized them further to sulfones. The different chem. correlated to a different material response: H2O2 increased the polarity of the nanoparticles, causing them to swell in H2O and to release the surface PEGylated emulsifier; the uncoated oxidized particles still exhibited very low toxicity. On the contrary, ClO- rapidly converted the nanoparticles into water-sol., depolymd. fragments with a significantly higher toxicity. The take-home message is that it is more correct to discuss smart materials in terms of an environmentally specific response to (REDOX) stimuli. Far from being a problem, this could open the way to more sophisticated and precisely targeted applications.
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    56. 56
      Rehor, A.; Tirelli, N.; Hubbell, J. A. A New Living Emulsion Polymerization Mechanism: Episulfide Anionic Polymerization Macromolecules 2002, 35, 8688– 8693 DOI: 10.1021/ma0211378
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      A New Living Emulsion Polymerization Mechanism: Episulfide Anionic Polymerization
      Rehor, A.; Tirelli, N.; Hubbell, J. A.
      Macromolecules (2002), 35 (23), 8688-8693CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      The anionic ring-opening polymn. of episulfides has been successfully applied in emulsion. The polymn. proceeded with a living mechanism but was characterized by a limiting conversion, presumably arising from the increase in viscosity in the polymer. To the knowledge of the authors, only two other cases of living anionic polymn. in emulsion are known (silicones and cyanoacrylates); the addnl. novelty presented by episulfides is the ease of end-functionalization. Furthermore, the emulsion polymn. allowed the prepn. of highly stable particles, which, due to their PEGylated surface and their appropriate diam., can be applied in the biomedical field as nanocarriers.
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    57. 57
      Rehor, A.; Hubbell, J. A.; Tirelli, N. Oxidation-Sensitive Polymeric Nanoparticles Langmuir 2005, 21 (1) 411– 417 DOI: 10.1021/la0478043
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      Oxidation-Sensitive Polymeric Nanoparticles
      Rehor, Annemie; Hubbell, Jeffrey A.; Tirelli, Nicola
      Langmuir (2005), 21 (1), 411-417CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      We have recently demonstrated the possible use of org. polysulfides for the design of oxidn.-sensitive colloidal carriers in the form of polymeric vesicles, which are particularly suitable for the encapsulation of hydrosol. drugs. In the present research we extend our efforts to carriers specifically suitable for hydrophobic mols. Exploiting the living emulsion polymn. of episulfides, we have produced new crosslinked polysulfide nanoparticles. Here we demonstrate how this process allows the prodn. of stable nanoparticles with a good control over their size and functionality. The nanoparticles showed negligible cytotoxicity on a fibroblast model; furthermore, they exhibited sensitivity to oxidative conditions, which first produce swelling and then solubilize the material.
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    58. 58
      Sokolovskaya, E.; Rahmani, S.; Misra, A. C.; Bräse, S.; Lahann, J. Dual-Stimuli-Responsive Microparticles ACS Appl. Mater. Interfaces 2015, 7, 9744– 9751 DOI: 10.1021/acsami.5b01592
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      58
      Dual-Stimuli-Responsive Microparticles
      Sokolovskaya, Ekaterina; Rahmani, Sahar; Misra, Asish C.; Braese, Stefan; Lahann, Joerg
      ACS Applied Materials & Interfaces (2015), 7 (18), 9744-9751CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The need for smart materials in the area of biotechnol. has fueled the development of numerous stimuli-responsive polymers. Many of these polymers are responsive to pH, light, temp., or oxidative stress, and yet very few are responsive toward multiple stimuli. Here we report on the synthesis of a novel dual-stimuli-responsive poly(ethylene glycol)-based polymer capable of changing its hydrophilic properties upon treatment with UV light (exogenous stimulus) and markers of oxidative stress (endogenous stimulus). From this polymer, smart microparticles and fibers were fabricated and their responses to either stimulus sep. and in conjunction were examd. Comparison of the degrdn. kinetics demonstrated that the polymer became water-sol. only after both oxidn. and irradn. with UV light, which resulted in selective degrdn. of the corresponding particles. Furthermore, in vitro expts. demonstrated successful uptake of these particles by Raw 264.7 cells. Such dual-stimuli-responsive particles could have potential applications in drug delivery, imaging, and tissue engineering.
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      Carampin, P.; Lallana, E.; Laliturai, J.; Carroccio, S. C.; Puglisi, C.; Tirelli, N. Oxidant-Dependent REDOX Responsiveness of Polysulfides Macromol. Chem. Phys. 2012, 213, 2052– 2061 DOI: 10.1002/macp.201200264
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      Oxidant-Dependent REDOX Responsiveness of Polysulfides
      Carampin, Paolo; Lallana, Enrique; Laliturai, Jureerat; Carroccio, Sabrina C.; Puglisi, Concetto; Tirelli, Nicola
      Macromolecular Chemistry and Physics (2012), 213 (19), 2052-2061CODEN: MCHPES; ISSN:1022-1352. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Poly(propylene sulfide) (PPS) is studied as an oxidn.-responsive macromol. building block, in the perspective of anti-inflammatory therapies. Here, we show that the nature of the oxidant has profound effects on the outcome of the oxidn. process. PPS was exposed to hydrogen peroxide (H2O2) and hypochlorite (OCl-), which are oxidizing species commonly encountered during inflammatory processes. It was found that the oxidn. with H2O2 converted thioethers into sulfoxides, producing water-sol. macromol. products with extremely low toxicity (L929 fibroblasts); on the contrary, the reaction with NaOCl produced sulfones in addn. to sulfoxides, and this was accompanied by depolymn., which appears to considerably affect the toxicity of the oxidn. products.
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    The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b02512.

    • Thiol–ene polymerization mechanism (Scheme S1), RT-FTNIR setup (Scheme S2), size reproducibility data (Table S1), fitted polymerization kinetics (Figure S1), 1H NMR spectrum of P1 (Figure S2), SEC traces of P1 synthesized by miniemulsion (M1), solution (S1), and bulk (B1) (Figure S3), effect of irradiance, PI, and Cmonomer on reaction kinetics (Figure S4), small-angle XRD pattern (Figure S5), DSC thermogram (Figure S6), POM images upon heating (Figure S7), degradation experiments of P2 latex (Figure S8) (PDF)


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