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International audienc

Summary: Iodine transfer polymerization of vinyl acetate in aqueous miniemulsion, initiated by UV radiation in the presence of an α,ω‐diiodo‐poly(dimethylsiloxane) macrophotoiniferter has been performed. The formation of a triblock copolymer latex PVAc‐b‐PDMS‐b‐PVAc has been evidenced by 1H‐NMR and size exclusion chromatography. The size of the PDMS and PVAc blocks were modulated thus opening the way to a wide range of copolymers with different properties. A detailed study of the reaction mechanism showed the importance of the aqueous dispersed medium to achieve a controlled polymerization.

The first synthesis of poly(styrene)-b-poly(dimethylsiloxane)-b-poly(styrene) triblock copolymer in miniemulsion has been achieved by controlled/living radical polymerization of styrene using a modified hydroxypropyl terminated poly(dimethylsiloxane) as a transfer agent for iodine transfer polymerization. First an R,ω-hydroxypropyl poly(dimethylsiloxane) was modified by esterification with 2-bromopropionic acid. The second step consisted in a nucleophilic substitution of bromine by iodine through the reaction with sodium iodide in acetone. Then, miniemulsion polymerization of styrene was performed in the presence of sodium dodecyl sulfate as surfactant, 2,2′-azobis(isobutyronitrile) as radical initiator, and the R,ω-diiodopoly(dimethylsiloxane) as both the hydrophobe and the macrotransfer agent. Stable white latexes were obtained with a good correlation between theoretical and experimental molecular weights. Considering the process and the polymerization type, rather low polydispersity indexes (around 1.7) were reached. A kinetic study showed an increase of the molecular weight with conversion. Last, a chain extension led to a shift of the molecular weight distribution giving evidence for the living character of the triblock copolymers.

Supramolecular zwitterionic silicones are synthesized by aza‐Michael reaction between acrylic acid and amine‐functional polydimethylsiloxanes. The in‐depth characterization of this chemistry, applied for the first time to silicones, is investigated first with model alkylamines (hexylamine, 2‐ethylhexylamine and N‐propylethylenediamine), a model oligosiloxane (3‐aminopropylmethyl bis(trimethylsiloxy)silane), and finally various amino‐polysiloxanes. It is shown that after a first acid–base reaction resulting in ionic pairing, aza‐Michael addition proceeds smoothly in mild conditions (50 °C, 1‐week reaction). Both monoadducts and di‐adducts, together with residual amine, are observed by NMR. The supramolecular assembly of the thus‐created zwitterionic moieties is highlighted by a concomitant increase in viscosity and phase separation, as observed by transmission electron microscopy, bringing an additional glass transition at –40 °C assigned to highly polar ionic clusters. Below the stoichiometry in acrylic acid, all zwitterionic silicones follow the same classical behavior of nonentangled polymers according to the Rouse model, whereas upon introducing an excess of acrylic acid to amino groups, an enhancement of the elasticity is observed. Finally, silicone elastomers with solid‐like behavior and elastomeric mechanical properties are obtained using a high molar mass polymer bearing bifunctional N‐(2‐aminoethyl)‐3‐aminopropyl units that favor a high degree of physical crosslinking.

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The Lewis acid B(C(6) F(5) )(3) in combination with hydrosilanes exhibits remarkable activity in the oligomerization of sulfone- and phosphonate-based monomers. This process opens new routes to high-tech silicone-based materials, i.e., thermoplastic elastomers and heat-resistant polysiloxanes.

International audienceThe synthesis of P(VA-co-VAc)-graft-PDMS copolymers has been achieved in microsuspension by direct reaction between an epoxy-terminated PDMS and some pendant alcohol groups in P(VA-co-VAc). In this synthesis, the copolymer is used both as dispersant and reactant. The hydrophilic/hydrophobic character of the final material can be varied at will by incorporating various contents of epoxy-functionalized PDMS through optimized reaction conditions. The final composition was determined by TGA and 1H NMR. Products prepared from monofunctional PDMS were easily redispersed in water whereas a film of crosslinked materials, arising from difunctional PDMS, showed the best waterproofing as shown by contact angle analysis