Synthesis of Poly(styrene)-b-poly(dimethylsiloxane)-b-poly(styrene) Triblock Copolymers by Iodine Transfer Polymerization in Miniemulsion

Abstract

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 α,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 α,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.