Amphiphilic gradient poly(styrene-co-acrylic acid) copolymer prepared via nitroxide-mediated solution polymerization.Synthesis,characterization in aqueous solution and evaluation as emulsion polymerization stabilizer

摘要

A well-defined,amphiphilic poly(styrene-co-acrylic acid) copolymer was synthesized in a single step by nitroxide-mediated controlled free-radical copolymerization of styrene and acrylic acid,without protection of the acid groups:M_n=6500 g mol~(-1),M_w/M_n= 1.5 and a composition of F_(AA)=0.70+-0.03 in acrylic acid.In addition to the good control over molar mass and molar mass distribution,the copolymer exhibited a narrow composition distribution with a slight gradient.Such copolymer was an efficient stabilizer for the emulsion polymerizations of styrene and of mixtures of methyl methacrylate and n-butyl acrylate,until 45 wt% solids.A low amount (typically 3-4 wt % based on the monomer(s)) was needed for a good stabilization.This is approximately a decade lower than the required amount of random,amphiphilic copolymers prepared via conventional free-radical polymerization.The performances were,however,below those of analogous diblock copolymers,but the great advantage is the very easy synthetic procedure.