FREE-RADICAL POLYMERIZATION IN MICELLAR MEDIA - EFFECT OF MICROENVIRONMENT

A micellar polymerization process has been used to prepare polyacrylam ide or poly(acrylic acid) hydrophobically modified with low amounts (1 -5 mol%) of an N-alkyl- or N-alkylarylacrylamide. The effect of the in itial monomer segregation on the copolymer microstructure and the copo lymerization mechanism has been investigated. This method leads genera lly to multiblock copolymers in which the number and length of the hyd rophobic blocks vary with the initial number of hydrophobes per micell e. Interestingly, the copolymerization of acrylamide with disubstitute d acrylamides leads to homogeneous samples with an average copolymer c omposition independent of the degree of conversion, in contrast to wha t is observed with monosubstituted acrylamides for which a drift in co mposition is observed. The difference in polarity between the bulk pha se and the micellar phase is responsible for this behavior. This micro environment effect modifies the reactivity ratios of those hydrophobes capable of forming hydrogen bonds, whereas the reactivity of the othe r hydrophobes remains unaffected.