Peculiar Behavior of Methyl Methacrylate Emulsion Polymerization-Induced Self-Assembly Mediated by RAFT Using...

Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of methyl methacrylate (MMA) is successfully performed in water in the presence of a poly(methacrylic acid) (PMAA) macromolecular chain transfer agent (macroCTA) leading to the formation of self-stabilized PMAA-b-PMMA amphiphilic block copolymer particles. At pH 3.7, the reactions are well-controlled with narrow molar mass distributions. Increasing the initial pH, particularly above 5.6, results in a partial loss of reactivity of the PMAA macroCTA. The effect of the degree of polymerization (DP_n) of the PMMA block, the solids content, the nature of the hydrophobic segment, and the pH on the morphology of the obtained diblock copolymer particles is then investigated. Worm-like micelles are formed for a DP_n of PMMA of 20 (PMMA₂₀), while "onion-like" particles and spherical vesicles are obtained for PMMA₃₀ and PMMA₅₀, respectively. In contrast, spherical particles are obtained for the DP_ns higher than 150. This unusual evolution of particle morphologies upon increasing the DP_n of the PMMA block seems to be related to hydrogen bonds between hydrophilic MAA and hydrophobic MMA units.