Peculiar Behavior of Methyl Methacrylate Emulsion Polymerization‐Induced Self‐Assembly Mediated by RAFT Using Poly(Methacrylic Acid) Macromolecular Chain Transfer Agent

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 (PMMA 20 ), while “onion‐like” particles and spherical vesicles are obtained for PMMA 30 and PMMA 50 , respectively. In contrast, spherical particles are obtained for the DP n s 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.