Iodine-influenced morphological evolution of micrometer-sized poly(methyl methacrylate)-block-poly(vinyl acetate) particles upon hydrolysis

Abstract

Iodine transfer polymerization was used to synthesize micrometer-sized block copolymer particles using two hydrophilic monomers, methyl methacrylate (MMA) and vinyl acetate (VAc) in a microsuspension system as the first attempt. Micrometer-sized poly(methyl methacrylate)-block-poly(vinyl acetate) (PMMA-b-PVAc) particles were obtained with a desired molecular weight (M_n) and relatively narrow molecular weight distribution (M_w/M_n = 1.33–1.60) despite a low degree of polymerization of the PVAc block (DP_VAc < 20). Notably, the hydrolysis of micrometer-sized PMMA-b-PVAc particles was conducted to explore the morphological evolution of the particles. Three morphologies were acquired after hydrolysis depending on the degree of polymerization ratios of PVAc to PMMA (DP_VAc/DP_MMA): spherical particles with hollows in the particle, multipods with hollows, and spherical particles with hollows near the surface. The formation mechanism of each morphology was proposed. We found that the cooperation of iodic ions generated from the degradation of iodine end groups, and relatively elongated poly(vinyl alcohol) (PVA) segments derived from PVAc is the key to influencing particle morphology at different DP_VAc/DP_MMA.