Synthesis of micrometer-sized poly(vinyl acetate) particles through microsuspension iodine transfer polymerization: effect of iodine species in a water medium

Abstract

Microsuspension iodine transfer polymerization (ms ITP) of vinyl acetate (VAc) was demonstrated for the first time with simulation of the polymerization rate in the aqueous phase (R^w_p). The high polymerization temperature induced the degradation of poly(vinyl acetate) with an iodine end group (PVAc-I) and the formation of a crosslinking structure, which was worsened by the presence of the dispersant—poly(vinyl alcohol) (PVA) used in this work. Furthermore, the increase in the molecular weight distribution (M_w/M_n) with the monomer conversion was attributed to PVAc-I degradation and iodine hydrolysis. Upon considering the effect of iodine species, the mechanism of ITP in an aqueous system was further clarified. The micrometer-sized particles consisting of well-defined poly(vinyl acetate) (PVAc) were finally achieved by performing the ms ITP using iodoform (CHI₃) as the chain transfer agent and 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as the initiator at a low polymerization temperature of 30 °C, where the particle size was 22.3 μm and the molecular weight (M_n = 26 000, M_n,th = 26 900) was effectively controlled. The prepared PVAc was further successfully hydrolyzed into PVA with a desired molecular weight and narrow molecular weight distribution.