Emulsion iodine transfer polymerization of nearly uniform submicrometer-sized polystyrene particles

Emulsifier-free emulsion iodine transfer polymerization (emulsion ITP) of styrene was carried out using unpurified and purified poly(methacrylic acid)-iodine (PMAA-I). PMAA-I was previously synthesized by solution ITP in dioxane. The solution ITP of methacrylic acid was completed at 40 degrees C for 24 h. Unexpectedly, 64% of added CHI3 remained in dioxane even after the polymerization. The emulsion ITP was carried out at pH similar to 9 with unpurified or purified PMAA-I. The number-average diameter (d(n)) of the polymer particles obtained using purified PMAA-I (148 nm at 93% conversion) was much smaller than that using unpurified PMAA-I (710 nm at 68% conversion). In both cases, in the early stage of the polymerization, polystyrene (PS) particles stabilized by some PMAA-b-PS copolymer chains were formed. This indicates that PMAA-I worked not only as a macro chain transfer agent but also as a colloidal stabilizer. In the unpurified system, the remaining CHI3 also operated as a chain transfer agent. It resulted in PS-I homopolymers having controlled molecular weight in the PS particles. On the other hand, many high molecular weight PS homopolymers were formed in the purified system by emulsion conventional radical polymerization in the PS particles. To depress emulsion conventional radical polymerization, the CHI3 was post-added after 90 min. Nearly uniform submicrometer-sized (82 nm) PS particles with narrow molecular weight distribution (M-w/M-n = 1.24) were achieved. These polymerization behaviors were reasonably explained from the results obtained by gel permeation chromatography and diffusion ordered spectroscopy (NMR)-N-1. (c) 2021 Society of Industrial Chemistry.