Visible-Light Initiated Dispersion Photopolymerization of Styrene

Polystyrene (PS) particles were synthesized in ethanol/water mixture by dispersion polymerization using visible light irradiation, with either a N-heterocyclic carbene borane-based photoinitiating system (PIS) or a disulfide. With the full PIS and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as stabilizer, the size distributions were broad and the amount of PEGMA had a strong impact on the experiment reproducibility. The addition of a base solved the problem, leading to faster polymerizations, narrower size distributions and larger particles. With the disulfide as sole PIS, bigger and narrowly distributed PS particles were again formed. Quantitative conversion was achieved in each system, with particle size ranging between 100 and 350 nm. The use of poly(N-vinylpyrrolidone) as stabilizer led to significantly larger particles, up to 1.2 mu m, with narrow size distributions. The production of such large latex particles by photoinitiated polymerizations is unprecedented. Styrene can be photopolymerized in dispersion using visible light and an optimized photo-initiating system, overcoming light scattering by the growing objects. Stable latexes with particle diameters up to 1.2 mu m were obtained using poly(N-vinylpyrrolidone) as stabilizer. This represents a fourfold increase in the largest particle size ever reached by a photochemical process in a dispersed medium.image