Styrene/potassium persulfate/water systems: effects of hydrophilic comonomers and solvent additives on the nucleation mechanism and the particle size

Emulsifier-free emulsion polymerizations based on styrene/potassium persulfate/water (St/kps/H2O) in the presence of a relatively hydrophilic comonomer, such as vinyl acetate (VAc) or methyl methacrylate (MMA), or the nonpolar solvent, such as ethyl acetate (EAc) or methyl isobutyrate (MIB) having structural similarity with VAc and MMA respectively, or the polar solvent such as glycerin or acetone etc., have been carried out. From the gel permeation chromatograph (GPC) analysis of polymers obtained in the presence of VAc or MMA comonomer, or even MIB or EAc nonpolar solvent, the presence of oligomers having the molecule weight of 1000 at the early stage of polymerization suggests a micellar nucleation mechanism. From the study for effects of additives on the rate of polymerization, we found that all curves for the conversion versus time showed concave upward at about the conversion of 45% but level off at about 80%. Moreover, when the polar or nonpolar solvent was used as an additive, a controllable particle size of monodisperse microspheres with the ranges 270–750 nm could be expected. Besides, the particle size of monodisperse microspheres was decreased with increasing of the addition amount of the polar solvent. Monosize polystyrene microspheres with smaller particle sizes can be obtained by adding of the polar solvent; on contrary, microspheres with larger particle sizes can be generated by a limited addition amount of the nonpolar solvent.