Effects of properties of the surface layer of seed particles on the formation of golf ball-like polymer particles by seeded dispersion polymerization

Micrometer-sized, monodisperse polystyrene (PS)/poly(styrene-co-sodium styrene sulfonate) (P(S-NaSS))/poly(n-butyl methacrylate) (Pn-BMA) composite particles having a ‘golf ball-like’ shape were prepared by seeded dispersion polymerization of n-butyl methacrylate with PS-core/P(S-NaSS)-shell seed particles with various shell thicknesses in the presence of dodecane droplets in a methanol/water (80/20, w/w) medium, followed by evaporation of the dodecane. The effects of the hydrophilic P(S-NaSS)-shell properties of seed particles on the formation of golf ball-like particles were investigated on the basis of thermodynamic and kinetic considerations. The dimples at the surface formed by the volume reduction of Pn-BMA/dodecane domains were deep when PS/P(S-NaSS) seed particles, the hydrophilic shell of which was thick, were used, whereas PS/P(S-NaSS)/Pn-BMA composite particles, the P(S-NaSS) hydrophilic shell of which was thin, exhibited a polyhedral shape. This is attributed to the fact that the molecular weight of the shell moiety comprising P(S-NaSS) was reduced by lowering the monomer concentration to decrease shell thickness, which seems to result in an increase in the mobility of Pn-BMA/dodecane domains at the particle surface. On the basis of this finding, when the molecular weight of the shell moiety of the seed particle was increased, golf ball-like particles were formed, even if the shell thickness of seed particles was thin. Polymer Journal (2010) 42, 66–71; doi:10.1038/pj.2009.313