An electron microscope study of the microstructure of some rubber-reinforced polystyrenes

Rubber-reinforced polystyrenes were prepared by graft copolymerization using various butadiene polymers and copolymers. Electron microscopy showed that variations in the pre-polymerization temperature, composition of the rubber, and molecular weight of the rubber influenced the size and structure of the dispersed rubber particles. Microstructures and impact strengths comparable to those of commercial materials were obtained from a limited range of conditions. Solution styrene-butadiene copolymers and a polybutadiene of low molecular weight gave unusual microstructures although polystyrenes of inferior impact strength were obtained. A particle size of 2 μm or greater was required to obtain reasonable improvements in impact strength. The particle size increased with an increase in the initial viscosity of the rubber in styrene solution provided that rubber type and concentration, and pre-polymerization temperature were constant. The effects of these three variables on particle size could not be related to viscosity changes.