Dynamic mechanical properties, structure, and composition of impact polystyrene

Two series of impact polystyrene were studied; they had been obtained by grafting and by mechanical mixing, at two different known polybutadiene levels. Their biphasic structure had been characterized by optical microscopy and physicochemical separation. The following factors were investigated: morphology and content of the dispersed phase and continuous phase, composition of the dispersed phase, and molecular weight of the continuous phase. The elastic shear modulus and mechanical damping were measured. It was found that the elastic shear modulus of the two series of materials does not depend on the total polybutadiene content, as is often suggested in the literature, but on the rubbery dispersed phase content. The polybutadiene concentration of this phase, although varying between 100% for the mechanical mixes and 34% for one of the grafted polymers, does not influence the mentioned correlation. The particle size of the dispersed phase and the molecular weight the continuous phase have very little or no influence. The found correlation agrees with the theories for the moduli of models consisting of dispersions of spheres or particles in a matrix, like those of Kerner,13 Hashin,14,15 and Mackenzie.18