Factors influencing the impact strength of high impact polystyrene

The relationship between synthesis factors and the impact resistance of high impact polystyrene (HIPS) is investigated in the light of its morphology and dynamic mechanical properties. A decrease in polymerization temperature results in an increase in T g , melt viscosity and molecular weight of the continuous polystyrene phase as characterized by gel permeation chromatography. The separated, occluded polystyrene phase however shows an invariant T g suggesting that the grafting and/or crosslinking effect overweighs the molecular weight effect. The observed high impact strength has been correlated with the homogeneous 1‐2 μ rubber particle size distribution, a comparatively sharp rubber T g transition at lower temperature, and a much lower occluded polystyrene content in the dispersed phase.