On the Influence of the Initial Stages of Styrene Copolymerization with Polybutadiene on High Impact Polystyrene Morphology

As has already been mentioned in previous publications, one of the main factors influencing the industrial properties of high impact polystyrene (HIPS) is the morphology of this composite material i.e. the rubber volume fraction (Vf) and mean size of dispersed particles (c). For instance, references 1 and 2 deal with the correlation between rubber phase volume and strength properties of HIPS. The conclusion was made that impact resistance is increased with the growth of Vf, whereas the tensile strength decreases. One should bear in mind that the increase in volume in mechanical mixtures may only be possible at the expense of introducing additional polybutadiene (PBD). In copolymerization the same effect is achieved due to polystyrene occlusions. Introducing free and graft polystyrene (PS) into rubber particles proves to have the same toughening effect (3-5). That is why so much attention is paid to studying the influence of graft copolymer on formation of HIPS morphology. As had previously been pointed out by us, a role is given to copolymer which was formed at the initial stages of the process. The growth in the number of graft branches at this period leads not only to better dispersion of the rubber (6), but also stimulates the appearance of occlusions and in this way promotes an increase in rubber phase volume.