Structure–Property Relationships of High‐Gloss High‐Impact Polystyrene Prepared by Bulk Polymerization

ABSTRACT

This study developed high‐impact polystyrene (HIPS) via bulk polymerization with high gloss and high elongation at break and systematically investigated the effects of rubber content and composition, chain transfer agent (CTA) concentration, and initiator system on its mechanical, morphological, rheological, and structural properties. At a 565T polybutadiene (PB) rubber content of 6 wt%, the impact strength reached 79.0 J/m, accompanied by an appropriate rubber‐particle size and interfacial structure. At a PB rubber 565T/A55AE ratio of 50:50 and an overall PB content of 6 wt%, the impact strength and elongation at break increased to 116.2 J/m and 62.5%, respectively, while the gloss remained at 98.4 GU. The corresponding number‐average and weight‐average molar masses ( M _n and M _w ) of the soluble PS fraction were 83,158 and 211,130 g/mol, respectively, while the grafting degree, defined as the mass of grafted PS relative to the initial rubber mass, reached 116.75%. Further investigation showed that 0.02 wt% CTA and the monofunctional initiator system provided a favorable combination of relatively high molar mass, stable interfacial grafting, and an appropriate rubber‐particle‐size distribution under the conditions investigated. In contrast, the multifunctional initiator systems maintained relatively high impact strength but markedly reduced elongation at break. These results demonstrate that the simultaneous achievement of high gloss and high elongation at break in HIPS depends on the synergistic balance among the molar mass of the continuous PS phase, rubber‐particle size, gel/grafted structure, and interfacial morphology.