Synthesis and Characterization of High Impact Polystyrene from a Heterogeneous Styrene‐Rubber‐Polystyrene Solution: Influence of PS Concentration on the Phase Inversion, Morphology and Impact Strength

Abstract

AbstractHigh Impact Polystyrene (HIPS) was synthesized by free radical polymerization through the bulk‐bulk technique. Polybutadiene (PB) and/or poly(butadiene‐b‐styrene) copolymer (S:B = 30:70) (at 8 wt‐%) were used as impact modifiers in the presence of 0, 5 and 7.5 wt‐% of polystyrene (PS) and styrene monomer. The interval of phase inversion (PI) was determined through the evolution of melt flow index (MFI) and transmission electron microscopy (TEM), the conversion (X) and grafting degree (GD) were gravimetrically determined and impact strength (IS) tests were performed. When PS was added from the beginning of the reaction in the presence of SB rubber, the PI shifted to lower values of polymerization time (from 270 min in the reference HIPS to 190 min when 5 and 7.5 wt‐% of PS was added, respectively). The morphology of the reference HIPS was of the core shell type and in the case of adding PS the morphology at the PI changed to a quasi‐salami type, due to a poor stability of the system as a consequence of the low GD. The final size of the disperse phase increased 292 and 51% in the presence of PS and the volume fraction increased 100% yielding HIPS with an IS from 20 (reference HIPS) to 30J/m for 7.5 wt‐% of added PS.In the system with PB as the precursor rubber the salami structure in the reference HIPS, increased its size from 0.5 µm to 2.1 and 2.6 µm for 5 and 7.5 wt‐% of added PS, but instead of that, the IS remained without significant changes.