Influence of Styrene-B-Butadiene Copolymer Types on Phase Morphology and Polymer Partitioning Between Demixed-Macrophases from Hips-Mimicking Unstable Blends

The effect of the copolymer type on stability, morphology and polymer partitioning between macrophases of high impact polystyrene (HIPS) mimicking-blends is studied. Two styrene-butadiene block copolymers with similar chemical composition and different molar masses and architectures were used to emulate different numbers of polystyrene (PS) branches like the graft copolymer formed in the synthesis of HIPS. Polymer partitioning was determined for the first time for three phases demixed from solution four-component blends and was correlated with the phase morphologies. The tapered diblock (emulating one grafted PS branch) had a higher affinity for PS- and polybutadiene (PB)-rich phases than the star copolymer (emulating 1 to 4 grafted PS branches). Polymer partitioning varied with the copolymer architecture more significantly at high simulated styrene grafting efficiency when a three-phase-demixing occurred. Regarding phase morphologies, it is highlighted that the greater miscibility of the PS in the styrenic domains of the tapered diblock compared to the star copolymer caused a change of the morphology of the diblock from a lamellar to a disordered structure. © 2021, The Polymer Society, Taipei.