Reactive processing of syndiotactic polystyrene with an epoxy/amine solvent system

Syndiotactic polystyrene (sPS) is a new semi-crystalline thermoplastic which is believed to fill the price-performance gap between engineering and commodity plastics. In order to reduce the high processing temperature of sPS (>290°C), an epoxy-amine model system was used as a reactive solvent. Such a processing aid can be used to achieve a 50 to 500 fold lowering of the melt viscosity. When initially homogeneous solutions of sPS in a stoechiometric epoxy-amine mixture are thermally cured, Reaction Induced Phase Separation (RIPS) takes place, leading to phase separated thermoplastic-thermoset polymer blends. We focus our study on low (wt% sPS < 20%) and high concentration blends (wt% sPS > 60%) prepared by two processing techniques (mechanical stirring in a laboratory reactor or internal mixer/ reactive extrusion respectively). These blends have different potential interests. Low concentration blends (sPS domains in an epoxy-amine matrix) are prepared to create new, tunable blend morphologies by choosing the nature of the phase separation process, i.e. either crystallisation followed by polymerization or polymerization followed crystallisation. High concentration blends (sPS matrix containing dispersed epoxy-amine particles after RIPS) are prepared to facilitate the extrusion of sPS. In this case, the epoxy amine model system served as a reactive solvent. The time to the onset of RIPS is in the order of 7-9 min for low concentration blends, while it increases to 20-45 min for high concentration samples, as the reaction rates are substantially slowed down due to lower epoxy and amine concentrations. During the curing reaction the melting temperature of sPS in the reactive solvent mixture evolves back from a depressed value to the level of pure sPS. This indicates a change in the composition of the sPS phase, caused by (complete) phase separation upon reaction. We conclude that our epoxy amine system is suited for reactive processing of sPS, where final properties depend strongly on composition and processing conditions.