Morphology−Interface−Property Relationships in Polystyrene/Ethylene−Propylene Rubber Blends. 1. Influence of Triblock Copolymer Interfacial Modifiers

Interfacial agents are often used to compatibilize immiscible polymer blends. They are known to reduce the interfacial tension, homogenize the morphology, and improve adhesion between phases. In this study, two triblock copolymers of styrene/ethylene−butylene/styrene (SEBS), of different molecular weights, were used to compatibilize a blend of 80 vol % polystyrene (PS) and 20% ethylene−propylene rubber (EPR). The emulsification curve, which relates the average minor phase particle diameter to the concentration of interfacial agent added, was used to quantify the effect of the interfacial agents on the blend morphology. Charpy and Izod impact tests were performed to determine the effect of the compatibilization on mechanical properties of the blend and to establish links between morphology, interface, and properties. Results suggest that for the lower molecular weight interfacial agent, a transition in fracture mechanisms, from fragile to ductile, occurs around 20% interfacial agent (based on the volume of the minor phase). This transition, however, is not observed with the high molecular weight interfacial agent.