BLENDS AND THERMOPLASTIC INTERPENETRATING POLYMER NETWORKS OF POLYPROPYLENE AND OCK-POLY(ETHYLENE-STAT-BUTYLENE)-BLOCK-POLYSTYRENE TRIBLOCKCOPOLYMER .1. MORPHOLOGY AND STRUCTURE-RELATED PROPERTIES

Blends of polypropylene (PP), the triblock copolymer ock-poly(ethylene -stat-butylene)-block-polystyrene (SEBS), and processing oil were foun d to form thermoplastic interpenetrating polymer network (IPN) structu res in a composition range from about 10 to 55% by weight polypropylen e. The IPN structure was confirmed by electron microscopy and by solve nt extraction. At high elongations, the cocontinuous blends showed a s tress-strain behavior similar to rubber and no signs of the typical ne cking phenomenon normally associated with polypropylene at large defor mations. The processing oil used to improve the processing properties of SEBS was found to partly dissolve in the polypropylene phase, causi ng a marked lowering of the polypropylene glass-transition temperature . The distribution coef ficient for oil between polypropylene and SEBS was estimated to be 0.35. While the degree of crystallinity of polypr opylene did not vary with blend composition, the melting temperature d ecreased from 162.7 degrees C in the pure polypropylene to 149.3 degre es C in the blend with lowest polypropylene content. The large melting point depression suggests that polypropylene, the EB fraction of SEBS , and the oil may form a homogeneous melt phase. This probably explain s the formation of an IPN structure on cooling.