POLY(STYRENE-G-ETHYLENE OXIDE) COPOLYMERS AS INTERFACIAL AGENTS IN IMMISCIBLE POLYMER BLENDS

A poly(styrene-g-ethylene oxide) copolymer with an average of 100 styr ene units between the graft points is studied with respect to its inte rfacial activity in binary incompatible mixtures of polymers having di fferent degrees of miscibility toward the graft copolymer components. The interfacial properties were studied by scanning electron microscop y, dynamic mechanical spectroscopy, and differential scanning calorime try. The data obtained are compared with previously published data fro m a graft copolymer with the same composition but with shorter PEO bra nches and only 20 styrene units between them. In spite of their struct ure, the two graft copolymers could reduce the size of the dispersed p hase in the case of athermal mixing. With a negative heat of mixing be tween only one graft component and the blend, the short branch graft h ad no effect, while the longer branch graft caused a reduction of the size of the dispersed phase. With a negative heat of mixing for the gr aft branches as well as for the backbone a strong compatibilizing effe ct was found for both types of graft copolymers. The results show that even very short parts of the backbone of a graft copolymer can contri bute to compatibilization in a polymer blend, especially when the back bone has a negative heat of mixing with one of the blend components.