CAN RANDOM COPOLYMERS SERVE AS EFFECTIVE POLYMERIC COMPATIBILIZERS

We investigate the compatibilizing performance of a random copolymer i n the melt state, using transmission electron microscopy. Blends of po lystyrene (PS) and poly(methyl methacrylate) (PMMA) are chosen as a mo del system, and a random copolymer of styrene and methyl methacrylate (SMMA) with 70 wt % styrene is used as a compatibilizer. From TEM phot ographs it is clear that SMMA moves to the interface between PS and PM MA domains during melt mixing, and forms encapsulating layers. However , the characteristic size of the dispersed phase increases gradually w ith annealing time for all blend systems studied. This demonstrates th at the encapsulating layer of SMMA does not provide stability against static coalescence, which calls into question the effectiveness of ran dom copolymers as practical compatibilizers. We interpret the encapsul ation by random copolymers in terms of a simple model for ternary poly mer blends. (C) 1997 John Wiley & Sons, Inc.