THERMAL-PROPERTIES OF POLY(ETHYLENE OXIDE)-POLY(METHYL METHACRYLATE) BLENDS AND COPOLYMERS COMPLEXED WITH SODIUM THIOCYANATE

The phase behaviour of poly(ethylene oxide) (PEG) and poly(methyl meth acrylate) (PMMA) blends, a partially miscible system, and of PEO/PMMA block copolymers, all cast from acetonitrile, were determined in the p resence of added NaSCN. The phase behaviour is dominated by the added salt, which forms an insoluble P(EO(3).NaSCN) complex and induces sepa ration of PEO and PMMA in homopolymer blends. In block copolymers the PEG was either complexed with NaSCN or miscible with the PMMA block. E ssentially the same phase diagram applies to the homopolymer blends an d PEG-rich copolymer with added NaSCN and is identical to that previou sly found for mixtures of PEO and NaSCN cast from methanol. For the PM MA-rich copolymer the phase diagram is similar except that there is no evidence of PEG crystallinity, which is replaced by a miscible PEO/PM MA phase. Block copolymers in the presence of added salt were found to exhibit an additional endotherm (similar to 280 degrees C) which is a ttributed to a disorganization of the microphase-separated system at t emperature above the melting point of the complex and is associated wi th a liquid-liquid phase separation. This process was found to be irre versible on cooling from the melt. (C) 1997 Elsevier Science Ltd.