UCST AND LCST BEHAVIOR IN POLYMER BLENDS CONTAINING POLY(METHYL METHACRYLATE-STAT-STYRENE)

Miscibility behaviour was investigated for the blends of homopolymer A with the random copolymer consisting of two components B and C, where the A homopolymer is miscible with homopolymer B but immiscible with homopolymer C. The copolymer employed was poly(methyl methacrylate-sta t-styrene) (MMA.S), and the homopolymers were polystyrene (PS), poly(v inyl methyl ether) (PVME), and poly(ethylene oxide) (PEG) or poly(ethy lene glycol) (PEG), where PS is immiscible with MMA homopolymer, PVME is miscible with S but immiscible with MMA, and PEO or PEG is miscible with MMA but immiscible with S. UCST-type miscibility was observed fo r the PEO/MMA.S blends though the homopolymer blends PEO/PMMA had been reported to be of LCST-type. UCST-type miscibility was found for PS/M MA.S as well. On the other hand, PVME/MMA.S showed LCST-type miscibili ty with miscibility window-like behaviour. Such contrasting miscibilit y behaviour, i.e. appearances of UCST and LCST, for a series of MMA.S copolymer blends was discussed on the basis of the Flory-Patterson fre e volume theory. As a result, it was suggested that contribution of th e free volume term decreases for PEO/MMA.S (UCST type), increases for PVME/MMA.S (LCST type) and is little changed for PS/MMA.S (UCST type), compared with that for the respective miscible component pairs, PEO/M MA, PVME/S and PS/S. Furthermore, the Flory-Huggins chi parameters bet ween different components were estimated as a temperature-dependent fu nction from dependence of miscibility on the copolymer composition in these blends. In this estimation, the chi parameters determined for PV ME/PS and PEO/PMMA by Han et al. and Ito et al., respectively, using n eutron scattering technique were used as a standard. The miscible/immi scible boundaries drawn using the X parameters obtained reproduced wel l the experimental results of the dependence of miscibility on the mol ecular weight as well as on the copolymer composition. Thus, it was sh own that the X parameters for immiscible pairs such as PS/PMMA, PEO/PS and PVME/PMMA can be evaluated by use of the blend type A/B.C dealt w ith here. (C) 1997 Elsevier Science Ltd.