POLY(STYRENE-B-METHYL METHACRYLATE) BLOCK COPOLYMERS AS COMPATIBILIZING AGENTS IN BLENDS OF POLY(STYRENE-CO-ACRYLONITRILE) AND POLY(2,6-DIMETHYL-1,4-PHENYLENE ETHER) .2. INFLUENCE OF CONCENTRATION AND MOLECULAR-WEIGHT OF SYMMETRICAL BLOCK COPOLYMERS

The influence of the molecular weight of the symmetric block copolymer poly(styrene-b-methyl methacrylate) (P(S-b-MMA)) in blends with high- molecular-weight poly(styrene-co-acrylonitrile) (PSAN) and poly(2,6-di methyl-1,4-phenylene ether) (PPE) is investigated by dynamic mechanica l analysis and transmission electron microscopy. Total molecular weigh ts of the block copolymers vary from 16 up to 275 kg mol Independent o f molecular weight, all block copolymers locate to the interface with strong dispersing efficiency. The different block copolymers also show ed approximately the same emulsifying efficiency. The degree of segmen tal mixing of the blocks with the respective phases is evaluated from the glass transition behaviour. A qualitative model is developed to re late the observed glass transition behaviour to the segmental distribu tion. In blends with large block copolymers, polystyrene blocks and PP E are rather uniformly mixed. The degree of mechanical coupling of the phases increases with the block copolymer molecular weight. The favou rable enthalpic interaction between the blocks and the blend component s is a major factor determining the phase behaviour. In contrast to th is, the molecular weight of PPE showed little influence on blend behav iour.