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-dimethyl-1,4-phenylene ether) (PPE) is investigated by dynamic mechanical analysis and transmission electron microscopy. Total molecular weights of the block copolymers vary from 16 up to 275 kg mol Independent of molecular weight, all block copolymers locate to the interface with strong dispersing efficiency. The different block copolymers also showed approximately the same emulsifying efficiency. The degree of segmental mixing of the blocks with the respective phases is evaluated from the glass transition behaviour. A qualitative model is developed to relate the observed glass transition behaviour to the segmental distribution. In blends with large block copolymers, polystyrene blocks and PPE are rather uniformly mixed. The degree of mechanical coupling of the phases increases with the block copolymer molecular weight. The favourable enthalpic interaction between the blocks and the blend components is a major factor determining the phase behaviour. In contrast to this, the molecular weight of PPE showed little influence on blend behaviour.