COMPATIBILIZING EFFECT OF BLOCK COPOLYMERS IN HETEROGENEOUS POLYSTYRENE POLY(METHYL METHACRYLATE) BLENDS

The morphology of heterogeneous polystyrene/poly(methyl methacrylate) (PS/PMMA) blends has been modified by the addition of diblock copolymers of PS and PMMA and investigated as a function of block copolymer composition, molecular weight and concentration by optical and electron microscopies. A sharp decrease in dispersed phase dimension is observed with the addition of a few per cent of block copolymers having equal segmental mass (50/50 PS/PMMA), followed by a levelling off as the copolymer content is increased above the critical micelle concentration. For concentrations below the critical value, the particle size reduction is linear with copolymer volume fraction and agrees well with the predictions of Noolandi and Hong. The compatibilizing efficiency of the copolymer is strongly dependent on its composition and molecular weight. The effects of processing conditions, such as casting solvents and compression moulding, on the phase morphology have also been studied. Finally, the conformation of the copolymer at the interface is discussed with the help of models: calculations based on the experimental results indicate that the compatibilizer is neither located entirely at the interface, nor penetrates completely into the corresponding homopolymer phases.