Blend encapsulation by random copolymers: C/B/A-ran-B and C/D/A-ran-B systems

Random copolymers with the same monomeric units as blended homopolymers A and B have a strong tendency to encapsulate the minor phase in A/B/A-ran-B ternary systems. In this study we investigate encapsulation when one or both monomeric units in the random copolymer are chemically distinct from, but completely or partially miscible with, the other blend components, i.e., a C/D/A-ran-B blend. As model polymers, a styrene/methyl methacrylate random copolymer (70% styrene by weight) (SMMA), and polystyrene (PS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and poly(phenylene oxide) (PPO) homopolymers are chosen; PPO is completely miscible with PS and PC is partially miscible with PMMA. Three blend systems were prepared by melt mixing: PS/PC/SMMA, PPO/PMMA/SMMA. and PPO/PC/SMMA. Transmission electron microscopy demonstrated that for all cases SMMA moves to the interface between the matrix and dispersed phases during melt mixing, and forms an encapsulating layer. However, the resulting average size of a dispersed phase droplet is not significantly decreased by the addition of SMMA. Moreover, this size increased significantly upon further annealing, except for the blend with a PPO matrix which has a very high melt viscosity, demonstrating that encapsulation by SMMA does not provide stability against static coalescence.