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 homopolymer s A and B have a strong tendency to encapsulate the minor phase in A/B /A-ran-B ternary systems. Tn this study we investigate encapsulation w hen one or both monomeric units in the random copolymer are chemically distinct from, but completely or partially miscible with, the other b lend components, i.e., a C/D/A-ran-B blend. As model polymers, a styre ne/methyl methacrylate random copolymer (70% styrene by weight) (SMMA) , and polystyrene (PS)I poly(methyl methacrylate) (PMMA), polycarbonat e (PC), and poly(phenylene oxide) (PPO) homopolymers are chosen; PPO i s 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 n ot significantly decreased by the addition of SMMA. Moreover, this siz e 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.