NANODOMAIN FORMATION IN A LIQUID POLYMER BLEND - THE INITIAL-STAGES OF PHASE-SEPARATION

The morphology of nanodomain structures in binary polymer blends of a random copolymer and a homopolymer is determined using electronic exci tation transport (EET) studies. The experimental system employed is a copolymer, 6.5% atactic poly(methyl methacrylate-co-2-vinyl naphthalen e) [P(MMA-2VN)], in atactic poly(vinyl acetate) (PVAc). The naphthalen e groups serve as chromophores in the EET experiments. The mixtures ar e prepared such that initially the P(MMA-2VN) chains are randomly dist ributed in the PVAc matrix. The nanodomains are formed while low-conce ntration mixtures of the P(MMA-2VN) in PVAc are held at constant tempe rature in the melt state (T>T-g), above the temperature at which phase separation occurs. In the melt the chains diffuse, and P(MMA-2VN) cha ins aggregate until the temperature is quenched below T-g. The structu res of the resulting domains are examined with rime resolved fluoresce nce depolarization measurements, and the data are analyzed using an an alytical theory to model EET among interacting polymer chains. The agr eement between theory and data is very good. The results of the analys is indicate that the nanodomains correspond to aggregates with a chara cteristic size equal to the radius of gyration of the copolymer, R(g). The number of P(MMA-2VN) chains in aggregates prepared under differen t conditions is determined. (C) 1995 American Institute of Physics.