MISCIBILITY AND MORPHOLOGY OF AB C-TYPE BLENDS COMPOSED OF BLOCK-COPOLYMER AND HOMOPOLYMER OR RANDOM COPOLYMER .2. BLENDS WITH RANDOM COPOLYMER EFFECT/

This work is an extension of the concept of miscibility window in homo polymer/random copolymer blends to blends containing block copolymers. The miscibility and morphology of THF-cast blends composed of the blo ck copolymer polyisoprene-block-poly(methyl methacrylate) (PI-b-PMMA) and the random copolymer poly(styrene-ran-acrylonitrile) (SAN) (22 wt. % AN) has been studied by transmission electron microscopy (TBM) and d ifferential scanning calorimetry (DSC). Most blends show miscibility b etween PMMA blocks and SAN, presenting a homogeneous microdomain struc ture. Coupling of microphase and macrophase separation occurs only whe n the ratio of molecular weights of SAN to the PMMA beck is very large and SAN becomes the dominant component. The excellent miscibility in the block copolymer/random copolymer blends can be understood by consi dering that the monomer unit composition of SAN is within the miscibil ity window in PMMA/SAN blends. The main driving force for the miscibil ity is repulsion between S and AN units rather than hydrogen bonding b etween SAN and PMMA, since a proton-acceptor type solvent does not sho w any effect on the miscibility in the blends. Apparent broadening of the glass transition of the 'hard phase' is observed and explained wit h the aid of the segment density gradient model.