ENTHALPIC INTERACTION IN BLOCK COPOLYMER HOMOPOLYMER BLEND SYSTEMS - MORPHOLOGICAL-STUDIES OF SOLVENT-CAST FILMS

We report morphological studies of solvent-cast polymer blend films containing a polystyrene/ poly (methyl methacrylate) (PS/PMMA) block copolymer with polymers that are miscible with one block copolymer segment, viz. polystyrene (PS), random styrene/acrylonitrile copolymers (SAN) and poly(methyl methacrylate) (PMMA). By utilizing SANs that have four different acrylonitrile (AN) contents, we vary the enthalpic interaction between the SAN copolymer and the block copolymer segments. With polystyrene as the minor constituent, and for a given overall composition ratio and specified molecular weights of the blend components, the morphology of the blends was found to change systematically from dispersed spheres to cylinders, vesicles and lamellae, depending on the strength of the enthalpic interaction between the matrix and the block copolymer segments. Selective staining of the PMMA block at the interphase in blends containing SANs was possible only for SANs of higher AN content. This is interpreted as an indication of interfacial microsegregation of the PMMA block from the SAN matrix as the AN content increases. These morphological changes can be explained by differences in the relative solubility of matrix polymer in the micellar corona, which are controlled by the balance between attractive and repulsive interactions with the miscible and immiscible blocks.