Homopolymer Distribution in Polystyrene - Poly(methyl methacrylate) Diblock Copolymer

Homopolymer distribution in block copolymer/homopolymer blends was investigated as a function of homopolymer concentration and homopolymer molecular weight. The deuterated poly (methyl methacrylate) or polystyrene was blended with a deuterated polystyrene-poly (methyl methacrylate) diblock copolymer up to a concentration of 20 wt%. Samples were characterized by small-angle X-ray scattering (SAXS), neutron reflectivity and transmission electron microscopy. The block copolymer with a thin-film geometry formed alternating lamellar microdomains oriented parallel to the substrate surface. By adding the homopolymer, the microdomain structure was significantly disturbed. As a consequence, a poorly ordered morphology appeared when the homopolymer concentration exceeded 15 wt%. Increasing the homopolymer concentration and/or the homopolymer molecular weight caused the microdomains to swell less uniformly, resulting in segregation of the homopolymer toward the middle of the microdomains.