RANDOM MULTIBLOCK COPOLYMER-HOMOPOLYMER BLENDS - EFFECT OF SEQUENCE DISTRIBUTION AND INTRAMOLECULAR REPULSION

Recently, Fredrickson, Milner, and Leibler [Macromolecules 25, 6341 (1992)] introduced a mean-field analysis of linear random A-B multiblock copolymer melts, taking the sequence distribution explicitly into account. Here, we extend this approach to mixtures with homopolymers P(C). Within the simple Flory-Huggins description, miscibility in random copolymer-homopolymer mixtures is often attributed to unfavorable A-B interactions described by a positive Flory-Huggins parameter AB (intramolecular repulsion). The introduction of the sequence distribution sets an upper limit to this effect. For sufficiently large values of AB the mixture phase separates again, very much like the pure copolymer melt. Likewise, miscibility improves in the direction of the alternating sequence distribution. Our analysis rationalizes frequently observed sequence distribution effects in random copolymer blends. © 1994 The American Physical Society.