MICROPHASES AND MACROPHASES IN POLYMER BLENDS WITH A DIBLOCK COPOLYMER

Blends A/alphabeta and C/alphabeta of a polymer A or C and a diblock c opolymer alphabeta with blocks alpha and beta of equal lengths were an alyzed, where A is chemically equal to a while C has attractive intera ctions with alpha. Films of the blends were cast, using nonselective s olvents. The random phase approximation model predicts a transition fr om microscale to macroscale fluctuations in the still homogeneous solu tions, the transition depending on the chain lengths of A or C, relati ve to that of alphabeta, on the interactions, in particular those of C and a, and on the temperature. This transition was observed, where pr edicted, in cast films of various blends of a diblock copolymer P(MMA- b-S) of methyl methacrylate and styrene. The microphase and macrophase morphologies of blends with PMMA as well as PS, SAN, poly(cyclohexyl methacrylate), and tetramethyl polycarbonate were characterized by ele ctron microscopy. Effects that are not predicted by the model are show n to come from secondary segregation processes. Quite a variety of mor phologies can be produced.