Segregation and conformational transition in triblock copolymers: Part 2. Light-scattering studies

Abstract

From light-scattering experiments carried out on a polystyrene (PS) sample, a poly(methyl methacrylate) (PMMA) sample, on a random copolymer of styrene and MMA and on an anionically prepared triblock copolymer PMMA-PS-PMMA, all of the same molecular weight, in various solvents over a range of temperature (18–65°C) it was shown that a conformational transition occurs for the triblock copolymer. At lower temperatures segregation occurs and the second virial coefficient A 2 is the weighted average between the A 2A and A 2B values for the corresponding homopolymers (PS and PMMA). At higher temperatures contacts between chemically unlike parts of the molecule become possible, and the additivity rules are no more valid for A 2 , as well as for the expansion coefficient. This change from a segregated to a ‘pseudo-gaussian’ conformation involves a change in specific volume of the molecule, and it there-fore brings with it an abnormal variation of the refractive index increment, which has been investigated on the same light-scattering diagrams.