Conformation “ségrégée” et conformation “statistique” dans les copolymères à trois séquences PMM‐PS‐PMM en solution diluée I. Etude viscosimétrique

The intrinsic viscosity of a triblock copolymer of styrene and methylmethacrylate prepared anionically was investigated in several solvents — chloroform, benzene, dioxane, tetrahydrofurane, and p‐xylene — as a function of temperature. In all cases a rather sharp break in the viscosity curve was observed, at a temperature depending upon the solvent. It can be assumed that at low temperature the triblock copolymer exhibits a “segregated” conformation in which no heterocontacts can be observed. A proof of this structure is that the viscosimetric expansion factor is identical with the weighted average between the corresponding homopolymers of identical molecular weight. At higher temperature, heterocontact interactions are rendered possible as the incompatibility between the corresponding homopolymers becomes less important. This happens at the transition temperature and the conformation becomes increasingly “gaussian”, as the number of heterocontacts increases with rising temperature.