Dielectric study on copolymers in dilute solution. Relaxation behavior of methyl methacrylate–styrene and methyl methacrylate–α‐methylstyrene copolymers

Abstract

Abstract Dielectric measurements were made on some methyl methacrylate (MMA)‐related polymers in dilute solution, in the frequency range of 1–150 MHz. Effects of the solvent viscosity upon the relaxation behavior were carefully examined. The dielectric relaxation of MMA–styrene copolymers with a high content of MMA units as well as that of the MMA–α‐methylstyrene copolymer was little affected by the solvent viscosity. With the aid of Kramers'rate constant for small friction, it was found that their dipolar relaxation is very similar to that caused by the internal rotation of a flexible side‐chain. On the other hand, MMA–styrene copolymer with a low content of MMA units showed a diffusion‐controlled relaxation process, which can be interpreted in terms of Kramers' theory for large friction. In the latter case, the dipolar relaxation appears to reflect a molecular motion such as sweeping out solvent molecules. These results indicate that it is not the dipole itself but its environment, or rather the local molecular structure containing dipoles, that principally controls the relaxation process. On this basis, we propose a criterion, for quantitatively distinguishing the two relaxation mechanisms from each other.