Dielectric absorption in polyoxymethylene obtained from tetraoxymethylene crystal by radiation induced polymerization

Abstract

AbstractIn order to study the dielectric behavior of polyoxymethylene prepared by radiation‐induced solid‐state polymerization, large crystals of tetraoxymethylene (2 cm in diameter) were prepared by Bridgman's method and polymerized by γ‐rays. The x‐ray diffraction pattern of the polymer did not reveal the existence of a so‐called amorphous region. In dielectric measurements, only one dielectric absorption was observed in the low‐temperature region, while in the high‐temperature region ε″ did not change up to about 120°C, where thermal decomposition started. When the specimen was stabilized by acetylating the endgroups in the solid state, ε″ did not change up to about 150°C. This dielectric absorption showed a significant anisotropy for the direction of an applied field. The dielectric absorption was much larger when the electric field was perpendicular to the fiber axis than when the field was parallel. The dielectric absorption was larger in a specimen which was estimated to be more imperfect according to DSC analysis. This leads to the conclusion that the dielectric absorption is attributable to defect regions. On the other hand, the dielectric absorption became larger with increasing numbers of terminal OH groups, and hence it is attributable to the response of the terminal OH groups. Moreover, the dielectric absorption was depressed by the acetylation of the OH groups in the solid state. It is, therefore, concluded that the dielectric absorption observed in polyoxymethylene prepared by solid‐state polymerization of tetraoxymethylene is due to the response of terminal OH groups localized in defect regions. Polyoxymethylene crystallized from the melt gives an asymmetric low‐temperature absorption. This asymmetry can be ascribed to the superposition of two relaxation processes. When its absorption curve is compared with that of the solid‐state polymerized polymer, the low‐temperature component can be assigned to crystal defects and the high temperature one to amorphous regions.