Molecular microstructure dependence of space charges in polymers. Coupling of thermal step (TS) and thermally stimulated discharge current (TSDC) methods in PVC after nucleophilic substitution

The space charge distribution, a basic electrical property of insulating materials, has been studied for a poly(vinyl chloride) (PVC) sample before and after nucleophilic substitution reaction up to various degrees with sodium benzenethiolate (NaBT) in cyclohexanone (CH) solution, so as to modify in a controlled way the content of the isotactic tetrad mmr and the heterotactic pentad rrmr located at the end of isotactic and syndiotactic sequences, respectively. We investigated the influence of mmr and rrmr structures on the number and type of electrical charges accumulated in the material when submitting it to an electrical field. To differentiate between the polarization charges and the trapped charges, coupling of the ''thermal step'' (TS) and the ''thermally stimulated discharge current'' (TSDC) techniques was applied. Both types of charges were proved to be related chiefly to the conformations GTTG-TT and GTGTT, having higher free volume and local mobility, characteristic of mmr structure.