Dielectric studies of mobility of polar molecules in polystyrene

Abstract

Dielectric measurements (5Hz–8.5 GHz) at temperatures from –30 to 100°C have been made on polar solutes molecularly dispersed in a polystyrene matrix. Rigid molecules of varying size and shape (camphor, anthrone, cholest-4-en-3-one, tetraphenyl cyclopentadienone) and β-naphthol are considered. By 80° all the molecules show their full dipole moments in polystyrene : the apparent (Eyring) activation energies ΔH^*_E for molecular dipole relaxations vary from 0.9 kcal mole^–1 for camphor to 130 kcal mole^–1 for tetracyclone. The apparent ΔH^*_E over limited temperature ranges themselves reflect changes in the polymer matrix relaxations, and the 130 kcal mole^–1 value may well be derived from the glass-transition process. The ΔH^*_E and ΔS^*_E correlate linearly and the former is dependent upon the molecular rotational volume. The “whole molecule” and hydroxyl group rotations are well resolved for β-naphthol with ΔH^*_E values of 11.2 and 0.5 kcal mole^–1 respectively.