Solvent effects on microwave dielectric relaxation in poly(ethylene glycols)

This paper reports the results of a systematic study of microwave dielectric relaxation times of poly(ethylene glycols), average molecular weight 200-9000, in dilute solutions of benzene at 9.83 GHz. These results are compared with the values of relaxation times obtained earlier in carbon tetrachloride solutions. This shows that the average relaxation times tau(0) and the relaxation time corresponding to segmental reorientation tau(1) are influenced by the solvent environment. The variation in chain flexibility in these polymers with the increase in degree of polymerization and formation of intra-and inter-molecular hydrogen bonding in benzene and carbon tetrachloride solutions is discussed with the help of relaxation data. The relaxation time tau(2) corresponding to group rotations has been determined. It is found that the tau(2) value is independent of solvent environment and degree of polymerization, and may be attributed to the rotation of chain -OH end-groups around the C-O bonds in dynamic equilibrium, with the formation of a five-membered ring due to intra-molecular hydrogen bonding at the end of the chain. (C) 1998 SCI.