Liquid properties of oligomers. Comparison of relaxational properties of propylene glycol oligomers with those of ethylene glycol oligomers

Abstract

Liquid properties such as dielectric relaxation and viscous flow of the two structurally homologous propylene glycol oligomers HO(CH(CH₃)CH₂O)_nH (n=1, 2, 3, 4, 5 and 34) and ethylene glycol oligomers HO(C₂H₄O)_nH (n=1, 2, 3, 4, 5 and 6) are studied in pure liquid state to clarify the degree of polymerization dependences of chain molecules on their liquid properties. These oligomers are, at room temperature, viscous liquid which shows dielectric relaxations in the frequency range from 10 Hz to 3 MHz. Propylene glycol oligomers (n=from 1 to 5) show the Davidson-Cole-type relaxations, but the higher glycol (n=34) shows superposition of the two different relaxations, i. e., small Debye-type relaxation in the lower-frequency region and large principal Havriliak-Negami-type relaxation in the higher-frequency region. Relaxation times vs. degree of polymerization do not increase linearly, but vary in zigzag lines. Above all, the dimers (dipropylene glycol and diethylene glycol) show longer relaxation times than the other glycols. This dielectric result does not agree with the degree of polymerization dependence of viscous flow.