Microwave absorption and molecular structure in liquids. XL. The dielectric relaxation of a polyester of 1,2‐propylene glycol and adipic acid in solution

Abstract

AbstractThe dielectric constants and losses have been measured at 20°C. and wavelengths of 1.25, 3.22, 10.0, 25, and 50 cm., and 575 m. for a series of dilute benzene solutions of a polyester of 1,2‐propylene glycol and adipic acid with molecular weight between 5,000 and 7,000. The dielectric constant and loss values are plotted against the weight concentrations of the solute and the slopes of the straight lines thus obtained are examined by four different methods of analysis. The data may be represented in terms of two parameters, a most probable relaxation time and a distribution factor, two relaxation times, or a distribution of relaxation times between two limiting values. The values obtained for the relaxation times are close to those previously found for long‐chain fatty acid esters and correspond to relaxation by twisting of short segments containing carboxy groups around bonds in the chain. A value 1.57 × 10—18 obtained for the effective dipole moment of the COOC group as compared to 1.9 × 10—18 in a small monoester indicates some restriction of rotation around the bonds because of mutual repulsion between the polar groups.