Heat Conduction and Molecular Structure in Rubberlike Polymers

Abstract

Abstract In this paper experimentally determined values are reported for the thermal diffusivity (k) of various rubberlike polymers. Corresponding values of the thermal conductivity (W) can be computed from the well-known relationship, W=kρcP, where ρ and cP denote the density and specific heat at constant pressure of the composition. Measurements were made on (1) pure-gum stocks prepared with natural rubber, Butyl (GR-I), Perbunan-18, Perbunan-26, Perbunan-35, Buna-S (GR-S), polybutadiene, Neoprene-GN, polyisoprene, Silastic-160, and Silastic-180; (2) pure-gum stocks of the first five rubbers listed under (1) containing in addition 20 parts of a hydrocarbon softener (Bardol), based on 100 parts by weight of the polymer; and (3) the Bardol stocks containing in addition 54 parts of carbon black (Kosmobile-66). From measurements of the rate of change of temperature within a rubber sphere suddenly subjected to a change in its surface temperature, it was found possible to determine the dependence of k on temperature. A satisfactory definition of the “mean” temperature of a sphere under these conditions is described. In a discussion of the effect of chemical composition and structure on heat conduction, the bearing of hindered rotation, cross-linking and branching and interatomic bond strength on the results is pointed out. Values are derived for certain other properties of some of the polymers, including their characteristic Debye temperatures, specific heats at constant volume, flexibility of the main valence chains, compressibilities, and sound velocities.