THERMAL TRANSPORT IN AMORPHOUS POLYMERS AT HIGH-TEMPERATURES

At low temperatures, heat conduction in amorphous polymers and inorganic glasses may be described in terms of low-frequency three-dimensional phonons contributing to the energy flow. Measurements of the conductivity as a function of molecular weight in polymers indicate preferential heat conduction along the chains, with the conductivity depending on the square root of the molecular weight for low molecular weights and saturating at high molecular weights. In this paper, the authors report simple calculations of the lifetimes of one-dimensional modes traveling along a chain and suggest that the molecular weight dependence of the amorphous polymer conductivity can be explained in terms of long-lived longitudinal modes which carry most of the heat. The model used is extremely simplistic and the parameters employed are difficult to quantify in terms of real polymers, but the basic ideas could be explored experimentally by measurements on crosslinked polymers.