Intra and interchain thermal conduction in polymers

Summary form only given. As it is the case for the electrical properties, polymer materials are generally considered as thermally insulating materials. However, it has been previously shown that their thermal conductivity which is due to the lattice vibrations can be increased by orders of magnitude by aligning the polymer chains. It has been previously shown that thermal conductivity values comparable to those observed in metallic alloys could be obtained in oriented polymers (polyethylene, polyacetylene, ...)/sup 1-3/. It will be shown here, on a more fundamental point of view, that the oriented polymers are also very good candidates to get a better understanding of the thermal conductivity in semi-crystalline polymers. Indeed, by measuring the thermal conductivity parallel and perpendicular to the polymer chain as a function of temperature, one may identify the thermal-transfer mechanisms along and across the polymer chains. We will also discuss the different mechanisms leading to the increase of thermal conductivity upon stretching and we will compare the longitudinal and the transverse thermal conductivities. We will also show that thermal-conductivity measurements could be used as a complementary tool to characterize structure and defects in these materials.