Thermal conductivity of high polymers

The thermal conductivity of several high polymers was measured in the temperature range from −190 to 90°C. with an automatic apparatus. In amorphous polymers a break has been found in the thermal conductivity at the glass transition temperature. This break can be explained by a model conception, which coordinates an elementary thermal resistance to every bond and which is also able to interpret the anisotropy of the thermal conductivity of stretched amorphous polymers. Even a rather universal relation between the anisotropies of the thermal expansion and the thermal conductivity can be derived. In partially crystalline polymers the thermal conductivity of the amorphous and the crystalline phases can be calculated from values measured with specimens of different crystallinities. The thermal conductivity of the crystalline phase of polyethylene shows the T−1‐law, valid for low molecular crystals. In other polymers we find a different behavior: the thermal conductivity of the crystalline phase is similar to that of the amorphous phase; we find that it can be described and calculated by means of the model derived from amorphous polymers. This model permits also to interpret the course of thermal conductivity at first‐order transition points.