Heat Capacity of Polyethylene from 2.5° to 30° K.

Heat?capacity measurements for three samples of polyethylene of varying density are reported for the range 2.5° to 30°K. In this range that heat capacity is strongly density?dependent, being linear in the crystallinity. Extrapolation to the cases of completely amorphous and completely crystalline material have been made and a table giving the heat capacity of these hypothetical materials is presented. In the lowest temperature range the heat capacities of all of the samples and of the extrapolated amorphous material do not show a cubic temperature dependence, but rather indicate an excess heat capacity similar to that found in some other amorphous materials. The extrapolated crystalline material does not display an excess heat capacity, but rather has a cubic temperature dependence to approximately 9°K. It is found that a simple continuum model represents the heat capacity of polyethylene quite well at low temperatures.