HEAT-CAPACITIES OF POLYETHYLENE AND LINEAR FLUOROPOLYMERS

Heat capacities at constant pressure, C//p, and at constant volume C//v, were calculated with the help of normal mode frequency spectra and compared to experimental data for crystalline or semicrystalline polyethylene, poly(vinyl fluoride), poly(vinylidene fluoride), polytrifluoroethylene and poly(tetrafluororethylene). A calculation scheme using a Tarasov function for 2N skeletal vibrational modes and an approximation of the residual 7 N normal modes from known data on polyethylene and polytetrafluoroethylene is developed for all homologous, linear fluoropolymers. For the two theta temperatures and the constant A//o used for C//v to C//p conversion, fluorine-concentration dependent curves are given. The relations are expected to hold also for copolymers and blends of intermediate fluorine contents. Recommended experimental (data bank) heat capacities agree to plus or minus 2. 5% with the calculations.