Volume Dependence of the Thermal Expansion of Polymers

Recent theoretical developments dealing with the equation of state of polymers make it possible to obtain some estimate of the volume dependence of the thermal expansion α of these materials. It is clear at this point that α should depend not only on the volume V and temperature T, but also on the degree of crystallinity Fc of the polymer in question. The calculations presented take this latter parameter into account and theoretical values of α for polyethylene (PE) are given as a function of V, T, and Fc. The values of α for crystalline PE are converted into values for poly chloro tri fluoro ethylene (Kel F) by simple corresponding states relations. The efficacy of these relations is shown by accurately converting P-V data on PE to P-V data on Kel F.