Specific Heat of Synthetic High Polymers. I. A Study of Polyethylene Including a Statistical Theory of Crystallite Length

Abstract

Data are given for the specific heat of granular, sheet, annealed, and drawn samples of polyethylene from −20° to 200°C. From the data, changes in enthalpy and entropy between these temperatures have been calculated and an estimate made of the free energy of the cold drawing process. The percentage of crystallinity calculated from the enthalpy value is given as a function of temperature and compared with similar estimates from x-ray and density measurements. The applicability of Flory's important theory of crystallization in high polymers to the polyethylene data is studied. A new statistical treatment of crystallite length distribution similar to, but more mathematically exact than Flory's, is also presented. Curves based partly on theory and partly on experiment are given for the weight distribution of crystallites as a function of chain length for annealed and drawn polythene.