Theory of melting in simple polymers.I.

A formalism is described whereby the Helmholtz energy of a polymer crystal or melt is found by solution of a set of self-consistent equations involving functionals of the distribution of torsional angles along a single chain. The interchain interactions are treated in a generalized mean-field framework which starts from a detailed computation of the molecular energetics of a pair of parallel and adjacent chain segments. Intrachain potentials for the cases of polymethylene and polytetrafluoroethylene were obtained from molecular orbital calculations, while interchain potentials were found by in addition using semiclassical techniques. Results are presented to describe the melt transition in these materials.