Calculation of Compressibilities of High Polymers from the Energy of Interaction between Chain Groups

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Abstract
A potential function for the interaction of long chain molecules in polymer lattices is formulated. The adopted model assumes polymeric substances to consist of imperfect assemblies of perfect chain crystals. The chains are infinitely long compared to the range of intermolecular forces so that end effects can be neglected. Each chain is composed of evenly spaced dipolar dispersion force centers, with dipole orientations perpendicular to and alternating along the chain axes. Pairs of force centers in neighboring chains interact according to a Lennard‐Jones (12–6) potential and the electrostatic interaction terms. The interaction between neighboring force centers within a chain is assumed to be Hookian with a force constant calculated from combined valence bond distortions and valence angle deformations. The lattice energies of five linear polymers are calculated. It is found that the contributions from induction terms are negligible. The contributions from dipole interaction terms depend on the mutual orientation of the chains and amount to only ca 0.1–1% of the lattice energies. To this accuracy, certain ``structure insensitive'' properties can be described by an equation of corresponding intermolecular states. This approach is shown to fail, if applied to ``structure sensitive'' properties, which depend strongly on the interplay of inter‐ and intramolecular degrees of freedom. Absolute calculations of specific polymer volumes over large pressure ranges are in agreement with experiment.

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