Neighbor Interactions and Internal Rotations in Polymer Molecules. IV. Solvent Effect on Internal Rotations

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Abstract
Solvent chain‐element interactions affect the probability distribution of the angles of internal rotation of a polymer chain and give rise to an average torque on the skeletal bonds of the chain. The average torque and its potential are derived in terms of polymer‐solvent interaction potentials and reduced distribution functions. The energy of the polymer molecule, as it was applied in the previous papers of this series, is shown to be the potential of the average torque in the neighbor interaction approximation. This approximation, though insufficient by itself, provides a theoretical basis for the application of the random flight model of polymer molecules and, at the same time, improves upon it by deriving the characteristic parameter of the model (the length of the statistical chain element) as a function of temperature, solvent, and the structural parameters of the polymer chain. Following these considerations, the complementary nature of the theories of neighbor interaction and excluded volume is discussed.