Local dynamics of freely rotating polymer chains in dense systems

Local dynamics of a chain in the bulk state is strongly controlled by the immediate environment of the chain. The excessive friction exerted by the environment precludes large scale kinetic displacements of the chain atoms. In the presence of strong constraining effects of the environment, a transition from one configuration to the other is expected to take place by strongly correlated and relatively small range rearrangements of torsional motions. In the present study, local dynamics of the chain is analyzed as a succession of configurational rearrangements such that the change in the chain radius of gyration at each step is minimum. The degree of cooperativity among neighboring bonds along the chain resulting from the constraint of the environment is found to be highly localized. A 120° rotation of an internal bond is observed to be possible by cooperative adjustments of a few bonds in its immediate neighborhood along the chain. Changes in the mean-square anisotropic polarizability tensor when the ends of a relatively short chain (n ≤ 50) are subject to a prescribed deformation, are also calculated. Calculations show that changes in the mean-square anisotropic polarizability depend strongly on chain length.