EFFECT OF MOLECULAR-STRUCTURE ON LOCAL CHAIN DYNAMICS - ANALYTICAL APPROACHES AND COMPUTATIONAL METHODS

Analytical and numerical approaches for the treatment of local chain dynamics are reviewed. Two main approaches are considered. First the dynamic rotational isomeric state (DRIS) formalism which has been developed as the dynamic counterpart of the classical rotational isomeric state theory of chain statistics is recapitulated and compared with other analytical treatments of chain conformational dynamics. The DRIS model is based on the solution of the multivariate master equation describing the time evolution of discrete chain configurations. The limitations and implications of the formalism are discussed. The real conformational and structural characteristics of the chain are rigorously included in the DRIS formalism. This feature makes it particularly suitable for application to specific polymer chains. However, the cooperative motion of relatively long chain segments is considered in the DRIS formalism through a mean field approximation, only. This shortcoming is overcome by a newly developed approach, referred to as the cooperative dynamics model. The latter takes account of the restrictions imposed on the mechanism of conformational transitions by chain connectivity and environmental frictional resistance in addition to those from internal conformational barriers. Comparison of both DRIS acid the cooperative kinematics approaches with Brownian simulations indicates that these approaches may be advantageously used for predicting the time evolution of bond rotameric states, the distribution of angular reorientations of bonds in the neighborhood of a rotating one, the types of coupled transitions which are most strongly favored by the particular chain structure. This type of information which would otherwise be extracted from the statistical analysis of long trajectories generated by Brownian or molecular dynamics simulations is readily obtainable from either the DRIS or the cooperative kinematics theories.