EXTENDED ROTATIONAL ISOMERIC MODEL FOR DESCRIBING THE LONG-TIME DYNAMICS OF POLYMERS

An extended rotational isomeric states (RIS) model is used in conjunct ion with the matrix expansion method for describing the long time dyna mics of flexible polymers in solution. The extended RLS model is deriv ed directly from the potential functions that contain hindered torsion al potentials, nonbonded interactions, etc. The matrix expansion metho d for describing the long time dynamics contains equilibrium conformat ional averages which are evaluated here from the extended RIS model. T he theory effectively assumes that the torsional barriers provide the dominant mechanism for the decay of orientational correlations in the polymer chains. The theory is applied to united atom alkane chain dyna mics where previous Brownian dynamics simulations with the same potent ials are available for an unambiguous, no-parameter test of the theory . The present computation of equilibrium averages with the extended RI S model represents a significant advancement over the prior treatments that evaluate the equilibrium averages using Brownian dynamics simula tions. The comparison with the previous approach indicates the degree to which bond angle fluctuations affect the orientational time correla tion functions. (C) 1996 American Institute of Physics.