POLYISOPRENE LOCAL DYNAMICS IN SOLUTION - COMPARISON BETWEEN MOLECULAR-DYNAMICS SIMULATIONS AND OPTIMIZED ROUSE-ZIMM LOCAL DYNAMICS

The optimized Rouse-Zimm local dynamics (ORZLD) approximation to the S moluchowski generalized diffusion approach has been used to predict th e local dynamics of cis-l,4-polyisoprene in dilute solution. The equil ibrium averages needed in the theory are calculated from a time averag e along a molecular dynamics trajectory. The first and second order or ientation autocorrelation functions for C-H, C-C, and virtual bonds in the repeat unit are calculated from the theory and compared to the sa me quantities calculated directly from the molecular dynamics trajecto ry. The correlation functions from the simulation and the theory decay on similar time scales (within a factor of two) and have somewhat sim ilar shapes. The theory predicts a universal relationship between P-1 and P-2 correlation functions which is obeyed to a good approximation by the correlation functions from the simulation. Variations in the lo cal dynamics along the chain contour are qualitatively well described by the theory. (C) 1998 American institute of Physics. [S0021-9606(98) 51203-2].