Atomistic Monte Carlo simulation of cis-1,4 polyisoprene melts.: II.: Parallel tempering end-bridging Monte Carlo simulations

Results are presented for the temperature dependence of the thermodynamic and conformational properties of cis-1,4 polyisoprene (PI) melts from detailed atomistic parallel-tempering end-bridging Monte Carlo (ptEBMC) simulations. The simulations have been performed with a C-80 cis-1,4 PI melt system which was simultaneously equilibrated at 10 different temperatures, ranging from T=328 K up to T=513 K, in the semigrand NnPT mu* statistical ensemble. This strategy allowed system equilibration at temperatures as low as T=328 K (where most available experimental data have been obtained), for which the performance of the single temperature end-bridging Monte Carlo (EBMC) algorithm was seen to deteriorate. Results for the variation of the specific volume of the cis-1,4 PI melt with temperature at constant mean chain length are found to be always within 1% of experimentally reported values and analytical fits to these values. Additional results for the equilibrium mean-square chain end-to-end distance <R-2> (0), which can be fully equilibrated with the algorithm employed here, show that the model predictions for <R-2> (0) are rather insensitive to temperature variations, at least over the range of temperatures studied here. This behavior is explained by investigating the temperature variation of the distributions of the three types of torsion angles in a PI molecule. The conformational predictions of the ptEBMC simulations are closest to experiment at the lower temperatures, where they almost match the measured value of <R-2> (0). Detailed results are also presented for the performance of the ptEBMC algorithm, demonstrating its unique capability to equilibrate the atomistically detailed cis-1,4 PI melt. (C) 2001 American Institute of Physics.