Atomistic Monte Carlo simulation of cis-1,4 polyisoprene melts. I. Single temperature end-bridging Monte Carlo simulations

Results are presented for the thermodynamic, conformational, and structural properties of cis-1,4 polyisoprene (PI) melts from detailed atomistic Monte Carlo simulations. All simulations have been executed by employing the very efficient end-bridging move, which alters chain connectivity and induces fast conformational and structural equilibration over the entire range of length scales in the melt. To use the end-bridging move, a geometric mapping of a cis-1,4 PI monomer onto an equivalent three-bead monomer is utilized. In the acceptance criterion of the move, however, the energy terms are calculated from the actual atomistic cis-1,4 PI chains, obtained after performing the reverse mapping. Simulation results are obtained at T=413 K with cis-1,4 PI melts of mean molecular length ranging from C40 to C200. The performance of the end-bridging Monte Carlo (EBMC) algorithm is explored as a function of average chain length. Results for the specific volume of the cis-1,4 PI melt are found to be within 1% of experimentally reported values and analytical fits to those values. Additional predictions concerning the conformational properties, the equilibrium mean square chain end-to-end distance 〈R2〉0, and the wide-angle neutron and x-ray diffraction patterns, demonstrate that our force field predicts reliably the physical properties of polyisoprene in the molten state.