Hierarchical Modeling of the Dynamics of Polymers with a Nonlinear Molecular Architecture: Calculation of Branch Point Friction and Chain Reptation Time of H-Shaped Polyethylene Melts from Long Molecular Dynamics Simulations

Abstract

Thoroughly equilibrated atomistic configurations of H-shaped polyethylene (PE) melts, obtained through a novel implementation of the double-bridging Monte Carlo algorithm [Karayiannis et al. J. Chem. Phys. 2003, 118, 2451], have been subjected to equilibrium NPT molecular dynamics (MD) simulations at T = 450 K and P = 1 atm, for times up to 4 μs. The simulated model H-shaped systems consist of PE chains possessing a main backbone (a “crossbar”) trapped between two branch points each of which is linked to two dangling arms. In our simulations, the average number of carbon atoms in the backbone ranged from 48 up to 300 corresponding to both unentangled and entangled crossbars, while the average arm length was kept relatively small (it ranged from 24 up to 50) corresponding always to unentangled arms. Our long MD simulation studies reveal the different relaxation mechanisms exhibited by an H-polymer: the rapid relaxation due to arm breathing (on the order of a few nanoseconds for the short, unentangled arms...