Dynamical Monte Carlo Study of Equilibrium Polymers: Effects of High Density and Ring Formation

An off-lattice Monte Carlo algorithm for solutions of equilibrium polymers (EP) is proposed. At low and moderate densities this is shown to reproduce faithfully the (static) properties found recently for flexible linear EP using a lattice model. The molecular weight distribution (MWD) is well described in the dilute limit by a Schultz-Zimm distribution and becomes purely exponential in the semi-dilute limit. Additionally, very concentrated molten systems are studied. The MWD remains a pure exponential in contrast to recent claims. The mean chain mass is found to increase faster with density than in the semi-dilute regime due to additional entropic interactions generated by the dense packing of spheres. We also consider systems in which the formation of rings is allowed so that both the linear chains and the rings compete for the monomers. In agreement with earlier predictions the MWD of the rings reveals a strong singularity whereas the MWD of the coexisting linear chains remains essentially unaffected.