Effect of Equilibration on Primitive Path Analyses of Entangled Polymers

We use recently developed primitive path analysis (PPA) methods to study the effect of equilibration on entanglement density in model polymeric systems. Values of N_e for two commonly used equilibration methods differ by a factor of two or three even though the methods produce similar large-scale chain statistics. We find that local chain stretching in poorly equilibrated samples increases entanglement density. The evolution of N_e with time shows that many entanglements are lost through fast processes such as chain retraction as the local stretching relaxes. Quenching a melt state into a glass has little effect on N_e. Equilibration-dependent differences in short-scale structure affect the craze extension ratio much less than expected from the differences in PPA values of N_e.