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 2–4 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 $N_e$.

• Received 1 July 2005

DOI:https://doi.org/10.1103/PhysRevE.72.061802