Influence of Entanglement Density on Polymer Glass Transition Temperature
Hao Sun, Yunhan Zhang, Fan Peng, Renkuan Cao, Ziwei Liu, Tingyu Xu, Liangbin Li
Abstract
Whether and how the glass transition of polymers is affected by entanglement remains a controversial topic. Experimental studies show varying trends in the change of T g with entanglement density (ρ e ), depending on the polymer type. In this simulation study, we construct polymer systems with different ρ e and observe that systems with higher ρ e exhibit longer structural relaxation times (τ α ), lower configurational entropy ( S c ), and higher T g . Notably, the change in T g with ρ e is only observed when ρ e exceeds a critical threshold, which may explain the discrepancies in previous experimental results. Further analysis suggests that the T g shift is primarily due to the restriction of chain mobility caused by entanglements. This restriction occurs near the entanglement points, where segment packing density increases due to the closer proximity of entangled chains as ρ e increases. We further examine this phenomenon in systems with varying chain rigidity and find that this phenomenon is universal regardless of polymer type.