Coarse-Grained Molecular Dynamics Simulation of Polycarbonate Deformation: Dependence of Mechanical Performance by the Effect of Spatial Distribution and Topological Constraints

Polycarbonate is an engineering plastic used in a wide range of applications due to its excellent mechanical properties, which are closely related to its molecular structure. We performed coarse-grained molecular dynamics (CGMD) calculations to investigate the effects of topological constraints and spatial distribution on the mechanical performance of a certain range of molecular weights. The topological constraints and spatial distribution are quantified as the number of entanglements per molecule ($N_{\mathrm{e}}$) and the radius of gyration ($R_{\mathrm{g}}$), respectively. We successfully modeled molecular structures with a systematic variation of $N_{\mathrm{e}}$ and $R_{\mathrm{g}}$ by controlling two simulation parameters: the temperature profile and Kuhn segment length, respectively. We investigated the effect of $N_{\mathrm{e}}$ and $R_{\mathrm{g}}$ on stress–strain curves in uniaxial tension with fixed transverse strain. The result shows that the structure with a higher radius of gyration or number of entanglements has a higher maximum stress (${\sigma }_{\mathrm{m}}$), which is mainly due to a firmly formed entanglement network. Such a configuration minimizes the critical strain (${\epsilon }_{\mathrm{c}}$). The constitutive relationships between the mechanical properties (${\sigma }_{\mathrm{m}}$ and ${\epsilon }_{\mathrm{c}}$) and the initial molecular structure parameters ($N_{\mathrm{e}}$ and $R_{\mathrm{g}}$) are suggested.