Effects of Constraint-Release on Entangled Polymer Dynamics in Primitive Chain Network Simulations

For the entangled polymer dynamics, in addition to reptation and contour length fluctuation (CLF), constraint release (CR) has been widely accepted as an essential relaxation mechanism. However, although conceptually established, the nature of CR has not been fully clarified yet. In this study, entangled polymer dynamics were observed via primitive chain network simulations in the melt, and in a matrix where CR is suppressed. The viscoelastic and end-to-end relaxation times, the diffusion constant, and the apparent plateau modulus were obtained as functions of molecular weight. All the obtained results are reasonably consistent with experimental data in the literature. In the results, CR accelerates the relaxation and the diffusion as expected, and the acceleration factor decreases as an increase of the molecular weight. Consequently, the power-law exponent for the molecular weight dependence of the relaxation time is affected by CR. Meanwhile, the plateau modulus is not affected by CR, yet the molecular weight dependence is consistent with the literature. These results explain the time-stress discrepancy, which has been reported as inconsistency between the relaxation time and the modulus.