Analysis of Elongational Viscosity of Entangled Poly (Propylene Carbonate) Melts by Primitive Chain Network Simulations.

Takashi Uneyama,Yuichi Masubuchi,Yuya Doi,Lixin Yang

doi:10.3390/polym14040741

Abstract

It has been established that the elongational rheology of polymers depends on their chemistry. However, the analysis of experimental data has been reported for only a few polymers. In this study, we analyzed the elongational viscosity of poly (propylene carbonate) (PPC) melts in terms of monomeric friction via primitive chain network simulations. By incorporating a small polydispersity of materials, the linear viscoelastic response was semi-quantitatively reproduced. Owing to this agreement, we determined units of time and modulus to carry out elongational simulations. The simulation with constant monomeric friction overestimated elongational viscosity, whereas it nicely captured the experimental data if friction decreased with increasing segment orientation. To see the effect of chemistry, we also conducted the simulation for a polystyrene (PS) melt, which has a similar entanglement number per chain and a polydispersity index. The results imply that PPC and PS behave similarly in terms of the reduction of friction under fast deformations.

Highlights

The nonlinear elongational rheology of polymers is out of the universality that has been established for the linear viscoelasticity and the nonlinear shear rheology [1]
Bach et al [9] and Nielsen et al [10] reported that the steady-state elongational viscosity of polystyrene (PS) melts monotonically decreases with increasing strain rate, even at elongation rates higher than the Rouse relaxation rate
We employed the multi-chain slip-link simulation based on the primitive chain network (PCN) model [33–37], other molecular models could be used as long as elongational rheology can be calculated for polydispersed systems with practical computation costs

Summary

Introduction

The nonlinear elongational rheology of polymers is out of the universality that has been established for the linear viscoelasticity and the nonlinear shear rheology [1]. At the higher strain rates, the viscosity increases with increasing elongation rate, and it approaches a steady value that is determined by the maximum stretch ratio [3] This behavior has been reported for polystyrene solutions [4–7] and a poly (n-butyl acrylate) (PnBA) melt [8]. Yaoita et al [15] analyzed stress relaxation after fast elongation of a PS melt and a PS solution to extract monomeric friction They reproduced the elongational behavior by incorporating the friction change into multi-chain slip-link simulations. We analyzed elongational data of a few poly (propylene carbonate) (PPC) melts to discuss the friction change This carbonate polymer does not have bulky side groups, and it does not exhibit crystallization under the usual experimental conditions.

Model and Simulations

Results and Discussion

Conclusions