Free radical polymerization simulation and molecular entanglement effect on large deformation behavior

Abstract

In this paper, we proposed a novel molecular dynamics (MD) free radical polymerization algorithm that can dynamically simulate chain growth of the thermoplastic network and produce unit cells having experimentally observed molecular weight distributions. In the proposed algorithm, a coarse-grained force field was implemented by combining bonded terms from the PCFF and nonbonded terms from the TraPPE-UA to alleviate computational times. We controlled molecular weight distribution by the number of initiator radicals. Effects of the molecular weight on density, and glass transition temperature were investigated. A linear relationship of the conversion ratio with specific volume change was discovered. More importantly, the PMMA system by the proposed MD polymerization algorithm could explain physical causes of stress-softening behavior often observed in the large deformation tensile tests in terms of molecular weight and unfolding of chain entanglement. The proposed polymerization algorithm will facilitate studies on large deformation nonlinear constitutive behavior and modelings of thermoplastic polymers.