Polymer materials have a complex set of structures and interactions that span various scales, and the precise atomistic structure is not measurable under most circumstances. These facts make detailed mechanistic modeling of the mechanical properties of polymer materials especially challenging. Nevertheless, there is a need to understand in more detail the mechanical properties that affect the lifetime under various loads as this will assist with better predictions and with designing new materials. Radical concentration increases have been observed in polymers under significant strain, which demonstrates that bonds are being broken, but a reliable estimate of the effect of strain or force on a single chain has not been available. This motivates a need to use quantum mechanics as part of a suite of multiscale modeling tools for mechanical properties. We use <i>ab initio</i> molecular dynamics simulations with a validated density functional theory method to get estimates of single chain polyethylene lifetimes under imposed strain and force for both a perfect chain and one with a radical. We describe the methodology and compare the results with experimental literature. We demonstrate the non-linear effects of force and strain on the activation energy. These data can be used in higher-scale models to test hypotheses about the effect of network structure and micro structure on the life time of polyethylene and suggest application of similar approaches on other polymer systems.

The effect of strain, force, and radicals on the life time of polyethylene chains from first principles

ACS Spring Meeting 2021

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