Isolating Chemical Reaction Mechanism as a Variable with Reactive Coarse-Grained Molecular Dynamics: Step-Growth versus Chain-Growth Polymerization

TL;DR

This paper introduces a method to isolate chemical reaction mechanisms in molecular dynamics simulations by using identical coarse-grained models, enabling comparison of different polymerization processes like chain- and step-growth.

Contribution

It demonstrates a novel approach to control and compare reaction mechanisms in coarse-grained molecular dynamics, preserving chemical resolution while reducing computational costs.

Findings

Morphologies resemble all-atom simulations

Mechanical testing aligns with experimental results

Reaction mechanism solely influences emergent properties

Abstract

We present a general approach to isolate chemical reaction mechanism as an independently controllable variable across chemically distinct systems. Modern approaches to reduce the computational expense of molecular dynamics simulations often group multiple atoms into a single "coarse-grained" interaction site, which leads to a loss of chemical resolution. In this work we convert this shortcoming into a feature and use identical coarse-grained models to represent molecules that share non-reactive characteristics but react by different mechanisms. As a proof of concept we use this approach to simulate and investigate distinct, yet similar, trifunctional isocyanurate resin formulations that polymerize by either chain- or step-growth. Since the underlying molecular mechanics of these models are identical, all emergent differences are a function of the reaction mechanism only. We find that the microscopic morphologies resemble related all-atom simulations and that simulated mechanical testing reasonably agrees with experiment.