Roadmap for Monomer Conversion and Chain Length-Dependent Termination Reactivity Algorithms in Kinetic Monte Carlo Modeling of Bulk Radical Polymerization

Abstract

Radical polymerization is prone to diffusional limitations on termination, leading to a rate acceleration by the gel-effect and molecular changes, with strong increases in average chain length in free radical polymerization (FRP) and improvement of the end-group functionality in reversible deactivation radical polymerization. What complicates the correct implementation of the termination rates in kinetic modeling studies is (i) the chain length and monomer conversion dependence of the individual (apparent) termination rate coefficients (k(t,app,ij) values; i,j: chain length) and (ii) the wide variations in macroradical chain length distribution (CLD) types and shapes along the polymerization and upon altering the reaction conditions, including variations in CLD modality and broadness. In this work, we compare four major kinetic Monte Carlo modeling algorithms to sample termination reaction events in bulk radical polymerization, using literature k(t,app,ij) values. We present a roadmap allowing one to select the most suited algorithm depending on the radical polymerization technique and reaction conditions, therefore opening the pathway to more correct representations of chain length and monomer conversion dependencies in radical polymerization. Case studies are related to bulk nitroxide-mediated polymerization, FRP, and pulsed laser polymerization, following an increasing complexity in the active macroradical CLD type and shape.