Secondary reactions during acrylate radical polymerization: Determining their rate coefficients

Abstract

Secondary reactions in the radical polymerization of acrylic monomers are challenging to include in the existing kinetic models. It is laborious to experimentally measure their rate coefficients as they occur in parallel to the main reactions, but with a much smaller rate. However, secondary reactions contribute to the formation of specific functional groups in polymer molecules, e.g., unsaturation, branching, etc., influencing the molecular and material properties of the polymers. Therefore, it is important to correctly account for them in the computer models/digital twins of the polymerization processes to correctly predict the polymer structures. Because of the large uncertainties on secondary rate coefficients, this work provides a systematic review of the experimental measurements and theoretical predictions of the secondary reactions’ rate coefficients, accounting for mid-chain radical propagation, backbiting, beta-scission, chain transfer to polymer, and monomer and macromonomer propagation. Special attention is devoted to the measurement techniques, outlining the accuracy and limitations of each method. For the theoretical calculations, we focus on the Arrhenius parameters predictions and try to make fairer comparisons with experiments.