Measurement and Modeling of Methyl Acrylate Radical Polymerization in Polar and Nonpolar Solvents

The influence of hydrogen bonding on the radical polymerization kinetics of methyl acrylate (MA) is studied by conducting in situ nuclear magnetic resonance and lab batch experiments in both toluene and ethanol/water (EtOH/H2O) solutions between 50 and 70 degrees C with initial monomer contents of 10-40 wt % and various initiator contents. While polymerization behavior is influenced by backbiting in both systems, the rate of monomer conversion was found to be significantly faster for reactions conducted in the polar solvent mixture. The experimental investigation also found that the average molar mass of poly(MA) was significantly higher in deuterated solvents compared to protonated solvents, a result attributed to an order of magnitude reduction in the abstractability of deuterium from C-D bonds compared to hydrogen from C-H bonds. A mechanistic model that included acrylate backbiting, the influence of solvent viscosity and radical chain length on termination, and the dependency of initiator efficiency on monomer content was implemented to describe the results, with the appreciable influence of monomer content and solvent composition on MA propagation kinetics in EtOH/H2O also accounted for. The model successfully captures MA polymerization behavior (i.e., monomer conversion and final product short chain branching levels and polymer molar mass distributions) in both solvent systems over the complete range of experimental operating conditions. The systematic approach adopted provides a roadmap to study the influence of monomer content and solvent composition on other acrylate polymerizations conducted in polar media.