Kinetic Study of the Copolymerization of Methyl Methacrylate and Methyl Acrylate Using Quantum Chemistry

Copolymerization of methyl methacrylate and methyl acrylate was studied using quantum chemistry and transition state theory to estimate the kinetic parameters for propagation (k(p), A, E-a). A terminal model and penultimate effect models were studied explicitly by examining 28 different addition reactions involving monomeric, dimeric, and trimeric radicals and monomers for both self- and cross-propagation. Reactant and product conformations were optimized using a combination of a conventional optimization algorithm and relaxed potential energy scans for individual single-bond rotors using unrestricted B3LYP/6-31G(d). The electronic energy was then calculated using MPWB 1 K/6-31G(d,p). Low frequencies were treated using a one-dimensional internal rotor model. A and E-a were regressed based on a plot of ln k(p) vs 1/T over a temperature range of 296.15-800 K. Reactivity ratios (r) characterizing the terminal model were calculated based on the monomeric, dimeric, and trimeric radical addition reactions, and ratios for the explicit penultimate model (r and s) were calculated based on the dimeric and trimeric radical addition reactions and compared to experimental values. The overall propagation rate constant (k(p,copo)) and composition of the copolymer (F) were calculated at different monomer fractions (f). The results based on radical addition of trimeric radicals showed very good agreement with those fitted based on experimental data. Finally, correlation of the activation energies (E-a) with the heats of reactions (Delta H-r) was examined, and the classic Evans-Polanyi relationship was shown to hold well for self- and cross-propagation of methyl acrylates.