DFT Study on the Propagation Kinetics of Free-Radical Polymerization of α-Substituted Acrylates

Abstract

The kinetics of the free-radical propagation of methyl acrylate (MA), methyl methacrylate (MMA), ethyl α-fluoroacrylate (EFA), ethyl α-chloroacrylate (ECA), ethyl α-cyanoacrylate (ECNA), and methyl α-hydroxymethacrylate (MHMA) have been calculated using quantum chemical tools. Various DFT functionals such as BMK, BB1K, MPW1B95, MPW1K, and MPWB1K were used to model the relative propagation kinetics of the monomers. Among the methodologies used, MPWB1K/6-311+G(3df,2p)//B3LYP/6-31+G(d) was found to yield the best qualitative agreement with experiment. We explored chain length effects by examining addition reactions of monomeric, dimeric, trimeric, and tetrameric radicals to the monomers. We have also modeled the tacticity of the widely used monomers MA and MMA by considering all of the alternatives of attack of the radical in the 3D space around the monomer. This study has qualitatively confirmed the experimental syndiotactic/isotactic ratio of 66/3 for MMA. Finally, the kinetics of the initiation to polymerization for MA and MMA is also successfully reproduced.