| The automobile coating industry is undergoing reformation driven by environmental regulations that demand low content of volatile organic compounds. Traditional solvent-borne acrylic resins consisting of high molecular weight polymers that are produced at low temperatures (< 80 degree celsius) need high levels of organic solvent (70%) to be processed as coatings. Alternatively, novel resin compositions consist of acrylic oligomers with multiple crosslinkable functional groups that can undergo reactions on the metal surface. Polymerization at high temperatures (> 120°celsius) is an economical approach to produce such pre-polymers. However, higher reaction temperatures can result in secondary reactions that affect oligomeric quality. Given the potential complexity of resin recipes and the diversity of the reactions that can occur during polymerization at high temperatures, it is desirable to have a method that can predict the characteristics of the final product. In particular, methods for predicting rate coefficients for copolymerization and side reactions such as intramolecular hydrogen transfer and scission would be valuable since these quantities are difficult to access experimentally.; In this research, ab initio calculations and transition state theory were employed to predict kinetic parameters of reactions relevant to acrylate polymerization. A methodology was developed that was able to handle the complexity of the large systems required to mimic polymeric systems accurately, which includes optimization of structures with many conformational degrees of freedom, selection of an accurate yet efficient level of theory, and treatment of low frequencies. The methodology was successfully applied to determine the propagation kinetic parameters of the homopolymerization of methyl methacrylate and methyl acrylate. The methodology was also extended to the copolymerization of methyl methacrylate and methyl acrylate and four secondary reactions in methyl acrylate polymerization. Kinetic Monte Carlo (KMC) was employed to predict the molecular weight distribution (MWD), average molecular weight (Mn, Mw) and average degree of branching with the predicted kinetic parameters for methyl acrylate polymerization. To our knowledge, this methodology is the first demonstration of the prediction of kinetic parameters for acrylate polymerization from first principles. |
