(259b) Kinetic Modeling Of Acrylate Polymerization At High Temperature

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 ºC) 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 crosslinking reactions on the metal surface. Polymerization at high temperatures (>120 ºC) 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 intermolecular and intramolecular hydrogen transfer and scission would be valuable since these quantities are difficult to access experimentally.

In our research, quantum chemistry calculations and transition state theory are employed to estimate kinetic parameters, including frequency factors and activation energies, of propagation, intramolecular transfer and mid-chain radical scission. Geometry optimization of high molecular weight species that are suitable mimics for polymeric compounds is challenging. To address this, stable conformations were located by combining conventional optimization with relaxed potential energy scans for all single bond dihedrals. Large molecules can also have numerous low frequency vibrations. It is known that treating these low frequency vibrations as harmonic oscillators can introduce substantial error in the values of the predicted rate coefficients. Therefore, a methodology for treating low frequencies was developed, in which low frequencies were treated using a hindered rotor model.

Our methodology was specifically applied to the study of methyl acrylate and methyl methacrylate polymers. Propagation rate coefficients of methyl methacrylate and methyl acrylate were estimated and shown to be in reasonable agreement with experimental values. 1,5 hydrogen transfer reactions of methyl acrylate and scission reactions of the transfer product were studied as well. Kinetic Monte Carlo was used to predict the molecular weight distribution and branching distribution based on the predicted kinetic parameters.