(749c) Computational Study of Chain Transfer to Monomer Reactions In Thermal Polymerization of Methyl Acrylate

North American regulations [1, 2] have required volatile organic content (VOC) of coatings to be less than 300 ppm by 2010. These and similar regulations [3] have been responsible for the changes in the paint and coatings industries in the last sixty years. Low temperature (50-80ºC) polymerization processes producing high molecular weight, low solids polymer resins have been replaced with high temperature (>100ºC) polymerization processes producing low molecular weight, high solids polymer resins [4]. It has also been reported that secondary reactions, such as backbiting, β-scission and chain transfer reactions, have stronger impacts on the dynamics of the processes at higher temperatures.

Previous studies [5-9] have shown the successful use of computational quantum chemistry to better understand self-initiation and propagation reactions in polymerization systems. To the best of our knowledge, no computational study of chain transfer to monomer reactions in polymerization of alkyl acrylates has been reported as of yet.

This paper presents a computational study of chain transfer to monomer reactions in self-initiated high-temperature polymerization of methyl acrylate. Density functional theory calculations are used to predict energy barriers and rate constants of the chain transfer to monomer reactions. The effect of polymer chain-length and radical centers (e.g., tertiary vs. secondary radical) on the energy barriers and rate constants of the reactions are studied. Intrinsic reaction coordinate calculations are carried out to determine the pathways for the mechanisms of interest. 

References:

[1] Superintendent of Documents, Title 1, US Government Printing Office, Washington, DC, 1990, p.1.

[2] Superintendent of Documents, Clean Air Act Amendments of 1990, Title 111, US Government Printing Office, Washington, DC, 1990, p.236.

[3] VOC’s Directive, EU Committee of the American Chamber of Commerce in Belguim, ASBL/VZw, Brussels, July 8, 1996.

[4] Adamsons, K.; Blackman, G.; Gregorovich, B.; Lin, L., Matheson, R.; Oligomers in the Evolution of Automotive Clearcoats : Mechanical Performance Testing as a Function of Exposure, Progress in Organic Coatings 1998, 34, 64-74.

[5] Heuts, J.P.A.; Gilbert, R.G.; Radom, L.; A Prior Prediction of Propagation Rate Coefficients in Free Radical Polymerizations: Propagation of Ethylene, Macromolecules, 1995, 28, p. 8771-81.

[6] Khuong, K.S.; H. Jones, W.H.; Pryor, W.A.; Houk, K.N.; The Mechanism of Self-Initiated Thermal Solution of a Classic Problem, J. Am. Chem. Soc. 2005. 127, 1265-77.

 [7] Yu, X.; Pfaendtner, J.; Broadbelt, L.J.; Ab Initio Study of Acrylate Polymerization Reactions: Methyl Methacrylate and Methyl Acrylate Propagation, J. Phys. Chem. A. 2008, 112, 6772-82.

[8] Srinivasan, S.; Lee, M.W.; Grady, M.C.; Soroush, M.; Rappe, A.M.; Computational Study of the Self-Initiation Mechanism in Thermal Polymerization of Methyl Acrylate, J. Phys. Chem. A 2009, 113, 10787-94.

[9] Srinivasan, S.; Lee, M.W.; Grady, M.C.; Soroush, M.; Rappe, A.M.; Self-Initiation Mechanism in Spontaneous Thermal Polymerization of Ethyl and n-Butyl Acrylate: A Theoretical Study, J. Phys. Chem. A 2010, 114, 7975-83.