(193p) Experimental and Macroscopic-Level Mechanistic Modeling Study of Self-Initiated High-Temperature Polymerization of Ethyl Acrylate

Free radical polymerization (FRP) has been used widely to prepare a variety of polymers with different properties [1]. Acrylic polymers are used in the paints and coatings industry, textiles, non-woven fibers, and medical devices [2, 3]. Acrylic resins provide good weather resistance, and resistance to hydrolysis in exterior applications. Due to their versatility and performance, acrylic coatings account for over 25% of all coatings, and their global annual sale is approaching $25 billion. However, due to environmental regulations limiting volatile organic contents (VOCs) of paints and coatings, the paints and coatings industries have had to produce these solvent-borne resins with less solvents [4, 5], making the resins poorly brushable and sprayable. To address this major problem, the average molecular weights of polymer chains in the resins had to be lowered. High-temperature (120–220 ̊C) polymerization has been used primarily to produce the low solvent-content, low average molecular weights resins [6]. At the high temperatures, polymerization reactions such as monomer self-initiation, β-scission, inter/intra-molecular chain transfer and backbiting should be accounted for [7]. These reactions positively contribute to the formation of the low molecular weight polymer chains. For example, in the presence of monomer self-initiation reactions, less external thermal initiators are needed (thermal initiators are typically the most expensive components of paints and coatings) and the level of unreacted thermal initiators in the final product is lower, improving the quality of the resins [8, 9].

This paper presents an experimental and theoretical study of the self-initiation reaction of ethyl acrylate (EA) in free-radical polymerization. To the best of our knowledge, this is the first reported experimental study of self-initiation of EA. At different high temperatures, thermal free-radical homo-polymerization of EA is carried out in the absence of any added conventional initiators, and EA conversion and polymer molecular weight measurements are made. A macroscopic-level mechanistic model is developed and validated. This model is based on (i) already-known reaction mechanisms that contribute to the polymerization and (ii) an EA self-initiation mechanism and a second-order reaction rate equation predicted with first-principles density functional theory (DFT) calculations [10]. The self-initiation kinetic parameters are also estimated from the polymer-property measurements, and these estimates are compared to those predicted by DFT.

References

1. Matyjaszewski, K.; Spanswick, J., Controlled/living radical polymerization. Materials Today 2005, 8 (3), 26-33.
2. Dittgen, M.; Durrani, M.; Lehmann, K., Acrylic polymers - A review of pharmaceutical applications. 1997; Vol. 7, p 403-437.
3. Ohara, T.; Sato, T.; Shimizu, N.; Prescher, G.; Schwind, H.; Weiberg, O.; Marten, K.; Greim, H., Acrylic acid and derivatives. Ullmann's encyclopedia of industrial chemistry 2003.
4. Lebduška, J.; Šnupárek, J.; Kašpar, K.; Čermák, V., Solution copolymerization of styrene and 2‐hydroxyethyl mechacrylate. Journal of Polymer Science Part A: Polymer Chemistry 1986, 24 (4), 777-791.
5. Arabi Shamsabadi, A.; Moghadam, N.; Srinivasan, S.; Corcoran, P.; Grady, M. C.; Rappe, A. M.; Soroush, M., Study of n-Butyl Acrylate Self-Initiation Reaction Experimentally and via Macroscopic Mechanistic Modeling. Processes 2016, 4 (2), 15.
6. Srinivasan, S.; Kalfas, G.; Petkovska, V. I.; Bruni, C.; Grady, M. C.; Soroush, M., Experimental study of the spontaneous thermal homopolymerization of methyl and n‐butyl acrylate. Journal of applied polymer science 2010, 118 (4), 1898-1909.
7. Riazi, H.; A. Shamsabadi, A.; Grady, M. C.; Rappe, A. M.; Soroush, M., Experimental and Theoretical Study of the Self-Initiation Reaction of Methyl Acrylate in Free-Radical Polymerization. Industrial & Engineering Chemistry Research 2018, 57 (2), 532-539.
8. Riazi, H.; Shamsabadi, A. A.; Corcoran, P.; Grady, M. C.; Rappe, A. M.; Soroush, M., On the Thermal Self-Initiation Reaction of n-Butyl Acrylate in Free-Radical Polymerization. Processes 2018, 6 (1), 3.
9. Quan, C.; Soroush, M.; Grady, M. C.; Hansen, J. E.; Simonsick, W. J., High-temperature homopolymerization of ethyl acrylate and n-butyl acrylate: Polymer characterization. Macromolecules 2005, 38 (18), 7619-7628.
10. Liu, S.; Srinivasan, S.; Tao, J.; Grady, M. C.; Soroush, M.; Rappe, A. M., Modeling spin-forbidden monomer self-initiation reactions in spontaneous free-radical polymerization of acrylates and methacrylates. The Journal of Physical Chemistry A 2014, 118 (40), 9310-9318.