(36h) Experimental and Macroscopic Mechanistic Modeling Studies of the Methyl Acrylate Self-Initiation Reaction

Acrylic polymers are widely used as adhesives and functional additives in the coating and paint industries. Environmental regulations that have imposed upper bounds on the level of volatile organic compounds, have limited the allowable level of solvents in acrylic coatings and paints [1]. High-temperature (120-180 °C) polymerization has been employed to produce resins with low molecular weights and low solvent concentrations [2]. The low molecular weight of polymer chains compensates for the low solvent concentration, which ensures an adequately-low viscosity of the products and thus their brushability and sprayability. However, at these temperatures secondary reactions, such as monomer self-initiation, β-scission, inter/intra-molecular chain transfer, and backbiting, influence the polymerization strongly. The self-initiation reaction of acrylates has several positive attributes [3, 4]. As its presence decreases the need for conventional thermal initiators, operation costs decrease (thermal initiators are typically the most expensive components of paints and coatings), and it also lowers the level of unreacted thermal initiators in the final product, thus improving the quality of the products.

In this paper, an experimental study on the self-initiation reaction of methyl acrylate (MA) in free-radical polymerization is presented. To the best of our knowledge, this is the first reported experimental study of self-initiation of MA. MA conversion and polymer molecular weight measurements from free-radical MA homo-polymerization initiated by only the monomer are presented at different high temperatures. A macroscopic mechanistic model that is based on (i) already-known reaction mechanisms that contribute to the polymerization and (ii) a theoretically-identified MA self-initiation mechanism and a second-order reaction rate equation [5, 6], is presented. Using the macroscopic model, the frequency factor and activation energy of the MA self-initiation reaction are estimated from the measurements. The frequency factor and activation energy estimates are compared with predictions obtained via our purely-theoretical quantum chemical calculations (electronic-level modeling) [5, 6].

References

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