Balancing O2 Consumption and Monomer Evaporation to Tune Alkene Polymerization in Protective Coatings

Alkene resins with acrylate-based cross-linkers are widely used as coatings to protect metal surfaces from corrosion. Environmental and safety concerns are stimulating the replacement of resin components. Especially, replacing volatile reactive diluents (i.e., styrene) with less volatile diluents and the cobalt(II) carboxylates that activate the alkyl peroxide initiators with benign transition-metal catalysts (e.g., Fe(II) complexes) is desirable. Polymerization of thin coatings (ca. 50–300 μm, depending on the application) involves both physical and chemical processes, including evaporation of diluent, diffusion-driven compositional gradients, and continuous ingress and consumption of O2. In this report, we deconvolute the effects of monomer evaporation and O2 uptake/consumption in air-exposed resin films and show that the final composition of the film is determined by the relative rates of catalyzed O2 depletion and O2 uptake from air and the increase in viscosity due to evaporation of the diluent. The one-dimensional diffusion-reaction model developed for O2 penetration/consumption enables rational tuning of loading of the commercially relevant catalyst Fe(II)-bispidine to provide similar performance as with the industry-standard Co(II) catalysts.