UV-curing of acrylate thin films onto Al₂O₃ particles via free-radical polymerization

The UV curing of ultrathin films of acrylates on AI₂O₃ particles has been stuusing photodifferential scanning calorimetry (photo-DSC). Effects on curing of the chemical structure of the monomers, thickness of the films, type of initiators, and the presence of oxygen were investigated. Results show that photopolymerization of ultrathin films on the particle surface is much more sensitive to oxygen poisoning than the thick films on flat surfaces, and the conversion of monomers depends on the types of monomers and initiators selected. When alpha hydroxyl ketones (Esacure KIP100F) were used as photoinitiators, the final double-bond conversions of both difunctional and trifunctional monomers can only reach up to 10% in the presence of air. The curing kinetics of monomers on particles in either air or nitrogen at the early stages of polymerization can be well fitted with calculations based on the quasi-steady-state assumption. Esacure 1001M, a sulfur-containing benzophenone, has been used together with 2-ethylhexyl-4-dimethylamino benzoate (Esacure EHA) as the initiating system to combat the oxygen-poisoning effect. It was found that this system is much more effective than Esacure KIP100F in achieving high conversions of monomers in the presence of oxygen. This has been further demonstrated by Fourier transform infrared spectroscopy (FTIR).