Effect of UV-curing conditions on the polymer structures: a comparison between coating and adhesive

Abstract

Radical photopolymerization of acrylate was carried out without a degassing process under conditions suitable for UV-curable coatings and UV-curable adhesives. We examined the differences in the resulting polymer structures obtained from the coating and adhesive by employing the same formulation. 2,2-Dimethoxy-2-phenylacetophenone was employed as a photoinitiator. The UV-curable coating yielded polymers terminated by either a hydroxyl group or a terminal carbonyl group as the main products. On the other hand, the UV-curable adhesive yielded a multitude of polymers that were terminated by disproportionation. In the latter case, some polymers underwent hydrogen abstraction from the polymer backbone, resulting in β-scission of the midchain radical to generate polymers with an α-substituted acryloyl group as the terminal group. We examined the differences between the resulting polymer structures in the cases of a coating and an adhesive employing the same formulation. The UV-curable coating yielded polymers terminated by either a hydroxyl group or a terminal carbonyl group as the main products, suggesting that bimolecular termination was strongly inhibited by oxygen. On the other hand, the UV-curable adhesive yielded a multitude of disproportionation products, whereas some polymers underwent hydrogen abstraction from the polymer backbone, resulting in β-scission of the midchain radical to generate polymers with an α-substituted acryloyl group.