Polymeric photoinitiators having benzoin methylether moieties connected to the main chain through the benzyl aromatic ring and their activity for ultraviolet-curable coatings

New polymeric UV photoinitiators, bearing the benzoin methyl ether moiety linked to the side chain through the 4' position, were synthetized by radical homopolymerization of the corresponding monomers, 4'-methacryloyloxy benzoin methyl ether and 4'-methacryloyloxy alpha-methyl benzoin methyl ether, prepared in turn after a thorough investigation of synthetic methods. For comparison, low molecular weight structural models of the repeating co-units of the polymers having the pivaloyloxy group linked to the 3' position of the benzoin methyl ether moiety were also prepared. All polymeric and model compounds were fully characterized and employed in the photoinitiated polymerization and crosslinking of a standard acrylic formulation for clear UV curable coatings. The photoinitiating activity of these systems, measured by microwave dielectrometry, indicates a higher cure fastness for the model compounds with respect to the corresponding polymeric derivatives, and such a behaviour is tentatively interpreted in terms of the fragmentation mechanism of the benzyl methyl ether radicals formed on alpha-photocleavage of the benzoin moiety. (C) 1999 Elsevier Science Ltd. All rights reserved.