Photocurable compositions

A method of forming a photocured coating comprising:

• (a) applying to a substrate (i) a first compound bearing an average of more than one photolabile onium group bonded to a chromophore group which is a phenyl or naphthyl group, via a linking group which is methylene, ethylidene or ##STR62## wherein the onium group is dialkyl sulfonium, trialkyl phosphonium or trialkyl ammonium, wherein each alkyl has from 1 to 4 carbon atoms or where two alkyl groups may be joined to form a 4 or 5 carbon atom alkylene which forms a ring with the onium, and said onium group is substantially free of unsaturated substituents which are photoreactive and has a compatible anion, and (ii) a second compound bearing at least one photo-reactive nucleophile, so as to form a coating of an intimate mixture of (i) and (ii) on the substrate, and
• (b) exposing the coating of the first compound and the second compound to electromagnetic radiation having sufficient energy at wavelengths in the range of from about 200 to about 310 nm to promote reaction of a plurality of onium groups with a plurality of nucleophile groups with extinction of the cationic charge on the onium groups reacted.

A method of forming a photocured coating comprising

• (a) applying to a substrate (i) a first compound bearing an average of more than one photolabile onium group bonded to a chromophore group via a linking group, wherein the onium is substantially free of unsaturated substituents which are photoreactive and has a compatible anion, and (ii) a second compound bearing at least one photo-reactive nucleophile, so as to form a coating of an intimate mixture of (i) and (ii) on the substrate, wherein the first and second compounds are polymers having the same composition and are derived from vinyl addition polymers of from about 1 to about 99 mole percent vinylbenzyl halide, from about 1 to about 50 mole percent of a vinyl group bearing photoreactive nucleophile moieties or precursors of these nulceophile moieties and from about 0 to about 98 mole percent of compatible vinyl monomers and a plurality of the benzyl halide groups have been reacted with precursors of photolabile onium groups, and
• (b) exposing the coating of the first compound and the second compound to electromagnetic radiation having sufficient energy at wavelengths in the range of from about 200 to about 310 nm to promote reaction of a plurality of onium groups with a plurality of nucleophile groups with extinction of the cationic charge on the onium groups reacted.