Photocurable compositions containing group via aromatic onium salts

Photocurable compositions consisting essentially of

• A. an epoxy resin polymerizable to a higher molecular weight state,
• B. from 0.1 to 15% by weight of a photodecomposable aromatic onium salt of a Group VIa element capable of effecting the cure of epoxy resin when exposed to radiant energy wherein said aromatic onium salt has the formula
• [(R).sub.a (R.sup.1).sub.b (R.sup.2).sub.c X].sub.d .sup.+ [MQ.sub.e ].sup.-(e-f)
• where R is a monovalent aromatic organic radical, R.sup.1 is a monovalent organic aliphatic radical selected from alkyl, cycloalkyl and substituted alkyl, R.sup.2 is a polyvalent organic radical forming a heterocyclic or fused ring structure selected from aliphatic radicals and aromatic radicals, X is a Group VIa element selected from sulfur, selenium and tellurium, M is a metal or metalloid, Q is a halogen radical, a is a whole number equal to 0 to 3 inclusive, b is a whole number equal to 0 to 2 inclusive, c is a whole number equal to 0 or 1, where the sum of a + b + c is a value equal to 3 or the valence of X,
• d = e - f
• f = valence of M and is an integer equal to from 2 to 7 inclusive
• e is >f and is an integer having a value up to 8 and
• C. from 0 to 100 parts by weight of filler, per 100 parts of epoxy resin.