Family of compounds crosslinkable by photon irradiation

A copolymer composition crosslinkable by ultraviolet light rays into a 3-dimensional network, said composition comprising, as the cross-linkable monomers:

• (i) from 40 to 80% by weight of 2,3 epithiopropyl alkyl acrylate monomer units of the formula:
• ##STR15## wherein R is hydrogen or a C.sub.1 to C.sub.4 alkyl;
• and (ii) from 60 to 20% by weight of vinyl monomer units of the formula:
• ##STR16## wherein R.sup.1 is hydrogen or an alkyl group of the formula C.sub.n H.sub.2n+1, where n is an integer from 1 to 10 and R.sup.2 is a C.sub.1 to C.sub.5 alkyl group, together with
• (iii) an ultraviolet-initiating amount of an aryl iodonium salt of the formula:
• ##STR17## wherein n is 0 or 1, T.sub.1 and T.sub.2, which are the same or different, are aromatic groups containing from 4 to 20 carbon atoms, Y is:
• ##STR18## where R.sub.3 is hydrogen, alkyl or acyl or ##STR19## where R.sub.4 and R.sub.5, which may be the same or different, are hydrogen, a C.sub.1 to X.sub.4 alkyl or a C.sub.2 -C.sub.4 alkenyl,
• M is Fe, Sn, Sb, Bi, B, P or As X is a halogen atom, and b is an integer from 1 to 5.