Hardenable composition and its use

A process for the polymerization of a material polymerizable by free radical polymerization, under the action of radiation, in the presence of a photoinitiator, complete hardening being effected by the heat of reaction produced and in the absence of external heating, which comprises

• irradiating
• (1) a material polymerizable by free radical polymerization, and
• (2) a mixture of
• (i) at least one iron compound of the formula I ##EQU4## wherein a is 1 or 2 and q is 1, 2 or 3,
• L is a divalent to heptavalent metal or non-metal,
• Q is a halogen atom,
• m is an integer corresponding to the sum of the valencies of L and q,
• R.sup.1 is an unsubstituted n6-benzene or is an n6-benzene which is monosubstituted or polysubstituted by identical or different halogen atoms or C.sub.1 -C.sub.12 -alkyl, C.sub.2 -C.sub.12 -alkenyl, C.sub.2 -C.sub.12 -alkynyl, C.sub.1 -C.sub.8 -alkoxy, cyano, C.sub.1 -C.sub.12 -alkylthio, C.sub.2 -C.sub.6 -monocarboxylic acid ester, phenyl, C.sub.2 -C.sub.5 -alkanoyl or benzoyl groups, and
• R.sup.2 is an unsubstituted cyclopentadienyl anion or is a cyclopentadienyl anion which is monosubstituted or polysubstituted by identical or different C.sub.1 -C.sub.8 -alkyl, C.sub.2 -C.sub.8 -alkenyl, C.sub.2 -C.sub.8 -alkynyl, C.sub.2 -C.sub.6 -monocarboxylic acid ester, cyano, C.sub.2 -C.sub.5 -alkanoyl or benzoyl groups, and
• (ii) at least one sensitizer for the compounds of the formula I, and
• (iii) at least one electron acceptor as an oxidizing agent.