Photopolymerizable composition

In a photopolymerizable composition comprising a monomer having at lest two ethylenically unsaturated bonds which is capable of photopolymerization upon exposure to actinic radiation, a photopolymerization initiator and, optionally, a linear organic polymer, the improvement which comprises said photopolymerization initiator comprising a combination of at least one compound represented by the formula (I) ##STR40## wherein Z represents the non-metal atoms necessary to form a nitrogen containing heterocyclic nucleus, R.sub.1 represents an alkyl group or a substituted alkyl group, and R.sub.2 represents an alkyl group or an aryl group, and at least one compound represented by the formula (II) ##STR41## wherein X represents a halogen atom, Y represents --CH.sub.3, --NH.sub.2, --NHR', --NR'.sub.2 or --OR' wherein R' represents an alkyl group or an aryl group, and R represents an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group or a substituted alkenyl group and wherein said photopolymerization initiator is present in an amount of 1 to 10% by weight based on the total weight of the polymerizable ethylenically unsaturated compound and the linear organic high molecular weight compounds and wherein the ratio of the compound represented by formula (I) to the compound represented by formula (II) of said photopolymerization initiator is 4:1 to 1:4.