This invention relates to a coating composition which can be cured by exposure to radiation energy in the presence of a cationic photoinitiator. The composition comprises a mixture of between about 1 and about 75 wt. % of a reactive vinyl or alk-1-enyl ether cyclocarbonate having the formula ##STR1## wherein R is hydrogen or lower alkyl; R' is C.sub.2 to C.sub.4 alkylene; n has a value of from 0 to 4 and n' has a value of from 1 to 4 and between about 99 and about 25 wt. % of a polymerizable compound containing an onium salt initiator which is normally insoluble in said polymerizable compound or a mixture thereof. The invention also relates to the use of the composition as a protective coating on a substrate.