Polymerization of acid activated compositions of acrylic monomers, peroxy initiators and ferrocene derivatives is inhibited by addition of 0.5-20% of a vinyl ether monomer. Bulk compositions activated by addition of a strong acid can be provided with a desired polymerization induction time directly related to the concentration of the vinyl ether. Compositions containing compounds which decompose to a strong acid upon exposure to actinic radiation, thereby activating polymerization, have increased shelf lives when vinyl ethers are included therein. The use of vinyl ether monomers having a functionality of two or more also provides increased adhesive bond strength after curing.