The polymerization of acrylic esters without direct use of light and/or heat is an important goal. We have investigated a system where the activating component is delivered in a flow of a carrier gas which has unrestricted access to a surface covered with to-be-polymerized monomers. The active ingredient (H2O2 vapor) reacts with coating components (tetraalkylborates) to generate free radicals and initiate polymerization in the surface layer. Differences in reactivity are explained by differing oxidation potentials and alkyl substituents on the boron atom. Radical trapping experiments support the mechanism proposed.