The behavior of six cyclic acetals and related compounds in the photoinitiation step of a radical photopolymerization was investigated As shown by the photopolymerization kinetic data obtained from FTIR spectroscopy most of them are efficient coinitiators in the presence of benzophenone (BP) with efficiencies close to a reference amine coinitator (ethyl dimethylaminobenzoate EDB) Laser flash photolysis and ESR spin trapping technique were used to study the photochemical mechanisms of the production of initiating radicals and explain the differences in reactivity (c) 2010 Wiley Periodicals Inc J Polym Sci Part A Polym Chem 48 5758-5766 2010