Organic peroxydicarbonates represented by the following graphic formula are described. ##STR1## In the formula, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently selected from an alkyl group containing from 1 to 4 carbon atoms. R.sub.1 and R.sub.2 and/or R.sub.3 and R.sub.4 can participate in a cycloalkyl group having from 3 to 6 carbon atoms. The peroxydicarbonates are useful as initiators for the polymerization or copolymerization of ethylenically unsaturated monomers or the cross-linking of unsaturated polyester resins. The organic peroxydicarbonates can be used in combination with commercially available peroxydicarbonates, particularly those having a longer half-life, or with peresters, diacylperoxides and azo compounds.