A method of homogeneously polymerizing styrene comprising admixing an ethylenically unsaturated monomer and an initiation system that is soluble in the monomer. This system includes a metal; a peroxide, hydroperoxide or mixture thereof; and a reductant. Under appropriate reaction conditions, the cyclic oxidation and reduction of the metal produces free radicals which initiate homogeneous polymerization of the ethylenically unsaturated monomer. The invention beneficially enables relatively low temperature processing with inexpensive initiation.