Methods of (co)polymerizing ethylenically-unsaturated materials, including the steps of providing a non-deaerated mixture of free radically (co)polymerizable ethylenically-unsaturated material in a batch reactor, exposing the non-deaerated mixture to a source of ionizing radiation for a time sufficient to initiate (co)polymerization of at least a portion of the free radically (co)polymerizable ethylenically-unsaturated material, and allowing the free radically (co)polymerizable ethylenically-unsaturated material to (co)polymerize under essentially adiabatic conditions while continuing to expose the mixture to the source of ionizing radiation for a time sufficient to yield an at least partially (co)polymerized (co)polymer. The ethylenically-unsaturated materials are selected from vinyl-functional monomers, vinyl-functional oligomers, vinyl-functional macromers, and combinations thereof. The mixture is preferably free of thermally-induced or UV-induced free radical polymerization initiators. The source of ionizing radiation may be a gamma ray source, an x ray source, an electron beam source with an emission energy greater than 300 keV, and combinations thereof.