Methods of forming an adhesive composition including the steps of (a) combining a non-deaerated mixture comprising at least one free radically (co)polymerizable ethylenically-unsaturated material with a sealable packaging, wherein the packaging contains the non-deaerated mixture; (b) sealing the non-deaerated mixture in the packaging to form a sealed packaging; and (c) exposing the non-deaerated mixture in the sealed packaging to a source of ionizing radiation for a time sufficient to initiate (co)polymerization of at least a portion of the at least one free radically (co)polymerizable ethylenically-unsaturated material to form an adhesive composition in the sealed packaging. The (co)polymerization takes place essentially non-adiabatically. At least a portion of the packaging is meltable and mixable with the adhesive composition so as to provide a flowable coatable adhesive composition when the sealed packaging containing the adhesive composition is heated to a temperature sufficient to melt at least a portion of the packaging.