AbstractThe positron lifetime measurement technique was applied to analyze the structural changes occurring in solid‐state polymerization of acrylamide and trioxane. Positronium (Ps) parameters, τ2andI2, which show a marked change as a function of the γ‐ray irradiation dose, signaled the presence of three clearly defined stages in the polymerization process: initiation, propagation, and saturation. The initial increase in τ2, may very well be the result of efficient trapping of Ps in vacancies created around the polymer nuclei. The complicated behavior ofI2may be explained as a chemical reaction between Ps precursors and the radiolysis products of this polymerization p