Methyl methacrylate (MMA) and tetraethylene glycol diacrylate (TEGDA), containing less than 0.01 mol % 2-dimethylamino-7-nitrofluorene (DANF), have been polymerized using Co-60 gamma radiation. Changes occurring in the effective polarity of the materials during the course of polymerization were monitored as changes in the fluorescence wavelength and decay time of DANF using laser flash photolysis. The difference in polymerization rate, the effect of oxygen, and the occurrence of the Trommsdorff effect could be monitored.