The free radical copolymerizations of dimethylacrylamide (DMA) with ethylene dimethacrylate (EDMA) and of DMA with methyl methacrylate (MMA) have been conducted over a wide range of conversion. Compositions of resultant crosslinked poly(DMA-co-EDMA) and of linear poly(DMA-co-MMA) were determined by nitrogen analysis and FTi.r., respectively. Appropriate modern procedures applied to the data yielded reactivity ratios of tau(DMA)=0.51 +/- 10.15, tau(MMA) = 2.07 +/- 0.19 and tau(DMA) = 0.9 +/- 0.2, tau(EDMA) = 1.8 +/- 0.6, the latter pair being obtained neglecting possible reactivity of pendant double bonds. gamma-Irradiation of DMA/MMA mixtures both in the absence and presence of EDMA yielded highly swellable crosslinked xerogels. The equilibrium water content of the hydrogels increased with increase of DMA in copolymer and with decreasing content of EDMA. Over the range of swelling temperature examined, 280-338 K, the swelling was found to be exothermic. At comparable molar compositions, these materials exhibited higher water contents than the corresponding hydrogels containing N-vinyl-2-pyrrolidone in place of DMA.