Network microstructures of poly(acrylamide)(PAAm) and poly(N,N-dimethylacrylamide) (PDMA) hydrogels were compared by static light scattering and elasticity measurements. The hydrogels were prepared by free-radicals crosslinking copolyymerization of the monomers acrylamide (AAm) or N,N-dimethylacrylamide (DMA) with N,N'-methylemebis(acrylamide) as a crosslinker. During the formation of PAAm gels, both a maximum and a minimum were observed, corresponding to the chain overlap threshold and the gel point, respectively. This difference in the time-course between the two gelling systems is due to the late onset of gelation in the DMA system with respect to the critical overlap concentrations. Compared to the AAm system, no significant scattered light intensity rise was observed during the crosslinking polymerization of DMA. It was shown that, regardless of the crosslinker ratio and of the initial manomer concentration, PDMA gel is much more homogeneous that the corresponding PAAm gel due to the shift of the gelation threshold to the semidilute regime of the reaction system. The results suggest that the spatial gel inhomogeneity can be controlled by varing the gel point with respect to the critical overlap concentration during the preparation of gels by free-radical mechanisms. (c) 2005 Elsevier Ltd. All rights reserved.