In situ photon transmission technique was used to monitor the free radical crosslinking copolymerization (FCC) of acrylamide (AAm) and N,N'-methylenebis (acrylamide) (Bis) in real-time. Gelation experiments were performed in various water contents at various wavelengths. It was observed that transmitted photon intensity, I-tr, decreased dramatically at a certain gelation time, which is attributed to the increase in scattered light intensity, I-sc, during FCC. Increase in I-sc was modeled using Rayleigh's equation where gelation time was found to be proportional to the volume of the microgels. The change in I-sc is found to be inversely proportional to the thirth power of the wavelength, lambda, fur high water content samples at early times. However, low water content samples produce smaller and constant power of lambda during FCC at all rimes. The sizes of microgel particles and phase-separated domains were estimated. (C) 2000 Elsevier Science Ltd. All rights reserved.