Photon transmission technique was used to monitor the free radical crosslinking copolymerization (FCC) of acrylamide (AAm) and N,N'-methylenebis (acrylamide) (Bis) in time. FCC experiments were performed with various Bis contents. 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 macrogel formation from interconnected microgels. Increase in I-sc was modeled using Rayleigh's equation where gelation time was found to be proportional to the volume of the microgels. (C) 2000 Elsevier Science Ltd. All rights reserved.