Kinetics and mechanism of aqueous polymerization of acrylamide by FeCl3-thiourea redox couple are investigated in homogeneous solution with a view to compare results with those observed after trapping metal oxidant in the montmarillonite layered space. The initial rate of polymerization and the intrinsic viscosity are ranged within (0.3-2.3) x 10(4) mol L-1 s(-1) and (14-137) mLg(-1) respectively in the farmer case. Linear termination by metal oxidants is checked in the latter instance resulting in the higher chain growth of the polymers. Formation of the acrylamide pairs in the interlayer positions of acidic montmorillonite, strong ＇cage effect＇ an the initiating thiourea radicals and the delayed termination process are identified as the major causes for the observed mechanistic modification in the montmorillonite gel phase reactions.