The hydrogen peroxide photosensitized polymerization of acrylamide in aqueous solution at 25°C using 3130A light proceeds at a rate proportional to the square root of the absorbed light intensity and the first power of the monomer concentration. The primary quantum yield for chain initiation is 0-87 & 0.05 and the values at 25" C of the rate constants determined by the rotating sector method are :The values of the viscosity of aqueous solutions of the polymer indicate that slight monomer transfer (rate constant kf,, ml) and slight initiator transfer (rate constant ktr, i) take place, approximate values of the constants being ktr, *, = 2.2 x 10-1 1. mole-1 sec-1 and ktr, = 9 1. mole-1 sec-1.Immediately following light extinction the rate of polymerization falls, rapidly at first, then more slowly, finally reaching a value which decays extremely slowly. The properties of this after-effect are described and explained in terms of the hypothesis that a polymer radical which is initially reactive goes through several cycles of activity and inactivity which are probably caused by tautomeric changes before it is destroyed by mutual termination. The kinetic consequences of this hypothesis are explored and shown to be in accord with the experimental findings.

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