POLYMERIZATION OF ACRYLAMIDE PHOTOSENSITIZED BY THE TRIS(2,2'-BIPYRIDINE)CHROMIUM(III) ION IN AQUEOUS-SOLUTION

The 365 nm continuous irradiation of acidic aqueous solutions of Cr(bpy)3(3+) and acrylamide yields polyacrylamide; the Cr(bpy)2(OH2)23+ aquation product is also produced. Upon pulsed-laser excitation, no chromium(II) product is observed, likely due to the low rate constant for the quenching of thermally-equilibrated 2T1/2E excited states of the photosensitizer by acrylamide and the low-cage escape yield of redox products. Nevertheless, Cr(bpy)3(3+) is a suitable photosensitizer even for excitation with visible light up to 450 nm. The positive dependence of the rate of polymerization on the intensity of absorbed light and [monomer]2 and the inverse dependence on [Cr(bpy)3(3+)] suggest that the termination step of the chain reaction involves the oxidative scavenging of the macro-radicals by the photosensitizer.