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(bp y)3(3+) and acrylamide yields polyacrylamide; the Cr(bpy)2(OH2)23+ aqu ation product is also produced. Upon pulsed-laser excitation, no chrom ium(II) product is observed, likely due to the low rate constant for t he quenching of thermally-equilibrated 2T1/2E excited states of the ph otosensitizer by acrylamide and the low-cage escape yield of redox pro ducts. Nevertheless, Cr(bpy)3(3+) is a suitable photosensitizer even f or 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 t he termination step of the chain reaction involves the oxidative scave nging of the macro-radicals by the photosensitizer.