C. Pizzocaro et al., POLYMERIZATION OF ACRYLAMIDE PHOTOSENSITIZED BY THE TRIS(2,2'-BIPYRIDINE)CHROMIUM(III) ION IN AQUEOUS-SOLUTION, Polyhedron, 12(8), 1993, pp. 855-858
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.