KINETICS AND MECHANISM OF THE REACTION OF HYDRATED CHROMIUM(III) WITHPARTIALLY HYDROLYZED POLYACRYLAMIDE

The kinetics of the cross-linking reaction of partially hydrolyzed pol yacrylamide (HPAAm) by Cr3+ have been studied over a range of experime ntal conditions by means of UV spectroscopy. The kinetic rate law, k = A exp(-E(a)/RT)[Cr3+][H+]-0.8[P]0.8, is in reasonable agreement with that reported previously for the uptake of Cr3+ by HPAAm for a differe nt range of compositions and agrees closely with that reported for the reaction of Cr3+ with carboxylate monomers. The frequency factor A (( 4.9 +/- 0.5) x 10(8) s-1) and activation energy E(a) (19 +/- 1.8 kcal/ mol) were derived for the polymer reaction in experiments conducted be tween 293 and 353 K. Earlier proposals that the rate determining step on the pathway to polymer cross-linking involves the oligomerization o f hydrated Cr3+ ions are excluded by the present results. EPR studies carried out on the Cr3+ solutions and dialyzed gels provide insight in to the nature of the cross-linking Cr3+ species produced subsequent to the rate determining step.