Investigation of the ceriumIV oxidation of poly(vinyl alcohol)

Initiation of ceric ion-induced grafting from poly(vinyl alcohol) (PVOH) was studied by examining the formation and lifetime of colored complexes between cerium^IV and (1) a commercial PVOH, (2) a diol-free PVOH, and (3) several model 1,2-diols. UV/visible spectroscopy was employed using a wavelength of 520 nm. Results showed that the 1,2-diols, which are an inherent defect in PVOH, are the sites most reactive toward ceric ion. The observed rate constant for the reaction was found to increase with decreasing Ce^IV] until the maximum rate was reached at which time reaction took place exclusively with 1,2-diols. The activation energy for oxidation of commercial PVOH at the maximum rate was 15.4 kcal/mol while that for diol-free PVOH was 22.4 kcal/mol. The 1,2-diols of PVOH displayed a high equilibrium constant for complexation with ceric ion, compared to the model 2,3-butanediol. It was suggested that the PVOH chain segments bring about crowding of the diol group, and this leads to a higher equilibrium constant for complexation. The lowest energy conformation of a PVOH chain segment containing a 1,2-diol linkage was calculated using the CHEMLAB-II molecular design program, and the 1,2-diol was predicted to be at the center of a sharp bend in the chain brought about by its presence.