Investigation of the ceriumIV oxidation of poly(vinyl alcohol)

Abstract

AbstractInitiation of ceric ion‐induced grafting from poly(vinyl alcohol) (PVOH) was studied by examining the formation and lifetime of colored complexes between ceriumIV 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 [CeIV] 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.