Ultraviolet-induced crosslinking of poly(vinyl alcohol) evaluated by principal component analysis of FTIR spectra

The crosslinking of poly(vinyl alcohol) (PVA) films under ultraviolet irradiation for between 1 and 4h was studied in air at 25 degreesC in the presence of sodium benzoate by Fourier-transform infrared spectroscopy (FTIR) using the attenuated total reflectance technique (ATR). Principal component analysis (PCA) is a mathematical procedure that allows treatment of the entire infrared spectrum and is very appropriate for analysing the chemical modifications initiated by sodium benzoate which occur in PVA upon UV irradiation. By PCA it was possible to clarify the mechanism of crosslinking of PVA. From this FTIR-PCA study, it is suggested that a free radical arising from the photolysis of sensitizer would abstract a tertiary hydrogen atom from the polymer chain to yield a polymeric radical. This radical reacts with O-H groups, leading to the formation of ether bonds between the polymeric chains and hence to crosslinking and insolubilization of the PVA. (C) 2001 Society of Chemical Industry.