Polymerization of hydroxyalkyl methacrylates characterized by combination of FT-Raman and step-scan FT-ir photoacoustic spectroscopy

The homopolymerizations of bisphenol-A-bis(2-hydroxypropyl methacrylate) (BisGMA) and 2-hydroxyethyl methacrylate (HEMA) were monitored using FT-Raman spectroscopy and those of BisGMA also by FT-i.r. photoacoustic spectroscopy. Raman spectroscopy was applied to quantify the conversion of C=C double bonds of the monomers. Changes of intensity and wavenumber of the carbonyl band observed in the Raman spectra during the polymerizations were complementally studied by use of FT-i.r. photoacoustic spectroscopy. The carbonyl vibrational band at 1700 cm(-1) was identified as the vibrational mode of the carbonyl group with hydrogen bonds and those at 1717 cm(-1) (Raman) as well as 1725 cm(-1) (i.r.) as the modes of the 'free' carbonyl group. Localization of the pi-electrons of the carbonyl group and decreasing strength of the hydrogen bonds caused by the polymerization reaction result in a decrease of the Raman intensity and an increase of the i.r. intensity as well as of the wavenumber of the carbonyl i.r. vibrational mode at 1700 cm(-1). (C) 1998 Elsevier Science Ltd. All rights reserved.