Fourier transform infrared study of poly (2-hydroxyethyl methacrylate) PHEMA

Abstract

Fourier transform infrared spectra in the wave number range 450-4500 cm^-1 of poly (2-hydroxyethyl methacrylate) PHEMA have been studied as functions of water content in the range 38–2.6 wt % and of temperature in the range 300–373 K. The results show changes in the intensities of the stretching frequencies of the carbonyl band, H-O-H bending vibration and O-H stretching vibration with a change in water content and temperature. The results confirm two types of water in the hydrogel polymer system, tightly bound water and loosely bound water. At low concentrations, water is mainly hydrogen-bonded to the polymer and is described as tightly bound water. However, at water concentrations greater than 18% by weight, part of the water exists in a different form and behaves as loosely bound water. For concentrations over 30%, there is some evidence that excess water behaves more loosely bound somewhat like bulk water. Infrared spectroscopic results supplement those obtained by means of NMR by Smyth et al. and by dielectric spectroscopy. Our results also show that some of the water continues to be hydrogen bonded to the polymer until at least a temperature of 373 K when the bulk water should have evaporated. FTIR is found to yield greater site-specific insight into the local behaviour of water in hydrated PHEMA.