FOURIER-TRANSFORM INFRARED STUDY OF POLY (2-HYDROXYETHYL METHACRYLATE) PHEMA

Fourier transform infrared spectra in the wave number range 450-4500 c m(-1) of poly (2-hydroxyethyl methacrylate) PHEMA have been studied as functions of water content in the range 38-2.6 wt % and of temperatur e 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 vibr ation and O-H stretching vibration with a change in water content and temperature. The results confirm two types of water in the hydrogel po lymer system, tightly bound water and loosely bound water. At low conc entrations, water is mainly hydrogen-bonded to the polymer and is desc ribed 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 li ke bulk water. Infrared spectroscopic results supplement those obtaine d 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 bond ed 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-spec ific insight into the local behaviour of water in hydrated PHEMA.