The structure of water sorbed to polymethoxyethylacrylate film as examined by FT-IR spectroscopy

The state of sorbed water and sorbing processes of water to four kinds of vinyl polymer films were studied by FT-IR. The O-H stretching band of water sorbed to the films gradually increased on contact with a water vapor of 50% relative humidity at 25°C and leveled off. The profile of the O-H stretching band of sorbed water changed with chemical structure of the polymers. Water sorbed to poly(methoxyethylacrylate) (PMEA), for example, had a sharp and large peak at 3625 cm^-1 and a neighboring broader peak with a long slope in the lower frequency region, which resembled the summation of the peaks for water sorbed to poly(methylmethacrylate) (PMMA, two sharp peaks) and poly(vinylmethylether) (PVME, two broader peaks in the lower frequency region) films. The peak frequencies of the sorbed water were consistent with the calculated values for water hydrogen-bonded to the model compounds by using a hybrid density functional method. When water droplets were put on the polymer film, furthermore, the O-H stretching band of water within the polymer matrix was obtained using an attenuated total reflection technique. An O-H profile similar to that of free water was observed for water incorporated within the matrix of PMEA and PVME films, whereas those profiles within the matrix of poly(2-hydroxyethylmethacrylate) (PHEMA) and PMMA films were largely different from that of free water. This might be in accordance with the difference in biocompatibility of four kinds of polymeric materials. The diffusion coefficients of water vapor in these polymer films were also determined by the time-resolved FT-IR method.