State of irremovable water in solid polymer films examined by Fourier transform infrared spectroscopy I: Poly(ethylene glycol) dimethyl ether

The state of the sorbed water, including the water that cannot be removed by the reduced pressure and water-sorption processes, into poly(ethylene glycol) dimethyl ether (PEG-DME) film was examined by Fourier transform infrared (FT-IR) spectroscopy. The spectrum of the irremovable water could be obtained without a thermal treatment frequently used as the dehydration procedure. It was found that the irremovable water mainly existed in the crystalline region of PEG-DME film, and that its hydrogen-bonding (HB) structure differed from that of the water sorbed from the air. Moreover, the amount of water having the same HB structure as the irremovable water increased with the water contents. These findings could not be revealed by the spectrum of the sorbed water obtained by the conventional dehydration procedure. The experimental procedure examined here allowed us to investigate the true aspects of the irremovable water and the water-sorption processes.