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Langmuir 2006, 22, 2422-2425
State of Irremovable Water in Solid Polymer Films Examined by Fourier Transform Infrared Spectroscopy I: Poly(Ethylene Glycol) Dimethyl Ether Makoto Gemmei-Ide, Tetsuya Motonaga, and Hiromi Kitano* Department of Chemical and Biochemical Engineering, UniVersity of Toyama, 3190 Gofuku, Toyama 930-8555, Japan ReceiVed NoVember 17, 2005. In Final Form: January 19, 2006 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.
Introduction Numerous researchers have investigated water-polymer systems using various techniques.1,2 Among them, a mid-infrared spectroscopy would be very suitable for the analysis of a very small amount of water because of its high sensitivity for the O-H stretching fundamentals of the water molecule.3 Taking this advantage, many researchers,1g-m including our group,2 have reported on the state of water sorbed into the solid polymers, including the biopolymers. In many cases, the spectrum of the sorbed water was obtained as a difference spectrum between dried and hydrated polymers. An absolute requirement for this method is that the “dried polymer” is literally in the completely dried state. This is very natural, but it is very difficult to verify whether water, which cannot be removed in vacuo, exists in solid polymers. However, the thermal treatment frequently used for the complete dehydration cannot be carried out, due to an anxiety that the true aspects of the hydrogen-bonding (HB) structure of the sorbed water and the water-sorption processes are hidden by the treatment inducing the degradation and/or the configuration change of the polymer. In many cases, the * To whom correspondence should be addressed. (1) For example, NMR: (a) Jayakody, J. R. P.; Stallworth, P. E.; Mananga, E. S.; Farrington-Zapata, J.; Greenbanm, S. G. J. Phys. Chem. B 2004, 108, 4260. (b) Horstmann, M.; Urbani, M.; Veeman, W. S. Macromolecules 2003, 36, 6797. (c) Baille, W. E.; Malvean, C.; Zhu, X. X.; Marchessault, R. H. Biomacromolecules 2002, 3, 214. (d) Arnold, K.; Lu¨sse, S. Macromolecules 1996, 29, 4251. DSC: (e) Hatakeyama, H.; Hatakeyama, T. Thermochim. Acta 1998, 308, 3. (f) Feldstein, M. M.; Shandryuk, G. A.; Kuptsov, S. A.; Plate´, N. A. Polymer 2000, 41, 5327, 5339. Vibrational spectroscopy: (g) Yarwood, J.; Sammon C.; Mura, C.; Pereira, M. J. Mol. Liq. 1999, 80, 93. (h) Sammon, C, Deng, C.; Mura, C.; Yarwood, J. J. Mol. Liq. 2002, 101, 35. (i) Philippe, L.; Sammon, C.; Lyon, S. B.; Yarwood, J. Prog. Org. Coat. 2004, 49, 302, 315. (j) Jamro´z, D.; Mare´chal Y. J. Mol. Struct. 2004, 693, 35. (k) Mare´chal Y. J. Mol. Struct. 1997, 416, 133. (l) Sutandar, P.; Ahn, D. J.; Franses, E. I. Macromolecules 1994, 27, 7316. (m) McDonough, L. A.; Dragnea, B.; Preusser J.; Leone, S. R. J. Phys. Chem. B. 2003, 107, 4951. (2) For example, (a) Kitano, H.; Tada, S.; Mori, T.; Takaha, K.; Gemmei-Ide, M.; Tanaka, M.; Fukuda, M.; Yokoyama, Y. Langmuir 2005, 21, 11932. (b) Kitano, H.; Imai, M.; Mori, T.; Gemmei-Ide, M.; Yokoyama, Y.; Ishihara, K. Langmuir 2003, 19, 10260. (c) Ide, M.; Mori, T.; Ichikawa, K.; Kitano, H.; Tanaka, M.; Mochizuki, A.; Oshima, H.; Mizuno, W. Langmuir 2003, 19, 429. (d) Kitano, H.; Ichikawa, K.; Ide. M.; Fukuda, M.; Mizuno, W. Langmuir 2001, 17, 1889. (3) (a) Bertie, J. E.; Labbeu, H. J.; Whalley, E. J. Chem. Phys. 1969, 50, 4501. (b) Ikawa, S.; Maeda, S. Spectrochim. Acta 1968, 24A, 655. (c) Schaaf, J. W.; Williams, D. J. Opt. Soc. Am. 1973, 63, 726. (d) Whalley, E. J. Glaciol. 1978, 21, 13.
dehydration procedure of the solid polymers in vacuo may be taken complete, and then the spectra for sorbed water were obtained. In this report, using poly(ethylene glycol) dimethyl ether (PEG-DME) as a model polymer, the experimental method, which can give the IR spectrum of the irremovable water in a polymer matrix without thermal treatment, was demonstrated, and the HB structure of the irremovable water and the watersorption processes were examined.
Experiment IR Spectroscopy. IR spectra of the polymer films were recorded on a Spectrum One NTS (Perkin-Elmer Instrument, U.S.A.) with a resolution of 4 cm-1 and a scanning time of 90 s. The spectrum of the sorbed water into the film was obtained as a difference spectrum between the hydrated and dried films. In this report, the dried film used as a background was prepared by the following two methods: (i) a cast film prepared from chloroform solution was dried in vacuo at 300 K for 24 h, and (ii) the film that was dried one time was rehydrated under D2O moisture, and this hydrated film was redried in vacuo at 300 K for 24 h. The former and latter dried films are denoted as “dried film” and “redried film”, respectively. Therefore, the two types of spectra for the sorbed water were obtained from the individual polymer spectra. For convenience, in this report, the former and latter spectra are denoted as the “difference spectrum” and “subtract spectrum”, respectively. Polymer Film. PEG-DME with Mw ) 2064 (Fluka, Switzerland) was purified by precipitation in ethanol-ether. The PEG-DME film was prepared from chloroform solution on sapphire substrates and dried at 300 K under
