Infrared absorption spectra of some polyaminopropylsiloxane (poly-APS) samples with different degrees of polymerization have been examined. The results show that this difference results in a marked variation in the environment of the NH2 groups. The thermal and adsorbed-water effects on the silane-coated layer of silica gel samples, modified with 3-aminopropyltriethoxysilane (APTS), have also been investigated using a diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic method. The results are summarized as follows. For the silica gel samples, the DRIFT spectral features in the CH stretch and NH2 bend modes are almost independent of temperature within the range 303-373 K, indicating stable environments for the aminopropylsilyl segments of the silane-coated layer. For a sample which was treated with a higher APTS concentration, the spectral features were little affected by adsorption of water, while the effect of adsorbed water on a sample treated with a small APTS concentration led to observation of pronounced spectral features. These results have been ascribed to the difference in the degree of polymerization of the silane-coated layer between the samples.
Shimizu, I., Okabayashi, H., Taga, K., Nishio, E., & O’Connor, C. J. (1997). Diffuse reflectance infrared Fourier transform spectral study of the thermal and adsorbed-water effects of a 3-aminopropyltriethoxysilane layer modified onto the surface of silica gel. Vibrational Spectroscopy, 14(1), 113–123. https://doi.org/10.1016/S0924-2031(97)00002-7