Time-resolved near-infrared and two-dimensional near-infrared correlation spectroscopic studies on polymerization of the silane coupling agent perfluorooctyltrimethoxysilane

Abstract

 The polymerization behavior of perfluorooctyltrimethoxysilane (PFOS) in ethanol, which is acid-catalyzed by 0.25 M HCl, has been examined using time-resolved near-IR and 2D near-IR correlation spectra. In the time-resolved near-IR spectra, the bands at 5164 and 4825 cm⁻¹ have been assigned to the combination bands of water and ethanol OH groups, respectively. It has been found that the absorbance variation of the two near-IR bands occurs in a two-step process. The absorbance of the 5164 cm⁻¹ band rapidly decreases in the initial step but increases exponentially in the second step, while that of the 4825 cm⁻¹ band rapidly increases both in the initial step and, exponentially, in the second step. These results indicate that the time-dependent absorbance variation of the two near-IR bands reflects the polymerization process of PFOS, in which consumption and release of water molecules and release of methanol in the two-step process occur as a consequence of the acid-catalyzed hydrolysis of methoxy groups and the formation of silanols (SiOH) to form a siloxane bond. It has also been found that this polymerization process is distinctly reflected in the 2D near-IR correlation spectra.