Molecular Structure of an Aminosilane Coupling Agent as Influenced by Carbon Dioxide in Air, pH, and Drying Conditions.

摘要

The molecular structures of the hydrolyzates of gamma-aminopropyltriethoxysilane (gamma-APS) were studied by Fourier transform infrared spectroscopy (FT-IR). The molecular structure of gamma-APS is a function of the pH of the solution and the drying conditions. In the partially cured film, cast from a 20% by weight gamma-APS aqueous solution at pH=2, the amine group exists as a protonated amine; and at pH=12 the amine group exists as a free NH2. The amine group exhibits different structures subject to drying conditions when prepared at natural pH. The sample dried in nitrogen exhibited hydrogen bonding between the SiOH and the NH2 group. Upon heating, the silanol groups condense and the amine groups no longer hydrogen bond. The increase in the availability of free amine groups was indicated by larger amounts of exchange of NH2 to ND2 when the sample was exposed to D20 vapor. When the hydrolyzed gamma-APS at natural pH was dried in C02 or in air, a bicarbonate structure was formed causing the appearance of bands at 1630, 1575, 1488, and 1332 per cm. These bands previously associated with the intramolecular zwitterions of Si0-...NH3+. E-glass fibers were treated with 2% gamma-APS and dried under different conditions, which show the various structures of gamma-APS as described above. Differences in gamma-APS structures may affect the curing reactions of composite materials.