Linking mechanical properties of silanes to their chemical structure: an analytical study of γ-GPS solutions and films

The effects of hydrolysis and condensation processes on the molecular structure of γ-glycidoxypropyltrimethoxysilane (γ-GPS) in aqueous solutions were investigated using Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy. Hydrolysis was characterized by monitoring the production of methanol and the decrease in concentration of SiOCH₃ groups in 1% solutions of deuterium oxide using proton NMR. Hydrolysis was found to be a very rapid process, whose rate could be increased or decreased by altering the pH of the solution. NMR spectroscopy showed that hydrolysis was completed in a 1% γ-GPS solution in deuterium oxide after 34 minutes. Condensation, on the other hand, took a relatively long time to occur. In the NMR spectra, condensation was observed by the broadening of peaks due to the protons on the carbon atom adjacent to the silicon atom. In addition to proton NMR, Si-29 NMR was used to characterize the siliane in 10% solutions of γ-GPS in water. The Si-29 NMR showed oligomer growth with respect to time . The oligomer growth was correlated to mechanical test results. Infrared spectroscopy was used to characterized the structure of the γ-GPS as a deposited film on aluminium during drying cycles at elevated temperature. The drying cycles caused increased oligomerization in the silane network and oxidation of the epoxide groups in the film.