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

The effects of hydrolysis and condensation processes on the molecular struc ture of gamma -glycidoxypropyltrimethoxysilane (gamma -GPS) in aqueous solu tions were investigated using Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy. Hydrolysis was characterized by monitoring the produ ction 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. MMR spectroscopy showed that hydrolysis was comple ted in a 1% gamma -GPS solution in deuterium oxide after 34 minutes. Conden sation, 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 p rotons on the carbon atom adjacent to the silicon atom. In addition to prot on NMR, Si-29 NMR was used to characterize the siliane in 10% solutions of gamma -GPS in water. The Si-29 NMR showed oligomer growth with respect to t ime. The oligomer growth was correlated to mechanical test results. Infrare d spectroscopy was used to characterized the structure of the gamma -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. (C) 2001 Elsevier Science B.V. All rights reserved.