Condensation of alkoxysilanes in alcoholic media: II. Oligomerization of aminopropylmethyldiethoxysilane and co-oligomerization with dimethyldiethoxysilane

In the context of the preservation of cultural heritage, the treatment of paper by an aminoalkylalkoxysilane, or its mixture with dimethyldiethoxysilane (DMDES), gave encouraging results. The condensation experiments presented here, carried out in alcohol medium using aminopropylmethyldiethoxysilane (AMDES) alone or with DMDES, were followed using (1)HNMR, (29)Si NMR and matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) spectroscopies. The aim was to determine whether DMDES and AMDES could copolymerize under the conditions used. An exchange reaction was observed for AMDES in ethanol in the absence of water, under conditions where no exchange took place for DMDES. In methanol, this reaction proceeded much more rapidly and the reactivity of methoxysilyl groups was higher than that of ethoxysilyl groups. In the same solvent, in the presence of water, hydrolysis, cyclization and oligomerization were observed using NMR and MALDI TOF spectroscopies. In ethanol, a kinetic study of a mixture of DMDES and AMDES showed that the condensation of the two monomers proceeded at comparables rates and MALDI-TOF analysis gave evidence that mixed oligomers were produced, containing from one to four AMDES units. It was concluded that the co-oligomerization did not lead to a mixture of homo-oligomers, which would be due to different hydrolysis and condensation kinetics, but induced the formation of co-oligomers. (C) 2010 Society of Chemical Industry