Abstract
Condensation reactions of trimethylethoxysilane (MOEt) and pentamethyldisiloxanol in n-heptane catalysed by hexachloro-1 λ-diphosphaza-1-enium salts were studied. Although the substrate conversion vs. time dependences point to domination by heterofunctional condensation, the process is more complex. Homofunctional condensation as well as fast consecutive hydrolysis and ethanolysis strongly contribute to the overall process. Results of kinetic studies point to inhibition of these component reactions by an excess of MOEt. Interactions of the hexachloro-1λ-diphosphaza-1-enium salts with MOEt, ethanol and silanol were studied by 31P NMR. It was demonstrated that a fast substitution reaction of chloride by ethoxy group takes place when ethanol or ethoxysilane is introduced into solutions of hexachlorodiphosphazenium salts. This process is responsible for the decrease in condensation activity of the catalyst.
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