Competition of aminolysis and alcoholysis in nucleophilic cleavage of a model compound for polysiloxane networks

Abstract

Base-catalysed aminolysis and ethanolysis of room temperature vulcanised poly(dimethylsiloxane) networks were studied with the aid of a model compound, tetrakis(trimethylsiloxy)-silane. Ethanol and ethylamine were used as nucleophilic reagents. The nucleophilicities of the reagents were enhanced by addition of potassium hydroxide. Kinetic models for the aminolysis and alcoholysis reactions at the initial stage were developed. The models reasonably predict the experimental data. Initial rate analysis was employed to determine the parameters of aminolysis and ethanolysis rate expressions. The overall activation energy of the aminolysis reaction is 14 kJ/mol. The initial rate of aminolysis was faster than that of ethanolysis. However, aminolysis reached equilibrium much faster than ethanolysis. When competition occurred in the reaction system, the aminolysis reaction dominates nucleophilic substitution at the initial stage and is followed by ethanolysis in a subsequent step.