Polycondensation is a chemical reaction in which monomers with two or more functional groups react with each other to form high-molecular compounds, while also generating small molecules.
Before discussing the synthesis of organosiloxanes through polycondensation reactions, it is necessary for us to first introduce various condensation reactions that can form Si-0-Si bonds: Si-0-SI bonds can be produced by the condensation of organosilanes with the same functional groups, such as
Among them, R is generally methyl or ethyl. Among these reactions, the condensation reaction of silanol is the most important one. The conditions for alkoxysilanes are rather strict. Generally, heating, pressurization and the addition of catalysts such as Lewis acids are required, while the condensation of acetoxy groups can only occur when heated above 175℃. Si-O-Si bonds can be generated by the mutual condensation between different organosilicon functional groups. The common condensation reactions of different functional groups include the following types:
Among them, R is generally methyl or ethyl, and M is a metal. From these reactions, it can be seen that silanol is the most common active functional group among them, which can be obtained through the hydrolysis of chlorosilane, alkoxysilane, etc. All of the above condensation reactions can theoretically be used to synthesize polysiloxanes, but in industry, only the hydrolysis and condensation of gaseous siloxanes are the main methods for preparing polysiloxanes.