Branching and Cross-Linking of Siloxane Copolymers Containing Hydromethyl-Siloxane Units by the Hydride Transfer Restructuring Reaction. Possible Route to Silicone Coatings

The restructuring reactions of three siloxane copolymers: poly(Me2SiO-co-HMeSiO), poly(PhMeSiO-co-HMeSiO) and poly(3,3,3-F3PrMeSiO-co-HMeSiO) in the presence of B(C6F5)3 (TPFPB) were investigated. The studied restructuring reactions are the result of the hydride transfer process between two silicon atoms, which is mediated by TPFPB. B(C6F5)3. Initially, the restructuring process produces high molecular weight, branched siloxane copolymers. These copolymers are soluble and capable of forming thin layers. Continuing this reaction leads to cross-linking of the siloxane polymer and the formation of an insoluble gel. The same restructuring process allows the resulting films to be converted into hard coatings after solvent evaporation. The restructuring process of siloxane copolymers was compared with the previously studied restructuring of polyhydromethylsiloxane homopolymer. Although the mechanism of branching and cross-linking is similar, diorganosiloxane units play an important role in the restructuring process as well as influence the properties of the obtained coatings.