Synthesis of Functionalized PDMS Fluids by Linear Chlorinated Phosphazene Acid Catalyst

In order to overcome the deficiency that chlorinated phosphazene base cannot prepare low-viscosity polysiloxanes, especially low-viscosity polysiloxane fluids containing Si–H bonds, linear chlorinated phosphazene acid was prepared using PCl₅ and NH₄Cl, and its application in the preparation of linear polysiloxanes by condensation reaction and equilibrium polymerization reaction was studied. The effects of the dosage of the catalyst, reaction time, passivator type (MgO, NaHCO₃, Fe₂O₃, MnO₂, CaO, ZnO), and its dosage on the structure and yield of the PDMS oligomers were investigated. NMR, GPC, refractometer, and TGA were used to test the structure and properties of the PDMS oligomer. Compared with commercial PDMS fluid, the PDMS fluid prepared with ZnO as a passivator has better thermal properties. When hydroxyl-terminated linear PDMS with low polymerization degree is used, with the addition of 5 ppm of catalyst and NaHCO₃ as a passivator, α, ω-bistrimethylsiloxy-terminated linear PDMS was obtained by means of the condensation reaction with a yield of 91.1%. Using octamethylcyclotetrasiloxane as the monomer, with the addition of 1000 ppm of catalyst and triethylamine as a passivator, various functionalized PDMSs were obtained with yields ranging from 73.7% to 80.4%. Compared with the equilibrium polymerization reaction, the molecular weight distribution of the PDMS prepared by the hydroxyl condensation reaction is narrower. This work provides a new approach to the synthesis of low-viscosity polysiloxanes, especially those terminated with active functional groups.

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