Preparation of hydroxy terminated polysiloxanes

Abstract From the Canadian patent

The specification discloses a method of preparing a polysiloxane by chain extension of a silicon compound having chain terminating units including a silicon-bonded hydroxyl group which comprises bringing about condensation of the siliconbonded hydroxyl groups at a temperature of less than 50°C in presence of an acidic condensation catalyst of the formula RSO3H and water, to an extent of less than 7 moles per mole of acidic condensation catalyst. The silicon compound may comprise a hydroxyl end-blocked polydimethylsiloxane having a viscosity at 25°C in the range 30 to 100,000 mm2/s, and it may be polymerised to provide an .alpha..omega. dihydroxy polydimethylsiloxane having a viscosity in …