| 摘要 |
PROBLEM TO BE SOLVED: To lower the hydroxyl content of terminal units at good efficiency by conducting the polymerization reaction at a subatmospheric pressure in producing an organopolysiloxane gum by the polymerization of a cyclic organosiloxane. SOLUTION: A cyclic organosiloxane is polymerized with a low-molecular- weight linear organopolysiloxane terminated with triorganosilyl groups in the presence of an alkaline catalyst. In this polymerization, the reaction is conducted at a pressure of, desirably, 50 mmHg or below, more desirably, 100-500 mmHg. The alkaline catalyst is desirably an alkali metal hydroxide, a quaternary ammonium phosphonium compound, a quaternary ammonium compound or a silanolate thereof. Especially, dimethyl polysiloxanate of potassium hydroxide and dimethyl polysiloxanate of tetra-n-butylphosphonium hydroxide are desirable. The cyclic organosiloxane is desirably one represented by the formula (wherein R1 and R2 are each a monovalent hydrocarbon group; and m is an integer of 3-8).
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