| 摘要 |
1291860 Organopolysiloxane compositions GENERAL ELECTRIC CO 31 Dec 1969 [6 Jan 1969] 63424/69 Heading C3T A silanol containing organopolysiloxane composition having a substantially constant viscosity over an extended period of time comprises: (A) 100 parts by weight of an organopolysiloxane having a viscosity up to 500,000 centipoises at 25‹ C. consisting essentially of units R<SP>1</SP> 2 SiO and terminal units HOR<SP>1</SP> 2 SiO (I) and optionally chain stopping units R<SP>11</SP>R<SP>1</SP> 2 SiO (II), the ratio of I : II units being >1, and (B) 10-50 parts of a pyrogenic silica filler having a surface area of at least 50 m.<SP>2</SP>/g. and which is substantially free from infra-red absorbance at 3760 cm.<SP>-1</SP> (i.e. free of silanol groups) and having from 1-20% by wt. of chemically combined triorganosiloxy units R 3 SiO; R is an optionally halogenated monovalent hydrocarbon radical, R<SP>1</SP> is R or cyanoalkyl and R<SP>11</SP> is R or R 3 CO. (A) may be a polydimethyl polysiloxane chain terminated with silanol groups and trimethylsiloxy or tertiary butoxy radicals. The pyrogenic silica may be prepared as described in copending Application 63425/69 and may contain 1-2% by wt. of trimethylsiloxy units and 5-10% by wt. of dimethylsiloxy units. |
