Patent GB-1493902-A (GB)
Title: Fluid organopolysiloxane compositions and their use for moulding after addition of a cross-linking agent
IPC: C08G77/38
Filed: 1976-02-09
Abstract: 1493902 Organopolysiloxane compositions RHONE-POULENC INDUSTRIES 9 Feb 1976 [10 Feb 1975] 4965/76 Heading C3T A storage stable fluid organopolysiloxane composition is prepared by a process which comprises (A) mixing for at least 2 hours at a temperature of 60 C. or below: (a) 100 p.b.w. of a diorganopolysiloxane oil of viscosity from 400-3000 cP. at 25 C., each of its chains being terminated by (CH 3 )SiO 0À5 , (CH 3 ) 2 CH 2 =CHSiO 0À5  or (CH 3 ) 2 C 6 H 5 SiO 0À5  units, the units of the chain being chosen from methyl, vinyl and/or phenyl radical-containing units of formulµ (CH 3 ) 2 SiO, CH 3 (C 6 H 5 )SiO, (C 6 H 5 ) 2 SiO, and C 6 H 5 (CH 2 =CH)SiO and up to 1% in number of units of formula R<SP>11</SP>SiO 1À5  where R<SP>11</SP> is methyl, vinyl or phenyl, such that said methyl, vinyl and/or phenyl radicals are in the numerical proportion of 40-100% of methyl radicals, 0-58% of phenyl radicals and 0-2% of vinyl radicals; (b) 30-75 p.b.w. of a silica of specific surface area greater than 80 m.<SP>2</SP>/g., e.g. pyrogenic silica, silica aerogel or xerogel or a precipitated silica; (c) 1À5-7 p.b.w. of water; and (d) 4-18 p.b.w. of a silylating agent with Si-N bonds of formula or R(CH 3 ) 2 SiNHR<SP>1</SP> wherein R represents methyl, ethyl, vinyl or phenyl and R<SP>1</SP> represents methyl or ethyl; and (B) removing the volatile materials from the mixture obtained under (A) by heating the mixture at 70-200 C. under a pressure of, at most, atmospheric pressure; and (C) introducing into 100 p.b.w. of the devolatilized mixture obtained from (B): (e) 45-120 p.b.w. of a dimethylpolysiloxane oil with terminal OH groups and having a viscosity of from 2000 to 60,000 cP. at 25 C., and (f) 25-120 p.b.w. of a silica of specific surface area less than 50 m.<SP>2</SP>/g., e.g. a diatomaceous silica or ground quartz. An organopolysiloxane elastomer may be prepared from the above composition by adding per 100 p.b.w. of the said storagestable fluid organopolysiloxane composition, 0À3 to 2À5 p.b.w. of a cross-linking agent chosen from (i) a monomer of formula where Q represents a C 1 -C 8  hydrocarbon radical G represents a C 1 -C 4  alkyl radical and w and t independently represent 0 or 1, and (ii) a polymer resulting from the partial hydrolysis of Si(OG) 4 , and 0À1 to 2À2 p.b.w. of a metal catalyst selected from organic derivatives of tin, metal salts of carboxylic acids and polymers with # TiOSn # chains. In stage C of the process, water in an amount of up to 1% of the weight of component (e), and an α,#-dihydroxydiorganopolysiloxane of viscosity 5-100 cp., as diluent, generally in an amount of from 0À5 to 6% of the weight of component (e), the organic radicals comprising at least 45% of CH 3 , up to 50% of phenyl and up to 10% of vinyl radicals, may additionally be added. A gelling agent such as a hydrogenated castor oil may be added to the storage-stable fluid composition generally in an amount of 1-4% of the weight of the composition. In making the elastomers the cross-linking agent and catalyst may be diluted with diorganopolysiloxane oils of type (a) above or oils of the same structure but having a viscosity of 5-50 cP. In the examples storage-stable fluid compositions are prepared from (a) either a dimethylpolysiloxane oil terminated by or (CH 3 ) 2 CH 2 =CHSiO 0À5  units of viscosity (1000 or 1800 cP.) or a methylphenylpolysiloxane oil (800 cP.) of units (CH 3 )C 6 H 5 SiO terminated by (CH 3 ) 3 SiO 0À5  units; (b) pyrogenic silica; (c) distilled water; (d) either hexamethyldisilazane or or (CH 3 ) 3 SiNHCH 3 ; (e) an OH-terminated dimethylpolysiloxane oil (16,000-25,000 cP.); (f) ground quartz; and as diluent an OH- terminated dimethylpolysiloxane (20-50 cP.). Elastomers are prepared from the above compositions by adding thereto: either n-propyl polysilicate or hexapropoxydisiloxane as crosslinking agent, and either dibutyl tin dilaurate or dibutyltin diacetate as catalyst and a (CH 3 ) 3 SiO 0À5  terminated dimethylpolysiloxane (20 cP.) as diluent. The compositions are spread on to glass plates and allowed to cure at room temperature.