Patent GB-1494670-A (GB)
Title: Manufacture of curable organopolysiloxane compositions
IPC: C08L83/04
Filed: 1975-07-10
Abstract: 1494670 Organopolysiloxane compositions WACKER-CHEMIE GmbH 10 July 1975 [12 July 1974] 29055/75 Heading C3T An organopolysiloxane composition curable to an elastomer is prepared by a process comprising mixing (a) a triorganosiloxy-terminated diorganopolysiloxane containing at least one vinyl group in each terminal unit and having a viscosity of from 10 to 5000 cP at 25 C.; (b) a triorganosiloxy-terminated organopolysiloxane comprising organohydrogenosiloxane units and diorganosiloxane units in such proportions that there are from 5 to 100 silicon atoms per siliconbonded hydrogen atom, and having a viscosity of from 2000-50,000 cP at 25 C.; (c) a filler having a BET surface area of at least 50 m<SP>2</SP>/g that either has previously been rendered hydrophobic, or is rendered hydrophobic during the process by reaction with an organosilicon compound, (d) a catalyst that can promote the addition of Si-bonded hydrogen atoms to vinyl groups, and optionally; (e) a diorganopolysiloxane terminated by one diorganohydrogenosiloxane unit and one diorganovinylsiloxane unit or by two diorganohydrogenosiloxane units, wherein at least the whole of one of components (b) and (e) is first mixed with at least 75% wt. of the amount of component (c) which, if not previously rendered hydrophobic, is simultaneously reacted with an organosilicon compound, and subsequently mixing the mixture so obtained with component (a) with any remaining component (c) and with any remaining component (b) or (e), component (d) being added at any stage. Component (a) may be represented by the formula where R is a monovalent unsubstituted or substituted hydrocarbon radical free of aliphatic unsaturation, e.g. methyl, ethyl, phenyl and trifluoropropyl. Component (b) may be represented by the formula R 3 SiO(RR<SP>1</SP>SiO) m SiR<SP>3</SP>, where R<SP>1</SP> is hydrogen or R. The preferred filler (c) is pyrogenic silicon dioxide. Other suitable fillers (c) are silicic acid hydrogels and xerogels, and pyrogenic aluminium oxide and titanium dioxide. The organosilicon compounds which are reacted with filler (c) may be those of the formula (R<SP>2</SP> 3 Si) a Z where R<SP>2</SP> is a monovalent unsubstituted or substituted hydrocarbon radical, Z is a halogen, hydrogen, oxygen or sulphur atom or -OH, -OR<SP>3</SP>, -NR<SP>3</SP>X, -SX, -ONR<SP>3</SP>X, -OOCR<SP>3</SP> or -NX- group, R<SP>3</SP> is a C 1 -C 4  alkyl group, X is hydrogen or a monovalent optionally substituted hydrocarbon radical, and a is 1 or 2. The amount of filler (c) used is preferably from 10-50% wt., based on the weight of the composition, calculated as non- hydrophobic filler. Suitable catalysts (d) are Pt; Pt on a carrier, e.g. on SiO 2  or active charcoal; Pt compounds, e.g. chloroplatinic acid and reaction products or complexes thereof with an organic or inorganic compound, e.g. cyclohexanone or divinyltetramethyldisiloxane; rhodium compounds; cobalt carbonyl compounds and manganese carbonyl compounds. Component (e) preferably has a viscosity of 500-3000 cP at 25 C. and may be of the general formulae and is preferably used in an amount of at least 20% wt. of component (b). Optional ingredients include fillers having a BET surface area of less than 50 m<SP>2</SP>/g, such as CaCO 3 , quartz powder and diatomaceous earth; pigments, e.g. red iron oxide; colorants; plasticizers, e.g. organopolysiloxanes free of Si-H bonds and aliphatic unsaturation; organic resins, e.g. polyvinyl chloride; organopolysiloxane resins; agents for retarding crosslinking, e.g. benzotriazole; and agents for improving adhesion to substrates, e.g. various silanes. In a typical example a composition is prepared by first heating a trimethylsiloxy terminated organopolysiloxane containing methyl-hydrogen siloxane units and dimethylsiloxane units (9300 cP at 25 C.), hexamethyldisilazane, water and pyrogenic silicon dioxide and then adding to the resulting mixture first a dimethylpolysiloxane (2000 cP at 25 C.) having one vinyldimethylsiloxy and one dimethyl hydrogenosiloxy terminal unit per molecule and then a vinyldimethylsiloxy-terminated dimethylpolysiloxane (151 cP at 25 C.), which has been reacted with a Pt-siloxane complex catalyst in a dimethylpolysiloxane diluent. The resulting composition was spread on a steel plate and cured to an elastomer film by heating.