Patent GB-1518350-A (GB)
Title: Method of preparing a platinum catalyst inhibitor
IPC: C08G77/04
Filed: 1975-10-15
Abstract: 1518350 Olefinic-containing siloxanes DOW CORNING CORP 15 Oct 1975 [2 Dec 1974] 42198/75 Headings C3S and C3T A method of preparing an olefinic siloxane compound having at least one unreacted silicon-bonded hydrogen atom per molecule comprises continuously passing a liquid mixture of an acetylenic alcohol and a siloxane compound having at least 3 silicon-bonded hydrogen atoms bonded to at least 3 different silicon atoms in the presence of a Pt catalyst through a heating means in which the liquid mixture is heated to a temperature which is above 100‹ C. and which is also above the temperature at which the olefinic-siloxane compound is no longer an inhibitor for the reaction, the temperature and residence time of the liquid mixture in the heating means being sufficient to produce the olefinic siloxane compound without more than 5% weight decomposition of reactants and product and the liquid mixture being under sufficient pressure to maintain the reactants and product in a liquid state at least until the mixture has passed through the heating means, the product being an olefinic siloxane compound having at least one unreacted Si-bonded hydrogen atom per molecule, which is, below 100‹ C. an inhibitor for the reaction between the acetylenic alcohol and the siloxane compound having at least 3 Si-bonded hydrogen atoms in the presence of a Pt catalyst. The residence time is generally from 5 sec. to 1 hour, the temperature is preferably from 150‹- 400‹ C. and the pressure may vary from 3À5 to 70À3 kg/sq. cm, and the amount of Pt catalyst is preferably from 0À05 to 2 ppm of Pt. The unreacted starting materials may be separated from the product by distillation. Suitable acetylenic alcohols are 3-methyl-1-butyn-3-ol, 1- ethynyl - cyclohexan - 1 - ol, 3,5 - dimethyl -1- hexyn-3-ol and 3-methyl-1-pentyn-3-ol. The siloxane compound may be straight-chain, cyclic or branched. Preferred siloxanes are:- (CH3)3SiO[(CH3)HSiO]3 Si(CH3)3, [(CH3)HSiO]3, [(CH3)HSiO]4 and Si[OSi(CH3)2H]4. Other siloxane are described which can contain from 3-50 siloxane units per molecule and which contain RHSiO units optionally together with R2SiO units and which are terminated with R3SiO and/or -SiR2H units, where R is a monovalent hydrocarbon radical having no aliphatic unsaturation or a fluorinated hydrocarbon radical. Suitable Pt catalysts are chloroplatinic acid, platinum chlorides, Pt salts, Pt deposited on silica, charcoal or alumina, and platinous halide complexes with olefins. The molar ratio of acetylenic alcohol to siloxane compound can vary from 10 : 1 to 1 : 10. More than 80% of the inhibitor olefinic siloxane compounds produced preferably comprise a mixture of the mono- and di-adducts. The inhibitors retard the room temperature reaction of vinyl compounds with Si-H in the presence of Pt but allow the reaction to occur rapidly at elevated temperature. In Examples 1-6 olefinic siloxane compounds comprising a mixture of the monodi- and tri-adducts are prepared by continuously passing under pressure a liquid mixture of either 3-methyl-1- butyn-3-ol, or 3,5-dimethyl-1-hexyn-3-ol, or 3-methyl-1-pentyn-3-ol, a siloxane of the formula (CH3)3SiO[(CH3)HSiO]3Si(CH3)3, and a complex of chloroplatinic acid hexahydrate and 1,3 - divinyl - 1,1,3,3 - tetramethyldisiloxane through a coil in a heating bath using various temperatures, pressures, residence times and molar ratios of reactants. The resultant product can be distilled to obtain single species adducts. In Example 7 compositions prepared comprising phenylmethylvinylsiloxy endblocked polydimethylsiloxane (400 cs), 5 micron quartz, (CH3)3SiO[(CH3)2SiO]3 [(CH3)HSio]5 Si(CH3)3, the Pt catalyst described above and the olefinicsiloxane adducts prepared as in Examples 1-6 are cured to elastomers at temperatures ranging from room temperature to 150‹ C.