Patent GB-788748-A (GB)
Title: Improvements relating to organopolysiloxanes
IPC: C07F7/08
Filed: 1955-05-20
Abstract: The invention comprises organopolysiloxanes which may be cured to the solid elastic state and which have the formula: <FORM:0788748/IV (a)/1> or <FORM:0788748/IV (a)/2> where Z is a vinyl, allyl or methallyl radical, R is a methyl, ethyl, phenyl, or chlorinated phenyl radical, R1 is a monovalent hydrocarbon radical, and n is an integer.  Examples of the radical R1 are alkyl, aryl, alkaryl, aralkyl and halogenated aryl radicals.  Compounds (1) may be prepared by reacting a polysiloxane [R12SiO]m with the disiloxane [ZR2Si]2O or with the silanol 2R2SiOH.  Compounds (2) are prepared in an analogous manner. Reaction conditions must be such as to prevent polymerization through the olefinic groups.  Catalysts, such as alkali metal hydroxides and certain ammonium and phosphonium compounds such as tetramethyl ammonium hydroxide and tetra-n-butyl phosphonium hydroxide, are preferably used.  Temperatures may range from about 80 DEG  to 175 DEG  C.  The products may be converted to rubbers by combining them with fillers and curing agents, and heating. Suitable fillers are titanium dioxide, calcium carbonate, lithopone, zirconium silicate, iron oxide, finely divided silica such as silica aerogel and fumed silicas.  Suitable curing agents are benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, tert. butyl perbenzoate, boron hydrides and various azobutyronitriles.  Curing may also be effected by high-energy electrons as described in Specification 757,024.  The products may also be copolymerized with compounds containing terminal CH2 = C< radicals, e.g. styrene, vinyl acetate and acrylonitrile, using the usual catalysts.  They may also be co-vulcanized with other elastomers such as natural rubber, butyl rubber, polychloroprene and butadiene-styrene copolymers, suitable agents being sulphur and various dithiocarbamates.  In the examples: (2) varying amounts of 1,1,3,3-tetraphenyl-1,3-divinyldisiloxane were heated with octamethylcyclotetrasiloxane in the presence of KOH to produce a series of vinyl diphenyl end-blocked polymethyl siloxanes in which the average number of [(CH3)2SiO] units varies from 242 to 8700.  One of these (n = 1450) is mixed with silica aerogel and cured with benzoyl peroxide; another is cured by irradiation with electrons; others are moulded into gels by heating with benzoyl peroxide alone; and others are mixed with titanium dioxide and benzoyl peroxide and coated and cured on glass cloth and glass plates.  In (6) the vinyl disiloxane of (2) is replaced by 1,1,3,3-tetraphenyl- and 1,1,3,3-tetramethyl-1,3-diallyldisiloxane respectively.  In (7) the disiloxane may be replaced by silanols, e.g. vinyldiphenylor allyldiethyl-silanol; and the cyclic siloxane may be mixed with up to 50 per cent of hexaphenylcyclotrisiloxane. (9) Dialkenyl endblocked polymers are prepared from diallylethylsilanol and octamethylcyclotetrasiloxane, and are cured as before.  1,1,3,3 - Tetraphenyl - 1,3 - divinyldisiloxane is prepared by reacting phenyl magnesium bromide with vinyl trichlorosilane to give diphenylvinylchlorosilane which is then hydrolysed by adding dropwise into water.  Diallylethylchlorosilane is prepared from ethyl magnesium bromide and diallyldichlorosilane. This is mixed with acetic anhydride to give diallylethylacetoxy silane, which on hydrolysis yields diallylethyl silanol. Specification 735,807 also is referred to.