POLYSILOXANES

摘要

1523654 Polysiloxanes GENERAL ELECTRIC CO 21 Oct 1975 [18 Dec 1974] 43126/75 Heading C3T A silanol chain stopped polysiloxane has the formula HOSi(R)2O-[-Si(R)2O-]x-[Si(R)(R<1>)O]y-# Si(R)2OH wherein R is a monovalent hydrocarbon radical free of vinyl unsaturation or a halogenated aryl or cyano-alkyl radical, R<1> is a hydrocarbon group having vinyl unsaturation, x and y are positive integers such that the polysiloxane has from 0À1 to 0À5 or R<1> groups and the inherent viscosity of the polymer ranges from 25,000 to 10<6> c.p. measured at 25‹ C. The polysiloxane of the above formula or one of the formula is prepared by a process comprising (a) homo. genizing a mixture of (i) (R2SiO)4, (ii) (RR<1>SiO)4 or R<1>R2Si-O-SiR2R<1>, (iii) a mono-C6-C18- alkyl-substituted benzene sulfonic acid, and (iv) water; (b) heating the homogenized mixture of (a) to polymerize the polysiloxane; and (c) adding an alkanolamine preferably of the formula (R<3>OH)3N, where R<3> is a C1-C8 alkyl radical, to neutralize the benzene sulfonic acid and to form a neutralized emulsion of said polysiloxane. Heating step (b) is preferably carried out at a temperature of 40-100‹ C. and is preferably followed by a cooling step. A platinum catalyst may be dispersed with the tetramers prior to polymerization or it may be dispersed into the emulsion after addition of the alkanolamine. In a modification of the above process a chain-stopper of the formula R3Si-O(SiR2O)2SiR3, may be included in step (a). The R groups may be alkyl, aryl, alkaryl, cycloalkyl, aralkyl, halo aryl or cyanoalkyl radicals, and the R<1> group may be vinyl or The resulting polysiloxane emulsion may be broken by the addition of an alkanol. The above polysiloxanes may be used in a process for rendering flexible sheet material, e.g. paper or cloth, non-adherent to surfaces which normally adhere thereto by (a) treating the sheet material with an aqueous emulsion containing: (i) the polysiloxane containing vinyl unsaturation produced by the above process, (ii) an organo-hydrogen polysiloxane having the average unit formula where a is 0-3, b is 0À005 to 2À0, a + b is 0À8 to 3, there being at least 2 Si-H groups per molecule; and (iii) a Pt catalyst, and (b) drying the treated material. In Examples 1-5 polysiloxane emulsions are prepared by homogenizing a mixture of and in the presence of dodecylbenzene-sulfonic acid, water and a Pt catalyst, then heating the resulting emulsion, followed by a cooling step and then adding triethanolamine. The resulting polysiloxane emulsions are used to prepare coating compositions additionally comprising an emulsion comprising a methylhydrogencontaining siloxane and a vinyl chain-stopped siloxane, water and as dispersant either a hydroxyethyl cellulose or a polyvinyl alcohol. The resulting compositions are coated on to semi-bleached Kraft paper and cured by heating to provide release coatings. In Examples 7 and 8 polysiloxane emulsions are prepared as in Examples 1 and 2 from the following materials: water, dodecylbenzene sulfonic acid and either (i) and as chain-stopper or (ii)