METHOD FOR MAKING HYDROPHOBIC ORGANOSILICATE-MODIFIED SILICA GELS UNDER NEUTRAL CONDITIONS

Abstract: The present invention is hydrophobic organosilicate-modified silica gels and a method for their preparation under neutral conditions. The method comprises two steps, where in the first step the pH of an organosilicate-modified silica hydrosol is adjusted with a base to within a range of pH 3 to pH 7 to facilitate formation of an organosilicate-modified silica hydrogel. In the second step, the organosilicate-modified silica hydrogel is contacted with an organosilicon compound in the presence of a catalytic amount of a strong acid to effect hydrophobing of the organosilicate-modified silica hydrogel to form a hydrophobic organosilicate-modified silica gel having a surface area within a range of 100 m<2>/g to 850 m<2>/g in the dry state. In a preferred process, the hydrophobic organosilicate-modified silica hydrogel is contacted with a sufficient quantity of a water-immiscible organic solvent to convert the hydrophobic organosilicate-modified silica hydrogel into a hydrophobic organosilicate-modified silica organogel. A water soluble compound of cerium or iron may be added in the second step to improve the heat stability of the hydrophobic organosilicate-modified silica gel.

Description: METHOD FOR MAKING HYDROPHOBIC ORGANOSILICATE-MODIFIED SILICA GELS UNDER NEUTRAL CONDITIONS The present invention is hydrophobic organosilicate-modified silica gels and a method for their preparation under neutral conditions. The method comprises two steps, where in the first step the pH of an organosilicate-modified silica hydrosol is adjusted with a base to within a range of pH 3 to pH 7 to facilitate formation of an organosilicate- modified silica hydrogel. In the second step, the organosilicate-modified silica hydrogel is contacted with an organosihcon compound in the presence of a catalytic amount of a strong acid to effect hydrophobing of the organosilicate-modified silica hydrogel to form a hydrophobic organosilicate-modified silica gel having a surface area within a range of 100m.2/g to 850m2/g in the dry state. In a preferred process, the hydrophobic organosilicate-modified silica hydrogel is contacted with a sufficient quantity of a water- immiscible organic solvent to convert the hydrophobic organosilicate-modified silica hydrogel into a hydrophobic organosilicate-modified silica organogel. The organic solvent can then be removed from the organogel to form a hydrophobic organosilicate-modified silica gel having a surface area within a range of 100 m^/g to 850 m^/g in the dry state. A water soluble compound of cerium or iron may be added in the second step to improve the heat stability of the hydrophobic organosilicate-modified silica gel. Although hydrophobic organosilicate-modified silica gels prepared by the present method are useful in many applications such as thermal insulation, reinforcing and extending filler in natural rubbers and as filler in floatation devices, they are particularly useful as reinforcing fillers in silicone rubber compositions. It is well known that silicone rubbers formed from the vulcanization of polydiorganosiloxane fluids or gums alone generally have low elongation and tensile strength values. One means for improving the physical properties of such silicone rubbers involves the incorporation of a reinforcing silica filler into the fluid or gum prior to curing. However, silica reinforcing fillers have a tendency to interact with the polydiorganosiloxane fluid or gum causing a phenomenon typically referred to as "crepe hardening." A great deal of effort has been made in the past to treat the surface of reinforcing silica fillers with organosilanes or organosiloxanes to make the surface of the silica hydrophobic. This surface treatment reduces or diminishes the tendency of the compositions to crepe harden and improves the physical properties of the cured silicone rubber. The prior art is represented by U.S. Patent No. 3,024,126; U.S. Patent No. 3,979,546; U.S. Patent No. 3,015,645; U.S. Patent No. 3,122,520; U.S. Patent No. 2,892,797; U.S. Patent No. 3,850,971; U.S. Patent No. 4,006,175; U.S. Patent No. 4,360,388; EP 0-690-023 A2 and EP 0-658,531 Al. The hydrophobic organosilicate-modified silica gels prepared by the present method have improved hydrόphobicity when compared to hydrophobic silica gels prepared without the presence of the organosilicate. The improved hydrophobicity can make the hydrophobic organosilicate-modified silica gels more compatible with organic rubber and silicone rubber compositions. The hydrophobic organosilicate-modified silica gels also have a lower refractive index, which makes them desirable for use in silicone rubber compositions requiring optical clarity. The neutral conditions for preparing the organosilicate-modified silica hydrogels provide advantages over a method where the silica hydrogel is prepared under strong acid conditions. The advantages include reduced use of acid in the method, the ability to use less acid resistant process equipment, and faster conversion of the organosilicate-modified silica hydrosol into the corresponding silica hydrogel. The present invention is hydrophobic organosilicate-modified silica gels and a method for their preparation under neutral conditions. The method comprises two steps, where in the first step the pH of an organosilicate-modified silica hydrosol is adjusted with a base to within a range of pH 3 to pH 7 to facilitate formation of an organosilicate- modified silica hydrogel. In the second step, the organosilicate-modified silica hydrogel is contacted with an organosihcon compound in the presence of a catalytic amount of a strong acid to effect hydrophobing of the organosilicate-modified silica hydrogel to form a hydrophobic organosilicate-modified silica organogel having a surface area within a range of 100 m^/g to 850 m^/g in the dry state. In a preferred process, the hydrophobic organosilicate-modified silica hydrogel is contacted with a sufficient quantity of a water- immiscible organic solvent to convert the hydrophobic organosilicate-modified silica hydrogel into a hydrophobic organosilicate-modified silica organogel. The organic solvent can be removed from the hydrophobic organosilicate-modified silica organogel to form a hydrophobic organosilicate-modified silica gel having a surface area within a range of 100 m2/g to 850 m^/g in the dry state. The present invention is hydrophobic organosilicate-modified silica gels and a method for their preparation under neutral conditions. The method for preparing the hydrophobic organosilicate-modified silica gels comprises: (A) adjusting the pH of an organosilicate-modified silica hydrosol comprising (i) 2 to 50 weight percent of Siθ2 and (ii) 1 to 50 weight percent of an organosilicate described by formula RlSiO3/2, where R.1 is a monovalent hydrocarbon radical comprising 1 to 6 carbon atoms, with a base to within a range of pH 3 to pH 7 at a temperature within a range of 10 to 250 C. to facilitate formation of an organosilicate- modified silica hydrogel, and (B) contacting the organosilicate-modified silica hydrogel with (1) a catalytic amount of a strong acid and (2) an organosihcon compound selected from organosilanes described by formula R aHb$iX4-a-b ^ anc organosiloxanes described by formula R^ j -SiO^n)^ (2) where each R^ is independently selected from hydrocarbon radicals comprising 1 to 12 carbon atoms and organofunctional hydrocarbon radicals comprising 1 to 12 carbon atoms, each X is independently selected from halogen and alkoxy radicals comprising 1 to 12 carbon atoms, a=0, 1, 2, or 3, b=0 or 1, a+b=l, 2, or 3 with the proviso that when b=l then a+b=2 or 3, and n is an integer of from 2 to 3 inclusive to form a hydrophobic organosilicate-modified silica hydrogel having a surface area within a range of 100 m^/g to 850 m^/g as measured in the dry state. The method of the present invention is a two-step procedure, comprising steps (A) and (B) for making hydrophobic organosilicate-modified silica gels. Step (A) of the method comprises adjusting the pH of an organosilicate-modified silica hydrosol with a base to form an organosilicate-modified silica hydrogel. Step (B) comprises contacting the organosilicate-modified silica hydrogel prepared in step (A) with an organosihcon compound which reacts with the organosilicate-modified silica hydrogel to give a hydrophobic organosilicate-modified silica hydrogel. Hydrophobic organosilicate-modified silica gels prepared by the present method are useful as reinforcing fillers in, for example, silicone rubber and organic rubber compositions. The method used to prepare the organosilicate-modified silica hydrosol is not critical and can be any of those known in the art. The organosilicate-modified silica hydrosol may be prepared by first preparing a silica hydrosol and then mixing the silica hydrosol with an organosilicate as described herein and acidifying the mixture. The organosilicate-modified silica hydrosol may be prepared by mixing a silica hydrosol with an acidified organosilicate. The organosilicate-modified silica hydrosol may be prepared by forming a mixture of sodium silicate and the organosilicate and acidying the mixture. Silica hydrosols useful for preparing the organosilicate-modified silica hydrosol can be prepared by deionizing sodium silicate by the use of an ion exchange resin. The silica hydrosol may be prepared by hydrolyzing a silane at a low temperature. The silica hydrosol may be prepared by acidifying a sodium silicate mixture. Organosilicates useful in the present method are described by formula RlSiO3/2, where R! is a monovalent hydrocarbon radical comprising 1 to 6 carbon atoms. R! can be alkyls such as methyl, ethyl, and hexyl; substituted alkyls such as 3,3,3- trifluoropropyl and chloromethyl; alkenyls such as vinyl, allyl and hexenyl; and aryls such as phenyl. The organosilicate-modified silica hydrosol requires the presence of 2 to 50 weight percent of Siθ2- Preferred is when the organosilicate-modified silica hydrosol comprises 5 to 20 weight percent of Siθ2- The organosilicate-modified silica hydrosol also requires the presence of 1 to 50 weight percent of an organosilicate described by formula R^SiO3 2, where R* is as described above. Preferred is when the organosilicate-modified silica hydrosol comprises 1 to 20 weight percent of the organosilicate. In step (A), the pH of the organosilicate-modified silica hydrosol is adjusted to within a range of pH 3 to pH 7 by addition of a base to facilitate formation of an organosilicate-modified silica hydrogel. Preferably, the pH of the organosilicate-modified silica hydrosol is adjusted by means of a base to within a range of pH 3.5 to pH 6. For the purpose of this invention, any base can be used. The base can be an inorganic base such as NH 4 OH, NaOH, KOH, and Na 2 O(SiO 2 )3.36- The temperature at which step (A) is conducted can be within a range of 10 to 250°C. Preferred is when step (A) is conducted at a temperature within a range of 75 to 150°C. Even more preferred is when step (A) is conducted at a temperature within a range of 90 to l lO°C. In step (A), the length of time required for the organosilicate-modified silica hydrosol to convert to the corresponding silica hydrogel varies with the temperature and pH. Generally the higher the temperature and the higher the pH the shorter the length of time needed. Step (A) must be continued until the organosilicate-modified silica hydrogel acquires a structure such that the final product after hydrophobing has a surface area in the dry state within a range of 100 m^/g to 850 rcx-lg as determined by the Brunauer Emmett and Teller (BET) method described in the Jour. Am. Chem. Soc. 60:309 (1938) and as further described in U.S. Patent No. 3,122,520. The surface area of the organosilicate-modified silica hydrogel at the conclusion of step (A) is immaterial provided it is such that the surface area of the dried product after the hydrophobing of step (B) is within the above described range. Generally the surface area of the organosilicate-modified silica hydrogel is reduced by the hydrophobing reaction, since the organosilyl groups which become attached to the surface of the organosilicate-modified silica hydrogel increase the average particle size. The surface of the organosilicate-modified silica hydrogel can be above 850 m^/g provided that the hydrophobing treatment brings it within a range of 100 m^ g to 850 m^/g. To determine the proper contact conditions when conducting step (A), it is necessary to proceed with the hydrophobing of step (B) and then measure the surface area of the resulting product in the dry state. If the surface area of the resulting product in the dry state is above 850 m^/g, then the contacting conditions of step (A) were too mild. If the surface area of the resulting product in the dry state is below 100 m^/g, then the contacting conditions of step (A) were too severe. Examples of suitable pH conditions, temperatures and times for conduct of step (A) are provided in the examples herein. If the surface area of the hydrophobic organosilicate-modified silica gel in the dry state is above or below the described range, the hydrophobic organosilicate-modified silica gels have diminished reinforcing properties in silicone elastomers. In an alternative embodiment of the present method, the organosilicate- modified silica hydrogel of step (A) can be aged at a pH within a range of pH 3.5 to pH 8. Preferred is when the organosilicate-modified silica hydrogel is aged at a pH within a range of pH 6 to pH 7.5. If necessary, the pH of the organosilicate-modified silica hydrogel can be adjusted for aging to within the described ranges by use of a strong base such as previously described for use in step (A). Generally, the organosilicate-modified silica hydrogel can be aged at a temperature within a range of 0 to 250°C. It is preferred that the organosilicate-modified silica hydrogel be aged at a temperature within a range of 20 to 150°C. Most preferred is when the organosilicate-modified silica hydrogel is aged at a temperature within a range of 80 to 130°C. The length of time for aging the organosilicate- modified silica hydrogel can be from 10 minutes to 76 hours or longer. A preferred length of time for aging the organosilicate-modified silica hydrogel is within a range of 1 hour to 24 hours. If desired, the organosilicate-modified silica hydrogel of step (A) may be subjected to a shearing force to reduce aggregate particle size and to create a more uniform particle size distribution prior to the conduct of the hydrophobing reaction of step (B). If shearing is conducted, it is preferred that shearing of the organosilicate-modified silica hydrogel be performed after any aging of the silica hydrogel is completed. The shearing force may be applied to the organosilicate-modified silica hydrogel by any of those methods known in the art. The shearing force may be applied by a mechanical means such as a highspeed mixer or by ultrasound. This reduction in aggregate particle size and improved uniformity in particle size distribution can provide for hydrophobic organosilicate-modified silica gels which when compounded into silicone elastomer compositions provide for lower viscosity compositions, more stable compositions, and for cured silicone elastomers having improved clarity and physical properties. In step (B) of the present method, the organosilicate-modified silica hydrogel of step (A) is contacted with one or more of the defined organosihcon compounds described by formula (1) and (2) in the presence of a catalytic amount of a strong acid and an organic solvent immiscible with water. The catalytic amount of strong acid can be added either prior to, simultaneously with, or subsequent to the addition of the organosihcon compound. In the case where the organosihcon compound is a chlorosilane, the catalytic amount of the strong acid can be generated in situ by hydrolysis of the chlorosilane or the reaction of the chlorosilane directly with hydroxyls of the organosilicate-modified silica hydrogel. By the term "catalytic amount", it is meant that the strong acid is present in an amount sufficient to effect reaction of the organosihcon compound with the organosilicate-modified silica hydrogel. Examples of useful acids include hydrochloric, hydroiodic, nitric, phosphoric, sulfuric and benzene sulfonic acids. It is preferred that in step (B) the strong acid catalyst provide a pH less than 2.5. The temperature at which the hydrophobing of step (B) is conducted is not critical and can be from 20 to 250°C. Generally, it is preferred that the hydrophobing of step (B) be conducted at a temperature within a range of 30 to 150°C. The hydrophobing of step (B) can be conducted at the reflux temperature of the water-immiscible organic solvent when it is present during hydrophobing. In step (B), the organosilicate-modified silica hydrogel of step (A) is reacted with an organosihcon compound described by formula (1) or (2). In formula (1) and (2), each R2 can be independently selected from hydrocarbon radicals comprising 1 to 12 carbon atoms and organofunctional hydrocarbon radicals comprising 1 to 12 carbon atoms. R2 can be a saturated or unsaturated hydrocarbon radical. R^ can be a substituted or non- substituted hydrocarbon radical. R^ can be alkyl radicals such as methyl, ethyl, t-butyl, hexyl, heptyl, octyl, decyl and dodecyl; alkenyl radicals such as vinyl, allyl and hexenyl; substituted alkyl radicals such as chloromethyl, 3,3,3-trifluoropropyl and 6-chlorohexyl; and aryl radicals such as phenyl, naphthyl and tolyl. R^ can be an organofunctional hydrocarbon radical comprising 1 to 12 carbon atoms where the functionality is mercapto, disulfide, polysulfide, amino, carboxylic acid, carbinol, ester, or amido. A preferred organofunctional hydrocarbon radical is one having mercapto functionality. In formula (1) each X is independently selected from halogen and alkoxy radicals comprising 1 to 12 carbon atoms. When X is a halogen, it is preferred that the halogen be chlorine. When X is an alkoxy radical, X may be methoxy, ethoxy and propoxy. Preferred is where each X is selected from chlorine atoms and methoxy. The viscosity of the organosiloxanes described by formula (2) is not limiting and can range from that of a fluid to a gum. Generally, higher molecular weight organosiloxanes will be cleaved by the acidic conditions of the present method allowing them to react with the organosilicate-modified silica hydrogel. The organosihcon compound may be provided to the present method as a single compound as described by formulas (1) or (2) or as a mixture of two or more organosihcon compounds described by formulas (1) and (2). Examples of useful organosihcon compounds include diethyldichlorosilane, allylmethyldichlorosilane, methylphenyldichlorosilane, phenylethyldiethoxysilane, 3,3,3- trifluoropropylmethyldichlorosilane, trimethylbutoxysilane, sym- diphenyltetramethyldisiloxane, trivinyltrimethylcyclotrisiloxane, hexaethyldisiloxane, pentylmethyldichlorosilane, divinyldipropoxysilane, vinyldimethylchlorosilane, vinylmethyldichlorosilane, vinyldimethylmethoxysilane, trimethylchlorosilane, hexamethyldisiloxane, hexenylmethyldichlorosilane, hexenyldimethylchlorosilane, dimethylchlorosilane, dimethyldichorosilane, mercaptopropylmethyldimethoxysilane, and bis{3-(triethoxysilyl)propyl}tetrasulfide. When the hydrophobic organosilicate-modified silica gel is to be used as a filler in silicone rubber, it is preferred that the organosihcon compound be hexamethyldisiloxane or dimethyldichlorosilane. The amount of organosihcon compound added to the method is that sufficient to adequately hydrophobe the organosilicate-modified silica hydrogel to provide a hydrophobic organosilicate-modified silica gel suitable for its intended use. Generally, the organosihcon compound should be added to the method in an amount such that there is at least 0.04 organosilyl unit per Siθ2 unit in the organosilicate-modified silica hydrogel. The upper limit of the amount of organosihcon compound added to the process is not critical since any amount in excess of the amount required to saturate the organosilicate-modified silica hydrogel will act as a solvent for the method. The hydrophobic organosilicate-modified silica hydrogel of step (B) may be used as is or may be recovered for use by such methods as centrifugation or filtration. The hydrophobic organosilicate-modified silica hydrogel may be dried by the use of such methods as heating or reducing pressure or a combination of both heating and reducing pressure. In a preferred method, a water-immiscible organic solvent in sufficient amount to convert the organosilicate-modified silica hydrogel or hydrophobic organosilicate-modified silica hydrogel to the corresponding organogel is added to the method. The organic solvent can be added prior to, simultaneously with, or subsequent to the addition of the organosihcon compound. That is, the organosilicate-modified silica hydrogel can be first converted into an organogel by replacement of the water with the organic solvent and then hydrophobed. On the other hand, the organosihcon compound and the organic solvent can be added simultaneously to the organosilicate-modified silica hydrogel. Under these conditions, the reaction of the organosilicate-modified silica hydrogel with the organosihcon compound and the replacement of the water in the hydrophobic organosilicate-modified silica hydrogel with the organic solvent may occur simultaneously. Finally, the organosihcon compound can be added prior to the organic solvent, in which case the organosilicate-modified silica hydrogel reacts with the organosihcon compound and the resulting product is then converted into an organogel by an addition of an organic solvent. In the latter two cases, the conversion to an organogel is accomplished by a phase separation in which the hydrophobic organosilicate-modified silica hydrogel passes into the organic solvent phase. A preferred method is where a water- immiscible organic solvent is added after formation of the hydrophobic organosilicate- modified silica hydrogel thereby effecting formation of the corresponding hydrophobic organogel. For purpose of this invention, any organic solvent immiscible with water can be employed. Suitable solvents include low molecular weight siloxanes such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, diphenyltetramethyldisiloxane and trimethylsilyl endblocked dimethylpolysiloxane fluids. When a siloxane is employed as a solvent, it may serve both as a solvent and as a reactant with the organosilicate-modified silica hydrogel. In addition, suitable solvents include aromatic hydrocarbons such as toluene and xylene; heptane and other aliphatic hydrocarbon solvents; cycloalkanes such as cyclohexane; ethers such as diethylether and dibutylether; and halohydrocarbon solvents such as methylene chloride, chloroform, ethylene chloride and chlorobenzene. The amount of water-immiscible organic solvent is not critical so long as there is sufficient solvent to convert the hydrophobic organosilicate-modified silica hydrogel into a silica organogel. Preferably, the water-immiscible organic solvent should have a boiling point below 250°C. to facilitate its removal from the hydrophobic organosilicate-modified silica organogel, however, the boiling point is not critical since the solvent may be removed from the hydrophobic organosilicate-modified silica organogel by centrifuging or other suitable means. The hydrophobic organosilicate-modified silica organogel may be used directly as a reinforcing agent in silicone rubber or in any other uses for which this type of product can be used. Alternatively, the water-immiscible organic solvent may be removed from the hydrophobic organosilicate-modified silica organogel and the resulting dry hydrophobic organosilicate-modified silica gel used. During the conduct of step (B) it may be desirable to add a surfactant or water miscible solvent to facilitate the reaction of the organosihcon compound with the organosilicate-modified silica hydrogel. Suitable surfactants can include anionic surfactants such as dodecylbenzene sulfonic acid, nonionic surfactants such as polyoxyethylene(23)lauryl ether and (Me3SiO)2MeSi(CH2)3(OCH2CH2)7OMe where Me is methyl, and cationic surfactants such as N-alkyltrimethyl ammonium chloride. Suitable water miscible solvents can include alcohols such as ethanol, propanol, isopropanol, and tetrahydrofuran. In step (B) of the present method, an effective amount of a heat stabilizing agent selected from water soluble compounds of cerium and iron may be added. By the term "effective amount", it is meant that the water soluble compound of cerium or iron is present in the hydrophobic organosilicate-modified silica gel product of the present method at a concentration sufficient to provide improved heat stability to those compositions in which the hydrophobic organosilicate-modified silica gel is incorporated. Such compositions can include silicone rubber, natural rubber and synthetic organic rubber. Generally, 0.01 percent weight/volume (% Wt./Nol.) to 10 Wt./Nol. of the water soluble compound of cerium or iron in relation to the volume of components in step (B), excluding any solvents, is considered useful in the present process. Preferred is where the water soluble compound of cerium or iron comprises 0.1 %Wt./Vol. to 1 Wt./Nol. on the same basis. Examples of water soluble compounds which may be useful in the present method include FeCl 3 , FeBr 2 , FeBr 3 .6H 2 O, FeCl 2 .4H 2 O, FeI 2 .4H 2 O, Fe(ΝO 3 ) 3 .6H 2 O, FePO 4 .2H 2 O, CeCl 3 .9H O, CeBr 3 .H 2 O, CeI 3 .9H 2 O, Ce(NO 3 ) 3 .6H 2 O, and Ce(Sθ4)2-2H2θ. A preferred water soluble compound of cerium and iron for use in the present method is selected from FeCl3 and CeCl3.9H2O. The following examples are provided to illustrate the present invention. These examples are not intended to limit the scope of the present claims. Example 1 An organosilicate-modified silica gel prepared and aged at pH 4, hydrophobed with hexamethyldisiloxane, and having incorporated therein FeCl3 as a heat stabilizing agent was prepared. A solution was prepared comprising 250 ml of PQ N Clear Sodium Silicate (PQ Corporation, Valley Forge, PA), 112 ml of sodium methyl silicate (DC® 722, Dow Corning Corporation, Midland, MI), and 759 ml of deionized water. This solution was added to a rapidly stirred solution, in a 5 L glass flask, comprising 129 ml of concentrated HC1 (Fisher Certified, Fisher Scientific, Fair Lawn, NJ) diluted with 352 ml of deionized water. The solution was adjusted to pH 4 by use of a dilute solution of PQ N Clear Sodium Silicate (PQ Corporation) and sodium methyl silicate (DC 722) in deionized water. An organosilicate-modified silica hydrogel was formed after stirring 70 minutes. The organosilicate-modified silica hydrogel was aged by stirring an additional 3 hours at room temperature. After aging, to the organosilicate-modified silica hydrogel, with stirring in the 5 L flask, was added 582 ml of concentrated HC1 (Fisher Certified), 727 ml of isopropanol, 376 ml of hexamethyldisiloxane, and 4.2 g of FeCl3. After stirring the flask content for 1 hour at room temperature, 1 L of toluene was added. After stirring the flask content for an additional 2 to 3 minutes, stirring was stopped and the aqueous phase drained from the flask. 250 ml of isopropanol and 50 ml of deionized water were added to the flask and the content of the flask rapidly stirred for 2 minutes. Then, 700 ml of deionized water were added to the flask and after stirring the flask content an additional 2 minutes the aqueous phase was drained from the flask. The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water. The toluene phase was poured into glass pans and the toluene evaporated leaving as product a hydrophobic organosilicate-modified silica gel. The organosilicate-modified hydrophobic silica gel was further dried 14 hours at 150°C. The yield of dried hydrophobic organosilicate-modified silica gel was 177 g. The BET surface area of the dried hydrophobic organosilicate-modified silica gel was determined by the method described supra; void volume, pore volume, average pore diameter, and particle size were characterized by standard methods; and carbon content was determined by CHN analysis using a Perkin Elmer Model 2400 CHN Elemental Analyzer (Perkin Elmer Corporation, Norwalk, CT). The result of these analysis are reported in Table 1. Example 2 An organosilicate-modified silica gel prepared and aged at pH 4, hydrophobed with hexamethyldisiloxane, and having incorporated therein FeCl3 as a heat stabilizing agent was prepared. A solution was prepared comprising 250 ml of PQ N Clear Sodium Silicate (PQ Corporation), 112 ml of sodium methyl silicate (DC® 722), and 759 ml of deionized water. This solution was added to a rapidly stirred solution, in a 5 L glass flask, comprising 129 ml of concentrated HC1 (Fisher Certified) diluted with 352 ml of deionized water. The pH of the solution was adjusted to 4 by use of a dilute solution of PQ N Clear Sodium Silicate (PQ Corporation) and sodium methyl silicate (DC 722) in deionized water. The solution was heated at 85°C. for 40 minutes, with stirring, to form an organosilicate-modified silica hydrogel. The organosilicate-modified silica hydrogel was aged by stirring an additional 16 minutes at 85°C. After aging, to the organosilicate-modified silica hydrogel, with stirring in the 5 L flask, was added 582 ml of concentrated HC1 (Fisher Certified), 727 ml of isopropanol, 376 ml of hexamethyldisiloxane, and 4.2 g of FeCl3. After stirring the flask content for 1 hour at room temperature, 1 L of toluene was added. After stirring the flask content for an additional 2 to 3 minutes, stirring was stopped and the aqueous phase drained from the flask. 250 ml of isopropanol and 50 ml of deionized water were added to the flask and the content of the flask rapidly stirred for 2 minutes. Then, 700 ml of deionized water were added to the flask and after stirring an additional 2 minutes the aqueous phase was drained from the flask. The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water. The toluene phase was poured into glass pans and the toluene evaporated leaving as product a hydrophobic organosilicate-modified silica gel. The organosilicate-modified hydrophobic silica gel was dried 14 hours at 150°C. The yield of dried hydrophobic organosilicate-modified silica gel was 167 g. The hydrophobic organosilicate-modified silica gel was characterized by the methods described in Example 1 and the results are provided in Table 1. Example 3 An organosilicate-modified silica gel prepared and aged at pH 4, hydrophobed with hexamethyldisiloxane, and having incorporated therein FeCl3 as a heat stabilizing agent was prepared. A solution was prepared comprising 250 ml of PQ N Clear Sodium Silicate (PQ Corporation), 112 ml of sodium methyl silicate (DC7 722), and 759 ml of deionized water. This solution was added to a rapidly stirred solution, in a 5 L glass flask, comprising 129 ml of concentrated HC1 (Fisher Certified) diluted with 352 ml of deionized water. The solution was adjusted to pH 4 by use of a dilute solution of PQ N Clear Sodium Silicate (PQ Corporation) and sodium methyl silicate (DC 722) in deionized water. The solution was heated at 100°C. for 40 minutes, with stirring, to form an organosilicate-modified silica hydrogel. The organosilicate-modified silica hydrogel was aged by stirring an additional 30 minutes at 100°C. After aging, to the organosilicate-modified silica hydrogel, with stirring in the 5 L flask, was added 582 ml of concentrated HC1 (Fisher Certified), 727 ml of isopropanol, 376 ml of hexamethyldisiloxane, and 4.2 g of FeCl3. After stirring the flask content for 1 hour at room temperature, 1 L of toluene was added. After stirring the flask content for an additional 2 to 3 minutes, stirring was stopped and the aqueous phase drained from the flask. 250 ml of isopropanol and 50 ml of deionized water were added to the flask and the content of the flask rapidly stirred for 2 minutes. Then, 700 ml of deionized water were added to the flask and after stirring an additional 2 minutes the aqueous phase was drained from the flask. The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water. The toluene phase was poured into glass pans and the toluene evaporated leaving as product a hydrophobic organosilicate-modified silica gel. The organosilicate-modified hydrophobic silica gel was dried 14 hours at 150°C. The yield of dried hydrophobic organosilicate-modified silica gel was 165 g. The hydrophobic organosilicate-modified silica gel was characterized by the methods described in Example 1 and the results are provided in Table 1. Example 4 An organosilicate-modified silica gel prepared and aged at pH 4, hydrophobed with hexamethyldisiloxane, and having incorporated therein FeCl3 as a heat stabilizing agent was prepared. A solution was prepared comprising 250 ml of PQ N Clear Sodium Silicate (PQ Corporation), 112 ml of sodium methyl silicate (DC® 722), and 759 ml of deionized water. This solution was added to a rapidly stirred solution, in a 5 L glass flask, comprising 129 ml of concentrated HC1 (Fisher Certified) diluted with 352 ml of deionized water. The solution was adjusted to pH 4 by use of a dilute solution of PQ N Clear Sodium Silicate (PQ Corporation) and sodium methyl silicate (DC 722) in deionized water. The solution was refluxed for 65 minutes, with stirring, to form an organosilicate- modified silica hydrogel. The organosilicate-modified silica hydrogel was aged by refluxing an additional 79 minutes. After aging, to the organosilicate-modified silica hydrogel, with stirring in the 5 L flask, was added 582 ml of concentrated HC1 (Fisher Certified), 727 ml of isopropanol, 376 ml of hexamethyldisiloxane, and 4.2 g of FeCl3. After stirring the flask content for 1 hour at room temperature, 1 L of toluene was added. After stirring the flask content for an additional 2 to 3 minutes, stirring was stopped and the aqueous phase drained from the flask. 250 ml of isopropanol and 50 ml of deionized water were added to the flask and the content of the flask rapidly stirred for 2 minutes. Then, 700 ml of deionized water were added to the flask and after stirring an additional 2 minutes the aqueous phase was drained from the flask. The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water. The toluene phase was poured into glass pans and the toluene evaporated leaving as product a hydrophobic organosilicate-modified silica gel. The organosihcate-modified hydrophobic silica gel was dried 14 hours at 150°C. The yield of dried hydrophobic organosilicate-modified silica gel was 153 g. The hydrophobic organosilicate-modified silica gel was characterized by the methods described in Example 1 and the results are provided in Table 1. Table 1 Characterization of Organosilicate-Modified Silica Gels Example Number Property 1 2 3 4 BET Surface Area (m 2 /g) 846 814 781 712 Void Volume (cm^/g) 1.98 5.02 5.54 5.89 Pore Volume (cmNg) 1.17 2.54 2.73 2.93 Ave. Pore Diameter (A) 44 90 98 111 Particle Size (μm) 105 75 58 53 Wt. % Carbon 15.4 14.0 13.0 12.6

Claims: Claims:: 1. A method for preparing a hydrophobic organosilicate-modified silica gel comprising: (A) adjusting the pH of an organosilicate-modified silica hydrosol comprising (i) 2 to 50 weight percent of Siθ2 and (ii) 1 to 50 weight percent of an organosilicate described by formula RlSiO3/2, where R! is a monovalent hydrocarbon radical comprising 1 to 6 carbon atoms, with a base to within a range of pH 3 to pH 7 at a temperature within a range of 10 to 250°C. to facilitate formation of an organosilicate-modified silica hydrogel, and (B) contacting the organosilicate-modified silica hydrogel with (1) a catalytic amount of a strong acid and (2) an organosihcon compound selected from organosilanes described by formula R^aHbSiX4-a-b anc * organosiloxanes described by formula R^ n SiO(4- n )/2 where each RX is independently selected from hydrocarbon radicals comprising 1 to 12 carbon atoms and organofunctional hydrocarbon radicals comprising 1 to 12 carbon atoms, each X is independently selected from halogen and alkoxy radicals comprising 1 to 12 carbon atoms, a=0, 1, 2, or 3, b=0 or 1, a+b=l, 2, or 3 with the proviso that when b=l then a+b=2 or 3, n is an integer of from 2 to 3 inclusive to form a hydrophobic organosilicate-modified silica hydrogel having a surface area within a range of 100 rn^/g to 850 m^/g as measured in the dry state. 2. A method according to claim 1 further comprising aging the organosilicate-modified silica hydrogel of step (A) at a pH within a range of pH 3.5 to pH 8 and a temperature within a range of 0 to 250°C. for a period of time within a range of 10 minutes to 76 hours prior to conduct of step (B). 3. A method according to claim 1 further comprising shearing the organosilicate-modified silica hydrogel of step (A) prior to conduct of step (B). 4. A method according to claim 1 where the contacting of step (B) is conducted at a temperature within a range of 30 to 150°C. 5. A method according to claim 1 where the organosilane is selected from vinylmethyldichloro-silane, vinyldimethylchlorosilane, hexenyldimethyl- chlorosilane, hexenylmethyldichlorosilane, dimethyldichlorosilane, and bis {3- (triethoxysilyl)-propyl } tetrasulfide. 6. A method according to claim 1 further comprising contacting the hydrophobic organosilicate-modified silica hydrogel with a water-immiscible organic solvent in sufficient amount to convert the hydrophobic organosilicate- modified silica hydrogel to a hydrophobic organosilicate-modified silica organogel. 7. A method according to claim 1 further comprising during the contacting of step (B) the presence of a surfactant which facilitates reaction of the organosihcon compound with the organo-silicate-modified silica hydrogel. 8. A method according to claim 1 further comprising during the contacting of step (B) the presence of a water-miscible solvent which facilitates reaction of the organosihcon compound with the organosilicate-modified silica hydrogel. 9. A method according to claim 1 further comprising mixing the silica hydrogel with an effective amount of a heat stabilizing agent selected from water soluble compounds of cerium and iron. 10. A composition prepared by the methods of claims 1, 2, 3, 6 or 9.

Inventors: BURNS GARY T, DENG QIN, HAHN JAMES R, REESE CLIFFORD C, BURNS, GARY, T., DENG, QIN, HAHN, JAMES, R., REESE, CLIFFORD, C.
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1998
Main classification: C01B33
IPC codes: C01B33, C09C1, C09C3