Adhesion additives and curable organosiloxane compositions containing same

Abstract: The novel organosiloxane compounds of the present invention are characterized by the presence of 1) a silicon atom containing at least two alkoxy or other hydrolyzable groups and the group -OR 1 Si≡ wherein R 1 represents a divalent organic group comprising carbon, hydrogen and, optionally, oxygen, and 2) a silicon-bonded hydrogen atom or alkenyl radical. A preferred method for preparing the compounds is by the reaction of A) a silane containing a silicon-bonded alkenyloxy group and at least two silicon-bonded hydrolyzable groups or a precursor of said hydrolyzable groups and B) an organohydrogensiloxane. The reaction is conducted in the presence of a hydrosilation catalyst.

Description: This invention relates to novel organosiloxane compounds that impart excellent adhesion to elastomers and gels prepared from organosiloxane compositions that cure by a hydrosilation reaction. These adhesion promoters are particularly effective at relatively low curing temperatures, particularly from ambient up to 70°C. A variety of silanes and organosiloxane compounds have been proposed for use as primers or adhesion promoters in hydrosilation reactions. These primers and adhesion promoters typically contain two types of reactive groups, one of which is a hydrolyzable group and the second of which is capable of reacting with either the substrate or the organosiloxane composition. For example, the prior art employing silicon-bonded hydrolyzable groups is represented by US-As 3,772,026; 3,873,334; 4,196,273; 4,329,273; 4,087,585; 4,732,932; 4,658,851; 4,719,262 and 4,906,686. The following patents describe silanes or organosiloxane compounds containing a silicon-bonded alkenyl radical or silicon-bonded hydrogen atom, in addition to silicon-bonded hydrolyzable groups. The use of these compounds as adhesion promoting additives for organosiloxane compositions that cure by a hydrosilation reaction is represented by US-A 4,786,701; EP-A 0,449,181; JP-A 4/311,766; US-A 4,721,764; EP-A 0,458,355 and EP-A 0,469,890. A shortcoming of the adhesion promoters described above is their lack of any indication that cohesive bonding of the composition to substrates can be achieved at curing temperatures below 100°C. US-A 3,887,602 further describes reaction products of alkoxysilanes containing a silicon-bonded hydrogen atom and allyl ethers of polymerized aldehydes. These reaction products are useful as coupling agents for bonding glass fibers to polymers based on formaldehyde or trioxane. The reaction products are represented by the formula (RO) 3 Si(CH 2 ) 3 (OCH 2 OR') n OCH 2 O(CH 2 ) 3 Si(OR) 3 , where R represents methyl or ethyl, R' is ethylene or n-butylene and the value of n is between 8 and 56. US 4,360,687 discloses an additive used to improve the physical properties of a composition which cures by the reaction between a polyorganosiloxane containing aliphatic unsaturation and an organohydrogensiloxane in the presence of a catalyst. The additive has the formula wherein R is selected from the group consisting of alkyl having 1 to 4 carbon atoms, trifluoromethyl and phenyl and x is an integer of 2 to 4. However, there is no disclosure that this additive improves the cohesive properties of the cured composition and there is no disclosure of the additives used in the present invention. An objective of this invention is to provide a novel class of organosiloxanes that will cohesively bond organosiloxane compositions to a variety of substrates during curing of the compositions by a platinum group metal catalyzed hydrosilation reaction at temperatures as low as 25°C. The organosiloxane compounds of the present invention are characterized by the presence of 1) a silicon atom containing at least two alkoxy groups or other hydrolyzable groups and the -ORSi≡ group wherein R represents an alkylene radical, and 2) a silicon-bonded hydrogen atom or alkenyl radical. This invention provides organosiloxane compounds represented by the formula X m R 2 (3-m) SiOR 1 [Si(R 3 ) 3 ] n wherein R 1 contains at least 3 carbon atoms, exhibits a valence of n +1 wherein n is 1 or 2 and is selected from the group consisting of -R 4 -, -R 4 OR 5 -, -R 4 OC(O)R 6 - and -R 7 C(O)OR 5 - when n is 1 and R 1 is -(R 4 O) 2 R 8 - when n is 2 and wherein R 5 , R 6 and R 8 are bonded to the oxygen atom in said formula; R 4 represents a hydrocarbylene or substituted hydrocarbylene radical containing at least 3 carbon atoms wherein the substituent is hydroxyl or alkoxy; R 5 contains from 2-12 carbon atoms and is selected from hydrocarbylene radicals or allyloxy-substituted hydrocarbylene radicals; R 6 represents a hydrocarbylene or substituted hydrocarbylene radical containing at least 3 carbon atoms wherein the substituent is hydroxyl or alkoxy; R 7 is selected from the group consisting of R 6 and a single bond; R 8 represents a trivalent hydrocarbon radical; each R 2 is individually selected from unsubstituted or substituted monovalent hydrocarbon radicals; each R 3 is individually selected from unsubstituted or substituted monovalent hydrocarbon radicals, silicon-bonded hydrogen atoms, X and siloxane units represented by the formula O[SiR 9 p O (3-p)/2 ] q where q is at least 1 and said siloxane units are sequential when q is greater than 1; and each R 9 is individually selected from the group consisting of X, hydrogen atom, substituted and unsubstituted monovalent hydrocarbon radicals, X m R 2 3-m SiOR 1 - and -R 11 [R 10 s SiO (3-s)/2 ] r where r is at least land the siloxane units represented by R 10 s SiO (3-s)/2 are sequential when r is greater than 1, with the proviso that at least one substituent represented by R 3 contains a silicon-bonded hydrogen atom or alkenyl radical; each R 10 is individually selected from the group consisting of monovalent hydrocarbon radicals, hydrogen atom and X; R 11 represents a hydrocarbylene or substituted hydrocarbylene radical containing at least 2 carbon atoms wherein the substituent is hydroxyl or alkoxy; the substituents present on the substituted hydrocarbon radicals represented by R 2 , R 3 , R 9 , R 10 and R 11 are selected from the group consisting of halogen, epoxy, amino, mercapto and 3-methacryloxypropyl; X represents a hydrolyzable group; m is 2 or 3; n is 1 or 2; p is 0, 1, 2 or 3; and s is 0, 1, 2 or 3. In one embodiment R 1 contains from 3 to 10 carbon atoms; at least one R 3 substituent is O [SiR 9 p O (3-p)/2 ] q wherein at least one of the R 9 substituents in said compound represents hydrogen; all unsubstituted or substituted monovalent hydrocarbon radicals, other than alkenyl radicals contain from 1 to 20 carbon atoms; R 4 , R 5 , R 6 and R 7 represent identical or different unsubstituted alkylene radicals; R 8 contains from 3 to 6 carbon atoms; and X is alkoxy or ketoximo, preferably the monovalent hydrocarbon radicals other than alkenyl present in said compound are selected from the group consisting of alkyl radicals containing from 1 to 4 carbon atoms; phenyl and 3,3,3-trifluoropropyl; R 4 and R 6 contain from 3 to 12 carbon atoms; R 5 contains from 2 to 12 carbon atoms; at least one of the siloxane units represented by the formula O[SiR 9 p O (3-p)/2 ] q is a diorganohydrogensiloxane unit and any remaining units include at least one member selected from diorganosiloxane units or organohydrogensiloxane units; and X is alkoxy containing 1 to 4 carbon atoms. In another embodiment R 1 contains from 3 to 10 carbon atoms; at least one R 3 substituent is O[SiR 9 p O (3-p)/2 ] q wherein at least one of the R 9 substituents in said compound represents R 11 [SiR 10 s O (3-s)/2 ] r ; R 4 , R 5 , R 6 and R 7 are individually selected from unsubstituted alkylene radicals; R 8 contains from 3 to 6 carbon atoms; and X is alkoxy containing from 1 to 4 carbon atoms, preferably the monovalent hydrocarbon radicals other than alkenyl present in said compound are selected from the group consisting of alkyl radicals containing from 1 to 4 carbon atoms, phenyl and 3,3,3-trifluoropropyl; wherein at least one of the three R 10 groups bonded to the terminal silicon atom is an alkenyl radical selected from the group consisting of vinyl, allyl, butenyl, and 5-hexenyl, more preferably at least one of the substituents represented by R 9 is R 11 Si (R 10 ) 2 OSiR 10 3 , where one of the three R 10 groups bonded to the terminal silicon atom is an alkenyl radical containing from 2 to 10 carbon atoms and the four remaining R 10 groups are alkyl radicals containing from 1 to 4 carbon atoms and R 11 is as defined above, and most preferably at least one of the monovalent hydrocarbon radicals bonded to each silicon atom containing these monovalent hydrocarbon radicals is methyl. This invention also provides curable organosiloxane compositions comprising A. a curable polyorganosiloxane; B. an amount of a curing agent sufficient to cure said composition; C. an amount of a catalyst sufficient to promote curing of said composition; and D. an adhesion promoting additive of the present invention, wherein said composition cures by a reaction selected from the group consisting of hydrosilation reactions, catalyzed by platinum group metals and compounds thereof; the reaction of silicon-bonded hydrogen atoms with silanol groups; the reaction of mercapto groups with one another in the presence of oxygen and a catalyst; the reaction of mercapto groups with alkenyl radicals in the presence of a catalyst; free radical and cationic reactions initiated by irradiation of photosensitive compounds with ultraviolet light, free radical reactions initiated by the thermally induced decomposition of a free radical precursor and reactions initiated by high energy radiation. The organosiloxane compounds of the present invention are represented by formula 1. (1) X m R 2 (3-m) SiOR 1 [Si(R 3 ) 3 ] n The substituent R 1 is bonded through an oxygen atom to the silicon atom containing the hydrolyzable groups. R 1 contains at least three carbon atoms, hydrogen and, optionally, oxygen together with any substituents, such as halogen and nitrogen, that may be present on the carbon atoms. R 1 preferably contains from 3 to 10 carbon atoms and exhibits a valence of two or three. The various alternative embodiments of R 1 are discussed below. R 2 represents a monovalent hydrocarbon radical. This radical can be unsubstituted or it can contain substituents such as halogen atoms, so long as the substituents do not adversely affect the curing or storage stability of our organosiloxane compositions which contain the present adhesion promoters or adversely affect the adhesion developed during composition curing. Other substituents present on R 2 can contribute to the adhesion developed by compositions containing the present compounds as adhesion promoters. These substituents include epoxy, 3-methacryloxypropyl, mercapto and amino (hereinafter referred to as adhesion promoting substituents). If the present compounds are prepared by a preferred method involving the reaction of 1) a silane containing an ethylenically unsaturated group that is bonded to silicon through an oxygen atom with 2) an organosilicon compound containing at least two silicon-bonded hydrogen atoms, then the hydrocarbon radical represented by R 2 must be free of ethylenic unsaturation. The reason for this limitation is to avoid formation of undesirable products resulting from the competing reaction of the unsaturated group present on R 2 , rather than the desired ethylenically unsaturated group, with silicon-bonded hydrogen atoms. The monovalent silicon-bonded hydrocarbon radicals other than alkenyl that are present in our compositions contain from 1 to 20 or more carbon atoms and can be alkyl such as methyl, ethyl or propyl; cycloalkyl such as cyclohexyl; aryl such as phenyl; alkaryl such as tolyl or xylyl and aralkyl such as benzyl. The substituents that can be present on these hydrocarbon radicals are halogens such as fluorine and chlorine or any of the adhesion promoting substituents defined above. The hydrocarbon radicals present on the various silicon atoms can be identical or different. These hydrocarbon radicals are preferably methyl, ethyl, 3,3,3-trifluoropropyl or phenyl, this preference being based on the starting materials, typically the corresponding chlorosilanes, used to prepare the present organosilicon compounds. At least one of the radicals present on any silicon atom is preferably methyl. Each of substituents identified as R 3 is individually selected from monovalent hydrocarbon radicals that are unsubstituted or substituted, silicon-bonded hydrolyzable groups represented by X and the group O[SiR 9 p O (3-p)/2 ] q where p is 0, 1, 2 or 3 and q is at least 1. It should be apparent that the identity of each of the three substituents identified as R 3 will depend upon the reactants used to prepare the present compositions. In a preferred method, a silane corresponding to the general formula X m SiR 2 3-m OR 1' is reacted with an organohydrogensiloxane containing at least two silicon-bonded hydrogen atoms. In this formula, R 1' represents an ethylenically unsaturated precursor of the group represented by R 1 . For example, when R 1 is n-propylene then R 1' is allyl. The group [Si(R 3 ) 3 ] in formula 1 represents the residue of the organohydrogensiloxane after removal of the silicon-bonded hydrogen atom involved in the reaction with the silane. Each of the groups represented by R 3 can be an unsubstituted or substituted monovalent hydrocarbon radical, a hydrogen atom or at least one siloxane unit represented by the formula SiR 9 p O (3-p)/2 . Using the preferred preparative method, at least one of the groups represented by R 3 is O[SiR 9 p O (3-p)/2 ] q and at least one of the R 9 substituents in one of the siloxane units is a silicon-bonded hydrogen atom. When the reaction product of the alkenyloxy-substituted silane (reactant D1) and the organohydrogensiloxane (reactant D2) is not further reacted, each of the substituents represented by R 9 is individually selected from a hydrogen atom and unsubstituted or substituted monovalent hydrocarbon radicals. When R 9 is a hydrocarbon radical, it is preferably an alkyl radical containing from 1 to 4 carbon atoms, phenyl or 3,3,3-trifluoropropyl. When more than one R 9 radical on a silicon atom represents a hydrocarbon radical, at least one of these hydrocarbon radicals is methyl. One embodiment of our claimed compounds can be prepared by reacting the reaction product of reactants D1 and D2 with a diene type of hydrocarbon containing two carbon-carbon double bonds, such as butadiene. In this embodiment, at least one of the R 9 substituents in one of the units represents an alkenyl radical. This alkenyl radical preferably contains from 2 to 6 carbon atoms and is terminally unsaturated. X in formula 1 represents a silicon-bonded hydrolyzable group. Groups of this type include alkoxy, carboxy, ketoximo, amino, amido and aminoxy. When adhesion promoting additives are incorporated into compositions that cure by a hydrosilation reaction, alkoxy and ketoximo groups are preferred, based on the tendency of nitrogen compounds to inhibit the platinum-group metal containing catalysts that are typically used as catalysts for these reactions. X is preferably an alkoxy group containing from 1 to 4 atoms, based on the volatility of the corresponding alcohols, which are formed as by-products during preparation of these compounds. In formula 1, m is either 2 or 3, preferably 3. In our preferred method, the bond between R 1 and the adjacent silicon atom shown in formula 1 is formed by the reaction of 1) a silane containing one or two ethylenically unsaturated substituents and two or three hydrolyzable groups with 2) an organosilicon compound containing at least two silicon-bonded hydrogen atoms. Classes of silanes that can be reacted with compounds containing at least two silicon-bonded hydrogen atoms to obtain ingredient D of the present compositions are described in US-A 4,719,262. The terminally unsaturated organosilicon compounds described in this patent can be prepared by reacting one of five classes of organic compounds with a silane containing at least three silicon bonded hydrolyzable groups. The five classes of organic compounds that can be reacted with a silane containing at least three hydrolyzable groups to form compound D1 are 1) terminally unsaturated alcohols, 2) ethers derived from the reaction of an alcohol of this type with either a saturated polyhydric alcohol or a polyhydric phenol, 3) esters derived from the reaction of a terminally, unsaturated alcohol with a saturated hydroxyl-substituted carboxylic acid; 4) esters derived from an ethylenically unsaturated carboxylic acid with a saturated alcohol containing at least two hydroxyl groups and 5) ethers derived from an ethylenically unsaturated monohydric alcohol and an alcohol containing at least 3 hydroxyl groups. Typically one mole of the ethylenically unsaturated hydroxyl-substituted organic compound used to prepare reactant D1 is reacted with each mole of a silane containing at least three hydrolyzable groups per molecule and represented by the formula X m+1 R 2 3-m Si, wherein m is 2 or 3. In the embodiment of ingredient D, wherein R 1 is an alkylene radical represented by R 4 , reactant D1 exhibits the formula CH 2 =C(R 12 )R 4' OSiX m R 2 (3-m) , R 4' represents an alkylene radical and the group -CH 2 CH(R 12 )R 4' - constitutes R 4 . In this embodiment, referred to as I, CH 2 =C(R 12 )R 4' O-represents the residue remaining following removal of the hydrogen atom from the hydroxyl group of a terminally unsaturated alcohol and R 12 represents a hydrogen atom or a monovalent hydrocarbon radical. As used herein, the term "terminally unsaturated" implies the presence of a hydrocarbon radical that includes a CH 2 =C(R 12 )- group. Terminally unsaturated monohydric alcohols useful for preparing embodiment I of reactant D1 contain from 3 to 20 carbon atoms and include 3-buten-1-ol, 3-buten-2-ol, 2-methyl-3-buten-2-ol, 5-hexen-1-ol, 9-decylen-1-ol, 10-undecylen-1-ol, 17-octadecylen-1-ol and the isomeric allyl substituted cyclohexanols. Preferred alcohols contain from 3 to 12 carbon atoms. Terminally unsaturated polyhydric alcohols or partial ethers thereof can also be substituted for the monohydric alcohol. A second embodiment of reactant D1, referred to hereinafter as II, is one wherein the ethylenically unsaturated group present in reactant D1 exhibits the general formula CH 2 =C(R 12 )R 4' OR 5 O- and the group represented by R 1 exhibits the formula -CH 2 CH(R 12 )R 4' OR 5 -. The radicals represented by R 4' and R 12 are defined above and R 5 represents a hydrocarbylene or substituted hydrocarbylene radical. In our embodiment II, the ethylenically unsaturated group represents the residue remaining after removal of the hydrogen from a free hydroxyl group of the saturated polyhydric alcohol portion of an ether derived from that alcohol and a terminally unsaturated alcohol containing at least one hydroxyl group. The unsaturated alcohol is preferably monohydric. The saturated polyhydric alcohol is preferably dihydric and is represented by the formula HOR 5 OH. Preferably R 5 represents unsubstituted alkylene, hydroxyalkylene, cycloalkylene or phenylene; this preference is commonly based on the availability of the corresponding alcohols. Suitable saturated polyhydric alcohols are ethylene glycol, the isomeric propylene glycols, glycerol, 1,1,1-trimethylolpropane, 1,4-cyclohexanediol and other alcohols containing at least two hydroxyl groups per molecule and up to 20 carbon atoms. R 5 preferably contains from 2 to 12 carbon atoms. Partially etherified polyhydric alcohols containing three or more hydroxyl groups, at least two of which are unreacted, are also suitable precursors for the alcohol portion of compounds corresponding to embodiment II. Suitable terminally unsaturated alcohols include those discussed in connection with embodiment I of reactant D1 in addition to allyl alcohol. In a third embodiment of reactant D1, the ethylenically unsaturated group exhibits the formula CH 2 =C(R 12 )R 4' OC(O)R 6 O- and the R 1 group in ingredient D exhibits the formula -CH 2 C(H)(R 12 )R 4' OC(O)R 6 -. R 4' and R 12 are as previously defined, R 6 is selected from the same group as R 4 and the -CH 2 C(H)(R 12 )R 4' - divalent group constitutes R 4 . This divalent group is derived from the ester of an unsaturated monohydric alcohol and a saturated hydroxycarboxylic acid. R 4 and R 6 preferably contain from 3 to 12 carbon atoms. In a fourth embodiment (IV) of reactant D1, the ethylenically unsaturated group exhibits the formula CH 2 =C(R 12 )R 7' C(O)OR 5 O- and the R 1 group in ingredient D exhibits the formula -R 7 C(O)OR 5 -, where R 7 is CH 2 =C(R 12 )R 7' . R 7 is selected from the same group as R 4 and R 7' is selected from the same group of radicals as R 4' or it can represent a single bond. For the compounds of embodiment IV, the ethylenically unsaturated group represents the residue remaining following removal of the hydrogen atom from one hydroxyl group of the alcohol portion of an ester derived from reaction of a terminally unsaturated carboxylic acid with a saturated aliphatic or saturated cycloaliphatic alcohol containing at least two hydroxyl groups. Suitable saturated alcohols are discussed in connection with embodiment II. The terminally unsaturated carboxylic acids used to prepare embodiment IV contain from 3 up to 20 carbon atoms. Representative members of this class include acrylic acid, 3-butenoic acid, 9-decenoic acid and 4-allylbenzoic acid. The fifth type of ethylenically unsaturated group that can be bonded to the silicon atom of preferred embodiments of reactant D1 is derived from the ether of a saturated polyhydric alcohol and an ethylenically unsaturated monohydric alcohol. This group exhibits the formula [CH 2 =C(R 12 )R 4' O] 2 R 8 - and the R 1 group in ingredient D exhibits the formula [CH 2 C(H)(R 12 )R 4' O] 2 R 8 -. R 4' and R 12 are as previously defined and R 8 is a trivalent hydrocarbon radical that preferably contains from 3 to 6 carbon atoms. Suitable reactants for preparing ethers of this type are discussed above in connection with other embodiments of reactant D1. In the formulae for the five embodiments of reactant D1, the radicals represented by R 5 , R 6 and R 8 are bonded to the oxygen atom in formula 1. Organosilicon compounds corresponding to any of the aforementioned five embodiments of reactant D1 are prepared by reacting a silane of the general formula X m+1 R 2 3-m Si with one of the terminally unsaturated, hydroxylated organic compounds described as precursors for embodiments I-V in the preceding paragraphs of this specification. The subsitutents represented by R 4 , R 5 , R 6 and R 7 are preferably unsubstituted alkylene radicals. The reaction between the organic and organosilicon compounds used to prepare reactant D1 is conducted under conditions that are typical for condensation reactions of silanes containing hydrolyzable groups with hydroxylated organic compounds. These reactions are typically conducted under an inert, anhydrous atmosphere such as nitrogen at temperatures from ambient to 200°C. and may also employ a catalyst. Useful catalysts are the titanium compounds later described in this specification. The hydrolyzable groups are preferably alkoxy or enoloxy. The weight of catalyst typically constitutes from 0.1 to 5 percent of the combined weight of all reactants. Reactions involving exchanges of the preferred silicon-bonded alkoxy and enoloxy groups typically generate the alcohol or ketone corresponding to the original silicon-bonded alkoxy or enoloxy group as a by-product. Because these reactions are often reversible, it is usually desirable to remove this by-product alcohol or ketone by distillation as the reaction progresses. The course of exchange reactions involving the generation and removal of alcohol or other by-products is readily followed by measuring the amount of by-product collected. Methanol and ethanol are the lowest boiling alcohols and it is therefore preferable that the hydrolyzable groups of reactant D1 be methoxy or ethoxy. For the same reason, when the hydrolyzable group is enoloxy, it is preferably isopropenyloxy. The reactants and catalyst used to prepare reactant D1 are heated for a period of time sufficient to achieve a substantially complete reaction, as indicated by the amount of alcohol or other by-product collected. This time period is typically from 1 to 5 hours and the reaction mixture is preferably heated from 50 to 200°C. It may be desirable to include in the reaction mixture a liquid diluent that may also function as a solvent for the reactants. Suitable diluents include aliphatic and aromatic hydrocarbons that are liquid at ambient temperature and boil within the range of from 50 to 250°C. Representative diluents include hexane, heptane and liquid aromatic hydrocarbons such as toluene and xylene. Some of the ethylenically unsaturated organic reactants used to prepare reactant D1 will polymerize at the temperatures used to react them with the organosilicon compound. It may, therefore, be desirable to include in the reaction mixture an effective amount of a free radical scavenger such as hydroquinone to completely suppress or at least inhibit the tendency of the organic reactant to polymerize during preparation of the present compounds. Those embodiments of reactant D1 that boil below 200°C. under ambient or reduced pressure are isolated by distilling the product from the reaction mixture. Higher boiling products are isolated using known chromatographic techniques with gases or liquids as the carrier. In some instances, the reaction mixture in which the compound is prepared can be used directly as reactant D1 without isolation or purification. In place of the group represented by X m R 2 (3-m) Si, reactant D1 can also contain a precursor that can be converted to this group following reaction with an organohydrogensiloxane (reactant D2). A preferred example of such a precursor group is the trimethylsiloxy group present in the silane (CH 3 ) 3 SiOCH 2 CH=CH 2 . Following reaction of this silane with reactant D2, the trimethylsiloxy group is hydrolyzed to form a hydroxyl group. The hydroxyl group is then reacted with silane containing 3 or 4 alkoxy groups or other hydrolyzable groups such as ketoximo to obtain the desired X m R 2 (3-m) SiO- group present in ingredient D, wherein X represents the hydrolyzable group. Compounds wherein one of the R 3 substituents in formula I represents an alkenyl radical are prepared by reacting compounds wherein R 3 is a silicon-bonded hydrogen atom with stoichiometric excess of a diene-type hydrocarbon such as butadiene. Reactant D2 is any organosiloxane compound containing at least two silicon-bonded hydrogen atoms per molecule. This reactant contains from 2 to 20 silicon atoms per molecule and the silicon-bonded hydrogen atoms can be located on terminal or non-terminal silicon atoms. This reactant provides the portion of the molecule represented by [Si(R 3 ) 3 ] n in formula 1. Compounds suitable for use as reactant D2 are symtetramethyldisiloxane, sym-dimethyldiphenyldisiloxane, dimethylhydrogensiloxy-terminated polydimethylsiloxanes, dimethylhydrogensiloxy-terminated dimethylsiloxane/phenylmethylsiloxane copolymers, dimethylhydrogensiloxy-terminated dimethylsiloxane/diphenylsiloxane copolymers, dimethylhydrogensiloxy-terminated dimethylsiloxane/methyl-3,3,3-trifluoropropylsiloxane copolymers, trimethylsiloxy-terminated polymethylhydrogensiloxanes, trimethylsiloxy-terminated dimethylsiloxane/methylhydrogensiloxane copolymers and copolymers containing dimethylhydrogensiloxy and SiO 4/2 units. A preferred embodiment of reactant D2 is a linear polydiorganosiloxane containing hydrogen atoms on the two terminal silicon atoms and are represented by the general formula H[(R 9 ) 2 SiO] q SiR 9 2 H, wherein q is at least 1 and all of the substituents represented by R 9 are monovalent hydrocarbon radicals. R 9 is preferably methyl, ethyl, phenyl or 3,3,3-trifluoropropyl, this preference being based on the availability of the intermediates used to prepare reactant D2 and q is preferably from 1 to 20. The only restriction on the number average molecular weight of reactant D2 is that the liquid or solubilized form of this reactant be compatible with reactant D1. The reaction between reactants Dl and D2 is a hydrosilation reaction and is typically conducted in the presence of a catalyst that is a metal from the platinum group of the periodic table or a compound of one of these metals. Due to the exothermic nature of many hydrosilation reactions and the requirement to react only a portion of the silicon-bonded hydrogen atoms on reactant D2, it is usually preferable to gradually add the ethylenically unsaturated silane (reactant D1) to a stoichiometric excess of the organohydrogensiloxane (reactant D2). The molar ratio of D1 to D2 is from 0.1-1 to 0.9-1, preferably from 0.5-1 to 0.8-1. It should be understood that higher relative molar concentrations of ingredient D2 are preferred when this ingredient contains more that two silicon-bonded hydrogen atoms per molecule. To avoid excessive overheating and formation of undesirable by-products, the temperature of the reaction mixture should be maintained below 100°C. and preferably at 70°C. In a preferred method for preparing our compounds, an organohydrogensiloxane containing at least two silicon-bonded hydrogen atoms per molecule is reacted with an organosilicon compound of the formula ZOR 13 where Z represents the group X m R 2 3-m Si- or a precursor of this group, X represents a hydrolyzable group and R 13 represents an alkenyl radical wherein the unsaturated carbon atoms are located at a terminal position. The reaction between preferred embodiments of a reactant D1 precursor and reactant D2 to form ingredient D is shown in the following general equations: In the foregoing equations, X preferably represents an alkoxy group containing from 1 to 4 carbon atoms, most preferably methoxy or ethoxy. Alternatively, X can represent a ketoximo group such as methylethylketoximo or other hydrolyzable group that will not interfere with the curing of organosiloxane compositions containing ingredient D as an adhesion promoting additive. An alternative method for preparing ingredient D is by the reaction of a carbinol-functional silane or organosiloxane with a silane containing a group reactive with the carbinol group and a silicon-bonded hydrogen atom or alkenyl radical. This method is shown in the following equations: CH 3 Si(OC 2 H 5 ) 3 + HOC 2 H 4 (CH 3 ) 2 SiO[Si(CH 3 ) 2 O] 3 SiO(CH 3 ) 2 CH=CH 2 → CH 3 (OC 2 H 5 ) 2 SiOC 2 H 4 Si(CH 3 ) 2 O[Si(CH 3 ) 2 O] 3 SiO(CH 3 ) 2 CH=CH 2 + C 2 H 5 OH Methods for preparing carbinol functional organosilicon compounds are described in the literature, for example, US-A 5,290,901. If the reaction product of the silane and the organohydrogensiloxane is subsequently reacted with a silane or siloxane containing at least two ethylenically unsaturated groups, referred to herein as reactant D3, one of the R 9 substituents in at least one of the [SiR 9 p O (3-p)/2 ] units is represented by the formula -R 11 [R 10 s SiO (3-s)/2 ] r . In this formula, R 11 represents the alkylene radical resulting from reaction of an ethylenically unsaturated group with a silicon-bonded hydrogen atom, each R 10 is individually selected from the group consisting of unsubstituted and substituted monovalent hydrocarbon radicals and hydrolyzable groups represented by X, r is at least 1 and the value of s is individually selected from 0, 1, 2 and 3 in each unit. The saturated monovalent hydrocarbon radicals are alkyl, most preferably methyl and one of the R 10 radicals in one or more of the siloxane units represents an ethylenically unsaturated hydrocarbon radical or an ethylenically unsaturated group such as acryloxypropyl or methacryloxypropyl. R 11 preferably contains the same number and configuration of carbon atoms as the unsaturated group represented by R 10 . The unsaturated hydrocarbon radical is preferably vinyl or allyl and R 11 is preferably ethylene or propylene. In preferred embodiments of reactant D3, the unsaturated groups are vinyl, allyl, 5-hexenyl or 3-methacryloxypropyl. Reactant D3 is preferably sym-tetramethyldivinyldisiloxane. The reaction between (1) the reaction product of reactants D1 and D2 and (2) reactant D3 is carried out under conditions similar to those used for the reaction of reactants D1 and D2. In this instance, reaction product (1) is gradually added to a stoichiometric excess of reactant D3. The purity of the reaction product is increased by the choice of catalyst and the stoichiometric ratio of alkoxysilane to organohydrogensiloxane. Curable compositions, suitable for use with the present adhesion-promoting organosiloxane compositions as adhesion promoters, can cure by any of the reactions known for curing organosiloxane compositions, with the exception of the reaction of silanol groups with silicon-bonded hydrolyzable groups that occurs in the presence of moisture. The curing reactions that can be used in the presence of the adhesion-promoting compositions of this invention include hydrosilation reactions catalyzed by platinum-group metals and compounds thereof, the reaction of silicon-bonded hydrogen atoms with silanol groups, the reaction of mercapto groups with one another in the presence of oxygen and a catalyst, the reaction of mercapto groups with alkenyl radicals in the presence of a catalyst, free radical and cationic reactions initiated by irradiation of photosensitive compounds with ultraviolet light, free radical reactions initiated by the thermally induced decomposition of a free radical precursor and reactions initiated by high energy radiation. As used herein, the term "cure" means the conversion of a liquid or semi-solid composition to a crosslinked elastomeric or resinous material by the reaction of groups present on the polyorganosiloxane referred to as ingredient A of the present compositions with the curing agent. The present inventors discovered that the compounds of this invention are particularly suitable for use with organosiloxane compositions that cure by a platinum-catalyzed hydrosilation reaction when the compounds are present in the curable composition. Unlike many of the known adhesion promoters for organosiloxane compositions, the present organosiloxane compounds are effective at curing temperatures from ambient to 70°C. To develop the cohesive bonding to a variety of substrates during curing of the present compositions, the concentration of ingredient D should be from 0.2 to 10 weight percent, based on the weight of the entire curable composition and preferably from 0.5 to 2.5 weight percent. The required and optional ingredients of preferred and alternative curable organosiloxane compositions suitable for use with our adhesion-promoting additives are explained in detail below. An alkenyl-containing polyorganosiloxane, hereinafter ingredient A, present in organosiloxane compositions that cure by a hydrosilation reaction is the principal ingredient of preferred curable compositions suitable for use with our claimed adhesion-promoting additives. To achieve curing of these compositions, the preferred embodiment of ingredient A contains at least two silicon-bonded alkenyl radicals in each molecule. Suitable alkenyl radicals contain from 1 to 10 carbon atoms and are exemplified by vinyl, allyl and 5-hexenyl. The silicon-bonded organic groups other than alkenyl radicals present in ingredient A are typically monovalent hydrocarbon and halogenated monovalent hydrocarbon radicals and are exemplified by alkyl radicals such as methyl, ethyl and propyl; aryl radicals such as phenyl; and halogenated alkyl radicals such as 3,3,3-trifluoropropyl. The molecular structure of ingredient A is not critical to the present invention and will be determined by the physical properties desired in the cured composition. To achieve a useful level of tensile properties in the elastomers and other products prepared by curing the present compositions, the number average molecular weight of this ingredient should be sufficient to achieve a viscosity at 25°C. of at least 0.1 Pa·s. The upper limit for the number average molecular weight of ingredient A is not specifically restricted and is typically limited only by the processability of the curable organosiloxane composition. The typical polyorganosiloxanes used range from pourable liquids to gum type polymers that are usually defined by Williams plasticity values. Preferred embodiments of ingredient A are polydiorganosiloxanes represented by the general formula 2 wherein each R 14 is individually selected from monovalent hydrocarbon radicals, R 15 represents a vinyl or other alkenyl radical and v represents a degree of polymerization equivalent to a viscosity of at least 100 centipoise (0.1 Pa·s), preferably from 0.1 to 10 Pa·s. As used herein, monovalent hydrocarbon radicals include alkyl containing from 1 to 20 carbon atoms, such as methyl, ethyl, n-hexyl and n-dodecyl; alkenyl such as vinyl or allyl; cycloalkyl such as cyclohexyl; aryl radicals such as phenyl or naphthyl; aralkyl such as benzyl or alkaryl such as tolyl and xylyl. The hydrocarbon radicals represented by R 14 are either unsubstituted or contain substituents such as halogen atoms that will not adversely affect the storage stability and curing of the claimed compositions or the properties of cured articles prepared from these compositions. The two R 14 substituents on each of the silicon atoms in formula 2 can be identical or different and contain from 1 to 20 carbon atoms. A range of from 1 to 10 carbon atoms is preferred based on the availability of the corresponding monomers. Most preferably, at least one of the hydrocarbon radicals on each silicon atom is methyl and any remainder are vinyl, phenyl and/or 3,3,3-trifluoropropyl. This preference is based on the availability of the reactants typically used to prepare the polydiorganosiloxane and the properties of cured elastomers prepared from these polydiorganosiloxanes. For the same reasons, R 15 is preferably vinyl or 5-hexenyl. Representative embodiments of ingredient A, which contain ethylenically unsaturated hydrocarbon radicals only at the terminal positions are dimethylvinylsiloxy-terminated polydimethylsiloxanes, dimethylvinylsiloxy-terminated polymethyl-3,3,3-trifluoropropylsiloxanes, dimethylvinylsiloxy-terminated-dimethylsiloxane/3,3,3-trifluoropropylmethylsiloxane copolymers and dimethylvinylsiloxy-terminated dimethylsiloxane/methylphenylsiloxane copolymers. Methods for preparing ingredient A of the present compositions by hydrolysis and condensation of the corresponding halosilanes or by condensation of the cyclic polydiorganosiloxanes are sufficiently disclosed in the patent and other literature that a detailed description in this specification is not necessary. For applications requiring high levels of physical properties such as tear strength, it may be desirable to include in the curable organosiloxane composition a second polydiorganosiloxane containing ethylenically unsaturated hydrocarbon radicals bonded to both terminal and non-terminal silicon atoms. The preferred curable organosiloxane compositions of this invention contain at least one organohydrogen-siloxane that functions as a curing agent for ingredient A. In the presence of the hydrosilation catalyst, ingredient C, the silicon-bonded hydrogen atoms in ingredient B undergo an addition reaction, referred to as hydrosilation, with the silicon-bonded alkenyl groups in ingredient A, resulting in crosslinking and curing of the composition. Ingredient B must contain at least 2 silicon-bonded hydrogen atoms in each molecule. If ingredient A contains only two alkenyl radicals per molecule, ingredient B must contain an average of more than two silicon-bonded hydrogen atoms to achieve a crosslinked structure in the final cured product. The silicon-bonded organic groups present in ingredient B are selected from the same group of monovalent hydrocarbon and halogenated hydrocarbon radicals as the organic groups of ingredient A. The organic groups in ingredient B are preferably substantially free of ethylenic or acetylenic unsaturation. The molecular structure of ingredient B can be straight chain, branch-containing straight chain, cyclic or network. While the number average molecular weight of ingredient B is not specifically restricted, viscosities in the range of 3 to 10,000 centipoise (0.003 to 10 Pa s) at 25°C. are preferred. The concentration of ingredient B is sufficient to provide a molar ratio of silicon-bonded hydrogen atoms to alkenyl radicals in the curable composition of from 0.5 to 20. A range of from 0.5 to 2 is preferred. When the curable composition contains less than 0.5 moles of silicon-bonded hydrogen atoms per mole of alkenyl radicals, it may not be possible to achieve the desired physical properties after curing. The physical properties of the cured article may vary with time when this ratio exceeds 20 moles of silicon-bonded hydrogen per mole of alkenyl radicals. Curing of the present compositions is catalyzed by a hydrosilation catalyst that is a metal from the platinum group of the periodic table or a compound of such a metal. These metals include platinum, palladium and rhodium. Platinum and platinum compounds are preferred based on the high activity level of these catalysts in hydrosilation reactions. Examples of preferred curing catalysts are platinum black, platinum metal on various solid supports, chloroplatinic acid, alcohol solutions of chloroplatinic acid and complexes of chloroplatinic acid with liquid ethylenically unsaturated compounds such as olefins and organosiloxanes containing ethylenically unsaturated hydrocarbon radicals bonded to silicon. Complexes of chloroplatinic acid with the aforementioned organosiloxanes containing ethylenically unsaturated hydrocarbon radicals are described in US-A 3,419,593, which teaches preferred catalysts. The concentration of ingredient C in the present compositions is equivalent to a platinum concentration of from 0.1 to 500 parts by weight of platinum metal, preferably from 1 to 50 parts by weight of platinum metal, per million parts (ppm), based on the combined weight of ingredients A and B. Curing does not proceed satisfactorily at below 0.1 ppm of platinum, while using more than 500 ppm results in no appreciable increase in cure rate and is therefore uneconomical. Mixtures of the aforementioned ingredients A, B and C may begin to cure at ambient temperature. To obtain a longer working time or "pot life", the activity of the catalyst under ambient conditions is retarded or suppressed by addition of a suitable inhibitor. Known platinum catalyst inhibitors include the acetylenic compounds disclosed in US-A 3,445,420. Acetylenic alcohols such as 2-methyl-3-butyn-2-ol constitute a preferred class of inhibitors that will suppress the activity of a platinum-containing catalyst at 25°C. Compositions containing these catalyst inhibitors typically require heating at temperatures of at least 70°C. to cure at a practical rate. When it is desired to increase the pot life of a curable composition under ambient conditions, this is accomplished using an alkenyl-substituted siloxane of the type described in US-A 3,989,667. Cyclic methylvinyl-siloxanes are preferred. Inhibitor concentrations as low as one mole of inhibitor per mole of platinum will in some instances impart satisfactory storage stability and cure rate. In other instances, inhibitor concentrations of 500 or more moles of inhibitor per mole of platinum are required. The optimum concentration for a given inhibitor in a given composition is readily determined by routine experimentation and does not constitute part of this invention. To achieve high levels of tear strength and other physical properties that characterize some types of cured elastomers that are prepared using the compositions of this invention, it may be desirable to include a reinforcing filler such as finely divided silica. Silica and other reinforcing fillers are often treated with one of more of the known filler treating agents to prevent a phenomenon referred to as "creping" or "crepe hardening" during processing of the curable composition. Finely divided forms of silica are preferred reinforcing fillers. Fumed silicas are particularly preferred because of their relatively high surface area, which is typically at least 50 square meters per gram. Fillers having surface areas of at least 200 square meters per gram are preferred for use in the present method. The amount of finely divided silica or other reinforcing filler used in the present compositions is at least in part determined by the physical properties desired in the cured elastomer. Liquid or pumpable polyorganosiloxane compositions typically contain from 10 to 60 percent by weight of silica, based on the weight of polydiorganosiloxane. This value is preferably from 30 to 50 percent silica. The filler treating agent is any of the low molecular weight organosilicon compounds disclosed in the art as being suitable for preventing creping of organosiloxane compositions during processing. The treating agents are typically liquid, hydroxyl-terminated polydiorganosiloxanes containing an average of from 2 to 20 repeating units per molecule and organosilicon compounds such as hexaorganodisiloxanes and hexaorganodisilazanes that hydrolyze and condense under the conditions used to treat the filler. Preferably, at least a portion of the silicon-bonded hydrocarbon radicals present on the treating agent are identical to a majority of the hydrocarbon radicals present in ingredients A and B. A small amount of water can also be added together with the silica treating agent(s) as a processing aid. It is believed that the treating agents function by reacting with silicon-bonded hydroxyl groups present on the surface of the silica or other filler particles to reduce interaction between these particles and the polyorganosiloxanes present in the curable composition. When a silica filler is used, it is preferably treated in the presence of at least a portion of the other ingredients of the present compositions by blending these ingredients together until the filler is completely treated and uniformly dispersed to form a homogeneous material. The ingredients that are present during treatment of the filler typically include the silica treating agents and at least a portion of the polydiorganosiloxane(s) referred to as ingredient A. The present organosiloxane compositions can also contain one or more additives that are conventionally present in curable compositions of this type to impart or enhance certain physical properties of the cured composition in addition to adhesion or to facilitate processing of the curable composition. Typical additives include non-reinforcing fillers, such as quartz, alumina, mica and calcium carbonate; pigments such as carbon black and titanium dioxide; dyes; flame retardants and heat and/or ultraviolet light stabilizers. Resinous organosiloxane copolymers can also be used in place of or in combination with one or more reinforcing fillers to improve the physical properties of the cured organosiloxane composition. A preferred type of resinous copolymer contains repeating units of the general formula SiO 4/2 in addition to triorganosiloxy units of the general formulae R 16 3 SiO 1/2 and diorganovinylsiloxy units of the general formula CH 2 =CH(R 17 ) 2 SiO 1/2 . In these formulae, R 16 and R 17 are individually monovalent hydrocarbon or substituted monovalent hydrocarbon radicals as previously defined for the R 15 radicals of ingredient A. The molar ratio of the combination of triorganosiloxy units and diorganovinylsiloxy units to SiO 4/2 units in the resinous copolymer is from 0.7 to 1.2, inclusive. The vinyl-containing units constitute from 2 to 8 percent by weight of the copolymer, which preferably contains at least two vinyl radicals per molecule. In preferred embodiments of the copolymer the ranges for the molar ratio of diorganovinylsiloxy to triorganosiloxy to SiO 4/2 units is 0.08-0.1 : 0.06-1 : 1. The resinous copolymers can be prepared as described in US-A 2,676,182 which teaches the preparation of and the scope of these resins. The copolymers described in this patent contain from 2 to 23 percent by weight of hydroxyl groups, which is considerably above the maximum level of 0.8 weight percent preferred for precursors of the present copolymers. The hydroxyl content of the precursor is conveniently reduced to the desired level by employing a higher concentration of triorganosiloxy units than the concentration range taught by said patent. In place of polyorganosiloxanes, curing agents and catalysts referred to above as ingredients A, B and C, our claimed adhesion promoting additives are used with organosiloxane compositions that cure by other types of reactions. These reactions include the reaction of silicon-bonded hydrogen atoms with silanol groups, the reaction of mercapto groups with one another in the presence of oxygen and a catalyst, the reaction of mercapto groups with alkenyl radicals in the presence of a catalyst, free radical and cationic reactions initiated by irradiation of photosensitive compounds with ultraviolet light, free radical reactions initiated by the thermally induced decomposition of a free radical precursor and reactions initiated by high energy radiation. The compositions of this invention are prepared by combining all of ingredients at ambient temperature. Any of the mixing techniques and devices described in the prior art can be used for this purpose. The particular device used will be determined by the viscosity of the ingredients and the final curable composition. Suitable mixers include paddle type mixers, kneader type mixers and two- and three-roll rubber mills. Cooling of the ingredients during mixing may be desirable to avoid premature curing of the composition. To maximize storage stability of preferred curable organosiloxane compositions that cure by a hydrosilation reaction, these compositions are preferably kept in closed containers until use. If greater storage stability is desired, the compositions are packaged in two or more containers with the organohydrogensiloxane (ingredient B) and the platinum group metal catalyst (ingredient C) stored in separate containers. Depending upon the types and concentrations of ingredients A and B, cured organosiloxane materials prepared using the present compositions will vary in properties from brittle resins to elastomers to gels and are useful in a variety of end-use applications as coatings or as molded or extruded articles. Unfilled materials are particularly useful as adhesives, protective coatings, encapsulants and potting compositions for protecting delicate electronic devices such as transistors and integrated circuits from damage by moisture and other materials present in the environment that can adversely affect operation of the device. The compositions can be used to coat either the individual devices or a circuit board containing a number of these devices together with other electronic components. The present compositions are applied to substrates by spraying, dipping, pouring, extrusion or by the use of a brush, roller or coating bar. The selection of a particular application method will be determined at least in part by the viscosity of the curable composition. The viscosity of the composition can be reduced using suitable solvents or reactive diluents as known in the art. Organosiloxane compositions containing our claimed adhesion additives cohesively bond to a variety of organic and inorganic substrates during curing at temperatures as low as 25°C. The ability of the present compositions to develop adhesion when cured at these relatively low temperatures make them suitable for application to substrates that cannot withstand the elevated temperatures of 100°C. or higher required to cure organosiloxane compositions containing prior art adhesion additives, some of which may inhibit platinum-group metal catalysts. Preferred compositions cure over a period of several hours under ambient conditions. As is true for other compositions that cure by a platinum-catalyzed hydrosilation reaction, curing can be accelerated by heating. Curing temperatures of from 25° to 80°C. are preferred. The following examples describe preferred curable compositions of the present invention. Unless otherwise specified all parts and percentages in the example are by weight and viscosities were measured at 25°C. Example 1 Preparation of (C 2 H 5 O) 3 SiO(CH 2 ) 3 Si(CH 3 ) 2 OSi(CH 3 ) 2 H Allyloxytrimethylsilane was prepared by charging a glass reactor with 100.1 g of allyl alcohol and 140.1 g of hexamethyldisilazane (HMDZ). The reactor was equipped with a water-cooled condenser and a nitrogen inlet. The contents of the reactor were heated at the boiling point for 4 hours under a nitrogen atmosphere, at which time 20.0 g. of additional HMDZ were added. Heating of the reaction mixture at the boiling point was continued for an additional 3 hours. Analysis of the reaction mixture indicated the substantial absence of unreacted allyl alcohol and a small amount of unreacted HMDZ. A reactor was charged with 259.1 g. of sym-tetramethyldisiloxane and 30 microliters of a 0.02 molar solution of hexachloroplatinic acid solution in isopropyl alcohol. The reactor was equipped with a water-cooled condenser, stirring means and an addition funnel containing 100.1 g. of the allyloxytrimethylsilane prepared above. The contents of the reactor were heated to 70°C., at which time the addition of the silane was begun. The temperature of the reaction mixture was maintained at 70°C. during the addition. Following addition completion, the reaction mixture was heated within the range from 77 to 110°C. for one hour. Unreacted tetramethyldisiloxane was removed during this heating period. Distillation of the reaction mixture yielded 69 g. of 95% pure Me 3 SiO(CH 2 ) 3 SiMe 2 OSiMe 2 H (I), where Me represents the methyl radical. Hydrolysis of the trimethylsiloxy group of this product was achieved by reacting 35 g. of the product with 35 g. of methanol and 1 drop of concentrated (37 weight percent) hydrochloric acid under ambient conditions for 18 hours. Volatile materials were then removed under reduced pressure at a temperature of 38°C. to yield HO(CH 2 ) 3 SiMe 2 OSiMe 2 H (II). The final product (ingredient D) was prepared by charging a reactor with 16.5 g. of tetraethyl orthosilicate and 0.25 g. of tetrabutyltitanate. The reactor was equipped with a distillation head, water-cooled condenser, a receiver cooled using "dry" ice and an addition funnel containing 15.23 g. of II. The contents of the reactor were heated to 75°C. while being maintained under a nitrogen atmosphere, at which time addition of II was begun. The addition required 23 minutes. Following addition completion, the temperature of the reaction mixture was increased sufficiently to remove the ethanol formed as a by-product of the reaction together with unreacted tetraethyl orthosilicate. 4.75 g. of liquid were collected. The product, a mixture of compounds exhibiting the general formula (C 2 H 5 O) x Si[O(CH 2 ) 3 Si(CH 3 ) 2 OSi(CH 3 ) 2 H] 4-x and a small amount of unreacted tetraethyl orthosilicate, remained as a residue in the reactor. The major reaction product was the compound in which x in the general formula is 3. Example 2 Preparation of (C 2 H 5 O) 3 SiO(CH 2 ) 3 Si(CH 3 ) 2 OSi(CH 3 ) 2 (CH 2 ) 2 Si(CH 3 ) 2 OSi(CH 3 ) 2 CH=CH 2 A reactor equipped with a water-cooled condenser and an addition funnel was charged with 176.2 g. of sym-tetramethyldivinyldisiloxane and 460 microliters of a 0.02 molar solution of hexachloroplatinic acid solution in isopropyl alcohol. 24.7 g. of the intermediate product of Example 1 (identified as I) were placed in the addition funnel. The contents of the reactor were heated to 80°C., at which time the contents of the addition funnel were added over a period of 1 hour, during which time the temperature of the reaction mixture was maintained between 82 and 89°C. Following completion of the addition, the temperature of the reaction mixture was increased to 138°C. and maintained at this level for 8 hours, at which time none of compound I could be detected using gas-liquid chromatography. Unreacted disiloxane was then removed by distillation to obtain Me 3 SiO(CH 2 ) 3 SiMe 2 OSiMe 2 (CH 2 ) 2 SiMe 2 OSiMe 2 CH=CH 2 (III). 24.77 g. of this product, together with 30.95 g. of methanol and 1 drop of concentrated (37 weight percent) hydrochloric acid, were placed in a reactor and stirred for 16 hours under ambient conditions, at which time volatile products were removed under reduced pressure and ambient temperature. The residue in the reactor will be referred to as material IV and was believed to be HO(CH 2 ) 3 SiMe 2 OSiMe 2 (CH 2 ) 2 SiMe 2 OSiMe 2 CH=CH 2 . The desired final product was prepared by charging a reactor with 8.12 g. of tetraethyl orthosilicate and 0.2 g. of tetrabutyl titanate. The reactor was equipped with a distillation head and an addition funnel containing 17.21 g. of the material IV. The contents of the reactor were heated to 75°C. while the contents of the addition funnel were added over a 45 minute period. Following addition completion, the reaction mixture was heated sufficiently to remove 1.02 g. of volatile material by distillation. Analysis by gas-liquid chromatography indicated that the residue in the reactor contained unreacted tetraethyl orthosilicate and a number of different reaction adducts, including at least one compound of the present invention as the major product. Example 3 This example demonstrates the adhesion to a variety of substrates that is achieved using the compounds of the present invention as adhesion promoters. The two part curable organosiloxane composition used to evaluate the adhesion promoters contained the following ingredients: Part A: 46 parts of a dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 0.4 Pa·s at 25°C. 46 parts of quartz having an average particle size of 5 micrometers; 7 parts of a dispersion containing 80 weight percent of a dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 0.4 Pa·s at 25°C., 13 weight percent of zinc oxide and 7 weight percent of lampblack; and 0.2 part of a reaction product of hexachloroplatinic acid and sym-tetramethyldivinyldisiloxane that had been diluted with a liquid, dimethylvinylsiloxy-terminated polydimethylsiloxane in an amount sufficient to achieve a platinum content of 0.7 weight percent. Part B 47 parts of a dimethylvinylsiloxy-terminated polydimethylsiloxane exhibiting a viscosity of 0.4 Pa·s at 25°C. (Ingredient A). 47 parts of quartz having an average particle size of 5 micrometers; 6 parts of a trimethylsiloxy-terminated polydiorganosiloxane containing an average of five methylhydrogensiloxane units and three dimethylsiloxane units per molecule with a silicon-bonded hydrogen atom content in the range from 0.7 to 0.8 weight percent (Ingredient B), and 0.1 part of cyclic methylvinylsiloxanes. Some of the compositions contained additional quantities of the organohydrogensiloxane. The amounts of parts A and B of the curable composition and the type and amounts of adhesion promoter used to prepare each of the compositions evaluated are summarized in Table 1. All of the compositions contained 0.01 part of tetrabutyl titanate. Two of the compositions contained additional amounts of the same organohydrogen-siloxane (ingredient B) present in the part A of the curable composition. Ingredient (parts) Composition 1 2 3 4 Part A 4.90 4.75 4.88 4.69 Part B 4.90 4.75 4.90 4.70 Adhesion Additive Example 1 1 2 2 Parts 0.25 0.52 0.28 0.51 Ingredient B 0 0 0.07 0.12 Portions of each of the four compositions were coated as 0.008 inch (0.2 mm.) thick films on the following substrates using a draw-down bar: glass microscope slides; mill finish aluminum panels containing an alloy coating and available as type 3003 H14 Q panels from Q-Panel Company; bare aluminum panels available as type 2024 bare aluminum Q panels from Q-Panel Company; an epoxy-fiberglass laminate available as FR4 boards from Kepro Circuit Systems; and copper panels. Each of the compositions evaluated was cured on each of the substrates at room temperature and for 30 minutes at 70°C. The coatings cured at room temperature were evaluated 1, 3 and 7 days after being coated and the coatings cured at 70°C. for 30 minutes were evaluated immediately after cooling upon removal from the oven and after 1, 3 and 7 days of additional curing at room temperature. The adhesion test consisted of scratching the cured coatings with the blade of a metal spatula to determine whether the coating could be removed without leaving a residue on the surface (adhesive failure) or whether failure occurred within the coating layer, resulting in at least a portion of the coating material in the test area adhering to the substrate (cohesive failure). Coatings exhibiting cohesive failure were further tested to determine if the residue on the substrate and the adjacent coating material could be removed by rubbing with a finger. If the coating could be removed in this manner, the pressure required to remove the coating was rated on a subjective scale as slight (WE), medium (WM) or high (WD). The results of the adhesion tests are summarized in Table 2. Comp. Cure Temp. Time Glass Bare Al Milled Al Copper Epoxy 1 RT 1 day CF AF CF CF CF 3 days CF CF CF CF CF 7 days CF CF CF CF CF 1 70°C. 30 min. AF AF AF AF AF 1 day WM WD AF WD AF 3 days CF CF CF CF WE 7 days CF CF CF CF CF 2 RT 1 day CF CF CF CF CF 3 days CF CF CF CF CF 7 days CF CF CF CF CF 2 70°C. 30 min. AF AF AF AF AF 1 day AF AF AF WD AF 3 days WM WE CF AF AF 7 days CF CF CF CF AF 3 RT 1 day CF AF CF AF AF 3 days CF WD CF AF AF 7 days CF CF CF CF AF 3 70°C. 30 min. CF AF AF AF AF 1 day CF AF CF AF AF 3 days CF AF CF AF AF 7 days CF CF CF CF WE 4 RT 1 day CF CF CF CF CF 3 days CF CF CF CF CF 7 days CF CF CF CF CF 4 70°C. 30 min. CF AF WE AF AF 1 day CF WE CF AF CF 3 days CF CF CF CF CF 7 days CF CF CF CF CF The data in Table 2 demonstrate the ability of compositions containing our claimed compounds to develop adhesion to a variety of substrates during curing of the compositions at room temperature. Compositions containing 5 weight percent of our adhesion promoters exhibited cohesive failure to all five substrates evaluated after curing for one day. Compositions containing the lower level of adhesion promoter achieved cohesive failure within seven days.

Claims: An organosiloxane compound represented by the formula X m R 2 (3-m) SiOR 1 [Si(R 3 ) 3 ] n wherein R 1 contains at least 3 carbon atoms, exhibits a valence of n +1 wherein n is 1 or 2 and is selected from the group consisting of -R 4 -, -R 4 OR 5 -, -R 4 OC(O)R 6 - and -R 7 C(O)OR 5 - when n is 1 and R 1 is -(R 4 O) 2 R 8 - when n is 2 and wherein R 5 , R 6 and R 8 are bonded to the oxygen atom in said formula; R 4 , R 6 and R 7 represent a hydrocarbylene or substituted hydrocarbylene radical containing at least 3 carbon atoms wherein the substituent is hydroxyl or alkoxy; R 5 contains from 2 to 12 carbon atoms and is selected from hydrocarbylene radicals or allyloxy-substituted hydrocarbylene radicals; R 8 represents a trivalent hydrocarbon radical; each R 2 is individually selected from unsubstituted or substituted monovalent hydrocarbon radicals; each R 3 is individually selected from unsubstituted or substituted monovalent hydrocarbon radicals, silicon bonded hydrogen atoms, X and siloxane units represented by the formula O[SiR 9 p O (3-p)/2 ] q where q is at least 1 and said siloxane units are sequential when q is greater than 1; each R 9 is individually selected from the group consisting of X, hydrogen atom, substituted or unsubstituted monovalent hydrocarbon radicals, X m R 2 3-m SiOR 1 - and -R 11 [R 10 s SiO (3-s)/2 ] r wherein r is at least 1 and the siloxane units represented by R 10 s SiO (3-s)/2 are sequential when r is greater than 1, with the proviso that at least one substituent represented by R 3 contains a silicon-bonded hydrogen atom or alkenyl radical; each R 10 is individually selected from the group consisting of monovalent hydrocarbon radicals, hydrogen atom and X; R 11 represents a hydrocarbylene or substituted hydrocarbylene radical containing at least 2 carbon atoms wherein the substituent is hydroxyl or alkoxy; the substituents present on the substituted hydrocarbon radicals represented by R 2 , R 3 , R 9 , R 10 and R 11 are selected from the group consisting of halogen, epoxy, amino, mercapto and 3-methacryloxypropyl; X represents a hydrolyzable group; m is 2 or 3; n is 1 or 2; p is 0, 1, 2 or 3; and s is 0, 1, 2 or 3. A compound according to claim 1 wherein R 1 contains from 3 to 10 carbon atoms; at least one R 3 substituent is O[SiR 9 p O (3-p)/2 ] q wherein at least one of the R 9 substituents in said compound represents hydrogen; all unsubstituted or substituted monovalent hydrocarbon radicals, other than alkenyl radicals contain from 1 to 20 carbon atoms; R 4 , R 5 , R 6 and R 7 represent identical or different unsubstituted alkylene radicals; R 8 contains from 3 to 6 carbon atoms; and X is alkoxy or ketoximo. A compound according to claim 2 wherein the monovalent hydrocarbon radicals other than alkenyl present in said compound are selected from the group consisting of alkyl radicals containing from 1 to 4 carbon atoms, phenyl and 3,3,3-trifluoropropyl; R 4 and R 6 contain from 3 to 12 carbon atoms; R 5 contains from 2 to 12 carbon atoms; at least one of the siloxane units represented by the formula O[SiR 9 p O (3-p)/2 ] q is a diorganohydrogensiloxane unit and any remaining units include at least one member selected from diorganosiloxane units or organohydrogensiloxane units; and X is alkoxy containing 1 to 4 carbon atoms. A compound according to claim 1 wherein R 1 contains from 3 to 10 carbon atoms; at least one R 3 substituent is O[SiR 9 p O (3-p)/2 ] q wherein at least one of the R 9 substituents in said compound represents R 11 [SiR 10 s O (3-s)/2 ] r ; R 4 , R 5 , R 6 and R 7 are individually selected from unsubstituted alkylene radicals; R 8 contains from 3 to 6 carbon atoms; and X is alkoxy containing from 1 to 4 carbon atoms. A compound according to claim 4 wherein the monovalent hydrocarbon radicals other than alkenyl present in said compound are selected from the group consisting of alkyl radicals containing from 1 to 4 carbon atoms, phenyl and 3,3,3-trifluoropropyl; wherein at least one of the three R 10 groups bonded to the terminal silicon atom is an alkenyl radical selected from the group consisting of vinyl, allyl, butenyl and 5-hexenyl. A compound according to claim 5 wherein at least one of the substituents represented by R 9 is R 11 Si(R 10 ) 2 OSiR 10 3 , where one of the three R 10 groups bonded to the terminal silicon atom is an alkenyl radical containing from 2 to 10 carbon atoms and the four remaining R 10 groups are alkyl radicals containing from 1 to 4 carbon atoms and R 11 is as defined above. A compound according to claim 6 wherein at least one of the monovalent hydrocarbon radicals bonded to each silicon atom containing these monovalent hydrocarbon radicals is methyl. A curable organosiloxane composition comprising A. a curable polyorganosiloxane; B. an amount of a curing agent sufficient to cure said composition; C. an amount of a catalyst sufficient to promote curing of said composition; and D. as an adhesion promoting additive, the organosiloxane compound of claims 1 - 7 wherein said composition cures by a reaction selected from the group consisting of hydrosilation reactions catalyzed by platinum group metals and compounds thereof, the reaction of silicon-bonded hydrogen atoms with silanol groups, the reaction of mercapto groups with one another in the presence of oxygen and a catalyst, the reaction of mercapto groups with alkenyl radicals in the presence of a catalyst, free radical and cationic reactions initiated by irradiation of photosensitive compounds with ultraviolet light, free radical reactions initiated by the thermally induced decomposition of a free radical precursor and reactions initiated by high energy radiation.

Inventors: GENTLE THERESA E, LUTZ MICHAEL A, GENTLE, THERESA E., LUTZ, MICHAEL A.
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1996
Main classification: C07F7
IPC codes: C08L83, C08G77, C07F7, H05K3, C08K5