GB2096630A

GB2096630A - Self-bonding silicone rubber compositions

Info

Publication number: GB2096630A
Application number: GB8129567A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1978-03-07
Filing date: 1979-02-14
Publication date: 1982-10-20
Also published as: JPS63118332A; DE2906220A1; JPS6323227B2; FR2419308A1; GB2018272A; JPS54135844A; JPH0258295B2; JPH0258296B2; GB2096630B; GB2018272B; JPS63118370A

Abstract

A partial hydrolysis product of an aliphatically unsaturated hydrolyzable alkoxy silane is obtained by carrying out a partial hydrolysis of a silane of the formula R<1>aSi (OR<3>)4-a' wherein R<1> is an aliphatic unsaturated radical selected from alkenyl radicals and alkynyl radicals of 2 to 8 carbon atoms, R<3> is selected from alkyl radicals and cycloalkyl radicals of 1 to 8 carbon atoms and a is 1 or 2, in solution in a dipolar aprotic solvent with 0.5 to 1.5 mole of water per mole of the silane.

Description

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GB2 096 630A 1

SPECIFICATION

Partial Hydrolysis product of an aliphati-cally unsaturated hydrolyzable alkoxy silane

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The present invention relates to additives for self bonding silicone rubber compositions. In particular, the present invention relates to a partial hydrolysis product of an aliphatically 10 unsaturated hydrolyzable alkoxy silane.SiH-olefin platinum catalyzed compositions are well known. Such compositions generally comprise a vinyl-containing polysiloxane polymer as the base polymer, a filler which may 15 be a reinforcing filler such as fumed silica or precipitated silica, or an extending filler such as fused quartz incorporated into the base vinyl containing polymer. Also, a vinyl containing silicone resin may be used with or in 20 place of reinforcing fillers. Such a mixture is generally stored separately. The cross-linking portion of the composition comprises a hydride siloxane which may either be a hydride containing polysiloxane or hydride containing 25 silicone resin. A platinum catalyst is used to promote the cure. Various other ingredients may be added to the composition so as to enhance its cured physical properties such as, for instance, there may be added to the 30 composition low viscosity vinyl-containing polymers. The platinum catalyst may either be incorporated with the base vinyl-containing poiymer and filler or it may be packaged with the hydride siloxane cross-linking agent. 35 When it is desired to cure the composition, the two packages or two components are mixed together and the composition is applied in the desired manner and cures at room temperature or at higher temperatures to form 40 a silicone elastomer. There may also be incorporated into such compositions well known inhibitors such as, for instance, acetylenic compounds and other types of compounds which inhibit the cure of the composition at 45 room temperature. When such an inhibited composition is heated at elevated temperatures, that is temperatures, above 100°C, the effect of the inhibitor is destroyed and the composition cures rapidly in a number of 50 minutes to produce a silicone elastomer. Such inhibitors are used in these SiH-olefin platinum catalyzed compositions so as to enhance their pot life or working life after the two packages are mixed and prior to cure. 55 There also has been developed a one-component SiH-olefin platinum catalyzed silicone rubber composition in which the inhibitor is a hydroperoxy compound which is so effective that the composition can be packaged as a 60 one package system for prolonged periods of time and yet when exposed to elevated temperatures can cure to form a silicone elastomer in a matter of minutes.

Such SiH-olefin platinum catalyzed compo-65 sitions find great use as for the preparation of silicone molds, for paper release coatings and as encapsulants. However, while such compositions are very suitable for paper release applications and for silicone molds because of 70 their good release properties, such silicone rubber compositions are utilized with some difficulty as encapsultants and for potting applications because of poor adherence to required bonding surfaces. For potting appli-75 cations, it is often desired to pot or enclose electric circuitry with a silicone composition to protect the electric circuitry from dirt, moisture and mechanical shock. There has been developed a clear SiH-olefin platinum cata-80 lyzed composition for such potting and encapsulating applications so that if there is a malfunction in the electric circuitry, the technician can view the circuitry through the clear potting composition to determine the correc-85 tive action to be taken.

Other relevant properties of such SiH-olefin platinum catalyzed compositions for potting and encapsulating electric circuitry are that they are non-conductive of electricity, resistant 90 to ozone and weathering, and water reppel-lent. These properties make such compositions ideal encapsulant and potting materials, However, such SiH-olefin platinum catalysed compositions still had difficulty with respect to 95 potting and encapsulating applications. Because of their good release properties these SiH-olefin platinum catalyzed silicone rubber compositions would not adhere very well to the electric circuitry and circuitry board sub-100 strates such that a very poor bond was formed between the elastomeric composition and the subtrates. Accordingly, because of the formation of such poor bonds between the silicone elastomeric composition and the encapsulated 105 substrate, the silicone elastomeric encapsulant or potting compound had a tendency to come loose from the substate and thus not fully protect the electric circuitry from moisture,

dirt and mechanical shock.

110 To solve this promblem, printers were developed for such SiH-olefin platinum catalyzed compositions to apply them to metal substrates and specifically, electric circuitry substrates and the electric circuitry itself so that 115 the cured silcone elastomer would adhere with good bond strength to the encapsulated and potted substrate. Such primer compositions are generally combinations of active ingredients dissolved in a volatile solvent or solvent 120 mixture. The primer is applied to the substrate to be encapsulated or potted, say by wiping or spraying. The solvent is allowed to evaporate, leaving a surface coating more suited to bonding. The silicone rubber potting compo-125 sition is applied thereover and allowed to cure to produce a silicone elastomer with a good bond between the silicon elastomer and the electric circuitry that is to be potted or encapsulated. Unfortunately, clear silicone potting 130 compounds that employ vinyl containing sili-

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GB2 096 630A

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cone resins rather than fillers for reinforcement still did not adhere satisfactorily even when such primers were employed. Examples of materials that are desired for electric circui-5 try substrates that are to be bonded to by such SiH-olefin platinum catalyzed compositions are for instance, glass, aluminum, steel, copper and stainless steel which, of course, includes the metals of the electric circuitry 10 itself. Accordingly, the use of such primers sometimes operated with effectiveness to blind such SiH-olefin platinum catalyzed compositions with good bond strengths to the foregoing metal substrates. However, even 1 5 when they worked well there were various promblems associated with primers.

First and foremost of all, it required an additional step in the preparation of the encapsulated or potted electric circuitry appara-20 tus, that is, the application of the primer to the substrate. In addition it increased the cost of the total operation both in the labor involved to apply the primer composition to the electric circuitry substrate and also in the cost 25 of manufacture and distribution of the primer composition itself. Further, such use of primer compositions made it necessary to set forth more detailed instructions than was usual in the preparations of the encapsulated appara-30 tus. Accordingly, for such encapsulated and potting applications it is highly desirable to have an SiH-olefin platinum catalyzed composition which has a self-bonding additive in it such that a primer is not needed for the 35 application of the composition to encapsulate 1 or pot electric circuitry. It is especially highly desirable to have a clear SiH-olefin platinum catalyzed composition which has a self-bonding additive in it, such that satisfactory adher-40 ence is obtained without the use of a primer. 1 Various attempts have been made to accomplish this but failed for one reason or another. One of the reasons why many of the additives that were added to the SiH-olefin platinum 45 catalyzed composition did not operate pro- 1

perly was that the additive would poison or deactivate the platinum catalyst such that the composition would not cure upon application. Other supposed self-bonding additives were 50 simply not effective in establishing a good 1

bond between the cured elastomer and the substrates of interest. Silyltriallylisocyanurates were, for instance, tried as self-bonding additives for room temperature compositions but 55 such additives did not perform as well as 1

would be desired. Such use of silyltriallylisocyanurates in traditional room temperature vulcanizable compositions are, for instance, set forth in Hardman and Berger, U.S. Patent 60 3, 882, 083 Another example of such an 1

SiH-olefin platinum catalyzed composition is to be found in Ballard USP 3, 527, 655. The adhesive component of this composition was the reaction product of a vinyltrichlorosilane 65 and a vinyl trialkoxy silane. Accordingly, it 1

was highly desirable to find a self-bonding additive for SiH-olefin platinum catalyzed compositions which would adhere such compositions with good bond strength and in the absence of a primer to such diverse substrates as glass, aluminum, steel, copper, stainless steel, so that such compositions would be desirable compositions for the encapsulation and potting of electrical circuitry.

Accordingly to the present invention, there is provided a process for producing a partial hydrolyzate of an aliphatically unsaturated hydrolyzable alkoxy silane which is an adhesion promoting additive comprising carrying out a partial hydrolysis by taking a silane of the formula,

R1a Si (0R3)4.a wherein R1 is an aliphatic unsaturated radical selected from alkenyl radicals and alkynyl radicals of 2 to 8 carbon atoms, R3 is selected from alkyl radicals and cycloalkyl radicals of 1 to 8 carbon atoms and a is 1 or 2 in solution with a dipolar aprotic solvent and 0.5 to 1.5 mole of water per mole of the silane. The partial hydrolysis product is most preferably that of vinyltriethoxysilane. It should be noted that the pure vinyltriethoxysilane will not function as a self-bonding additive in SiH-olefin platinum catalyzed compositions. On the other hand, the completely hydrolyzed vinyltriethoxysilane cannot be used as a self-bonding additive in SiH-olefin platinum catalyzed compositions since it is in the form of a resinous gel and is not miscible with the composition and thus will not perform a self-bonding function. Further, such a gel cannot be beneficially incorporated into SiH-olefin platinum catalyzed compositions since its presence would seriously detract from their final cured physical properties. It is the advantage of the self-bonding additive of the instant case that when properly used in the appropriate concentrations that it will not detract significantly from the final cured physical properties of the silicone elastomer that is formed. To produce the proper partial hydrolysis product of the aliphatically unsaturated silane, it is desirable that 16 to 49% of the available hydrocarbonoxy groups of said alkoxy silane be hydrolyzed in the process for producing the partial hydrolyzate. If less than 16% is hydrolyzed then too large an amount of the vinyltriethoxysilane which does not act as a self-bonding additive and which further dilutes the effectiveness of the partial hydrolis product may remain in the hydrolyzate mixture. If more than 49% of the available hydrocarbonoxy groups in the silane is hydrolyzed, then you encounter the aforementioned problems of the formation of gels which is undersirable in the final product.

The hydride cross-linking agent may be either a hydride containing linear polysiloxane polymer or it may be a hydride containing

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GB2096630A

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silcone resin composed of monofunctional and tetrafunctional siloxy units or a hydride-containing silicone resin composed of monofunc-tional,tetrafunctionaI and/or difunctional si-5 loxy units.

It should also be noted that when the self-bonding additive of the present invention is used with a self catalyzed silicone composition, the composition must be cured at ele-10 vated temperatures since the self-bonding additive acts as an inhibitor and it does not permit the composition to cure at room temperatures for prolonged periods of time such as, two weeks after the two components are 1 5 mixed. In addition, in the proposeduse of the self-bonding additive it is desirable that the self-bonding additive not be incorporated into the component two component SiH-olefin platinum catalyzed compositions which con-20 tain the platium catalyst, since it may deactivate the platinum catalyst. However, if the self-bonding additive is incorporated into the component that does not contain the platinum catalyst, then the composition as two separate 25 components can be stored as long as desirable without any deleterious effects.

When it is desired to cure the composition, the two components are simply mixed together and applied and cured at elevated 30 temperatures, that is temperatures above

100°C, within a two week period of time after mixing to form the desired selfbonding silicone elastomer of the instant invention.

It should be noted that with respect to the 35 self-bonding additive that it should not be present in the total composition for a period of time of more than two weeks prior to cure of the composition, that is the self-bonding additive will act as an inhibitor and as such after 40 the two components of the composition are mixed, they should be cured at elevated temperatures within a two week period. If more than a two week period lapses until the composition is cured at elevated temperatures, 45 then the composition may not cure in a totally satisfactory fashion.

The partial hydrolysis readily and properly takes place in the presence of a dipolar apro-tic solvent where there is sufficient quantities 50 of the solvent such that there is a homogeneous reaction medium. With such a homogeneous hydrolysis medium the reaction can take place with rapidity and also efficently so as to produce the desired partial hydrolysis 55 product in the most efficient manner.

It is well known that acids, and specifically strong acids, will operate as catalysts for such hydrolyses of aliphatically unsaturated hydrolyzable alkoxy silanes and in accordance with 60 the instant invention are used to advantage.

As already stated, the aliphatically unsaturated hydrolyzable silane has the formula

(2) R1 Si (OR3)4_a where R1 is an aliphatically unsaturated radical selected from alkenyl and radicals of 2 to 8 carbon atoms, R3 is selected from alkyl radicals and cycloalkyl radicals of 1 to 8 70 carbon atoms, and a is a whole number that varies from 1 to 2. Although R1 can be an alkynyl radical it is preferably an alkenyl radical since the acetylenic radical or the alkynyl radicals are more efficient inhibitors than the 75 alkenyl radicals which may be unesirable in the composition. Accordingly, it is desirable and preferable that the R1 radical be selected from alkenyl radicals of 2 to 8 carbon atoms such as, vinyl, and etc., the most preferred 80 radical being vinyl.

With respect to the hydrolyzable radical, R3 preferably selected from alkyl radicals or cycloalkyl radicals of 1 to 8 carbon atoms such as, methyl, ethyl, cyclohexyl, cycloheptyl and 85 etc. It should be noted that many other hydrolyzable radicals will not perform in ther self-bonding additive of the instant case, that is, additives having radicals such as, hydroxy, ketoximino, aminoxy, acetoxy, are undersira-90 ble for use as self-bonding additives in the instant composition since irrespective of their self-bonding properties it has been found that compounds with such hydrolyzable radicals may deactivate the platinum catalyst in the 95 SiH-olefin platinum catalysed compositions. Most preferably, R3 is selected from akyl radicals of 1 to 5 carbon atoms such as, methyl, ethyl and propyl.

In addition, while a may be 1 or 2, it is 100 more preferable that a have a value of 1,

since if there is too much unsaturation in the self-bonding additive then the unsaturation may unduly inhibit the cure of the composition and/or alter the physical properties of 105 the cured elastomer. The most preferred radical for R3 is ethyl or methyl. Accordingly, the most preferred compounds of formula (2) above is the partial hydrolysis products of the compounds of formula (2) where R1 is vinyl 110 such as, vinyltrimethoxy silane or vinyltri-ethoxy silane. Vinyltriethoxy silane is more preferred since the alcohol that is given off during the hydrolysis is not toxic and can be tolerated at high levels.

115 It should be noted that the compounds of formula (2) above by themselves cannot be used as self-bonding additives,that is they have little or no capability as self-bonding additives. What must be utilized as a self-120 bonding additive is the partial hydrolysis product of the compounds of formula (2), such that the compound of formula (2) is hydrolyzed such that 16 to 49% mole percent of the OR3 groups are hydrolyzed. Of course, 125 this is the average number of hydolyzed OR3 groups that would be in a particular composition noting that in a particular molecule of the silane one or more of the OR3 groups would be hydrolyzed. If more than 49% on 130 the average of OR3 groups is hydrolyzed then

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GB2096 630A 4

the partial hydrolyzate of compounds of formula (2) tends to approach the gel stage and thus is undesirable in SiH-olefin platinum catalyzed compositions for two reasons. First of 5 all the composition does not have good self-bonding properties, and secondly, the gel form of the compound of formula (2) tends to seriously detact from the physical properties of the SiH olefin platinum catalyzed compo-10 sition. If less than 16% of the OR3 groups are hydrolyzed then the partial hydrolyzate may contain too much of the monomer of formula (2) which does not impart any self-bonding properties to the composition and dilutes the 1 5 effects of the partial hydrolyzate.

More preferably the average number of OR3 groups hydrolyzed in the monomer of formula (2) varies anywhere from 25 mole percent to 40 mole percent and is most preferably 33 20 mole percent. The optimum value for the amount of hydrolyzed OR3 groups in the monomer silane of formula (2) is 33 mole percent since it is found that the optimum self-bonding properties as well as curing pro-25 perties of the SiH-olefin platinum catalyzed composition is obtained when on the average only one of the OR3 groups in the silane of formula (2) is hydrolyzed.

The reaction for producing the partial hydro-30 lyzate is a simple but exacting reaction. Generally, it is desired that the hydrolysis reaction take place in a homogeneous hydrolysis medium and to this end there is utilized in the hydrolysis medium to carry out the 35 hydrolysis reaction a dipolar aprotic solvent that is capable of dissolving the compound of formula 1a (2), as well as the amount of water that is necessary to partially hydrolyze it. Examples of dipolar aprotic solvent are, for 40 instance, acetone, diethylketone, methylethyl ketone, and tetrahydrofuran. The most preferable solvent is acetone since it has the desirable solvent properties for the silane of formula (2), as well as the water that is neces-45 sary to partially hydrolyze it and is sufficiently volatile to permit its easy removal from the crude hydrolysis product.

In the preferred hydrolysis procedure, both the water and the compound of formula (2) 50 are mixed with the solvent at the same time. It has been found that the best partial hydrolyzate compositions are reached in this fashion.

In another hydrolysis procedure the water is 55 dissolved in the solvent and the silane added to the solution in which the hydrolysis reaction takes place. Yet another procedure is add the water to the silane and solvent.

Generally, in such hydrolysis reactions in 60 accordance with the amount of partial hydrolyzate that is desired there will be added anywhere from 0.5 to 1,5 moles of water per mole of the silane of formula (2). The resulting addition may be carried out under agita-65 tion although agitation is not strictly necces-

sary since the reaction takes in a homogeneous hydrolysis medium. It should be noted that enough of the solvent is utilized so that there is always a homogeneous hydrolysis 70 medium during said partial hydrolysis. It can be appreciated that the reaction can take place without the presence of a solvent or with other types of solvents. However, when there are two phases present in the hydrolysis 75 medium then the reaction will take place but takes place at a much slower rate, and not in the most preferred manner as described above.

In addition, as stated previously, anywhere 80 from 0.5 moles to 1.5 moles of water may be utilized per mole of the silane of formula (2) so as to hydrolyze and obtain a partial hydrolyzate with the before stated average number of hydrolyzed OR3 substituent groups in the 85 compound of formula (2). Most preferably, of course there is utilized 1 mole of water per mole of the silane of formula (2) so as to obtain a partial hydrolyzate in which the average number of OR3 substituent groups hydro-90 lyzed is 33 mole percent in the compound of formula (2). It should be noted further that it is preferable that the reaction take place near normal ambient temperatures although temperatures in the range of 10°C to 50°C can 95 be tolerated.

The criticality in the above process for producing the partial hydrolyzate lies in the use of dipolar aprotic solvent in producing a homogeneous hydrolysis medium during the 100 reaction. There is also a second aspect in the process for producing the partial hydrolyzate in accordance with the invention and that is the presence of an acid catalyst during the hydrolysis. It has been found that without an 105 acidic catalyst in the homogeneous hydrolysis medium that the hydrolysis takes place very slowly or over a prolonged period of time. Accordingly, in order to speed up the reaction, there should be present a catalytic 110 amount of acid in the hydrolysis medium, that is, acetic acid or hydrochloric acid, sulfuric acid, that is, any type of mild or strong acid in sufficient quantities so as to raise the acidity of the hydrolysis medium of anywhere from, 115 generally, 10 to 500 parts per million and more preferably from 10 to 50 parts per million.

It has been found that with the use of such acids in the hydrolysis medium and with the 120 temperature range of 10 to 50°C the reaction will proceed to yield desirable compositions in a period of anywhere from 0.5 to 12 hours and that without an acidic catalyst the reaction reaches this completion only after much 125 longer period of time. It should be noted with the acidic catalyst in the foregoing concentrations that the reaction is substantially complete in as little as 0.5 hours. Accordingly, with the above acid concentration in a homo-1 30 geneous hydrolysis medium, the partial hydro

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lysis will be complete in a period of time as little as 0.5 hours. It should be noted that the catalyst may be any acidic catalyst; a few of the well known acidic catalysts having been 5 given previously. Further, it is preferred that not too much of the acidic catalyst be added so that no difficulty will be encountered in removing the excess acid after the hydrolysis reaction is completed. To utilize the self-bond-10 ing additive, that is, the partial hydrolyzate of the compound of formula (2) as a self-bonding additive in SiH-olefin platinum catalyzed compositions, its acidity has to be below 10 parts per million, otherwise, the excess acidity will 1 5 affect the cure and final physical properties of the elastomer that is formed. Accordingly, to facilitate in the purification and preparation of the final partial hydrolysis product, it is desired that a lower amount of acidity be used 20 in the homogeneous hydrolysis reaction.

In any case, there has to be added a neutralizing agent such as, sodium bicarbonate, to the homogeneous hydrolysis medium after the hydrolysis reaction is complete to 25 substantially neutralize the acid and then the solution is filtered to remove the salts formed therefrom. If the acidity is not too high-say 10 ppm or less, then the partial hydrolyzate product may be obtained in its final form by 30 simply stripping off the solvent, the unreacted water and some unreacted silane of formula (2) still remaining in the composition, by heating the mixture at a temperature in the range of 100 to 125°C, either at atmospheric 35 pressure or preferably sub-atmospheric pressure. If the composition has excess acidity as noted previously, sodium bicarbonate is added to the homogeneous hydrolysis medium after the hydrolysis reaction is complete to neutral-40 ize the excess acid and then the solution is filtered and then finally the solvent and water and some unreacted silane of formula (2) is stripped off by heating the solution at a temperature in the range of 100 to 125°C, 45 preferably at sub-atmospheric pressure until these ingredients are removed. At any rate, by this prodcedure there is obtained a partial hydrolyzate product which is the self-bonding additive of the instant case.

50 To insure its optimum with the SiH-olefin platinum catalyzed compositions it is necessary to further dry the partial hydrolyzate so as to remove substantially all residual water. Anhydrous sodium or magnesium sulfate 55 among other dessicants may be utilized for this purpose to sufficiently dry the partial hydrolyzate product. It should be noted that even with small quantities of water in the partial hydrolyzate product such water will 60 interfere with the SiH-olefin platinum catalyzed composition and result in the evolution of hydrogen which may cause the composition to foam or in the alternative may result in there not being enough of the hydride cross-65 linking agent to cross-link with the vinyl polysiloxane polymer of formula (1) which results in a soft elastomer being obtained, that is, an elastomer that does not have good physical properties.

70 Accordingly, after the above procedure there is obtained a partial hydrolysis product of the compound of formula (2) which is a self-bonding additive. It should be noted that such partial hydrolyzate product consists of 75 some silane of formula (2) mixed with a partial hydrolyzate which generally comprises olefinically containing siloxanes which may be dimers, trimers, tetramers, and etc., that is, mainly linear siloxanes or branched chain si-80 loxanes of low molecular weight having olefinically substituent groups as well as containing the unhydrolyzed OR3 radicals in the polymer chain.

Although the self-bonding additive of the 85 present invention may be used with high viscosity compositions, nevertheless, it is more desirable in low viscosity compositions. The self-bonding additive of the instant case can be utilized with any two component high 90 viscosity SiH-olefin platinum catalyzed composition, however, it is more effective as a self-bonding additive in low viscosity SiH-olefin platinum catalyzed compositions. It is especially effective in low viscosity compositions 95 that are clear and use vinyl containing silicone resin in place of reinforcing fillers. Accordingly, the self-bonding additive of the instant case finds wide application as a self-bonding additive for low viscosity Siholefin platinum 100 catalyzed compositions.

The examples below are given for the purposes of illustrating the reduction to practice of the present invention. All parts in the examples are by weight.

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EXAMPLE 1

An adhesion promoting additive composition was prepared as follows: Into a 1 -quart bottle there were charged 250 parts acetone, 191 110 parts vinyltriethoxysilane, and 18 parts of water. The bottle was capped and shaken moderately. A mild exotherm ensued. During the exotherm the bottle was vented several times. After the exotherm waned the mixture 115 stood overnight. A titration then showed the product mixture was 10 ppm acid, no doubt owing to trace residual silyl chloride in the vinyltriethoxysilane. The mixture was stripped to 100°C at maximum vacuum (25 inches) in 120 a rotary evaporator. Thre final product weighed 103 parts. It was a clear, water-white liquid. Anhydrous sodium sulphate was employed to dry the material prior to analysis and use. Analyses of the stripped product by 125 gas chromatography showed some reactant silane survived (up to 5%) but that more substantial vinyl silicone was present as dimer (approximately 40%) and higher mers (approximately 40%). A trace of ethyl alcohol 130 was also present in the stripped product.

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EXAMPLE II

An adhesion promoting additive composition was prepared as follows:

5 Into an all reaction apparatus fitted for reagent addition were charged 1 35 parts of acetone, 255 gm vinyl-triethoxysilane, and a few drops of 12 molar hydrochloric acid.

While stirring gently, 24 parts of water was 10 admitted at a rate sufficient to generate a mild exotherm, but keeping the reaction temperature below 50°C. The reaction mixture was allowed to stir gently for 2 hours following water addition and then cooled to room tem-15 peratire. Approxiametly 5 parts of sodium bicarbonate was added to neutralize the acid. This mixture stirred an additional hour and was then filtered through celite at the pumop. The filtrate was stripped under vacuum (28") 20 at 100°C and dried over anhydrous magnesium sulphate. Approximately 100 parts of product was obtained.

The product was a clear, water-white liquid, it contained less than 10 ppm acid and con-25 tained less than 0.05% by weight of water. An infrared spectrum was in agreement with the expected composition, showing bands due to vinyl at 6.25 microns and siloxy at 9-10 microns, etc. Analyses by gas chromatography 30 indicated that about 5-10% by weight of the mixture was unconverted vinyltriethoxysilane, the remainder being dimer and higher mers. A small amount (< 1 %) of ethyl alcohol was detected.

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EXAMPLE III

There was prepared a clear resin reinforced potting/encapsulating composition after the teaching of USP 3, 425, 967 to Modic. The 40 composition consisted of two packages, A and B. Package A was comprised of 75 parts of a base polymer of the average formula,

ch3 ch3

i i

Si - 0 - Si - CH=CH2

i i ch3 ch3

— — x

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where x was such that the polymer had a viscosity of 4000 cps at 25 °C, 25 pts of a resin of the average formula.

and 10 ppm Pt in the form described in USP 3, 220, 972 to Lamoreaux. Package B was comprised of 50 pts. of the above described 65 base polymer present in Package A and 50

pts. of a resin crosslinker of the average formula,

_Si *»],

2

75 To 100pts. of Package A was added 1 pt. by weight of the adhesion promoting addition composition of Example I. This mixture was then combined immediately with 10 pts. of Package B and mixed thoroughly. The mixture 80 did not cure at ambient laboratory temperatures. The mixture did cure at elevated temperatures. For example, after 1 hours time at 100°C, the mixture cured to form a clear silicone elastomer. For up to 14 days follow-85 ing its preparation, the mixture cured satisfactorily on exposure to 100°C for 1 hour. Following the 14-day period, unsatisfactory cures were obtained at this raised temperature (100°C) in that the final elastomer was too 90 soft.

The physical properties of the compositions with and without the self- bonding additive were as follows:

95 Without With

Tensile 920 psi 820

Elongation 150% 160

100 Durometer—Shore A 35 28

Tear—40 lbs./in 20

Thus, no significant reduction in physical properties of the cured elastomer resulted from 105 the additive being present at the level of the example.

EXAMPLE IV To the above SiH-olefin platinum catalyzed 110 composition of Example III there was added 1 part by weight of the partial hydrolysis vinyl siloxy silane of Example 1. During the 14-day period of satisfactory elevated temperature cure detailed in Example III, a 60 mil thick-115 ness of RTV composition of Example III was applied to each substrate tested and cured in place by baking one hour at 300°F. Again no substantial reduction in the physical properties of the cured rubber was observed.

120 The 60 mil thickness of RTV was applied to each substrate tested and cured in place as described. All surfaces were clean in the usual sense. The cured silicone elastomer which was a clear SiH-olefin platinum catalyzed com-125 position had good clarity at this thickness. The following bonds were obtained:

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CH,

CH =Ch - Si - 0 i i

CH,

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h -

i 3 Si - 0.

i

CH,

1/ 2

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TABLE OF BONDING PROPERTIES

Substrate

Bond glass excellent aluminum (bare)

marginal steel (carbon)

excellent copper excellent stainless steel excellent

An excellent bond is taken to mean a cohesive failure bond was noted when attempts to remove the cured elastomer from the surface 15 were made. No bonds developed without the additive present. The bond to aluminum was improved to excellent by priming the surface with a silicone primer. These same results were obtained in each of three instances when 20 the bonding tests were repeated during the 14 day period of satisfactory raised temperature cure.

Claims

25 1. A process for producing a partial hydrolyzate of an aliphatically unsaturated hydrolyzable alkoxy silane which is an adhesion promoting additive comprising carrying out a partial hydrolysis by taking a silane of the 30 formula,

R1 Si (OR3)4_a wherein R1 is an aliphatic unsaturated radical 35 selected from alkenyl radicals and alkynyl radicals of 2 to 8 carbon atoms, R3 is selected from alkyl radicals and cycloalkyl radicals of 1 to 8 carbon atoms and a is 1 or 2 in solution with a dipolar aprotic solvent and 0.5 to 1.5 40 mole of water per mole of the silane.
2. A process as claimed in claim 1 wherein said dipolar aprotic solvent is selected from acetone, methylethylketone, dioxane and tetrahydrofuran.

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3. A process as claimed in claim 1 or claim 2 wherein there is present an acidic catalyst in said solution such that the solution has an acidity of 10 to 500 parts per million during said partial hydrolysis. 50
4. A process as claimed in any one of the preceding claims wherein said partial hydrolysis mixture is taken after the partial hydrolysis reaction and there is stripped from it acid, water, solvent and some unreacted 55 monomer silane at a temperature in the range of 100 to 125°C to yield the final partial hydrolysis product, preferably at less than atmospheric pressure.
5. A process as claimed in claim 4 wher-60 ein prior to stripping said partial hydrolysis mixture and after the hydrolysis reaction said mixture is neutralized with a mild base.
6. A process as claimed in claim 4 or claim 5 wherein after said stripping step said

65 final partial hydrolyzate is dried.
7. A process as claimed in claim 1 for producing a partial hydrolyzate of an aliphatically unsaturated hydrolyzable alkoxy silane substantially as herein-before described in Ex-

70 ample 2.

8. A partial hydrolyzate of an aliphatically unsaturated hydrolyzable alkoxy silane when produced by a process as claimed in any one of the preceding claims.

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CLAIMS (12 May 1982)

1. A process for producing a partial hydrolyzate of an aliphatically unsaturated hydrolyzable alkoxy silane which is adhesion promot-80 ing additive comprising carrying out a partial hydrolysis in the presence of an acid catalyst with a silane of the formula,

R1 Si (OR3) 4_a

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wherein R1 is an aliphatic unsaturated radical selected from alkenyl radicals and alkynyl radicals of 2 to 8 carbon atoms, R3 is selected from alkyl radicals and cycloalkyl radicals of 1 90 to 8 carbon atoms and a is 1 or 2, a dipolar aprotic solvent and 0.5 to 1.5 mole of water per mole of the silane, to form a silane with 16 to 49% of the alkoxy groups hydrolysed.

4. A process as claimed in any one of the 95 preceding claims wherein said partial hydrolysis mixture is taken after the partial hydrolysis reaction and there is stripped from it acid, water, solvent and some unreacted monomer silane at a temperature in the range

100 of 100 to 125°C to yield the final partial hydrolysis product.

5. A process as claimed in claim 4 wherein the stripping reaction is carried out at less than atmospheric pressure.

105 6. A process as claimed in claim 4 or claim 5 wherein prior to stripping said partial hydrolysis mixture and after the hydrolysis reaction said mixture is neutralized with a mild base.

110 7. A process as claimed in any one of claims 4 to 6 wherein after said stripping step said final partial hydrolyzate is dried.
8. A process as claimed in claim in claim 1 for producing a partial hydrolyzate of an

115 aliphatically unsaturated hydrolyzable alkoxy silane substantially as herein-before described in Example 1 or Example 2.
9. A partial hydrolyzate of an aliphatically unsaturated hydrolyzable alkoxy silane when

120 produced by a process as claimed in any one of the preceding claims.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd.—1982.

Published at The Patent Office, 25 Southampton Buildings,

London, WC2A 1AY, from which copies may be obtained.