Process for Preparing Alkoxy-Terminated Organosiloxane Fluids Using Organo-Lithium Reagents

1. Field of the Invention

The present invention relates to the preparation of silyl-containing materials having alkoxy end groups. More specifically, this invention relates to the use of organolithium reagents in the preparation of organopolysiloxane materials having alkoxy terminal groups. These materials can also have olefin functionality, thereby allowing for dual cure by means of moisture and photo curable mechanisms.

2. Description of the Prior Art

It is known that alkoxy terminated polymers can be prepared by reacting di-, tri or tetralkoxysilanes with diorganosiloxanes having silanol terminal groups at each end of the polymer chain. This reaction requires the use of specific catalysts such as amines, inorganic oxides, potassium acetate, organic titanium derivatives, titanium/amine combinations, carboxylic acid/amine combinations as well as carbamates and oxime-containing organic compounds. All of these catalyst systems have significant drawbacks, however. For example, amine catalyst systems are particularly slow and this lack of speed is often further exaggerated, depending upon the reactivity of the particular alkoxysilane. In addition, amines and carboxylic acid catalysts are corrosive and require special handling and removal processes once the reaction has proceeded to the desired state of completion. Catalyst reaction residue is particularly detrimental on the storage stability of the organosiloxane fluids and the properties of the resulting crosslinkable product. Removal of these catalysts is often difficult, requiring extra steps which are laborious and costly. Furthermore, many of these catalysts are particularly offensive to the body, giving off unpleasant odors and being dangerous to eyes and skin.

Organic titanium catalysts such as titanium tetra isoproprionate have also been commonly used for these type of reactions but suffer from the deleterious effect of "thick-phasing", a result of titanium-silicon complexing. Before the intended reaction between the silanol-terminated organopolysiloxane and the alkoxy silane is complete, a thick gel-like phase forms, requiring additional shear forces and energy from the mixing blades to overcome this phase and allow the reaction to proceed. Thick-phasing is a particularly difficult problem when industrial-sized batches of the polymer are being prepared and the shear forces necessary to overcome thick-phasing are high.

More recently, U.S. Pat. No. 5,079,324 to Cocco et al. discloses the use of lithium hydroxide as a catalyst for the reaction of diorganosiloxanes having terminal silanol groups, with a polyalkoxysilane of the formula:

wherein R' and R" may be, for example, a monovalent hydrocarbon radical that may contain functional groups C.sub.1-13 ; and R"' is an aliphatic radical C.sub.1-8.

However, lithium hydroxide is an inorganic solid which requires use of a polar solvent such as methanol to introduce it as a solution into the reaction. Due to the presence of methanol, this catalyst system has the distinct disadvantage of being continually regenerated in the form of lithium methoxide. The resultant polymer product exhibits a rapid lowering of viscosity due to attack of the regenerated lithium catalyst upon the siloxane. The viscosity drop, although generally rather immediate, becomes more pronounced over time and shelf life is therefore greatly affected. Furthermore, subsequent curing of this functionalized polymer is also deleteriously affected. It is believed that the viscosity drop is directly related to cleavage of the siloxane bond by the regenerated lithium, resulting in a significantly lower molecular weight and product instability.

The use of butyl lithium in combination with hexamethylphosphoroamide as initiators for the oligomerization of hexamethylcyclotrisiloxane with methylmethoxysilanes is disclosed in Eur. Plym J., Vol. 21, No. 2, pp. 135-140, 1985 entitled "The Anionic Oligomerization of Hexamethylcyclotrisiloxane with Methylmethoxysilanes". This reference discloses the use of butyl lithium as well as inorganic bases as a means to ring-open hexamethylcyclotrisiloxane in the presence of methylmethoxysilane.

EPA 362710 to Toray Silicone Company discloses a method of synthesizing a diorganopolysiloxane in which a polymerizable functional group is present at one or both molecule chain ends. The synthesis involves the opening of a cyclotrisiloxane using an alkali metal silanolate, which bears the polymerizable functional group, as a polymerization initiator in the presence of an organosilane or organopolysiloxane. This reference states that if the reaction is run at equilibrium, a mixture of products is produced, i.e. polymer with functional groups at both ends and polymer without functional groups at either end. This reference does not teach a method of endcapping with alkoxy groups on both ends of the polymer but rather a polymerization reaction using cyclic trisiloxane as the living polymerization monomer.

U.S. Pat. No. 3,878,263 to Martin discloses a polymerization reaction which uses organo-lithium catalysts in aprotic solvent as well as inorganic lithium catalysts to polymerize a cyclic organopolysiloxane with an acrylate functional silane or siloxane. This reference begins with different starting materials from the present invention to perform a ring-opening reaction, i.e. siloxane cleavage. The resultant polymers have only one end terminating in an alkoxy group, the other end terminated with the acrylate group. The polymerization reaction is controlled by the terminating methacryloxy group. Those catalysts disclosed include lithium alkoxide compounds such as lithium methoxide; lithium alkyls such as ethyl lithium, isopropyl lithium, n-butyl lithium, vinyl lithium; lithium aryls such as phenyl lithium; lithium hydride, lithium aluminum hydride, lithium silanolate and lithium hydroxide.

There is a definite need for a process for making viscosity stable alkoxy silyl-containing materials, such as alkoxy terminated organopolysiloxanes, which is noncorrosive, fast and does not suffer from the unpleasant odors and other disadvantages of the prior art catalyst systems. Additionally, there is a need for such compositions which exhibit stable shelf life and can be useful for making such products as sealants, adhesives, coatings and the like.

In one embodiment, the present invention relates to a process for preparing an alkoxy silyl-terminated material, which has at least one alkoxy group at a terminal end, said process comprising reacting in the presence of a catalytically effective amount of an organo-lithium reagent an alkoxysilane first reactant with a second reactant having at least one end of its chain terminating in a silano) group. The alkoxy silyl-terminated material may have a variety of polymer backbone types such as silicone, polyurethane, polyamide and the like. These materials are intended to cure by either moisture cure or by dual moisture and photo cure mechanisms.

The alkoxy silyl-terminated material is preferably an organopolysiloxane having at least one terminal alkoxy group. Such a material is a product of the reaction of an organopolysiloxane, having at least one end and preferably both ends terminated with a silanol group, with a silane containing at least two alkoxy groups, said reaction occurring in the presence of a catalytically effective amount of an organo-lithium reagent. The resultant alkoxy-terminated organopoly-siloxanes are substantially stable materials as measured by their ability to maintain substantially constant viscosity values (cps) over time. Additionally, removal of residual organo-lithium catalyst, if any, is purely optional but easily accomplished through filtration. This catalyst system also does not generate offensive odors as do other catalysts.

In a more preferred embodiment, the alkoxy terminated organopolysiloxanes of the present invention have vinyl and preferably acrylate functionality as well, allowing for dual photo and moisture curing. One such example is the reaction product of vinyltrimethoxysilane with a silanol terminated polydimethylsiloxane fluid in the presence of a catalytic amount of an organo-lithium catalyst.

The present invention further relates to compositions capable of curing by both moisture and photo curing mechanisms and having a substantially shelf stable viscosity, said compositions comprising:

(a) a reactive organopolysiloxane having at least one alkoxy group on at least one terminal end and at least one photocurable group on at least one terminal end;

(b) an effective amount of a photoinitiator; and

(c) an effective amount of a moisture curing catalyst;

wherein said reactive organopolysiloxane of (a) is the reaction product of an organopolysiloxane having at least one end terminating with a silanol group with a silane containing at least two and preferably three alkoxy groups and at least one photo-curable group, said reaction occurring in the presence of a catalytically effective amount of an organo-lithium reagent.

The novel use of catalytic amounts of organo-lithium reagents in the inventive process provides a new method of endcapping an organopolysiloxane fluid with alkoxy groups without the disadvantages heretofore enumerated. 0f particular significance is that the resultant alkoxy endcapped organopolysiloxanes maintain a viscosity substantially equivalent (i.e. substantially no viscosity drop) to the viscosity of the silanol terminated siloxane starting material, which indicates both completeness of reaction, e.g. substantially no silanol groups remaining unreacted, as well as stability of the final polymer.

The organo-lithium reagents useful in the present invention are represented by the formula LiR.sup.14 wherein the organo group R.sup.14 is selected from the group consisting of C.sub.1 to C.sub.18 alkyl, aryl, alkylaryl, arylalkyl, alkenyl, and alkynyl groups; amine-containing compounds; and organosilicone-containing compounds. R.sup.14 can have from 1 to 18 carbon atoms in the chain (C.sub.1-18). These reagents are present in catalytically effective amounts and are critical both to the process and the quality of product made therefrom.

More particularly those alkoxy-terminated organosiloxanes of the present invention are represented by the formula: ##STR1## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may be identical or different and are monovalent hydrocarbon radicals having up to 10 carbon atoms(C.sub.1-10) or halo or cyano substituted hydrocarbon radicals; R.sup.3 may also be a monovalent heterohydrocarbon radical having up to 10 carbon atoms (C.sub.1 -C.sub.10) wherein the hetero atoms are selected from the group consisting of halo atoms, O, N, and; R.sup.5 is alkyl(C.sub.1-10), preferably methyl, ethyl or isopropyl; R.sup.5 may also be CH.sub.2 CH.sub.2 OCH.sub.3 ; n is an integer; a is 0, 1 or 2; b is 0, 1 or 2; and a+b is 0, 1 or 2.

A most preferred embodiment has the following formula where R.sup.3 is a methacryloxy-propyl group, CH.sub.2 C(CH.sub.3)--COOC.sub.3 H.sub.6, R.sup.4 and R.sup.5 are methyl, and R.sup.1 and R.sup.2 are as described in Formula I above to give the following formula. ##STR2## wherein MA is the methacryloxypropyl group, n is from 1 to 1,200 and c is 0 or 1.

Due to the presence of both alkoxy and acrylate groups, this preferred embodiment has the capability of curing by both moisture and photo curing mechanisms. Thus, for example, this polymer fluid material or a composition comprising the material can be subjected to UV light in the presence of a photoinitiator to partially cure or gel the material, which can then be allowed to cure further by moisture in ambient conditions.

The silanol-terminated reactant can be virtually any useful silanol-terminated material having the general formula: ##STR3## wherein A represents a polymer or copolymer backbone, which can be any number of combinations of polyurethane, silicone, polyamide, polyether and the like; R.sup.6 and R.sup.7 may be identical or different and are monovalent hydrocarbon radicals having up to 10 carbon atoms (C.sub.1-10) or halo or cyano substituted hydrocarbon radicals; and R.sup.8 is a monovalent hydrocarbon radical C.sub.1-10 or OH.

Preferably, however, this reactant is a silanol-terminated organopolysiloxane having the formula: ##STR4## wherein R.sup.6, R.sup.7 and R.sup.8 are defined as in formula III above. Preferred groups for R.sup.6 and R.sup.7 are alkyl C.sub.1-10 and most preferably methyl, ethyl and isopropyl, although aryl groups such as phenyl are contemplated, as well as vinyl groups. The preferred group for R.sup.8 is OH. The number of repeating units will determine the molecular weight and hence the viscosity of this starting material. Thus, n can be, for example, an integer which, for example, can be from about 1 to about 1200, preferably from about 10 to about 1,000. The viscosity of these materials is not critical and can easily be chosen to fit a particular product application, particularly because the alkoxy terminated end product of this reaction will have substantially the same viscosity as the silanol-terminated reactant. Viscosities of these silanol-terminated organopolysiloxanes can range from about 1 cps to about 150,000 cps (Brookfield, 25.degree. C.). The preferred range for those used in the present invention are about 100 to about 60,000 cps.

An example of one such silanol-terminated organopolysiloxane is polydimethylsiloxane having the formula: ##STR5##

The second reactant is a silane containing at least two alkoxy groups and having the formula:

wherein R.sup.9, R.sup.10 and R.sup.11 can be identical or different monovalent hydrocarbon R.sup.9 may also be a monovalent heterohydrocarbon radical having 1 to 10 carbon atoms wherein the hetero atoms are selected from the group consisting of halo atoms, O, N and S; a is 0, 1 or 2; b is 0, 1 or 2; and a+b is 0, 1 or 2.

Preferably, R.sup.9 and R.sup.10 are selected from the group consisting of methyl, ethyl, isopropyl, vinyl and phenyl; and R.sup.11 is preferably selected from the group consisting of methyl, ethyl, isopropyl and CH.sub.2 CH.sub.2 OCH.sub.3. Of particular usefulness in the present invention are vinyltrimethoxysilane and methyltrimethoxysilane.

Other representative polyalkoxysilanes useful in the present invention include: ##STR6##

The organo-lithium reagents useful in the present invention are represented by the formula LiR.sup.14 wherein the organo group R.sup.14 is selected from the group consisting of C.sub.1-18 alkyl, aryl, alkylaryl, arylalkyl, alkenyl, and alkynyl groups; amine-containing compounds; and organosilicone-containing compounds. R.sup.14 can have from 1 to 18 carbon atoms in the chain (C.sub.1-18). These reagents are present in catalytically effective amounts and are critical both to the process and the quality of product made therefrom.

The organo-lithium catalyst is preferably an alkyl lithium such as methyl, n-butyl, sec-butyl, t-butyl, n-hexyl, 2-ethylhexyl butyl and n-octyl butyl lithium. Other useful catalysts include phenyl lithium, vinyl lithium, lithium phenylacetylide, lithium (trimethylsilyl) acetylide, lithium silanolates and lithium siloxanolates. The organo group can also be an amine-containing compound, such as dimethylamide, diethylamide, diisopropylamide or dicyclohexylamide, or a silicone-containing compound.

Useful lithium silanolates have the formula LiOSiR.sup.11 R.sup.12 R.sup.13 wherein R.sup.11 and R.sup.12 are monovalent hydrocarbon radicals C.sub.1-10, preferably alkyl such as methyl, ethyl and butyl, as well as aryl such as phenyl; and R.sup.13 is an alkyl or aryl group with C.sub.1-18.

Useful lithium siloxanolates have the formula Li(OSiR.sup.11 R.sup.12 O).sub.t SiR.sup.11 R.sup.12 R.sup.13 wherein R.sup.11 and R.sup.12 are as described above; R.sup.13 is as described above and t is an integer, preferably from 1 to 10.

The organo-lithium reagents are used in catalytically effective amounts. Generally, this amount will vary with the specific catalyst and reactant materials but about 1 to 1000 ppm based on the atomic weight of lithium are useful. A more preferred range is 15-250 ppm.

Neither polar nor aprotic solvents should be introduced to the catalyst solution or the reaction mixture in order to prevent undesired and uncontrolled catalyst regeneration and subsequent siloxane bond cleavage. However, insignificant amounts of alcohol are produced in situ during the reaction. The presence of this minor byproduct is so small that no perceptible drop or effect on the viscosity stability of the final product is observed. These minor amounts of alcohol byproduct can be optionally removed during or immediately subsequent to the reaction.

The reaction process of the present invention comprises the addition of the silanol terminated organosiloxane, alkoxysilane and organo-lithium solution into a reactor vessel. The mixture is then heated with stirring and in the absence of moisture, for example under nitrogen conditions, for about 1/2 to about 5 hours at temperatures of from ambient to about 110.degree. C., preferably from 25.degree. C. to about 60.degree. C., or until alkoxy endcapping has been completed. One indication that endcapping is complete is the absence of thick phasing when titanium catalyst is added. The mixture is then quenched with bubbled or liquid carbon dioxide or dry ice and further cooled. The formation of lithium carbonate can be easily removed, if desired, through filtration. Neutralization of the catalyst is optionally carried out, preferably with carbon dioxide in the form of dry ice. Acids may also be used for neutralization, as well as compounds such as silyl phosphate, silyl acetate and the like. Condensation moisture aids in the neutralization process. Volatile materials, if any, are vacuum stripped. Equimolar amounts of the silanol-terminated organopolysiloxane (based on the moles of SiOH functionality) and the alkoxysilane can be used in the reaction, but excess alkoxysilane is preferred. In the preparation of a one-part dual curing composition, it is preferred to add only a slight excess of alkoxysilane to control the potential viscosity increase. Thus, for example, in such cases 1.0 to 1.5 moles of alkoxysilane is preferred for every mole of silanol.

The resultant fluid can then be mixed with other conventional additives such as fillers, initiators, promoters, pigments, moisture scavengers and the like to form a one-part curable composition. Fillers such as hydrophobic fumed silica or quartz serve to impart desirable physical properties to the cured material. Moisture scavengers such as methyltrimethoxysilane and vinyltrimethyloxysilane are useful.

These curable compositions are obtained by adding to 100 parts (by weight) of the functionalized polymer prepared according to the process of the present invention:

(a) 0 to 250 parts of inorganic filters;

(b) 0 to 20 parts, preferably 0 to 10 parts of adhesion promoters such as silanes or polysiloxanes simultaneously bearing per molecule:

(i) at least one C.sub.3 -C.sub.15 organic group bonded by a SiC bond to the silicon atom and substituted by amino, glycidoxy or mercapto radicals and the like; and

(ii) at least one C.sub.1 -C.sub.3 alkoxy radical or a C.sub.3 -C.sub.6 alkoxyalkyleneoxy radical; and

(c) an effective amount of a condensation catalyst.

By "effective amount" of condensation catalyst is intended, for example, from about 0.1 to about 5% by weight and preferably about 0.25 to about 2.5% by weight of at least one compound of a metal which is typically selected from among titanium, tin, zirconium and mixtures thereof. Tetraisopropoxytitanate and tetrabutoxytitanate are preferred. U.S. Pat. No. 4,111,890 lists numerous others that are useful.

Thus, the alkoxy-terminated organosiloxane fluids of the present invention can be formulated into one part curable systems which demonstrate substantially no viscosity drop over time, thus imparting storage stability to the final product. For example, this invention contemplates a composition capable of curing by both moisture and photo cure mechanisms and having a substantially shelf stable viscosity, said composition comprising:

(a) a reactive organopolysiloxane having at least one alkoxy group attached to the silicon atom at least one terminal end and at least one photo curing group on at least one terminal end;

(b) an effective amount of a photoinitiator; and catalyst;

wherein said reactive organopolysiloxane is the reaction product of an organopolysiloxane having at least one terminal silanol group with a silane containing at least two and preferably three alkoxy groups and at least one photo-curable group, said reaction occurring in the presence of a catalytically effective amount of an organolithium reagent.

It should be appreciated that the reactive organopolysiloxane materials prepared in accordance with the present invention may be curable by moisture alone.

In formulating useful dual curing compositions of the invention it is necessary to include in the formulation a moisture curing catalyst, such as a titanium catalyst, in the formulation.

The dual curing compositions utilized in the invention also include a photoinitiator. Any known radical photoinitiator can be used as well as mixtures thereof without departing from the invention hereof. Sample photoinitiators include benzoin and substituted benzoin compounds, benzophenone, Michler's ketone dialkoxybenzophenones, dialkoxyacetophenones, and the like. Photoinitiators made compatible with silicones by binding photoinitiating groups to organosiloxane polymer backbones may also be used.

The amount of photoinitator used in the composition will typically be in the range of between about 0.1% and 5% of the composition. Depending on the characteristics of the particular photoinitiator, however, amounts outside of this range may be employed without departing from the invention so long as they perform the function of rapidly and efficiently initiating polymerization of the acrylic groups. In particular, higher percentages may be required if silicone bound photoinitiators are used with high equivalent weight per photoinitiating group.

It should also be understood that while the photoinitiator is used as a separate ingredient, the formulations used in the inventive method are intended to include formulations in which photoinitiating groups are included on the backbone of the same organopolysiloxane polymer which includes the photo curing and alkoxy groups discussed above. Preferred photo curing groups which may be attached to the organopolysiloxane include acrylate, methacrylate and glycidoxy groups.

The inventive compositions may also contain other additives so long as they do not interfere with U.V. and moisture curing mechanisms. These include adhesion promoters such as glycidoxypropyltrimethoxysilane, aminopropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, triallyl-S-tria-zine-2,3,6(1H.3H.5H)-trione aminoethylaminopropyltrimethoxysilane and others known to those skilled in the art; fillers such as silica, microballoon glass and the like are useful for their conventional purposes.

The invention may be further understood with reference to the following non-limiting examples. Percent weights are per the total composition unless otherwise specified. Viscosities are measured using a Brookfield viscometer with either a spindle #6 or #4 at 10 rpm, 25.degree. C., unless otherwise specified.

A lithium n-butyldimethylsilanolate catalyst solution was prepared by first dissolving 25 g of hexamethylcyclotrisiloxane in 25 g of hexane followed by adding 172 ml of a 1.6 M n-butyl lithium (0.275 mole) in hexane (120 g) into this hexamethylcyclotrisiloxane solution. Exothermic reaction was noted upon mixing. The resulting solution after cooling to room temperature was used as the endcapping catalyst.

A 50,000 cps (spindle #6) silanol terminated polydimethylsiloxane fluid with a GPC analysis showing weight average molecular weight of 99,000 and number average molecular weight of 72,500 (relative to polystyrene standard) was used for endcapping by vinyltrimethoxysilane. Five kilograms of this fluid, 48 g of vinyltrimethoxysilane and 6.5 g of the above lithium n-butyldimethylsilanolate solution was mixed in a reactor. The mixture was heated to 55.degree. C. for 3 hours. A few small pieces of dry ice totalling 5 g was then placed into the mixture. After cooling, the mixture was vacuum stripped for 15 minutes at room temperature to remove any volatile materials. The viscosity of the mixture was found to be 45,000 cps (spindle #6) and the mixture was found to be stable during storage. GPC analysis of this mixture showed weight average molecular weight of 101,000 and number average molecular weight of 74,000.

Sixty-five parts of this mixture was then mixed with 27.5 parts of a hydrophobic fumed silica, 7 parts of vinyltrimethoxysilane (moisture scavenger) and 0.5 parts of titanium isopropoxide in the absence of air and moisture to form a sealant or coating composition. No thick phasing was observed during mixing indicating complete endcapping. In contrast, when silanol fluid alone was used with vinyltrimethoxysilane instead of the endcapped fluid, immediate thickening upon the addition of titanium isopropoxide to the mixture was noted.

The sealant thus prepared was allowed to cure in ambient conditions for 7 days. The following properties were observed for the cured rubber: Tensile 956 psi; Elongation 700%; Hardness (Shore A) 36; and Tensile at 100% elongation 90 psi. The surface of the cured material was non-tacky and dry to the touch.

The above example was repeated using a 16,000 (spindle #6) cps silanol terminated polydimethylsiloxane fluid. Five kilograms of the silanol fluid, 67 g of vinyltrimethoxy-silane, and 6.5 g of the above-described catalyst solution were used. The silanol terminated polydimethylsiloxane fluid was found to have a weight average molecular weight of 79,000 and a number average molecular weight of 57,000. After endcapping, the material showed a viscosity of 14,000 cps (spindle #6), weight average molecular weight of 74,000, and number average molecular weight of 53,000.

Sixty-five parts of the endcapped fluid was compounded with 27.5 parts of the hydrophobic fumed silica, 7 parts of the moisture scavenger vinyltrimethoxysilane and 0.5 parts of the moisture curing catalyst titanium isopropoxide. No thick phasing of the mixture was noted. The compounded sealant after 7 day cure at ambient conditions gave the following properties: Tensile 800 psi; Elongation 530%; Hardness (Shore A) 40; and Tensile at 100% elongation 116 psi. The cured material was surface dry.

This example demonstrates the preparation of a dual cure system. Five hundred grams of a 2,000 cps (spindle #4) silanol terminated polydimethylsiloxane fluid was placed in a 1000 ml three neck round bottom flask. Fourteen grams of methacryloxypropyltrimethoxysilane then was added. To the stirred mixture was further added 0.65 g of the lithium n-butyldimethylsilanolate solution previously prepared (i.e., 15 ppm Li). The mixture was stirred at room temperature under nitrogen for 3 hours. The temperature of the mixture rose to 50.degree. C. due to shearing. A gentle stream of carbon dioxide was bubbled into the system for 10 minutes for catalyst quenching. The mixture was then heated to 110.degree. C. under nitrogen sparge for 30 minutes to remove volatile materials. The mixture was then allowed to cool down to room temperature. The mixture showed a viscosity reading of 3,100 cps (spindle #4) (Brookfield Viscometer, spindle #4 at 10 rpm). The mixture showed substantially no viscosity change during 4 months of storage.

A formulation for coating or sealing was prepared by mixing 49.10 g of this endcapped material with 0.75 g of diethoxyacetophonone and 0.15 g titanium isopropoxide. The mixture was subjected to UV cure using a Fusion System UV chamber with an H bulb. The material was placed in between 2 layers of polyethylene films with 1 mm thickness which are 0.075" apart. The films were held in a glass plate fixture. The material was cured by UV with an intensity of 75 mw/cm.sup.2 for one minute on each side. The cured material showed a hardness of 41 (Shore OO). The material was further moisture cured in 3 days to give a hardness of 61 (Shore OO). In contrast, simply mixing silanol terminated polydimethysiloxane fluid with 3-methacryloxypropyltrimethoxysilane and diethoxyacetophenone did not produce a UV curable material.

The endcapped material described in Example 3 was further formulated into a sealant composition by mixing 90 g of the fluid with 10 g of a hydrophobic fumed silica, 0.75 g of diethoxyacetophenone and 0.3 g titanium isopropoxide. The mixture was subjected to UV cure as described in Example 3. The material after initial UV cure gave a hardness of 66 (Durometer Shore 00). After the initial UV cure, the material was further moisture cured in ambient conditions for 3 days. The material then gave the following properties: Hardness 88 (Shore OO); Tensile 180 psi; Elongation 120%; and Tensile at 100% elongation 150 psi.

In contrast, simply mixing silanol terminated polydimethylsiloxane with 3-methacryloxypropyltrimethoxysilane, fumed silica, diethoxyacetophenone and titanium isopropoxide caused immediate thickening (thick-phasing) and did not yield a material useful as a sealant.

A catalyst solution of lithium t-butyl dimethyl silanolate catalyst was prepared by first mixing 3.8 g of hexamethylcyclotrisiloxane in 3.8 g of hexane followed by adding 15 g of a 1.7 M t-butyl lithium (0.04 mole) in pentane to this solution. No exothermic reaction was noted.

Example 3 was repeated using the above catalyst solution (0.65 g) instead. The reaction was run at room temperature for 3 hrs. The catalyst was then neutralized by the bubbling of carbon dioxide. The cooled mixture showed a viscosity of 2,840 cps (spindle #4), and was stable during storage.

The mixture was formulated into a curable composition by adding 0.75% diethoxyacetophenone and 0.3% titanium isopropoxide. One portion of the mixture was subjected to UV cure as described above. The UV cured material showed a hardness of 42 (Shore OO). Another portion of the material was only subjected to moisture cure for 3 days. The moisture cured only material showed a hardness of 55 (Shore OO). The initially UV cured material after further moisture cure for 3 days gave a hardness reading of 68 (Shore OO).

Example 3 was repeated, but instead of lithium n-butyldimethylsilanolate, 1 ml of a 1.6 M n-butyl-lithium in hexane solution was used. The mixture after endcapping showed a viscosity of 2,640 cps (spindle #4).

A formulation prepared by mixing 98.5% of this endcapped fluid with 1.5% of the photoinitiator diethoxyacetophenone was subjected to UV cure. No titanium moisture cure catalyst was used. The cured material gave a hardness of 41 (Shore OO).

This example is intended as a model to show that the use of methanol with organo-lithium results in unstable viscosity in a non-reactive polydimethylsiloxane and fluid. It is believed that the attack on and cleavage of the siloxane bond which results in a viscosity drop in this non-reactive fluid is an appropriate model for the same attach which occurs and results in viscosity deterioration in reactive fluid compositions employing aprotic or polar solvents.

To 300 g of 10,000 cps (spindle #4) trimethylsilyl terminated polydimethylsiloxane fluid was added 1 ml of a 1.6N lithium n-butyldimethylsilanolate in hexane solution. The mixture was then divided into 2 equal fractions of 150 g each. To one of the two fractions was further added 1 ml of methanol. Both fractions were kept in closed containers in a 25.degree. C. water bath and their viscosities were monitored over a period of 6 days. The results are shown below:

It is clear from Table I that use of methanol has a clear detrimental effect on the viscosity over time as evidenced by the significant viscosity drop in Fraction B.

A silanol terminated polydimethylsiloxane fluid with a viscosity of 47,000 cps (spindle #6) was used for three comparative studies.

(1) Three kilograms of the silanol terminated fluid was mixed with 29 g of vinyltrimethoxysilane and 3.7 g of a lithium n-butyldimethylsilanolate in hexane solution containing 1.21% (15 ppm) lithium (by weight lithium atom) as lithium silanolate. The mixture was heated to 50.degree. C. with mixing for 3 hours. A few pieces of dry ice were then added to the mixture to quench the catalyst. The mixture was then cooled to room temperature and equilibrated at 25.degree. C. for 2 days. The viscosity of the material was determined to be 44,500 cps, substantially similar to the 47,000 cps (spindle #6) starting material.

(2) The above procedure was repeated, but instead of the lithium n-butyldimethylsilanolate in hexane solution, 26.7 g of a 1% lithium hydroxide monohydrate in methanol solution was used (15 ppm Li). The viscosity of the material was determined to be 33,900 cps, substantially lower than the starting material.

(3) This example was used as a control. Three kilograms of the silanol terminated fluid was mixed with 29 g of vinyltrimethoxysilane and 26.7 g of methanol. No lithium catalyst was used. Due to the dilution of the polydimethylsiloxane by vinyltrimethoxysilane and methanol, the viscosity of the mixture was determined to be 41,100 cps. This example indicates that the viscosity drop is not as severe as with the lithium hydroxide monohydrate/methanol combination.

A 3,500 cps silanol terminated polydimethylsiloxane fluid was used for two comparative studies. In the first study, lithium hydroxide monohydrate in methanol solution was used whereas in the other study lithium n-butyldimethylsilanolate in hexane solution was used. In both cases, two molar equivalents of silane per molar equivalent of silanol group were added to the silanol terminated fluid. Fifteen parts per million of lithium either as a 1% lithium hydroxide in methanol solution or as a lithium n-butyldimethylsilanolate in hexane solution was then added to the respective mixtures. Both reactions were mixed under nitrogen at room temperature. The viscosities of the mixtures were monitored periodically. The results are shown below in Table II.

As is evident from Table II, the alkoxy terminated organosiloxane fluids prepared using lithium hydroxide in methanol as the catalytic reagent demonstrated a marked drop in viscosity over a 24 to 48 hour period. In contrast, the alkoxy terminated organosiloxanes prepared using lithium silanolate in hexane demonstrated no substantial change in viscosity.

A mono-silanol terminated polydimethylsiloxane is first prepared by the following reaction. 100 parts of hexamethylcyclotrisiloxane is dissolved into 200 parts of a hydrocarbon solvent such as hexane. One part of a 1.6 M butyl lithium in hexane solution and 3 parts of dimethylsulfoxide are then added to the mixture. The mixture is stirred for about 3 hours and then quenched with 1 part of glacial acetic acid. The resulting material is washed with water to remove lithium salt and dimethylsulfoxide, and the washed hexane solution is stored over andydrous sodium sulfate to remove any trace water in solution. The solution is then vacuum stripped to remove the solvent to yield a .alpha.-hydroxy-.omega.-butyldimethylsilyl-polydimethylsiloxane.

This material is then used as a reactant in the present invention as follows. To the mono-silanol terminated polydimethylsiloxane prepared above is further added 0.5 part of methacryloxypropyltrimethoxysilane and 0.1 part of the 1.6 M butyl lithium in hexane solution. The mixture is stirred at room temperature for about 1 hour. Dry ice is then added to quench the lithium base to yield a compound in accordance with present invention, .alpha.-methacryloxypropyldimethoxysilyl-.omega.-butyldimethylsilylpolydim ethylsiloxane.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications are intended to be included within the scope of the following claims: