Clear, non-slumping silicone sealants

Abstract: A process for producing a silicone sealant which is stable in the absence of moisture and having a slump of less than 1 inch mixes a polydiorganosiloxane polymer having hydroxyl or alkoxysilethylene endblocking, an alkoxysilane crosslinker and a titanium catalyst; then adds a reinforcing filler.

Description: This invention relates to neutral curing silicone sealants which cure upon exposure to moisture at room temperature. The method of this invention prepares a sealant by mixing in the absence of moisture an alkoxysilethylene endblocked polydiorganosiloxane, di- or tri-functional alkoxysilane and titanium catalyst, then admixing a reinforcing filler. This invention is a method of mixing the ingredients so that the resulting sealant is not a flowable material, but remains in place when extruded from it's storage tube. This invention is a process of producing silicone sealants containing polydiorganosiloxane having alkoxy endblocking, alkoxy functional cross linker and/or chain extender and titanium catalyst, wherein the improvement comprises a process comprising (A) mixing in the absence of moisture (1) 100 parts by weight of a polymer of the formula where each R is free of aliphatic unsaturation and is at least one selected from the group consisting of monovalent hydrocarbon, monovalent halohydrocarbon and monovalent cyanoalkyl radicals of 1 to 18 inclusive carbon atoms, each D is selected from the group consisting of hydroxyl radical and radical of the formula where each R'' is at least one selected from the group consisting of methyl, ethyl, propyl and butyl, Z is a divalent hydrocarbon radical or a combination of divalent hydrocarbon radicals and siloxane radicals, m is 0 or 1 and x is of a value such that the polymer has a viscosity of from 0.5 to 3000 Pa·s at 25°C.; (2) from 0.1 to 14 parts by weight of a crosslinker of the formula R' a Si(OR'') 4-a where R' is at least one selected from the group consisting of methyl, ethyl, propyl, phenyl and vinyl, R'' is as defined above and a is 0, 1 or 2; and (3) from 0.2 to 6.0 parts by weight of titanium catalyst; and (C) storing the mixture in the absence of moisture, wherein (B) from 5 to 60 parts by weight of reinforcing filler are added to the mixture resulting from the mixing of components (i) to (iii) recited in step (A) above after said components (i) to (iii) are mixed together and before the storage comprising step (C) to give a sealant which has a slump of less than 25.4 millimetres (less than 1 inch) when measured in accordance with ASTM D 2202. The method of this invention uses a polymer of the formula where each R is free of aliphatic unsaturation and is at least one selected from the group consisting of monovalent hydrocarbon, monovalent halohydrocarbon and monovalent cyanoalkyl radicals of 1 to 18 inclusive carbon atoms, each D is selected from the group consisting of hydroxyl radical and radical of the formula where each R'' is at least one selected from the group consisting of methyl, ethyl, propyl and butyl, Z is a divalent hydrocarbon radical or a combination of divalent hydrocarbon radicals and siloxane radicals, m is 0 or 1 and x is of a value such that the polymer has a viscosity of from 0.5 to 3000 Pa·s at 25°C. When D of the above polymer (1) is hydroxyl, the polymer is the well known hydroxyl endblocked polydiorganosiloxane commonly used in the production of siloxane sealants. The polymer is well known in the art and its description and method of manufacture are also well known and need no further description. When D of the above polymer (1) is alkoxy silane, the polymer is of the formula where each R is free of aliphatic unsaturation and is at least one selected from the group consisting of monovalent hydrocarbon, monovalent halohydrocarbon and monovalent cyanoalkyl radicals of 1 to 18 inclusive carbon atoms, each R'' is at least one selected from the group consisting of methyl, ethyl, propyl and butyl, Z is a divalent hydrocarbon radical or combination of divalent hydrocarbon radicals and siloxane radicals, m is 0 or 1 and x is of a value such that the polymer has a viscosity of from 0.5 to 3000 Pa·s at 25°C. R can be any of those monovalent hydrocarbon, monovalent halohydrocarbon or monovalent cyanoalkyl radicals of 1 to 18 inclusive carbon atoms which are known to be useful in silicone sealant materials. The preferred radicals are methyl, ethyl, propyl, phenyl and trifluoropropyl. Z is a divalent hydrocarbon radical or combination of divalent hydrocarbon radicals and siloxane radicals. The divalent hydrocarbon radical can be from 2 to 15 carbon atoms in the form of a divalent alkylene or arylene radical such as ethylene, propylene, hexylene, phenylene and A preferred Z may be represented by the formula where R is as defined above, b is 0 or 1 and c is from 1 to 6. The preferred viscosity of polymer (1) is from 1 to 1000 Pa·s at 25°C. Lower viscosities give cured sealants which are very hard with high modulus because of the high amount of cross linking while higher viscosities give sealants with a very low extrusion rate. A preferred polymer is represented by the formula where R and R'' are as defined above, m is 0 or 1, b is 0 or 1, c is from 1 to 6 and x is such that the viscosity is from 0.5 to 3000 Pa·s at 25°C. A preferred polymer, obtained when b is 0, is of the formula or, when b is 1 and c is 1, is of the formula where R and R'' are as described above. Methyl radical is preferred for R and R''. The radicals can be the same or combinations of the above where at least 50 mole percent of the radicals are methyl radicals. The polymer of formula (II) can be manufactured by reacting a vinyl endblocked polydiorganosiloxane with an endcapping composition of the formula where R and R'' are as defined above, m is 0 or 1 and c is 1 to 6. This endcapping composition can be produced by a method comprising (A) mixing 1 mole of a composition (a) of the formula where R, R'' and m are as defined above, with greater than 2 moles of a composition (b) of the formula where R is as defined above and c is from 1 to 6, in the presence of a platinum catalyst and allowing to react, then, (B) optionally stripping the excess composition (b) from the product, to give an endcapping composition of the formula as given above. When c is equal to 1, the product obtained is the endcapping composition shown above which is used to produce the polymer of formula (IV). A preferred endcapping composition is that obtained when c is equal to 1 and m is equal to 0. The above endcapping composition, it's method of manufacture and it's use in the manufacture of silicone sealants, having an alkoxy functional silane crosslinker and a titanium catalyst, is taught in U.S. patent application Serial No. 148,196, filed January 28, 1988, assigned to the assignee of the instant application. The polymer of formula (III) may be produced by reacting a hydrogen endblocked polydiorganosiloxane with a silane of the formula in the presence of a platinum catalyst such as chloroplatinic acid at a temperature of from 30 to 150°C. Methods of making these polymers are taught in U.S. Patent No. 3,175,993, issued March 30, 1965, to Weyenberg, which shows methods of manufacturing polymer of formula (III). The polymer of formula (IV) can be manufactured by reacting a vinyl endblocked polydiorganosiloxane with an endcapping composition of the formula where R is as defined above, using a platinum catalyst to cause the materials to react. This endcapping composition is prepared by reacting ViR m Si(OR'') 3-m , where Vi is vinyl radical, with (R₂HSi)₂O in the presence of a platinum catalyst where only one end of the disilane is reacted. This can be done by combining 1 mole of the ViR m Si(OR'') 3-m with greater than 2 moles of the disilane. When this mixture is combined with a platinum catalyst, there is a slightly exothermic reaction after a few minutes at room temperature. The color changes from clear to light yellow. A byproduct will be present consisting of product produced by the reaction of ViR m Si(OR'') 3-m to both ends of the silane. This byproduct can be left in the material. At a 1 to 2 ratio, there is about 15 percent byproduct produced. If the ratio is changed to 1 to 4 the byproduct drops to about 5 percent. The excess silane is then stripped from the product. The product can be purified by distillation if desired. A series of polymers similar to those shown above as polymers II, III and IV can be produced where not all of the vinyl endblocking groups on the polydiorganosiloxane are reacted with an alkoxysilane. A polymer results in which, on average, some of the ends are vinyl endblocked and some of the ends are alkoxysilethylene endblocked. Useful materials have been produced in which on average from 3 to 40 percent of the endblocking groups are vinyl radicals and the remainder are alkoxysilethylene radicals. As an example, when the endcapping composition is of the formula where Me is methyl radical and the vinyl endblocked polydiorganosiloxane is a polydimethylsiloxane having a viscosity of about 55 Pa·s at 25°C. then the degree of endblocking versus the amount of endcapping composition used can be estimated from the following: Parts by Weight of Endcapper Percent of Alkoxysilethylene Endblocks 0.9 100 0.8 89 0.7 78 0.6 67 0.5 55 When these polymers having a portion of the endblocking present as vinyl radicals are formulated into moisture curing sealants, the modulus of the cured sealant is lower than if all of the endblocking groups were alkoxysilethylene groups. By adjusting the degree of endcapping, the modulus of the resulting elastomer can be controlled at the desired level. The above polymers can also be produced by using similar siloxanes and silanes in which the location of the hydrogen atom and the vinyl group which react together are reversed. Useful silicone elastomeric sealants are commonly produced with a filler as one of the ingredients. These fillers are well known in the industry. They are added to the mixture to provide reinforcement of the polymer so as to control the physical properties of the sealant after curing. Reinforcing fillers (ingredient 4), such as fumed silica, precipitated silica and diatomaceous earth are used to give the highest physical strengths to the sealants. Reinforcing fillers are generally recognized as being very fine particles having a surface area from about 50 to 700 m²/g. These fillers may be used with untreated filler surfaces or with treated filler surfaces, the treatment being used to modify the filler surface so that it properly reacts with the polymer and the other ingredients in the sealant. Calcium carbonate fillers are now available which are produced by precipitation which have a surface area of about 20 m²/g that give a reinforcing effect also. Extending fillers such as titanium dioxide, zirconium silicate, calcium carbonate, iron oxide, ground quartz and carbon black may be used. The amounts of filler used can obviously be varied within wide limits in accordance with the intended use. For example, in some cases the sealant could be used with no filler, but it would have very low physical properties. Reinforcing fillers are commonly used in amounts from about 5 to 60 parts by weight to give the highest physical properties, such as tensile strength. Extending fillers are finely ground in that the average particle size is in the range of from about 1 to 10 micrometers. Extending fillers are used to modify the sealant properties and to provide opacity in some cases. A crosslinker (2) of the formula R′ a Si(OR″) 4-a where R′ is at least one selected from the group consisting of methyl, ethyl, propyl, phenyl and vinyl, R″ is as defined above and a is 0, 1 or 2, is added as a moisture scavenger and as a modulus control agent. These alkoxy silanes and their method of manufacture are well known. The amount of crosslinker preferably is from 0.1 to 14 parts by weight, with from 2 to 8 parts most preferred. when a is 2, the silane is a chain extender; in this case, it is preferable that the polymer (1) be trialkoxy endblocked, so that crosslinking as well as chain extension takes place. It is possible to produce useful sealants without using a crosslinker when the polymer of this invention is present because of the functionality of the polymer itself, but from a practical viewpoint, the crosslinker is useful in that it contributes to the excellent shelf life of the sealant. It is also useful in controlling the degree of cross linking in the cured elastomeric sealant; more of the trifunctional cross linker results in a harder, lower elongation elastomer, while more of the difunctional silane acts as a chain extender to give a softer, higher elongation elastomer. The sealants of this invention are cured through the use of a titanium catalyst (3). The titanium catalyst can be any of those known to be useful in catalyzing the moisture induced reaction of alkoxy containing siloxanes or silanes. Preferred are a titanium catalyst such as titanium naphthenate, titanium esters such as tetrabutyltitanate, tetra-2-ethylhexyltitanate, tetraphenyltitanate, triethanolaminetitanate, organosiloxytitanium compounds such as those described in U.S. Patent No. 3,294,739 and beta-dicarbonyl titanium compounds such as those described in U.S. Patent No. 3,334,067 both patents show titanium catalyst and methods of manufacture. Preferred catalysts include tetrabutyltitanate, tetraisopropyltitanate, bis-(acetylacetonyl)-diisopropyltitanate and 2,5-di-isopropoxy-bis-ethylacetoacetate titanium. The amount of catalyst is from 0.2 to 6.0 parts by weight per 100 parts by weight of polymer (1). Preferred are from 0.5 to 3.0 parts by weight. The method of this invention is used to produce an improved silicone elastomeric sealant, having a reduced tendency to flow and an increased cure rate. The preferred method mixes the alkoxysilethylene ended polymer (1) with a deaired mixture of crosslinker (2) and titanium catalyst (3), which are added in the absence of exposure to moisture. The crosslinker (2) and titanium catalyst (3) can be added separately or they can be mixed together and then added as a mixture. They are thoroughly stirred to give a uniform mixture. Then the reinforcing filler is added in the absence of moisture and stirred until uniform. The uniform mixture is then preferably deaired, then sealed into storage containers, sealant tubes for example, to store it until it is to be used. The composition produced by the method of this invention has less tendency to flow when compared to comparable compositions made with conventional mixing methods. When the composition produced by the method of this invention is exposed to moisture, it cures to give an elastomeric silicone. The composition is useful as a sealant material for filling spaces and gaps as in sealing buildings particularly where the spaces and gaps are in a vertical plane. The following examples are included for illustrative purposes only and should not be construed as limiting the invention which is properly set forth in the appended claims. All parts are parts by weight. A polydiorganosiloxane having endblocking of trialkoxysilethylene was prepared by mixing 100 parts of dimethylvinylsiloxy endblocked polydimethylsiloxane having a viscosity of about 55 Pa·s at 25°C. with 0.8 part of a tetramethyldisilane in which one of the hydrogen atoms is replaced with a trimethoxysilethylene group, the silane having the formula and 0.01 part of chloroplatinic acid complex of divinyltetramethyldisiloxane diluted with dimethylvinylsiloxy endblocked polydimethylsiloxane to provide 0.7 weight percent platinum and allowing the mixture to react to give a polydiorganosiloxane having the above described endblocking group. This polymer is referred to as polymer A in the examples. In an analogous procedure, 100 parts of the polydimethylsiloxane was reacted with 1.04 parts of a dimethoxysilethylene hydride, rather than the trimethoxy shown above as (V). This polymer was completely endblocked with dimethoxysilethylene groups. This polymer is referred to as polymer B in the examples. Polymer C was prepared in the same manner as polymer A, except the reactants were 100 parts of the dimethylvinylsiloxy endblocked polydimethylsiloxane and 0.7 parts of the tetramethyldisilane (V) to give a polymer having about 80 percent of the polymer ends blocked with trimethoxysilethylene and 20 percent with vinyl groups. Example 1 A comparison of the prior art method of mixing and the method of mixing of this invention was made. A comparative base was prepared by mixing 100 parts of polymer A and 10 parts of fumed silica having a surface area of about 250 m²/g until uniform, putting in a container and exposing to vacuum to remove the air. Then this base was further mixed by adding, in the absence of moisture, 4 parts of methyltrimethoxysilane and 1.5 parts of tetrabutyltitanate. After storage for 18 hours at 50°C. (an accelerated storage test), the sealant was tested for suitability for use in vertical joints by measuring the slump in accordance with ASTM D 2202. The slump was greater than 102 mm (4 inches), showing that the sealant was very flowable. A composition was prepared in accordance with this invention by mixing 100 parts of polymer A, 4 parts of methyltrimethoxysilane and 1.5 parts of tetrabutyltitanate in the absence of moisture until uniform. Then 10 parts of the above described silica was admixed, without exposure to moisture. After storage for 18 hours, the sealant was tested as above. The slump was 18 mm (0.7 inches), showing the sealant had a greatly reduced amount of flow. Both compositions were of the same formulation, only the method of compounding the compositions was different. Example 2 A comparative composition was prepared by mixing 100 parts of polymer B, 4 parts of dimethyldimethoxysilane and 10 parts of the above fumed silica until uniform, in the absence of moisture. Then 2 parts of tetrabutyltitanate were admixed in the absence of moisture until uniform. After storage overnight, the sealant was tested as above. The slump was greater than 102 mm(4 inches) showing that the sealant was very flowable. A composition was prepared in accordance with this invention by mixing 100 parts of polymer B, 4 parts of dimethyldimethoxysilane and 1 part of tetrabutyltitanate, in the absence of moisture, until uniform. Then 10 parts of the above fumed silica was admixed, without exposure to moisture. Finally another 1 part of tetrabutyltitanate was added. After storage, the sealant was tested as above. The slump was 20 mm (0.8 inches). A composition was prepared in accordance with this invention by mixing 100 parts of polymer B, 4 parts of dimethyldimethoxysilane and 2 parts of tetrabutyltitanate, in the absence of moisture, until uniform. Then 10 parts of the above fumed silica was admixed, without exposure to moisture. After storage, the sealant was tested as above. The slump was 5 mm (0.2 inches). Example 3 A comparative composition was prepared by mixing 100 parts of polymer B, 3 parts of methyltrimethoxysilane and 10 parts of the above fumed silica until uniform, in the absence of moisture. Then 2 parts of tetrapropyltitanate were admixed in the absence of moisture until uniform. After storage overnight, the sealant was tested as above. The slump was 69 mm (2.7 inches), showing that the sealant was flowable. A composition was prepared in accordance with this invention by mixing 100 parts of polymer B, 3 parts of methyltrimethoxysilane and 1 part of tetrapropyltitanate, in the absence of moisture, until uniform. Then 10 parts of the above fumed silica was admixed, without exposure to moisture. Finally another 1 part of tetrapropyltitanate was added. After storage the sealant was tested as above, giving a slump of 3.8 mm (0.15 inches). Example 4 A comparative composition was prepared by mixing 100 parts of polymer C with 8 parts of fumed silica having a surface area of about 150 m²/g and then putting in a container and deairing. Then 7 parts of methyltrimethoxysilane and 2 parts of chelated titanate catalyst, 2,5-di-isopropoxy-bis-ethylacetoacetate titanium, were admixed in the absence of moisture. The slump, skin over time (SOT) and tack free time (TFT) of the sealant were measured with the results shown in Table I. The skin over time is defined as the time required for the material to cure to the point where it no longer adheres to a clean fingertip lightly applied to the surface. The cure conditions are 23°C. and 50 percent relative humidity. The tack free time is defined as the time in minutes required for a curing material to form a non-tacky surface film. A sample is spread on a clean smooth surface and timing is begun. Periodically, a clean strip of polyethylene film is laid upon a fresh surface and a 28.35 weight (one ounce weight) applied to it. After 4 seconds, the weight is removed and the strip gently pulled off. The time when the strip pulls cleanly away from the sample is recorded as the tack free time. A composition of this invention was prepared by mixing 100 parts of polymer C with 7 parts of methyltrimethoxysilane and 2 parts of the above chelated titanate catalyst, in the absence of moisture. Then 8 parts of the above fumed silica was admixed in the absence of moisture. The slump, skin over time (SOT) and tack free time (TFT) of the sealant were measured with the results shown in Table I. The composition of this invention has a lower slump and a much faster cure rate than the comparative composition having the same formulation but made in the conventional mixing manner rather than by the method of this invention.

Claims: A process of producing silicone sealants containing polydiorganosiloxane having alkoxy endblocking, alkoxy functional crosslinker and/or chain extender and titanium catalyst, wherein the improvement comprises a method comprising (A) mixing in the absence of moisture (1) 100 parts by weight of a polymer of the formula where each R is free of aliphatic unsaturation and is at least one selected from the group consisting of monovalent hydrocarbon, monovalent halohydrocarbon and monovalent cyanoalkyl radicals of 1 to 18 inclusive carbon atoms, each D is selected from the group consisting of hydroxyl radical and radical of the formula where each R'' is at least one selected from the group consisting of methyl, ethyl, propyl and butyl, Z is a divalent hydrocarbon radical or a combination of divalent hydrocarbon radicals and siloxane radicals, m is 0 or 1 and x is of a value such that the polymer has a viscosity of from 0.5 to 3000 Pa·s at 25°C., (2) from 0.1 to 14 parts by weight of a crosslinker of the formula R' a Si(OR'') 4-a where R' is at least one selected from the group consisting of methyl, ethyl, propyl, phenyl and vinyl, R'' is as defined above and a is 0, 1 or 2 and (3) from 0.2 to 6.0 parts by weight of titanium catalyst and (C) storing the mixture in the absence of moisture, characterised in that (B) from 5 to 60 parts by weight of reinforcing filler are added to the mixture resulting from the mixing of components (i) to (iii) recited in step (A) above after said components (i) to (iii) are mixed together and before the storage comprising step (C), to give a sealant which has a slump of less than 25.4 millimetres (less than 1 inch) when measured in accordance with ASTM D 2202. A silicone sealant containing polydiorganosiloxane having alkoxy endblocking, alkoxy functional crosslinker and/or chain extender and titanium catalyst together with a reinforcing filler, said sealant being obtainable by the method of Claim 1, and having the characteristic feature of a slump of less than 25.4 millimetres (less than 1 inch) when measured in accordance with ASTM D 2202.

Inventors: KAMIS RUSSELL PETER, KLOSOWSKI JEROME MELVIN, LOWER LOREN DALE, KAMIS, RUSSELL PETER, KLOSOWSKI, JEROME MELVIN, LOWER, LOREN DALE
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1989
Main classification: C09K3
IPC codes: C08K5, C08L83, C08K13, C09K3, C08K3