Silacyclobutane functional polymers and their production

Abstract: The silacyclobutane functional polydiorganosiloxane copolymers of the invention have the following structure: wherein M is selected from wherein R a , R b , R c , R d , R e and R f are independently monovalent radicals; m, n, p and x are integers of from 0 or more, with the proviso that there is at least one silacyclobutane group in the copolymer. The copolymer can be made by reacting a hydroxyl endblocked polydiorganosiloxane with either a difunctional chain extending silacyclobutane or with a monofunctional chain stopper or a mixture of chain extender and chain stopper. The copolymer can be made into curable compositions by use of suitable catalyst.

Description: Silacyclobutane monomers are known and have been polymerized. To applicants' knowledge, however, stable silacyclobutane functional polyorganosiloxanes have not previously been made in high yield by a method which allows controlled design of the polymer structure. The polymers of the invention are useful intermediates for formulating room temperature vulcanizable and hot air vulcanizable silicone elastomers. US-A 3 719 696 discloses silacyclobutane functional polymers which are prepared from siloxanes having terminal hydroxy groups and silacyclobutanes. The most preferred polymers are those having terminal silacyclobutane groups. FR-A 2 081 923 also discloses silacyclobutane functional polymers having terminal silacyclobutane groups. US-A 3 694 427 is concerned with the reaction of silanoles having at least two hydroxyl groups with silacyclobutanes. A composition is provided which shall crosslink to give rubbers or adhesives. The consistency of the polymer is regulated by the ratio of the components employed. FR-A 2 081 924 also discloses the reaction of silanol and a silacyclobutane. From Chemical Abstract, vol.63, no.2, abstract no. 1904D it is known to cohydrolyse organosilicon monomers with mono- or dichloro-substituted silacyclobutane. Silacyclobutane functional polydiorganosiloxane copolymers which can be crosslinked to give a useful 3-dimensional network structure are prepared from a hydroxyl endblocked polydiorganosiloxane, a dihydrolyzable silacyclobutane and a monohydrolyzable silane. The silacyclobutane functional polydiorganosiloxane copolymers obtained with the process of the present invention have the following structure: wherein M is selected from wherein R a , R b , R c , R d , R e and R f are independently hydrogen, alkyl, substituted alkyl, aryl, alkaryl, alkenyl or alkynyl; m is an integer of 1 or greater, n, p and x are integers of from 0 or more, with the provision that there is at least one silacyclobutane group in the polymer. Generally, the copolymer will have an average molecular weight between 1,000 and 1,000,000. The present invention is concerned with a process for making silacyclobutane functional polydiorganosiloxane copolymers consisting essentially of reacting a siloxane of the formula HO(R a ₂SiO) m H with either a chain extending silacyclobutane of the formula alone or together with a chain stopper selected from those of the formula wherein Y is a radical or atom reactive with the SiOH group and selected from the group consisting of, wherein R is independently hydrogen, alkyl, substituted alkyl, aryl, alkaryl, alkenyl or alkynyl, as are R a , R b , R c , R d , R e , R f and R g and wherein q is an integer of from three to five and z is an integer of from one to three. Exemplary of suitable monovalent radicals for the R, R a , R b , R c , R d , R e , R f and R g groups are hydrogen, the hydrocarbons or substituted hydrocarbons. Thus, for example, these groups can be alkyl such as methyl, ethyl, propyl or octadecyl; substituted alkyl such as aminopropyl or thiopropyl; haloalkyl such as chloropropyl; aryl such as phenyl, xenyl or naphthyl; alkaryl such as tolyl or xylyl; aralkyl such as benzyl; unsaturated alkenyl such as vinyl, propenyl or hexenyl; and unsaturated alkynyl such as acetylenyl or propynyl. R a , R e and R f are preferably methyl, vinyl, phenyl, ethyl, hydrogen or trifluoropropyl and most preferably methyl. R d is preferably methyl, ethyl, vinyl, phenyl or hydrogen and most preferably methyl. R b , R c and R g are preferably methyl or hydrogen and most preferably hydrogen. The cyclobutane ring containing the R b and R c radicals can be substituted or unsubstituted. The term "silacyclobutane" throughout this disclosure is intended to include either the unsubstituted cyclobutane ring or the substituted ring. Suitable groups include Suitable groups include Suitable groups include Suitable groups include It is preferred that the Y groups of the difunctional chain extender be the same as the Y group of the monofunctional endblocker. Further, the use of a monofunctional endblocker is optional if the polymer composition is required to crosslink upon mixing of the silanol terminated polysiloxane and the difunctional silacyclobutane chain extender. The use of a monofunctional silacyclobutane endcapper is preferred if a room temperature stable, fluid polymer is desired. The polymers can be prepared by mixing the ingredients together at a mild temperature between -50°C. and 100°C., at atmospheric pressure and, optionally, with a solvent. Suitable solvents include toluene, tetrahydrofuran, diethyl ether, benzene, chloroform and methylene chloride. For best results, the polydiorganosiloxane, HO(R a ₂SiO) m H, has a hydroxyl stoichiometry equivalent to or up to 10 percent less than the reactive groups (Y) on the silacyclobutane, wherein the proportion of hydroxyl groups of the siloxane is from 80 to 100 percent of the moles of (Y). The solvent and volatile byproducts can be removed by reduced pressure distillation and a fluid polymer recovered. It will be seen from the examples that, without an end blocker, a gel is formed as the polymer molecular weight is uncontrollable and partial crosslinking may occur. There may be some unreacted hydroxyl groups present in the copolymer also, depending upon the ratio of the ingredients used in the preparation. The silacyclobutane functional polydiorganosiloxane copolymers of the invention may be cured to useful elastomers by vulcanization to cause ring opening polymerization of the silacyclobutane groups and formation of a crosslinked network of polydiorganosiloxanes. Generally, a temperature of greater than 150°C. is required to crosslink the polydiorganosiloxane copolymers in a useful time of less than 1 day. A catalyst may be used to lower the cure temperature and accelerate the rate of cure. Useful catalysts include compounds and supported metals of the noble (platinum group) metals and compounds of aluminum, zinc and tin. Preferred are homogeneous compounds and supported heterogeneous metal catalysts of platinum, palladium, rhodium, ruthenium and iron and most preferred are homogeneous and heterogeneous catalysts of platinum. Metal concentrations of from 0.1 to 1000 ppm may be used with a preferred range of 5 to 50 ppm metal. In the presence of this type of catalyst, the vulcanization time will vary with the form of catalyst, concentration of catalyst and temperature. Vulcanization temperatures of greater than 100°C. are preferred to cure the silacyclobutane functional polydiorganosiloxane copolymers in a useful time, but vulcanization can be slowly accomplished even at room temperature in the presence of a catalyst. The rate of vulcanization can be further accelerated by the addition of an organosilicon compound containing an SiH bond. Further, the degree of crosslinking and hence the physical properties of the cured elastomer can be predictably varied by adjusting the concentration of SiH functional material. Useful SiH organosilicon compounds may contain one or more silicon atoms and one or more SiH bonds. The concentration of the SiH functional organosilicon compound can be described by the ratio of SiH functionality to silacyclobutane group and may vary from greater than zero with no upper limit. A preferred SiH to silacyclobutane ratio is from 0.001 to 2.0 and most preferred is a ratio of 0.1 to 0.5 with the understanding that the preferred ratio of SiH to silacyclobutane depends upon the degree of crosslinking required for the product elastomer. The preparation of polyorganosiloxane elastomers by vulcanization is generally accomplished in the art by heating the polymer formulation in the presence of organic peroxides or by heating a formulation of ethylenically unsaturated and SiH functional polyorganosiloxanes in the presence of a metal, preferably platinum, catalyst. For the latter, crosslinking is accomplished by the addition of the SiH bond to the unsaturated group, a reaction known as hydrosilation. For this cure system, the ratio of SiH to unsaturated groups is generally kept greater than 1. The vulcanization of silacyclobutane functional polydiorganosiloxanes with SiH functional materials thus requires the use of less SiH functional material than the vulcanisation of unsaturated functional polydiorganosiloxanes. Additionally, the vulcanization of silacyclobutane functional polydiorganosiloxanes in the presence of SiH functional materials leads to a higher crosslink density than vulcanization of comparable vinyl functional polydiorganosiloxanes in the presence of SiH functional materials. The vulcanization of silacyclobutane functional polydiorganosiloxane copolymers may be performed in the presence of additives known in the art to improve the processing, cure and resultant physical properties of the material. Such additives include, but are not limited to, fillers such as fumed silica, carbon black, iron oxide and calcium carbonate; process aids such as silicone fluids; pigments; adhesion promoters; mold release agents; stabilizers such as metals and their oxides; and catalysts. Vulcanization of the silacyclobutane functional polydiorganosiloxanes may be accomplished by heating in a mold or oven. Heating may also be performed by irradiation with infrared, ultraviolet, photomagnetic or microwave radiation and, optionally, in the presence of a material which absorbs the incident radiation. Heating may also be performed inside an oscillating magnetic field in the presence of paramagnetic material, a process known as induction heating. The silacyclobutane group has been shown to be inert to free radicals in the condensed phase and at or near room temperature. Therefore, crosslinking of silacyclobutane functional polydiorganosiloxanes by ultraviolet irradiation in the presence of a photoinitiator or electron beam irradiation is not expected to occur. However, the silacyclobutane functional polydiorganosiloxanes were found to undergo crosslinking under ultraviolet light when a photoinitiator was present at rates slightly faster than in control experiments with polydiorganosiloxanes containing only methyl functionality. Similarly, the silacyclobutane functional polymers underwent electron beam curing at rates slightly faster than the polymers containing only the methyl group. The silacyclobutane functional polydiorganosiloxane copolymers of the invention may also be crosslinked upon exposure to atmospheric moisture, a process known as room temperature vulcanization (RTV). This process can be accelerated in the presence of a nucleophilic or basic catalyst. Hydrolysis of the silacyclobutane group is thought to provide an n-propyl silanol which can undergo condensation to give a siloxane bond: Thus, when the silacyclobutane groups are attached to a polymer chain, they can react with water and condense to form a siloxane bond between the polymer chains. This cure system has a distinct advantage over conventional RTV cure systems used in the art to crosslink silicones: no volatile condensation byproducts such as acetic acid, alcohol, ketone, oxime or amine are generated during curing and therefore no byproducts are released. An RTV silicone which does not release condensation byproducts is desireable in confined spaces where the byproduct cannot dissipate or in applications where the cure byproduct poses a safety, flammability, toxicity, irritation or environmental hazard. Additionally, a cure system which evolves no condensation byproduct is desired to give lower shrink upon exposure to moisture. The silacyclobutane functional polymers of the invention may be formulated into one part RTV sealants consisting of the following parts: A. The silacyclobutane functional polymer as defined previously B. Catalyst C. Optional filler and other additives The catalyst (B.) is HONR₂ or diorganoaminoxy functional polyorganosiloxane such as R₃SiO(R₂SiO) a (RXSiO) b SiR₃ or (RXSiO) c (R₂SiO) d where X is -ONR₂ , a and d are equal to or greater than 0, b is equal to or greater than 1, c plus d is equal to or greater than 3 and R is a monovalent radical. The preferred catalyst is diethylhydroxyl amine. The optional fillers include silica, alumina, metal carbonates and metal oxides. The sealant may be extruded and cured by atmospheric exposure. Another preferred embodiment is a two part curable composition comprising the polymer according to the present invention and a catalyst selected from the group consisting of platinum, palladium, rodium, ruthenium, aluminum, zinc, tin, iron and their salts in one part and an organosilicon compound containing one or more SiH bonds in the second part. The following examples will serve to illustrate the invention. All parts and percentages in said examples and elsewhere in the specification and claims are by weight unless otherwise indicated. Example 1 To 100 g of Ho(Me₂SiO) x H (1.82 percent OH by weight and an Mn of 2,400), Polymer B was added 9.94 g and 10 ml toluene. The solution was stirred for 15 days and then stripped to 81°C. at 533 Pa (4 mm Hg) to give a slightly hazy fluid. To 0.50 g of the product polymer was added 3.1 mg of a 0.4 percent solution of di-mu-chloro-dichlorobis(tri-n-butylphosphine)diplatinum in toluene to give 55 ppm platinum. The mixture was vulcanized at 135°C. for 20 minutes to give a hard crosslinked elastomer. To another 0.5 g of the product polymer was added 5.5 mg of a 5.0 percent solution of tris(triphenylphosphine)rhodium chloride in toluene to give 60 ppm rhodium. The mixture was heated at 205°C. for 20 minutes to give a hard crosslinked elastomer. In the absence of a catalyst, the polymer showed no sign of crosslinking after heating at 205°C. for 2 hours. In the absence of catalyst, the product polymer remained fluid after 16 months. Example 2 To a solution of 50.0 g Polymer B in 100 g toluene was added a solution of 2.06 g in 15 ml toluene. The mixture was stirred 20 minutes at 25°C., then 16 hours at 70°C., then 72 hours at 25°C. Enough toluene was added to give 167 g total solution which was divided as follows: A. To 55.4 g of the solution was added 0.24 g in 10 ml toluene. The mixture was stirred at 70°C. for 7.5 hours, then at 25°C. for 20 hours. The mixture was stripped to 75°C./133 Pa (1 mm Hg) to yield 17.0 g viscous fluid with a slight haze having a Mw of 21,000, a Mn of 7,000 and a Mw/Mn of 3. To 2 g of the product polymer was added 64 mg of a catalyst prepared from chloroplatinic acid complex of divinyl tetramethyldisiloxane to provide 0.7 weight percent platinum, to give 200 ppm platinum. The mixture was poured into an aluminum cup and heated 10 minutes at 150°C. to give a hard elastomer. The product polymer did not cure after 30 minutes at 200°C. in the absence of catalyst. B. As a comparative example, no endblocker was added to a portion of the solution and solvent removal as above gave a crosslinked gel. The remainder of the solution was stripped to 75°C. at less than 133 Pa (1 mm of Hg) to give a clear, viscous fluid. The fluid gelled to a crosslinked solid after 24 hours. Example 3 To a mixture of 75.0 g of Ho(Me₂SiO) x H, (0.23 percent OH by weight and a Mn of 14,500), Polymer A, 3.16 g of triethylamine and 10.2 g of anhydrous magnesium sulfate in 227 g diethyl ether was added 1.53 ml 1-acetoxy-1-methylsilacyclobutane. This mixture was stirred 48 hours, filtered and stripped to 73°C. and 0.6 mm Hg to give 73.5 g of clear colorless fluid having a Mw of 39,000, a Mn of 22,000 and a Mw/Mn of 1.8. To 1 g of this polymer was added 1.9 mg of the catalyst of Example 2. The mixture was poured into an aluminum cup and heated at 155°C. for 5 minutes to give a crosslinked elastomer. In the absence of catalyst, the polymer failed to cure upon heating for 20 minutes at 180°C., but cured to a weak elastomer upon heating for 20 minutes at 202°C. Example 4 To a mixture of 152 g Ho(Me₂SiO) x H, (0,14 percent OH by weight and a Mn of 24,000), Polymer C and 15.3 g anhydrous magnesium sulfate in 352 g diethyl ether was added a solution of 0.197 g 1-acetoxy-1-methylsilacylobutane and 1.15 g 1,1-diacetoxysilacyclobuane in 50 ml diethyl ether. The mixture was stirred for 3 hours, filtered and stripped to 75°C./200 Pa (1.5 mm Hg) to give 149.2 g of clear colorless copolymer having a Mw of 340,000, a Mn of 88,000 and a Mw/Mn of 3.9. To 47 g of the product polymer was milled in 0.14 g of the catalyst of Example 2 to give 20 ppm platinum. The catalyzed gum was heated at 180°C. for 22 minutes in an electric press to yield an elastomer with tensile strength of 214 kPa (31 psi), elongation of 266 percent and modulus at 200 percent elongation of 145 kPa (21 psi). Example 5 To 10 g Polymer A was added 0.09 g 1,1-diacetoxysilacyclobutane and 0.04 g trimethylsilylacetate. Following mixing and 23 hours in a vacuum chamber to remove volatiles, the product copolymer was a clear colorless fluid having a Mw of 561,000, a Mn of 110,000 and a Mw/Mn of 5.1. To 1 g of the product polymer was added 1.9 mg of the catalyst of Example 2 to give 11 ppm platinum. The mixture was poured into an aluminum cup and heated at 156°C. for 20 minutes to give a crosslinked elastomer. Example 6 This formulation contained no end blocker and gave a crosslinked elastomer. To 10.1 g Polymer A was added 0.11 g 1,1-diacetoxysilacyclobutane. The mixture was placed in a vacuum chamber to remove volatiles and solidified to an elastomeric foam after 23 hours. Example 7 To 10.1 g of Polymer A was added 0.185 g 1-methyl-1-(N-methylacetamido)silacyclobutane, to give a hazy fluid having a Mw of 38,000, a Mn of 19,000 and a Mw/Mn of 2. To 1.1 g of the product polymer was added 2.4 mg of the catalyst prepared in Example 2 to give 14 ppm platinum. The mixture was poured into an aluminum cup and heated at 157°C. for 20 minutes to yield a weak elastomer. Example 8 To a mixture of 189 g Polymer C and 19.8 g anhydrous magnesium sulfate in 353 g of tetrahydrofuran was added a solution of 1.60 g 1,1-bis(N-methylacetamido)silacyclobutane and 0.26 g 1-methyl-1(N- methylacetamido)silacyclobutane in 50 ml tetrahydrofuran. The mixture was stirred for 41 hours, filtered and stripped to 75°C. at 107 Pa (0.8 mm Hg) to give 165 g of hazy viscous fluid having a Mw of 183,000, a Mn of 95,000 and a Mw/Mn of 1.9. Into 23 g of the product polymer was milled 7.7 mg of the catalyst of Example 2 to give 20 ppm platinum. The mixture was heated at 180°C. for 20 minutes to yield a weak elastomer. The catalyzed polymer cured to an elastomer after five months at room temperature. The uncatalyzed polymer remained a viscous fluid after six months. Example 9 To 10 g of Polymer A was added 0.047 g N-methyl-N-(trimethylsilyl)acetamide. After stirring, 0.416 g of a 22.56 percent by weight solution of 1,1-bis(N-methylacetamido)silacyclobutane in chloroform was stirred in to give a viscous fluid having a Mw of 147,000, a Mn of 61,000 and a Mw/Mn of 2.4. To 1.1 g of the product polymer was added 7.9 mg of the catalyst of Example 2 to give 47 ppm platinum. The mixture was heated at 157°C. for 20 minutes to yield a weak elastomer. Example 10 To a mixture of 10 g Polymer A and 0.184 g Me₃SiO(Me₂SiO)₃H was stirred in 0.854 g of a 22.56 percent by weight solution of 1,1-bis(N-methylacetamido)silacyclobutane in chloroform to give a viscous fluid having a Mw of 106,000, a Mn of 44,000 and a Mw/Mn of 2.4. To 1.1 g of the product polymer was added 6.7 mg of the catalyst of Example 2 to give 39 ppm platinum. The mixture was heated at 157°C. for 20 minutes to give a crosslinked gel. Example 11 This composition contained no endblocker and gave a crosslinked elastomer. To 10 g of Polymer A was added 1.13 g of a 22.52 percent solution of 1,1-bis(N-methylacetamido) silacyclobutane in dimethylformamide. Upon stirring, the composition gelled to a weak elastomer.

Claims: A process for making silacyclobutane functional polydiorganosiloxane copolymers consisting essentially of reacting a siloxane of the formula HO(R a ₂SiO) m H with either a chain extending silacyclobutane of the formula alone or together with a chain stopper selected from the group consisting of those of the formula wherein Y is a radical or atom reactive with the SiOH group and selected from the group consisting of wherein R is independently hydrogen, alkyl, substituted alkyl, aryl, alkaryl, alkenyl or alkynyl, as are R a , R b , R c , R d , R e , R f and R g and wherein m is an integer of 1 or greater, q is an integer from three to five, x is an integer of 0 or more and z is an integer of from one to three, the moles of hydroxyl of the siloxane being from 80 to 100 percent of the moles of Y. The process of claim 1 wherein the process is carried out by mixing the ingredients at a temperature of between -50°C. and 100°C. and allowing them to react.

Inventors: BANEY RONALD HOWARD, BILGRIEN CARL JOSEPH, BURNS GARY THOMAS, FIEDLER LAWRENCE DALE, LEE CHI-LONG, BANEY, RONALD HOWARD, BILGRIEN, CARL JOSEPH, BURNS, GARY THOMAS, FIEDLER, LAWRENCE DALE, LEE, CHI-LONG
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1990
Main classification: C08G77
IPC codes: C08K5, C08G77