Method of forming siloxane polymers using a heteropoly catalyst having a Keggin structure

Abstract: Disclosed herein is a method of forming siloxane polymers using a heteropoly catalyst having a Keggin structure. The method comprises contacting a fluid having at least one siloxane polymer precursor selected from cyclic siloxanes (I) having the formula (RR'SiO) a or linear siloxanes (II) having the formula where R is a substituted or unsubstituted monovalent hydrocarbon having from 1 to 6 carbon atoms, R' is hydrogen atom and a substituted or unsubstituted monovalent hydrocarbon having from 1 to 6 carbon atoms, a is at least 3 and b is at least 1; with an effective amount of a heteropoly catalyst having a Keggin structure, selected from the group consisting of heteropoly acids (III) having the formula H n XM 12 O 40 , salts thereof and mixed acid-salts thereof, where X is B +3 , Si +4 , Ge +4 or P +5 , M is Mo +6 or W +6 and n is 3, 4 or 5, as required for the valence of the heteropoly acid to equal 0, at a temperature ranging from 23°C. to the boiling point of the siloxane polymer precursor.

Description: This invention provides a method of forming siloxane polymers using a heteropoly catalyst having a Keggin structure. Many methods for forming linear siloxane polymers have been described in the art. See for example Noll, W., Chemistry and Technology of Silicones, Academic Press, Inc. 1968, pp. 209-233. Ring-opening polymerization reactions of cyclodialkylsiloxanes, considered a chain growth process, are initiated by either acids, such as acid clays, HF, H 2 SO 4 amd CF 3 SO 3 H; or bases, such as GOH, GOSi=, GOR and GR, where G is an alkali metal or a quaternary ammonium or phosphonium group and R (depending on G) is an alkyl, polystyryl or poly(trimethylsilylvinyl) group. Step growth polymerization in linear polysiloxanes often consists of homocondensations of silanol-ended siloxanes catalyzed by either strong acids or bases, or mild amines or carboxylic acids combined with quaternary ammonium salts. Termination of both chain growth and step growth polymerization is usually effected by neutralization of the acid or base. Nevertheless, there are some disadvantages to these methods of forming siloxane polymers. One disadvantage is that branching, often described as "T" branching, often occurs with these methods due to cleavage of R-Si groups. It has been found, for example, that siloxane polymers having an average degree of polymerization (DP) of 200 have on average about one "T" branch per polymer chain. Another disadvantage is that neutralization of the acid or base is required to terminate the polymerization reaction. This is an additional step which can poison the catalyst and cause additional waste products. In addition, unless all traces of acid or base are eliminated, the reverse reaction may be catalyzed. Further, the catalyst may not be easily recoverable. The literature describes catalytic effects of inorganic metal-oxygen clusters, see for example Misono, M., Catal. Rev. Sci. Eng., 1987 , 29, 269. These clusters are referred to in the literature as "isopolyanions" when only a polyvalent metal and oxygen are involved and are represented by the formula (M m O y ) p- . If an additional metallic or non-metallic element is present, these clusters are referred to as "heteropolyanions" and are represented by the formula (X x M m O y ) q- . In the above formulae, M is a polyvalent metal such as molybdenum, tungsten and less frequently vanadium; X is a "heteroatom" and can be almost any element in the periodic table, other than a noble gas; O is oxygen; x, m and y are integers where x is less than m, and p and q represent the charge on the anion. When x=1, m=12 and y=40, the heteropolyanion usually adopts a Keggin structure. Within this Keggin structure, the central heteroatom in a XO 4 tetrahedron is surrounded by 12 MO 6 octahedra that share edges and corners to form a heteropolyanion with an overall tetrahedron symmetry. The heteropolyanions are typically negatively charged and easily associate with various cations, including hydrogen atoms, alkali metals, alkaline earth metals and ammonium cations. When hydrogen is the cation, heteropoly acids are formed. Salts may be formed by adding any of the other types of cations described above and acid-salt mixtures are obtained when both hydrogen and other types of cations are present. The addition of appropriate amounts of the various cation(s) having positive charges will balance the negative charge of the anion so the overall valence of the heteropoly compound is zero. These neutral heteropoly compounds when m is 12 and y is 40 are referred to herein as "heteropoly catalysts having a Keggin structure" or "heteropoly catalysts." These heteropoly catalysts having a Keggin structure are particularly suitable for catalysis reactions because they are stable in solution and in solid form. Large scale industrial processes using heteropoly catalysts, include, hydration of propene, oxidation of methacrolein and polymerization of tetrahydrofuran. The main advantages of heteropoly catalysts and heteropoly acids over traditional protic acids, such as sulfuric acid, hydrochloric acid and hydrofluoric acids are their versatility towards catalytic molecular design and their low environmental hazard. The former advantage is due to the heteropoly catalyst having at least three parts as a cationic part, an anionic part and a solvation sphere. Altering any of these parts produces a catalyst having different surface activity, charge and reactivity. In addition to their versatility, heteropoly catalysts are important because they are easily recovered, recrystallized if necessary and reused. The catalysis is terminated at will without having to use neutralization steps that can poison the catalyst and create additional waste products. An object of the present invention is the preparation of siloxane polymers from precursors which have less branching than siloxane polymers produced by other methods. Another object is to form siloxane polymers using a catalyst which does not require neutralization. These objectives are achieved by forming siloxane polymers using a heteropoly catalyst having a Keggin structure. Our method comprises contacting a fluid having at least one siloxane polymer precursor with a heteropoly catalyst having a Keggin structure. This method is effective for opening siloxane ring structures also known as cyclic siloxanes and for the chain extension of opened structures or linear siloxanes. Our invention claims a method of forming siloxane polymers, the method comprising contacting a fluid comprising at least one siloxane polymer precursor selected from cyclic siloxanes (I) having the formula (RR'SiO) a or linear siloxanes (II) having the formula where R is a substituted or unsubstituted monovalent hydrocarbon having from 1 to 6 carbon atoms, R' is hydrogen atom or a substituted and unsubstituted monovalent hydrocarbon having from 1 to 6 carbon atoms, a is at least 3 and b is at least 1; with an effective amount of a heteropoly catalyst having a Keggin structure, selected from the group consisting of heteropoly acids (III) having the formula H n XM 12 O 40 , salts thereof and mixed acid-salts thereof, where X is B +3 , Si +4 , Ge +4 or P +5 , M is Mo +6 or W +6 and n is 3, 4 or 5, as required for the valence of the heteropoly acid to equal 0, at a temperature ranging from 23°C. to the boiling point of the siloxane polymer precursor. The fluid comprises at least one siloxane polymer precursor. The siloxane polymer precursors useful in this invention are described by formulas (I) and (II) and are either commercially available or are made by known methods. Substituents R and R' in both (I) and (II) are individually selected from substituted or unsubstituted monovalent hydrocarbons having 1 to 6 carbon atoms. Examples include alkyl radicals such as methyl, ethyl, isopropyl and hexyl; alkenyl radicals such as vinyl, allyl and hexenyl; alkynal radicals such as propargyl; cycloaliphatic radicals such as cyclopentyl, cyclohexyl and cyclohexenyl; aromatic hydrocarbons such as phenyl; halogenated hydrocarbon or carbon radicals such as 3,3,3-trifluoropropyl, tridecafluoro-(1,1,2,2-tetrahydrooctyl)-1-methyl and perfluoroalkyl. R' can also be hydrogen atom. R and R' are preferably methyl, vinyl, phenyl or 3,3,3-trifluoropropyl radicals. R' is also preferably hydrogen atom. Most preferably, R and R' are each methyl radicals. Subscripts a and b represent the number of - (RR'SiO)- repeating units in (I) and (II) respectively. The value of a is at least 3 and is preferably a positive integer from 3 to 7, most preferably from 3 to 6. The value of b is at least 1. Since our method will polymerize siloxane monomers on lower molecular weight siloxane oligomers and polymers into higher molecular weight siloxane polymers, the upper limit of b is limited primarily by one's ability to mix the fluid so it contacts the heteropoly catalyst. Preferably, the value of b is a positive integer from 2 to 100. The term "siloxane polymer precursor" as used herein can comprise one type of cyclic siloxane or linear siloxane or it can comprise mixtures of one type of cyclic siloxane and linear siloxane or it can comprise mixtures of different types of cyclic siloxanes or linear siloxanes. Therefore, the siloxane polymers prepared by this invention can be homopolymers, copolymers or terpolymers. Preferred siloxane polymer precursors are low molecular weight hydroxy-endblocked polydimethylsiloxane fluids and the cyclic siloxanes 3,3,3-trifluoropropyl(methyl)cyclic trimer (CF 3 (CH 2 ) 2 MeSiO) 3 , (Me 2 SiO) 4 , (Me 2 SiO) 5 , (Me 2 SiO) 6 , (HMeSiO) 4 and (HMeSiO) 5 . In addition to the siloxane polymer precursors, the fluid may also comprise other components including materials which will endblock the siloxane polymers formed by our method. The useful endblockers are triorganosilyl endblockers that contain a radical of the formula R 2 R 3 R 4 Si- wherein each R 2 , R 3 and R 4 is independently selected from hydrogen atom, alkyl groups having from 1 to 6 carbon atoms, alkenyl groups having from 2-8 carbon atoms, aryl groups, arylalkyl groups and perfluoroalkylethyl groups having the formula C n F 2n+1 CH 2 CH 2 where n is 1 to 6. The groups R 2 , R 3 and R 4 can be the same or different as desired. Alkyl groups suitable as R 2 , R 3 and R 4 in the method of this invention include methyl, ethyl, propyl, butyl,hexyl and octyl; alkenyl groups exemplified by vinyl or 5-hexenyl; aryl groups exemplified by phenyl or naphthyl; arylalkyl groups exemplified by phenylmethyl, phenylpropyl and phenylhexyl; and perfluoroalkylethyl groups include perfluoromethylethyl, perfluorodiethyl and perfluorooctylethyl. The source of triorganosilyl endblocker radicals are any material which under the reaction conditions used will form the triorganosilyl radical R 2 R 3 R 4 Si-. Examples of triorganosilyl endblocker are octamethyltrisiloxane, hexomethyldisiloxane, tetramethyl-3,3,3-trifluoropropyldisiloxane, trimethylchlorosilane and dimethylvinylchlorosilane. The preferred endblocker is octamethyltrisiloxane. The amount of triorganosilyl endblocker useful herein is dependent on the desired siloxane polymer chain length and is conveniently determined experimentally by one skilled in the art. It is preferred to add the endblocker in an amount from 0.1 to 75 weight percent of the siloxane polymer precursors. The fluid is contacted with an effective amount of a heteropoly catalyst having a Keggin structure. The heteropoly catalysts useful in our method are selected from the group consisting of heteropoly acids having the formula H n XM 12 O 40 , salts thereof and mixed acid-salts thereof, where X is B +3 , Si +4 , Ge +4 or P +5 , M is Mo +6 or W +6 and n is 3, 4 or 5 as required for the valence of the heteropoly acid to equal 0. The portion of the formula represented by (XM 12 O 40 ) q- is described in the literature as a "heteropolyanion" having a Keggin structure, with X being described as a "heteroatom" and the metal-oxygen cluster M 12 O 40 being described as an "isopolyanion". The heteropolyanions having a Keggin structure are important because they are stable and do not dissociate in solution or solid form. Substituent M is a polyvalent metal, and in the present method, is tungsten (W +6 ) or molybdenum (Mo +6 ). Substituent X is B +3 , Si +4 , Ge +4 or P +5 and is preferably P +5 and Si +4 . These heteropolyanions have open valences and are therefore charged species. The charge q of the heteropolyanion is dependent on the valences of X, M and O. The charge is determined by multiplying the valences of the atoms associated with X, M and O by the value of the integer associated with that atom and by adding the products together. For the heteropolyanion (XM 12 O 40 ) q- where X is Si +4 and M is tungsten or molybdenum, the charge is equal to the sum of the valence of silicon (+4), 12 times the valence of M (+6) and 40 times the valence of oxygen (-2), which totals -4. Since the heteropolyanion has a negative charge, it will associate with cations. When the cation is hydrogen atom, represented in the formula as H, a heteropoly acid is formed. The subscript n describes the number of hydrogen atoms in a heteropoly acid required to neutralize the negative charge of the heteropolyanion. For this invention, n is 3, 4 or 5 depending on X. In the above example, when X is Si +4 and M is W +6 or Mo +6 , 4 hydrogen atoms are needed to neutralize the -4 charge. Examples of heteropoly acids are phosphotungstic acid (H 3 PW 12 O 40 ), phosphomolybdic acid (H 3 PMo 12 O 40 ), silicotungstic acid (H 4 SiW 12 O 40 ) and silicomolybdic acid (H 4 SiMo 12 O 40 ). If a cation other than hydrogen associates with the heteropolyanion, a heteropoly salt forms instead of a heteropoly acid. Examples of such cations include: alkali metals such as Li + , Na + , K + , Cs + or Rb + ; alkaline earth metals such as Ba +2 , Mg +2 or Ca +2 ; and R'' 4 N + , where each R'' is individually selected from hydrogen atom or monovalent hydrocarbon radicals having from 1 to 24 carbon atoms. These monovalent hydrocarbon radicals are the same as those for R as well as dodecyl, octadecyl, octenyl, tolyl, xylyl, naphthyl, benzyl or gamma- tolylpropyl. Preferably, each R'' is hydrogen atom. To form a neutral salt, the number of cations required is 2, 3, 4 or 5, depending on X and the valency of the cation. A typical salt is (NH 4 ) 3 PMo 12 O 40 . If both hydrogen and other cations, as described above for the heteropoly salt, are present with a heteropolyanion, a mixed heteropoly acid-salt results. To form a neutral mixed acid-salt, the number of cations required ranges from 2 to 5, including fractional numbers, depending on X and the valency of the cations. Examples of mixed acid-salts are Cs 2.5 H 1.5 SiW 12 O 40 and Cs 2.5 H 0.5 PW 12 O 40 . Heteropoly acids and mixed acid-salts are preferred heteropoly catalysts. More preferred are H 3 PW 12 O 40 , H 3 PMo 12 O 40 , H 4 SiW 12 O 40 , Cs 2.5 H 1.5 SiW 12 O 40 and Cs 2.5 H 0.5 PW 12 O 40 . The heteropoly catalysts useful in this method are commercially available or are prepared by known methods. In a preferred method, the heteropoly catalyst is thoroughly dried prior to use. Various means are used to dry the heteropoly catalyst and persons skilled in the art can determine the most convenient method. It was found, however, that heating the heteropoly catalyst at 320°C. for 3 hours provided a very active catalyst. The heteropoly catalysts useful in this invention are solid materials which are not soluble in siloxane polymer precursors or the siloxane polymers produced by our method. The heteropoly catalyst may be added to the fluid in solid form, dissolved in a suitable solvent or supported on an appropriate carrier. Suitable solvents are those that will dissolve the heteropoly catalyst and in particular those that may assist in the transfer of protons and charges. Examples of suitable solvents are polar solvents such as water, acetone or alcohols. These heteropoly catalysts may be dissolved in the solvent prior to addition to the fluid or the solvent may be added to the fluid after addition of heteropoly catalyst. Methods for preparing heteropoly catalysts supported on carriers are known. In general, the heteropoly catalyst is dissolved in water and mixed under heat with a carrier until the water evaporates. Preferably, the supported catalyst is then dried by conventional methods. Examples of carriers include silica, alumina and carbon. A preferred carrier is silica. The amount of catalyst added depends on the loading desired. As used herein, "loading" means the weight percent of heteropoly catalyst in the support-heteropoly catalyst mixture. Typical loading for a heteropoly catalyst on a support is 0.1 to 75 weight percent. Preferred loading for a heteropoly catalyst on a support is 10 to 20 weight percent. It is preferred to add the heteropoly catalyst in its solid form or supported on a carrier. Having the heteropoly catalyst in solid form or supported on a carrier simplifies removal of the catalyst, which is all that is required to terminate the polymerization process. The removal may also be done by filtration. It is more preferred that the heteropoly catalyst be a heteropoly acid or mixed acid-salt supported on silica, and in particular that it be H 3 PW 12 O 40 supported on silica. An effective amount of heteropoly catalyst is that amount which is necessary to catalyze the polymerization reaction and ranges from 0.0001 to 5 weight percent of the siloxane polymer precursor. Preferably, the amount of heteropoly catalyst used is from 0.1 to 2 weight percent, and most preferably from 0.1 to 1 percent of the siloxane polymer precursor. The critical step of this method requires that there be contact between the fluid and the heteropoly catalyst. This contact is achieved, among other ways, by mixing the heteropoly catalyst with the fluid. This mixing may also be done by conventional means, including stirring. Generally, this polymerization reaction takes place at temperatures ranging from 23°C. to the boiling point of the siloxane polymer precursor. The reaction could be conducted at temperatures below 23°C. but the rate of reaction may become impractically slow. In addition, the reaction may be conducted above the boiling points of the siloxane polymer precursors if higher pressure or special apparatus could be employed to handle gaseous materials. Preferably, the polymerization reaction is conducted at temperatures ranging from 80°C. to 150°C., and more preferably from 100°C. to 150°C. Depending on a number of factors such as reaction temperature, whether the heteropoly catalyst is dried, the compatibility of the siloxane polymer precursor with the heteropoly catalyst, the solubility of the heteropoly catalyst in the fluid, the diffusion rate, the reactivity of the cyclic siloxane, i.e. whether the equilibrium constant favors the cyclic or linear siloxane and potential steric hindrance between the heteropoly catalyst and siloxane polymer precursor, the time for reaction may range from minutes to days. The specific siloxane polymers formed by our method depend on numerous factors including the siloxane polymer precursor used as a starting material, the endblocker added and the time of reaction. Other than catalyzing the polymerization, the heteropoly catalyst is unaffected and does not become a part of the siloxane polymer. The heteropoly catalyst also does not require neutralization to terminate the polymerization reaction, but rather just needs to be removed from the mixture. It also appears, depending on the reaction conditions, that the siloxane polymers produced by this method may have reduced branching, relative to that produced by using standard acids and bases. The following examples describe preferred embodiments of the claimed method. When used in the examples, "Vi" means vinyl, "Me" means methyl and "Ph" means phenyl. For expediency, a number of experiments were terminated relatively quickly and no analytical data was obtained if it did not appear that a reaction had occurred during that time. Examples 10 and 11, in particular illustrate that the artisan will need to determine the optimum conditions for each siloxane polymer precursor and each heteropoly catalyst. Factors that are considered, in addition to temperature and time that can change with each siloxane polymer precursor and each heteropoly catalyst, include the compatibility of the siloxane polymer precursor with the heteropoly catalyst, the solubility of the heteropoly catalyst in the fluid, the diffusion rate, the reactivity of the cyclic siloxane, i.e. whether the equilibrium constant favors the cyclic or linear siloxane and even steric hindrances. (A) Preparation of phosphotungstic acid (H 3 PW 12 O 40) . The phosphotungstic acid was prepared according to the method of Bailar Jr., J.C. In Inorganic Syntheses, ed. Booth, H.S., 1939 ; Vol 1, p.132. (B) Preparation of phosphotungstic acid (H 3 PW 12 O 40) supported on silica. This preparation is an adaptation of the method published by Rocchiccioli-Deltcheff et.al., J. Catal. 1990 , 126, 591. 10 g of synthetic amorphous precipitated silica [surface area, 450 m 2 /g (BET method); particle size, 4.5 mm (Coulter counter method); pH, 7] were added to a 100 ml water solution containing 2 g of dissolved H 3 PW 12 O 40 . The resulting cloudy suspension was allowed to stir at 55°C. until all the water evaporated. The white paste was dried in a vacuum oven overnight. A fluffy dried powder was obtained. The estimated loading of H 3 PW 12 O 40 was 16.7%. (C) Preparation of silicotungstic acid. The silicotungstic acid was prepared according to the method of North, E.O., In Inorganic Syntheses, ed. Booth, H.S., 1939; Vol 1, p.129. Example 1 (a) In a 250 ml flask equipped with condenser, thermometer and stirring shaft, 100 g of OH-endblocked polydimethylsiloxane (PDMS) fluid, having a degree of polymerization (DP) of approximately 14, was heated to 100°C. Then, 0.1217 g (4.2x10-5 mol) H 3 PW 12 O 40 that had been dried at 320°C. for 3 hr was added and the mixture stirred at 100°C. Half an hour after addition, the mixture became cloudy presumably due to generation of H 2 O which is not miscible with PDMS fluid. Approximately 4 hours after addition, the viscosity of the mixture had increased substantially. A portion of the mixture was withdrawn from the reaction vessel, pressure filtered through a #1 Whitman paper to remove the catalyst and characterized by 29 Si nuclear magnetic resonance (NMR) spectroscopy. The average DP was estimated from the ratio of the integrals of the resonances that correspond to the -OSi*Me 2 O-, nuclei to the resonance that corresponds to the terminal HO-Si*Me 2 O-nuclei, to be 352. The average chain length of the polymer was therefore 354. The spectrum also revealed the presence of weak resonances at -65 to -67 ppm which correspond to "T" structures (MeSiO 3/2 branching) from the cleavage of Me-Si bonds. (b) 190 g of OH-endblocked PDMS fluid having a DP of approximately 14 was heated to 82°C. in the apparatus described in Example 1(a), next 0.0292 g of H 3 PW 12 O 40 were added and the mixture stirred. The reaction was stopped after 6.5 hours since there was no obvious viscosity change of the mixture. 29 Si NMR characterization showed the presence of a few short PDMS linear segments having a DP of approximately 20 in addition to unreacted starting material. (c) 103.5 g of OH-endblocked PDMS fluid having a DP of 14 was heated to 80°C. in the apparatus described in Example 1(a). Then, 0.1011 g of H 3 PW 12 O 40 , which had not been dried before use, was added and the mixture stirred. After 3 hours, the viscosity appeared unchanged and the reaction was terminated. Example 2 100 g of trifluoropropyl(methyl) trimer (CF 3 (CH 2 ) 2 MeSiO) 3 was heated under vigorous stirring in the apparatus described in Example 1(a). When the solution temperature reached 110°C., 0.1033 g (3.6x10-5 moles) of H 3 PW 12 O 40 , that had been dried at 320°C. for 3 hours, was added and the mixture was allowed to reach 120°C. Within 40 minutes, the mixture attained a hazy appearance and increased in viscosity. The reaction was allowed to continue for a total of 5 hours. Analysis by 29 Si NMR spectroscopy showed the mixture was composed of 60% linear trifluoropropyl(methyl) polymer and 40% of starting trifluoropropyl(methyl) trimer. The average DP of the linear trifluoropropyl(methyl) polymer was estimated to be 270. The next day the polymerization reaction was reinitiated for 4 more hours giving a very viscous, creamy material. Based on 29 Si NMR analysis, the mixture was composed of 99.5% linear trifluoropropyl(methyl) siloxane with an average DP of 832. Example 3 100 g of (Me 2 SiO) 4 cyclic siloxane was heated to 120°C. in the apparatus described in Example 1(a) with stirring and then 2 g of SiO 2 -supported H 3 PW 12 O 40 , prepared as described in (B), was added and produced a fine dispersion. In a few minutes, the viscosity of the mixture increased substantially. The reaction was terminated after 20 minutes since stirring became ineffective and the polymer had the consistency of a gum. The unfiltered polymer mixture was characterized by 29 Si NMR spectroscopy to have an average DP of 4600. Analysis by gel permeation chromatography (GPC) provided a number average molecular weight (M n ) of 2.316x10 5 for the mixture. The mixture composition was estimated from the areas of the peaks to be 73% linear PDMS, 6% short chain PDMS and 21% mixed cyclic siloxanes. Example 4 (a) 101.1 g of (Me 2 SiO) 4 cyclic siloxane was heated to 120°C. in the apparatus described in Example 1(a) with stirring. Then, 0.1215 g of H 3 PMo 12 O 40 , which had been dried for 3 hours at 320°C. was added. A color change from colorless to yellow to green occurred. Dried phosphomolybdic acid is yellow. The mixture was heated under 500 rpm stirring for 2 hours and 20 minutes with no apparent change in viscosity. When stirring was stopped, the green H 3 PMo 12 O 40 quickly settled out of solution. The heating was interrupted overnight. The next day, the mixture was sonicated for a few seconds with the intent to increase the dispersion of the catalyst, but no apparent change occurred. The mixture was next heated to 140°C., within minutes its viscosity increased and a thick lime colored suspension was obtained. The reaction was interrupted 20 minutes later since it was not possible to effectively stir the mixture. Based on 29 Si NMR data, the average DP of the linear siloxane polymer in the mixture was 6800. The amount of "T" structures (MeSiO 3/2 branching) was estimated from the integral at -67 ppm to be 14%. Analysis by GPC provided a number average molecular weight (M n ) of 1.493x10 5 for the composition. The mixture composition was estimated from the areas of the peaks to be 78% linear PDMS, 3% short chain PDMS and 18% mixed cyclic siloxanes. Example 5 (a) In a 250 ml flask equipped with a mechanical stirrer, thermometer and a condenser fitted at the top, to be able to maintain a N 2 blanket, 150 g of (Me 2 SiO) 4 cyclic siloxane was heated to 120°C. Then, 0.15 g of (4.68x10 -5 moles) of Cs 2.5 H 1.5 SiW 12 O 40 , that had been dried at 320°C. for 3 hours was added and the mixture stirred for 2 hours. During the first 10 minutes, the liquid turned from whitish and slightly translucent to opaque and milky white. As no viscosity increase was noted, the temperature was raised to 140°C. within 10 minutes. The material was then heated at 140°C. for 2.5 hours. After 1 hour, the viscosity was observed to have increased moderately and continued to increase slowly during the remaining 1.5 hours. After bottling and standing overnight the material remained milky white and opaque with the catalyst unable to settle out due to the high viscosity. 29 Si NMR indicated a DP of 3300 and approximately 0.21 "T" units (MeSiO 3/2 ) per polysiloxane chain. (b) To 150 g of (Me 2 SiO) 4 cyclic siloxane heated to 120°C. in the apparatus described in Example 5(a) were added 0.15 g (3.6x10 -5 mole) of Cs 2.5 H 0.5 PW 12 O 40 , that had been dried for 3 hours at 320°C. Within 6 minutes, the material was observed to be considerably more viscous. At 14 minutes, the material was very difficult to stir and the experiment was terminated. Analysis by GPC (PDMS standard) showed a M n of 2.536X10 5 and 13.5 area percent cyclics. (c) To 150 g of (Me 2 SiO) 4 cyclic siloxane heated to 120°C. in the apparatus described in Example 5(a), was added 0.15 g (5.29x10 -5 mole) of (NH 4 ) 3 PMo 12 O 40 , that had been dried 3 hours at 200°C. Initially, the slurry was bright yellow, then slowly developed a greenish cast. An increase in viscosity was noted after 13 minutes and became extremely viscous after 46 minutes. Thereafter, the experiment was terminated. 29 Si NMR showed 24.9% (Me 2 SiO) 4 remaining with no evidence of "T" (MeSiO 3/2 ) structures. (d) To 150 g of (Me 2 SiO) 4 cyclic siloxane heated to 120°C. in the apparatus described in Example 5(a), was added 0.15 g (4.4x10 -5 mole) of Cs 4 SiW 12 O 40 that had been dried for 3 hours at 320°C. The material was heated at 120°C. for 2 hours, then 140°C. for 1 hour, next 150°C. for 1 hour and finally 160°C. for 0.5 hour. No change in viscosity was noted and the experiment was terminated. We believe the compatibility of the salt and cyclic may have been reduced which contributed to slowness in the reaction. Example 6 To a 100 ml flask, fitted as the apparatus described in Example 5(a), were added 50 g of a 50/50 mixture of (HMeSiO) 4 and (HMeSiO) 5 cyclic siloxanes. The methylhydrogen cyclics were heated to 100°C. at which time 0.1 g (3.5x10 -5 mole) of H 4 SiW 12 O 40 were added. After 25 minutes, the material became too difficult to stir terminating the experiment. 29 Si NMR showed (HMeSiO) 4 (-32 to -32.6 ppm) and (HMeSiO) 5 (-34.2 to -34.5 ppm) to be greatly reduced and the appearance of methylhydrogen linears at -34.7 ppm. Allowed to sit more than one week, the very viscous liquid was found to have turned to a very tough rubbery material. Example 7 23.94 g of (Me 2 SiO) x=4,5,6 cyclic siloxanes were mixed with 0.06 g (2.08x10 -5 mole) of H 4 SiW 12 O 40 (dried at 320°C. for 3 hours) in a vial at ambient temperature and the viscosity of the mixture was monitored over a period of several days. The vial with the mixture was infrequently agitated. 3 weeks from the beginning of the reaction, a viscous liquid was obtained that took about 15 minutes to flow upon inversion of the vial. The mixture had a viscosity of 4.5x10 6 Pa.s and a M n was estimated from GPC to be 2.2x10 5 . It contained 12.5% (Me 2 SiO) x=4,5,6 and 87.5% polydimethylsiloxane. 29 Si NMR spectrum showed no evidence of "T" structures (MeSiO 3/2 groups). Example 8 (a) A stock solution was prepared by mixing 1957.2 g, (6.6 mol) of (Me 2 SiO) 4 cyclic siloxane and 42.8 g (0.17 mol) of Me 3 SiO(Me 2 SiO)SiMe 3 having a viscosity of 1 Pa·s. Various experiments were done using flasks equipped with a magnetic stirrer, glass stirring gland sealed at the top with a rubber septum (for the removal of samples via a glass syringe and a large bore needle), a thermometer connected to a Therm-o-watch™ for temperature control and a water condenser. For each experiment, 300 g of the stock solution were added and kept under a blanket of N 2 gas and 0.1 weight percent of either H 4 SiW 12 O 40 or H 3 PW 12 O 40 was also added. The drying conditions for the catalyst and the heating temperatures were varied. The results provided in Table 1. (b) The same procedure was followed as in Example 8(a), except a comparison catalyst of trifluoromethanesulfonic acid, CF 3 SO 3 H was used, also in an amount to give 0.1 weight percent. Results are also provided in Table 1. Heteropoly Catalyst Drying conditions Temp (°C) Time (hr) viscosity (m 2 /sec) DP % cyclics H 4 SiW 12 O 40 3 hr at 320°C 80 5.2 partial gel - - H 4 SiW 12 O 40 3 hr at 320°C 100 5.5 - 124 36 H 4 SiW 12 O 40 3 hr at 320°C 120 5.5 1.82 174 8 H 4 SiW 12 O 40 3 hr at 320°C 150 36 0.36 94 34 H 3 PW 12 O 40 as made 120 5.5 0.21 55 44 H 3 PW 12 O 40 24 hr at 125°C 120 5.5 0.03 - - H 3 PW 12 O 40 3 hr at 320°C 120 5.5 2.20 177 5 FC-28 N/A 70 4.0 2.36 168 4 (c) 300 g (1.01 mole) of (Me 2 SiO) 4 cyclic siloxane and 0.3 g (1.04x10 -4 mole) of H 4 SiW 12 O 40 , that had been dried 3 hours at 320°C., were mixed in the apparatus described in Example 8(a) having the modification of the insertion of a glass pipette into a glass stirring gland. The pipette was used to estimate the increase in viscosity during the experiment, without having to withdraw samples from the solution. The material was heated to 120°C. for 1.5 hours at which time it became too viscous to stir. Example 9 (a) 300 g of a 3.5 m 2 /sec mixture of PDMS linears and cyclic siloxanes were placed in the apparatus described in Example 8(a) and kept under N 2 blanket. After heating at 150°C., 1 g (3.5x10 -4 mole) H 3 PW 12 O 40 was added and heating was maintained for 4 hours. Table 2 gives the results obtained. (b) The procedure described in Example 9(a) was used, except that 4.96 g of an acid washed montmorillonite clay were added instead of the heteropoly catalyst. This example provides the comparison data shown in Table 2. Example 10 (a) To a 3.7 ml (2 dram) vial was added less than 0.1 g (<5.3x10 -4 mole) (NH 4 ) 3 PMo 12 O 40 , that had been dried 3 hours at 200°C., and approximately 3 g of (ViMeSiO) 4 cyclic siloxane and heated for 12-15 hours at 55°C. An increase in viscosity was noted with 29 Si NMR showing 26.3% linear - (SiMeViO) n - species formed. No further increase in viscosity was noted after standing at room temperature for several days. (b) 125 g of (ViMeSiO) 4 cyclic siloxane was heated at 120°C. using the apparatus described in Example 5(a) and 2 g of silica supported H 3 PW 12 O 40 prepared as described in (B), were added. The catalyst, a puffy white material turned a light brown color when it was added and turned darker with time. The material was heated sequentially for 1 hour each at 120°C., 140°C. and 150°C. with no observed change in viscosity. The experiment was then terminated. (c) 125 g of (ViMeSiO) 4 cyclic siloxane was heated at 120°C. using the apparatus described in Example 5(a) and 0.25 g (8.69x10 -5 moles) of H 4 SiW 12 O 40 , that had been dried at 320°C. for 3 hours was added. After heating at 120°C. for 2 hours with no apparent change in viscosity, the temperature was increased to 140°C. and held for 1 hour. No increase in viscosity was noted and the experiment was terminated. Example 11 (a) 150 g of (MePhSiO) 4 cyclic siloxane was added to the apparatus described in Example 5(a), heated to 120°C. and 0.3 g (1.04X10 -4 mole) of H 4 SiW 12 O 40 , which had been dried 3 hours at 320°C. was added. The mixture was heated for almost 4 hours at 120°C. without any apparent increase in viscosity. During this time, the mixture turned from whitish hazy to faint green to green and then to very gray in color. The temperature was increased to 130°C for 0.5 hour and then 140°C. for 35 minutes. No increase in viscosity was noted and the experiment was terminated. (b) 100 g of mixed phenylmethyl cyclic siloxanes were heated to 150°C in the apparatus of Example 1(a) under stirring. To the hot liquid, 2 g of silica supported H 3 PW 12 O 40 , prepared in a manner similar to that described in (B), and having a 20% loading, were added and the mixture continued to be heated and stirred. The reaction was terminated after 6 hours and no further increase in viscosity was observed.

Claims: A method of forming siloxane polymers comprises contacting a fluid comprising at least one siloxane polymer precursor selected from cyclic siloxanes (I) having the formula (RR'SiO) a or linear siloxanes (II) having the formula where R is a substituted or unsubstituted monovalent hydrocarbon having from 1 to 6 carbon atoms, R' is hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon having from 1 to 6 carbon atoms, a is at least 3 and b is at least 1; with an effective amount of a heteropoly catalyst having a Keggin structure, selected from the group consisting of heteropoly acids (III) having the formula H n XM 12 O 40 , salts thereof and mixed acid-salts thereof, where X is B +3 , Si +4 , Ge +4 or P +5 , M is Mo +6 or W +6 and n is 3, 4 or 5, as required for the valence of the heteropoly acid to equal 0, at a temperature ranging from 23°C. to the boiling point of the siloxane polymer precursor, to form siloxane polymers. The method of claim 1 wherein the effective amount of heteropoly catalyst is from 0.0001 to 5 weight percent based on the siloxane polymer precursor. The method of claim 2 wherein the heteropoly catalyst is a heteropoly acid or a heteropoly mixed acid salt. The method of claim 3 wherein the heteropoly catalyst is dried prior to contacting the siloxane polymer precursor. The method of claim 4 wherein R is a vinyl radical, a methyl radical, a phenyl radical or a 3,3,3 trifluoropropyl radical and R' is R or hydrogen atom. The method of claim 5 wherein R is a methyl radical or a 3,3,3 trifluoropropyl radical; R' is R or hydrogen atom; a is a positive integer from 3 to 7 and b is a positive integer from 2 to 100. The method of claim 3 wherein the heteropoly catalyst is selected from H 3 PW 12 O 40 , H 3 PMo 12 O 40 , H 4 SiW 12 O 40 , H 4 SiMo 12 O 40 , (NH 4 ) 3 PMo 12 O 40 , Cs 2.5 H 1.5 SiW 12 O 40 and Cs 2.5 H 0.5 PW 12 O 40 . The method of claim 7 wherein the heteropoly catalyst is supported on a carrier with a loading of from 0.1 to 75 weight percent. The method of claim 8 wherein the heteropoly catalyst is H 3 PW 12 O 40 supported on silica at a loading of 10 to 20 weight percent. The method of claim 9 wherein a is 4, 5 or 6. The method of claim 10 wherein R and R' are each methyl radicals.

Inventors: KATSOULIS DIMITRIS ELIAS, KERYK JOHN ROBERT, KATSOULIS, DIMITRIS ELIAS, KERYK, JOHN ROBERT
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1996
Main classification: C08G77
IPC codes: C07F7, C08G77