Method for preparation of methacryloxypropyldimethylchlorosilane

Abstract: The instant invention pertains to a method for the preparation of methacryloxypropyldimethylchlorosilane that is very efficient, yields a very pure product and produces minimal alpha-methylpropionyloxypropyldimethylchlorosilane impurity. It comprises the addition reaction between allyl methacrylate and dimethylchlorosilane in the presence of hydrosilylation catalyst, wherein the water content of the allyl methacrylate does not exceed 200 ppm.

Description: Methacryloxypropyl-functional organosilicon compounds readily copolymerize with radically polymerizing monomers such as methyl methacrylate and styrene. For this reason they are often used as starting materials for copolymers and as modifiers for polymers prepared from polymerizing monomers. Among the methacryloxypropyl-functional organosilicon compounds, methacryloxypropyldimethylchlorosilane is typically employed as an endblocker or terminating agent for methacryloxy-functional silicone macromonomers. Methacryloxypropyldimethylchlorosilane is generally prepared by an addition reaction between allyl methacrylate and dimethylchlorosilane followed by isolation by distillative purification of the reaction product (see Polymer , Volume 26, page 437, 1985). One drawback generally associated with this method is the pronounced tendency for gelation to occur during the reaction and distillative purification. Another drawback has appeared when the methacryloxypropyldimethylchlorosilane product is used as an endblocker for methacryloxy-functional silicone macromonomers. This drawback is the frequent occurrence of low copolymerization conversions with radically polymerizing vinylic organic compounds. EP-A-0 323 436discloses a method for making an acryl-functional halosilane having the general formula comprising reacting an unsaturated organic compound having the formula A-R'CH=CH 2 with a halosilane having the formula in which A is a group selected from acryloxy or methacryloxy radicals, R' is selected from a divalent hydrocarbon radical having 1 to 11 carbon atoms, an aryl group or an aryl-containing alkylene group, R is selected from alkyl radicals having 1-6 carbon atoms or the phenyl radical, X is selected from chlorine or bromine radicals and p is 0, 1 or 2, in the presence of a platinum hydrosilation catalyst and a stabilizing amount of phenothiazine, wherein the reaction mixture is contacted with a gas composition comprising at least 0.1 percent by volume of oxygen. We have now found that alpha-methylpropionyloxypropyl-dimethylchlorosilane is produced as an impurity in the manufacture of methacryloxypropyldimethylchlorosilane, and that this impurity causes the reduced copolymerization conversions with radically polymerizing vinylic organic compounds. We have also found that the production of the alpha-methylpropionyloxypropyl-dimethylchlorosilane impurity is substantially reduced by minimizing the water content in the starting allyl methacrylate to the maximum extent possible. Therefore, it is an object of the instant invention to provide a method for the preparation of methacryloxypropyldimethylchlorosilane that is very efficient, yields a very pure product, and produces minimal alpha-methylpropionyloxypropyldimethylchlorosilane impurity. This invention introduces a method for the preparation of methacryloxypropyldimethylchlorosilane that achieves this objective. Our method comprises reacting an allyl methacrylate containing less than 200 ppm water and a dimethylchlorosilane in the presence of hydrosilylation catalyst. The invention provides a method for the preparation of methacryloxypropyldimethylchlorosilane by an addition reaction between allyl methacrylate and dimethylchlorosilane in the presence of hydrosilylation catalyst and a polymerization inhibitor specified below, wherein the water content of the allyl methacrylate does not exceed 200 ppm. The water content in the allyl methacrylate of the instant invention must not exceed 200 ppm, and preferably does not exceed 180 ppm. Allyl methacrylate, containing less than 200 ppm water, is generally prepared by subjecting a commercial allyl methacrylate to a dehydration treatment. Any dehydration treatment may be used for this purpose as long as the allyl methacrylate is not reacted or modified by the treatment, and the treatment has no adverse effects on the ensuing addition reaction. The following dehydration methods are preferred for their simplicity and economics: (i) azeotropic dehydration by heating with a water-immiscible organic solvent, or (ii) use of a dehydrating agent such as molecular sieve, sodium sulfate, and others. These methods will reduce the water content in allyl methacrylate to 200 ppm or less. For azeotropic dehydration, the water-immiscible organic solvent is preferably n-hexane, n-heptane, and cyclohexane. These solvents are preferred for several reasons. First, they lack functional groups they will affect the ensuing addition reaction. Second, they have optimal boiling points which suppress methacryloxypropyl group polymerization during the azeotropic dehydration, while also making possible a satisfactory reaction rate in the ensuing addition reaction. The water content in allyl methacrylate is measured for our purposes by the Karl Fischer™ method, which is a well-known method for determining the water content of organic compounds. This method uses the Karl Fischer™ reagent as an analytical reagent for the determination of water. In the instant invention, the allyl methacrylate to dimethylchlorosilane mixing ratio is not crucial. However, it is preferred to use larger allyl methacrylate to dimethylchlorosilane molar ratios since this produces less alpha-methylpropionyloxypropyldimethyl-chlorosilane impurity. As a result, allyl methacrylate to dimethylchlorosilane molar ratios of 1:1 to 3:1 are preferred, while the range of 1.1:1.0 to 2.0:1.0 is particularly preferred based on economic efficiency. Transition metal catalysts from Group VIII of the Periodic Table are preferred for use as the hydrosilylation catalyst in our method. Among these, the platinum-based catalysts are the most preferred. The platinum-based catalysts are exemplified by alcohol solutions of chloroplatinic acid, platinum-olefin complexes, and complexes between chloroplatinic acid and vinyl-containing siloxanes. The catalyst is added in an amount that induces development of the addition reaction, and as a general rule is used at 0.01 to 100 ppm based on the total weight of the allyl methacrylate and dimethylchlorosilane. There is added a polymerization inhibitor to this reaction system to inhibit the methacryloxypropyl group polymerization that occurs as a secondary reaction during the addition reaction between the allyl methacrylate and the dimethylchlorosilane. This inhibitor is selected from phenothiazine, hindered phenol compounds, amine compounds, beta-diketone compounds and quinone compounds. The quantity of polymerization inhibitor are not crucial as long as its addition does not hinder development of the addition reaction and does inhibit methacryloxypropyl group polymerization. A beta-diketone compound, for example, acetylacetone, benzoylacetone, and dibenzoylmethane, may be added as taught in JP-A 5-301881. The method of the instant invention may be run under solventless conditions or may be run in the presence of a solvent. Useful solvents are aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; ethers such as tetrahydrofuran, or diethyl ether; ketones such as acetone and methyl ethyl ketone; or esters such as ethyl acetate and butyl acetate. This solvent may be the same as, or may differ from, the organic solvent used during azeotropic dehydration of the allyl methacrylate. The method of our invention may be run at room temperature, but it is preferably run with heating to obtain good reaction rates. The general range for the reaction temperature is 30 to 100°C, while the preferred range is 40 to 80°C. The methacryloxypropyldimethylchlorosilane produced by the addition reaction is preferably isolated by distillation of the addition reaction product. A polymerization inhibitor, as described above, may be added to the reaction system to inhibit the methacryloxypropyl group polymerization that occurs as a secondary reaction during this distillative purification phase. A metal halide may be added to this distillation to serve as a gelation inhibitor as described in U.S. Patent 5,262,555 which broadly teaches the preparation and use of these inhibitors. The metal halide is exemplified by the chlorides, bromides, and iodides of chromium, cobalt, nickel, germanium, zinc, tin, mercury, copper, iron, palladium, tungsten, silver, vanadium, molybdenum, ruthenium, platinum, antimony, bismuth, selenium, and tellurium. The distillation may be conducted according to well-known distillation methodologies, and distillation under reduced pressures will typically be employed. The methacryloxypropyldimethylchlorosilane yielded by the method of our invention is characterized by an extremely low content of alpha-methylpropionyloxypropyldimethylchlorosilane impurity. This methacryloxypropyldimethylchlorosilane is useful, for example, as an endblocker or terminating agent in the preparation of methacryloxy-functional silicone macromonomers. In the following examples "%" refers to "weight%". The water content in the allyl methacrylate was measured by the Karl Fischer™ volumetric titration method in accordance with JIS K 0068. In this titration method, the titration solvent was placed in a titration receptacle and rendered anhydrous by dripping in Karl Fischer™ reagent, and the allyl methacrylate was then added with dissolution. This was followed by titration with Karl Fischer™ reagent, and the water content was determined from titrant addition. Example 1 A commercial allyl methacrylate was obtained and the water content was measured at 2,194 ppm. 100 parts of this allyl methacrylate were allowed to stand for 24 hours at room temperature over 5 parts of molecular sieve (Molecular Sieve 4A from Wako Junyaku Kabushiki Kaisha) as dehydrating agent. The water content of the resulting allyl methacrylate was measured at 171 ppm. While operating in a nitrogen atmosphere, chloroplatinic acid/1,3-divinyltetramethyldisiloxane complex was mixed into a mixture of 44.1 g (349.2 mmol) of the dried allyl methyacrylate and 0.3 g phenothiazine in a sufficient quantity to provide 20 ppm platinum metal based on the weight of the allyl methacrylate. The resulting mixture was heated to 70°C while stirring and a small amount of dimethylchlorosilane was added dropwise. After confirmation of the initiation of an addition reaction, a reaction was run by adding 30 g (317.5 mmol) dimethylchlorosilane dropwise while maintaining the temperature at 60°C to 75°C by adjusting the water or air cooling, and by stirring for an additional 30 minutes. After first distilling the low boilers from the reaction product under reduced pressure at room temperature, a fraction at 91°C to 96°C was obtained by distillation at 133.3 Pa (1 mm Hg). The results of various analyses confirmed this fraction to be methacryloxypropyldimethylchlorosilane. Analysis of this fraction by capillary gas chromatography (detector: FID, hereinafter abbreviated as capillary GC) and gas chromatography/mass spectroscopy (hereinafter abbreviated as GC/MS) confirmed that it contained 0.49% alpha-methylpropionyloxypropyldimethylchlorosilane as impurity. Example 2 A commercial allyl methacrylate was obtained and its water content was measured at 2,194 ppm. 100 parts of this allyl methacrylate were allowed to stand for 24 hours at room temperature over 5 parts of molecular sieve (Molecular Sieve 4A) as dehydrating agent. The water content of the resulting allyl methacrylate was measured at 171 ppm. While operating in a nitrogen atmosphere, chloroplatinic acid/1,3-divinyltetramethyldisiloxane complex was mixed into a mixture of 60.2 g (476.3 mmol) of the dried allyl methacrylate and 0.3 g phenothiazine in a sufficient quantity to provide 20 ppm platinum metal based on the weight of the allyl methacrylate. The resulting mixture was heated to 70°C while stirring and a small amount of dimethylchlorosilane was added dropwise. After confirmation of the initiation of an addition reaction, a reaction was run by adding 30 g (317.5 mmol) dimethylchlorosilane dropwise while maintaining the temperature at 60°C to 75°C by adjusting the water or air cooling, and by stirring for an additional 30 minutes. After first distilling the low boilers from the reaction product under reduced pressure at room temperature, a fraction at 91°C to 96°C was obtained by distillation at 133.3 Pa (1 mm Hg). The results of various analyses confirmed this fraction to be methacryloxypropyldimethylchlorosilane. Analysis of this fraction by capillary GC and GC/MS confirmed that it contained 0.27% alpha-methylpropionyloxypropyldimethylchlorosilane as impurity. Comparative Example 1 An addition reaction was run as in Example 1, but in this case using commercially available undehydrated allyl methacrylate (water content = 2,194 ppm). A fraction was again obtained by distillative purification of the reaction product as in Example 1. The results of various analyses confirmed this fraction to be methacryloxypropyldimethylchlorosilane. Analysis of this fraction by capillary GC and GC/MS confirmed that it contained 1.2% alpha-methylpropionyloxypropyldimethylchlorosilane as impurity. Example 3 A commercial allyl methacrylate was obtained and its water content was measured at 2,194 ppm. While operating under a nitrogen blanket, 44.1 g (349.2 mmol) allyl methacrylate, 20 g n-hexane, and 0.3 g phenothiazine were mixed, and this mixture was subjected to an azeotropic dehydration by heating under reflux for 1 hour. The water content of the resulting mixture was measured at 150 ppm. Sufficient platinum/1,3-divinyltetramethyldisiloxane complex to provide 20 ppm platinum metal based on the weight of the allyl methacrylate was blended into the dried mixture. The resulting mixture was heated to 70°C while stirring and a small amount of dimethylchlorosilane was added dropwise. After confirmation of the initiation of an addition reaction, a reaction was run by adding 30 g (317.5 mmol) dimethylchlorosilane dropwise while maintaining the temperature at 60°C to 75°C, by adjusting the water or air cooling, and by stirring for 30 minutes more. After first distilling the low boilers from the reaction product under reduced pressure at room temperature, a fraction at 91°C to 96°C was obtained by distillation at 133.3 Pa (1 mm Hg). The results of various analyses confirmed this fraction to be methacryloxypropyldimethylchlorosilane. Analysis of this fraction by capillary GC and GC/MS confirmed that it contained 0.33% alpha-methylpropionyloxypropyldimethylchlorosilane as impurity. Example 4 A commercial allyl methacrylate was obtained and its water content was measured at 2,194 ppm. While operating under a nitrogen blanket, 60.2 g (476.3 mmol) allyl methacrylate, 20 g n-hexane, and 0.3 g phenothiazine were mixed, and this mixture was subjected to an azeotropic dehydration by heating under reflux for 1 hour. The water content of the resulting mixture was measured at 150 ppm. Sufficient platinum/1,3-divinyltetramethyldisiloxane complex to provide 20 ppm platinum metal based on the weight of the allyl methacrylate was blended into the dried mixture. The resulting mixture was heated to 70°C while stirring and a small amount of dimethylchlorosilane was added dropwise. After confirmation of the initiation of an addition reaction, a reaction was run by adding 30 g (317.5 mmol) dimethylchlorosilane dropwise while maintaining the temperature at 60°C to 75°C, by adjusting the water or air cooling, and stirring for 30 minutes more. After first distilling the low boilers from the reaction product under reduced pressure at room temperature, a fraction at 91°C to 96°C was obtained by distillation at 133.3 Pa (1 mm Hg). The results of various analyses confirmed this fraction to be methacryloxypropyldimethylchlorosilane. Analysis of this fraction by capillary GC and GC/MS confirmed that it contained 0.30% alpha-methylpropionyloxypropyldimethylchlorosilane as impurity. Example 5 A commercial allyl methacrylate was obtained and its water content was measured at 2,194 ppm. While operating under a nitrogen blanket, 1,375.0 g (10,869.6 mmol) allyl methacrylate, 618 g n-hexane, and 8.2 g phenothiazine were mixed, and this mixture was subjected to an azeotropic dehydration by heating under reflux for 1 hour. The water content of the resulting mixture was measured at 150 ppm. Sufficient platinum/1,3-divinyltetramethyldisiloxane complex to provide 20 ppm platinum metal based on the weight of the allyl methacrylate was blended into the dried mixture. The resulting mixture was heated to 70°C while stirring and a small amount of dimethylchlorosilane was added dropwise. After confirmation of the initiation of an addition reaction, a reaction was run by adding 646.5 g (6,841.3 mmol) dimethylchlorosilane dropwise while maintaining the temperature at 60°C to 75°C by adjusting the water or air cooling, and by stirring for an additional 30 minutes. After first distilling the low boilers from the reaction product under reduced pressure at room temperature, a fraction at 91°C to 96°C was obtained by distillation at 133.3 Pa (1 mm Hg). The results of various analyses confirmed this fraction to be methacryloxypropyldimethylchlorosilane. Analysis of this fraction by capillary GC and GC/MS confirmed that it contained 0.36% alpha-methylpropionyloxypropyldimethylchlorosilane as impurity. Comparative Example 2 An addition reaction was run as in Example 5, but in this case using the commercially available undehydrated allyl methacrylate (water content = 2,194 ppm) in place of the mixture (water content = 150 ppm) of allyl methacrylate, n-hexane, and phenothiazine. At the point at which approximately one-half of the dimethylchlorosilane had been added dropwise, we found that the reaction mixture thickened; lost its fluidity; and finally gelled. The method according to the instant invention comprises the use of allyl methacrylate containing less than 200 ppm water in the preparation of methacryloxypropyldimethylchlorosilane by an addition reaction between allyl methacrylate and dimethylchlorosilane in the presence of a hydrosilylation catalyst. As a result, our method produces minimal alpha-methylpropionyloxypropyldimethylchloro-silane impurity and is able to efficiently produce a very pure methacryloxypropyldimethylchlorosilane. The method of our invention also exhibits a secondary stabilizing effect in that methacryloxypropyl group polymerization is inhibited even when the reaction and distillative purification are run using conditions under which the methacryloxypropyl group polymerization would normally occur and the system would ultimately gel.

Claims: A method for the preparation of methacryloxypropyldimethylchlorosilane wherein said method comprises an addition reaction between allyl methacrylate and dimethylchlorosilane in the presence of hydrosilylation catalyst, characterized in that in said reaction polymerization is inhibited by phenothiazine, hindered phenol compounds, amine compounds, beta-diketone compounds, and quinone compounds and, the water content of said allyl methacrylate is less than 200 ppm. A method as claimed in claim 1 wherein the allyl methacrylate and dimethylchlorosilane are reacted at a mole ratio of 1:1 to 3:1. A method as claimed in claim 1 wherein the hydrosilylation catalyst is transition metal catalyst selected from Group VIII of the Periodic Table. A method as claimed in claim 3 wherein the hydrosilylation catalyst is a platinum-based catalyst. A method as claimed in claim 4 wherein the hydrosilylation catalyst is a platinum/1,3-divinyltetramethyldisiloxane complex. A method as claimed in claim 1 wherein there is additionally present during the addition reaction a solvent selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, ethers, ketones, and esters. A method as claimed in claim 1 wherein the addition reaction is carried out at a temperature of 30°C to 100°C. The method of claim 1 further comprising the step of recovering the methacryloxypropyldimethylchlorosilane by distillation of the addition reaction product in the presence of polymerization inhibitor which is a metal halide.

Inventors: OKAWA TADASHI, YAMADA SHUJI, OKAWA, TADASHI, YAMADA, SHUJI, OKAWA, TADASHI, DOW CORNING TORAY SILICONE, YAMADA, SHUJI, DOW CORNING TORAY SILICONE
Applicants: DOW CORNING TORAY SILICONE, DOW CORNING TORAY SILICONE COMPANY, LIMITED
Application year: 1995
Main classification: C07F7
IPC codes: C07B61, B01J31, C07F7