Method of producing branched polyorganosiloxane

Abstract: A method is provided for producing a branched polyorganosiloxane to use in improving properties of silicone oil fluid. The method eliminates the occurrence of by-products, such as hydrochloric acid, which easily decompose the branched polyorganosiloxane. This method of producing a branched polyorganosiloxane involves reacting a compound which has at least three silanol groups per molecule and which is soluble in an organic solvent with a linear polydiorganosiloxane having a polymerization degree of at least three and having only one chain end terminated with a group containing a nitrogen atom which is bonded to a silicon atom.

Description: As reported in the J. Am. Chem. Soc. No. 112, page 7077 (1990), a branched polyorganosiloxane was prepared by use of a reaction between silanol groups and silicon-bonded chlorine atoms. However, hydrochloric acid is produced and tends to decompose the resulting branched polyorganosiloxane. To make matters worse, hydrochloric acid is a strong acid and difficult to work with or remove. The use of branched polyorganosiloxanes to improve the fluid properties of silicone oils is desired by the industrial world. This invention is intended to eliminate by-product hydrochloric acid that easily decomposes branched polyorganosiloxanes during their manufacture. This invention is the result of the inventors' investigations into possible solutions for the problems outlined above. The major characteristic of this invention is the method of producing a branched polyorganosiloxane that involves reacting a compound which has at least three silanol groups per molecule and which is soluble in an organic solvent with a linear polydiorganosiloxane having a polymerization degree of at least three and having only one chain end terminated with a group containing a nitrogen atom which is bonded to a silicon atom. The branched polyorganosiloxane produced by the method of this invention is easily dispersed in silicone oil. When this branched polyorganosiloxane is mixed with the oil, the effects of good dispersion of branched polyorganosiloxane in silicone oil is achieved only when the branched polyorganosiloxane is soluble in an organic solvent. Thus, it is necessary that one of the raw materials, the compound which has at least three silanol groups per molecule, is soluble in organic solvents. When this condition is satisfied, the branched polyorganosiloxane produced in this invention can also be used as an additive in silicone rubbers. One of the starting compounds employed in this invention is a compound which has at least three silanol (SiOH) groups per molecule, and there are no limitations on the structure of the compound as long as it contains three or more silanol groups available for reactions. Silicone resins generally have three or more silanol groups per molecule and are commercially available. A silicone resin is a compound having at least one unit chosen from triorganosiloxane (R 1 3 SiO 1/2 unit), diorganosiloxane (R 2 2 SiO unit), monoorganosiloxane (R 3 SiO 3/2 unit), and silicate (SiO 4/2 unit) units. An ordinary silicone resin contains uncondensed silanol groups in its molecules. (See Ito, Kunio, ed, Silicon Handbook, (Nikkan Kogyo Shinbunsha, August, 1990). For the silicone resins desired for this invention, the radical represented by R 1 , R 2 and R 3 in the formulas above is a hydrogen atom, alkyl group, aryl group, alkenyl group, or halogenated alkyl group. Among the groups that fit this description, the easiest to acquire industrially are hydrogen atoms, methyl groups, ethyl groups, propyl groups, phenyl groups, vinyl groups, allyl groups, hexenyl groups, chloromethyl groups, chloropropyl groups, and trifluoropropyl groups. Examples of compounds other than silicone resins that have three or more silanol groups per molecule include organosilane triol, poly(hydroxydiorganosilyl)benzene, poly(hydroxydiorganosilyl)alkane, and poly(hydroxydiorganosilyl)alkene. Another ingredient of our branched polyorganosiloxane, and one that is also characteristic of the method of this invention, is a linear polydiorganosiloxane having a polymerization degree of at least three and having only one chain end terminated with a group containing a nitrogen atom which is bonded to a silicon atom. Examples of the group containing a nitrogen atom which is bonded to silicon include substituted and nonsubstituted amino groups such as alkylamino groups, dialkylamino groups, alkenylamino groups, dialkenylamino groups, and anilino groups; substituted and nonsubsituted amido groups, e.g. N-alkylacetamido groups, propionamido groups, and N-alkyl propionamido groups; substituted and nonsubstituted imido groups, e.g. phthalimido groups, succinimido groups, isocyano groups, thioisocyano groups, piperidino groups, morpholino groups, and N-imidazolinyl groups. For efficient production of branched polyorganosiloxane, it is desirable that the reactivity of the groups containing nitrogen atoms with silanol groups is very high. However, hydrolysis ordinarily occurs easily with such highly reactive groups, and handling in the atmosphere can also present problems. Thus desirable groups with appropriate reactivities are dimethylamino groups, diethylamino groups, di(iso)propylamino groups, and (N-methyl)acetamido groups. Also, considering the ease of removing compounds that arise from a reaction with a silanol group, it is better if the molecular weight of these groups is relatively low. It is necessary for the groups containing nitrogen atoms which bond to silicon atoms to be bonded to only one chain end of the linear polydiorganosiloxane. When the groups are bonded at two ends or at a side chain, there is a strong likelihood that gelling will occur when the linear polydiorganosiloxane is reacted with a compound containing at least three silanol units per molecule. The polymerization degree of these linear polydiorganosiloxanes is three or more, because otherwise the effect of branching would be diminished. There is no upper limit on the degree of polymerization, but 1,000 is preferred from the point of view of reaction properties and operations. The most preferred range lies between 3 and 500. The examples of organic groups shown above for R 1 , R 2 and R 3 are examples of the organic groups bonded to the silicon atoms of the linear polydiorganosiloxane. From the economical point of view, the most preferred organic groups are methyl groups. Examples of the group that terminates the chain end of the linear polydiorganosiloxane that is opposite the chain end terminated with a group containing a nitrogen atom include triorganosilyl groups. Examples of the organic groups of the triorganosilyl groups include the same examples of organic groups shown above for R 1 , R 2 and R 3 . There are no special limitations on the production methods for the linear polydiorganosiloxane having a polymerization degree of at least three and having only one chain end terminated with a group containing a nitrogen atom which is bonded to a silicon atom. For instance, polydiorganosiloxanes that have a chlorine atom bonded to the silicon atom at the one unterminated end of the molecule can be reacted with amine or amide compounds in the presence of a hydrogen chloride scavenger. One method of producing the polydiorganosiloxanes that have a chlorine atom bonded to the silicon atom at the one unterminated end of the molecule is described in "Preparation of Poly(dimethylsiloxane) Macromonomers by the 'Initiator Method'", by T. Suzuki, Polymer, Volume 30, (1989), page 333-337. There are no special limitations on conditions for the method of producing the branched polyorganosiloxane of this invention. The reaction between the compound which has at least three silanol groups per molecule and which is soluble in an organic solvent and the linear polydiorganosiloxane, having a polymerization degree of at least three and having only one chain end terminated with a group containing a nitrogen atom which is bonded to a silicon atom, may be done at room temperature, in a cool environment, or in a heated environment. Pressure conditions for the reaction may be normal, low, or high. The reaction temperature ordinarily can be carried out in the range of -80°C to 200°C. The preferred range is -25°C to 150°C. The branched polyorganosiloxane of this invention can be prepared out in the appropriate solvent or without a solvent. There are no particular limitations when the solvent used is one that does not adversely affect the reaction and one in which the raw materials and polymers are soluble. Examples of acceptable solvents include aliphatic hydrocarbons, e.g. pentane, hexane, heptane, octane; aromatic hydrocarbons, e.g. benzene, toluene, and xylene; diethyl ether, dibutyl ether, diphenyl ether, dioxane, tetrahydrofuran, and other ether solvents; ethyl acetate, butyl acetate, and other ester solvents; acetone, methylethyl ketone, methylbutyl ketone, and other ketone solvents; carbon tetrachloride, chloroform, trichloroethane, trichloroethylene, tetrachloroethylene, and other halogenated solvents; dimethyl formamide; dimethylsulfoxide; and phosphorus hexamethyltriamide. Since the reaction that produces the branched polyorganosiloxane of this invention is a condensation reaction between the silanol groups of the compound having at least three silanol groups per molecule and the group containing a nitrogen atom which is bonded to a silicon atom at only one chain end of the linear polydiorganosiloxane, by-products of the reaction include amines, amides, imides, and related compounds. These nitrogen-containing reaction by-products differ from the hydrochloric acid by-product of the prior art. Under normal conditions the polyorganosiloxane chain is not cleaved on contact with these nitrogen-containing reaction by-products, thus avoiding damage to the branched polyorganosiloxanes due to by-products. The circumstances are particularly favorable if raw materials that produce amides or imides are chosen. Amides and imides are neutral, which makes the probability of damaging side reactions extremely low. The method of this invention provides a way of producing a branched polyorganosiloxane that allows the branched polyorganosiloxane to be dissolved in an organic solvent without being damaged by by-products of the reaction. The branched polyorganosiloxane produced through the method of this invention can be used as a constituent of silicone rubber or as an additive to improve the fluid characteristics of silicone oil. In the examples below the molecular weights were determined by gel permeation chromatography (GPC), using standard polydimethylsiloxane samples as references. 29 SiNMR denotes the silicon 29 nuclear magnetic resonance spectroscopy (with tetramethylsilane as the standard). The abbreviation Me stands for a methyl group, and Et for an ethyl group. Example 1. One hundred mL of tetrahydrofuran, and 4.0g of a silicone resin made of a unit of Me 2 HSiO 1/2 , a unit of Me 2 (HO)SiO 1/2 , and a unit of SiO 4/2 (the molar ratio was 2:8:10, the weight average molecular weight was 1800) were placed in a flask and agitated. Then, 58g of polydimethylsiloxane which had a diethylamino group at the one chain end and a vinyl group at the other, described by formula Et 2 N-(Me 2 SiO) p -SiMe 2 C=CH 2 , were added. This was agitated for two hours in a nitrogen atmosphere at room temperature. Low-pressure distillation was used to eliminate the solvent and by-product diethylamine, yielding a transparent, sticky fluid. The weight average molecular weight of the product was 30100. The 29 SiNMR analysis established the peaks of a dimethylvinylsilyl group (approximately -4.0 ppm), dimethylsiloxane unit (approximately -21.8 ppm), Me 2 HSiO 1/2 unit (approximately -7.0 ppm), and SiO 4/2 unit (approximately -110 ppm), but the peaks for silanol (approximately -12.2 ppm) and diethylaminosilyl (approximately -4.2 ppm) were not detected. The result showed that the reaction of the diethylamino groups on the one chain end of the polydimethylsiloxanes with the silanol groups in the silicone resin was complete and a branched (star) polyorganosiloxane was formed having the silicone resin as the core. Example 2. 30 mL of tetrahydrofuran and 14 grams of a silicone resin made of a unit of Me 3 SiO 1/2 , and a unit of SiO 4/2 (the molar ratio of the respective units was 7:10, the weight average molecular weight was 2500), and the percentage by weight of the silanol, which had not been subjected to condensation and which was bonded to the SiO 4/2 , was 2.4%) were placed in a flask and agitated. Then, 3.7 grams of a siloxane that had an N-methylacetamido group at one end as indicated by the formula MeCON(Me)-(Me 2 SiO) 3 -SiMe 2 CH=CH 2 was added. The mixture was agitated for two hours in a nitrogen atmosphere at room temperature. The product was precipitated in methanol, washed with methanol, and finally the solvent was removed by vacuum distillation. A colorless solid was obtained as a result. The weight average molecular weight of the product was 4200. The 29 SiNMR analysis established the peaks of the dimethylvinylsilyl group (approximately - 4.2 ppm), dimethylsiloxane unit (approximately -21.0 ppm), and SiO 4/2 unit (approximately - 110 ppm), but the peak for the N-methylacetamidosilyl group (approximately -7.2 ppm) was not detected. This result showed that the reaction of the N-methylacetamidosilyl groups on one end of the polydimethylsiloxane with the silanol groups in the silicone resin was complete and a branched (star) polyorganosiloxane was formed containing the silicone resin as the core.

Claims: A method of making a branched polyorganosiloxane comprising: reacting a compound which has at least three silanol groups per molecule and which is soluble in an organic solvent with a linear polydiorganosiloxane having a polymerization degree of at least three and having only one chain end terminated with a group containing a nitrogen atom which is bonded to a silicon atom. A method according to claim 1, wherein the compound with at least three silanol groups per molecule is a silicone resin having at least one unit selected from R 1 3 SiO 1/2 , R 2 2 SiO, R 3 SiO 3/2 and SiO 4/2 , where each R 1 , R 2 and R 3 is independently selected from hydrogen atom, alkyl, aryl, alkenyl, and halogenated alkyl. A method according to claim 2, wherein each R 1 , R 2 , and R 3 is independently selected from hydrogen atom, methyl, ethyl, propyl, phenyl, vinyl, allyl, hexenyl, chloromethyl, chloropropyl and trifluoropropyl. A method according to claim 2, wherein the compound with at least three silanol groups per molecule is selected from organosilane triol, poly(hydroxydiorganosilyl)benzene, poly(hydroxydiorganosilyl)alkane, and poly(hydroxydiorganosilyl)alkene. A method according to claim 1, wherein the linear polydiorganosiloxane has one chain end terminated with a group containing a nitrogen atom which group is selected from alkylamino, dialkylamino, alkenylamino, dialkenylamino, anilino, N-alkylacetamido, propionamido, N-alkylpropionamido, phthalimido, succinimido, isocyano, thioisocyano, piperidino, morpholino, and N-imidazolinyl. A method according to claim 1, wherein the degree of polymerization of the linear polydiorganosiloxane is in a range of three to 1,000; organic groups bonded to silicon atoms of the linear polydiorganosiloxane are independently selected from alkyl, aryl, alkenyl, and halogenated alkyl; and the chain end of the linear polydiorganosiloxane opposite the end terminated with a group containing a nitrogen atom is terminated with a triorganosilyl group. A method according to claim 6, wherein the degree of polymerization of the linear polydiorganosiloxane is in a range of three to 500; organic groups bonded to silicon atoms of the linear polydiorganosiloxane are independently selected from methyl, ethyl, propyl, phenyl, vinyl, allyl, hexenyl, chloromethyl, chloropropyl and trifluoropropyl; and the triorganosilyl group is selected from dimethylvinylsilyl and trimethylsilyl. A method according to claim 7, wherein the organic groups of the linear polydiorganosiloxane are independently selected from methyl and 3,3,3-trifluoropropyl. A method according to claim 1, wherein the compound which has at least three silanol groups per molecule and which is soluble in an organic solvent is a silicone resin having at least one unit selected from a group consisting of R 1 3 SiO 1/2 , R 2 2 SiO, R 3 SiO 3/2 and SiO 4/2 , where R 1 , R 2 and R 3 are independently selected alkyl, aryl, alkenyl, and halogenated alkyl; the degree of polymerization of the linear polydiorganosiloxane is in a range of three to 1,000; organic groups bonded to silicon atoms of the linear polydiorganosiloxane are independently selected from alkyl, aryl, alkenyl, and halogenated alkyl; the chain end of the linear polydiorganosiloxane opposite the end terminated with a group containing a nitrogen atom is terminated with a triorganosilyl group; and the group containing a nitrogen atom is selected from alkylamino, dialkyl-amino, alkenylamino, dialkenylamino, anilino, N-alkylacetamido, propionamido, N-alkylpropionamido, phthalimido, succinimido, isocyano, thioisocyano, piperidino, morpholino, and N-imidazolinyl.

Inventors: OGAWA TAKUYA, SUZUKI TOSHIO, OGAWA, TAKUYA, SUZUKI, TOSHIO, OGAWA, TAKUYA C/O DOW DORNING ASIA, LTD., SUZUKI, TOSHIO C/O DOW CORNING ASIA, LTD.
Applicants: DOW CORNING ASIA LTD, DOW CORNING ASIA, LTD.
Application year: 1993
Main classification: C08G77
IPC codes: C07F7, C08G77, C08G81