Alkoxy-functional organopolysiloxanes and processes for preparing them

Abstract: Alkoxy-functional organopolysiloxanes can be prepared in high yields by reacting a hydroxyl-containing organic silicon compound with an α-alkoxysilyl ester in the absence of a catalyst. The alkoxy-functional organopoly-siloxanes are useful modifiers and surface treating agents a well as raw materials for silicone resins and rubbers.

Description: This invention relates to a novel process for preparing alkoxy-functional organopolysiloxanes. Alkoxy - functional organopolysiloxanes having an alkoxysilyl group are useful modifiers and surface treating agents for inorganic and organic materials as well as useful raw materials for preparing silicone resins and rubbers of the dealcoholysis curing type. In the past, such alkoxy - functional organopoly - siloxanes having an alkoxysilyl group were prepared by effecting condensation reaction between an organosilane having a silanol group or an organosiloxane terminated with a silanol group and an alkoxysilane, in the presence or absence of a catalyst such as an amine, carboxylic acid, or carboxylates of zinc, tin, iron or similar metal. This process suffered from a problem of low reaction yield in that reaction did not proceed well in the absence of a catalyst, while in the presence of a catalyst much by-product was formed particularly when the reactant has two or more alkoxy groups per molecule. With the catalyst present, there arose another problem namely that removal of the catalyst (amines, carboxylic acids, metal carboxylates and the like) from the reaction product was difficult so that the recovered product contained a substantial proportion of the catalyst as an impurity. For example EP-A-354 138 (equivalent to US-A-5055502) discloses the production of linear diorganopolysiloxanes having at least two terminal alkoxy groups, using a zinc complex such as zinc bisacetylacetonate to catalyse reactions between a hydroxyl-terminated diorganopolysiloxane and a polyalkoxysilane. Another known process for preparing organopolysiloxanes having an alkoxysilyl group is by reacting chlorosilane and an organic silicon compound having a silanol group in the presence of a hydrogen halide acceptor such as an amine (see JP-A-247756/1986). This process forms a hydrogen halide acceptor salt which is difficult to remove by stripping or other fractionating means even when it has a low molecular weight, and almost impossible to remove if it has a high molecular weight. The problem addressed herein is to provide new processes for preparing an alkoxy-functional organopolysiloxane having an alkoxysilyl group, preferably in high yields without inviting the problems of residual catalyst and by-products. The inventor has found that an α -alkoxysilyl ester compound of the general formula (A): wherein R 1 , R 4 , and R 5 are independently selected from substituted and unsubstituted monovalent hydrocarbon groups free of aliphatic unsaturation, R 2 is substituted or unsubstituted monovalent hydrocarbon group, R 3 is hydrogen atom or methyl group, and n is 1, 2 or 3, is effective in reacting with an equimolar amount of a silanol group in a catalyst-free system to form an alkoxysilyl group. Therefore, the present invention provides a process for preparing an alkoxy - functional organopolysiloxane by reacting a hydroxyl-containing organic silicon compound with an at least equimolar amount per mol of the hydroxyl group of said compound of an organic silicon compound of formula (A). The first reactant used in the process of the present invention is a hydroxyl - containing organic silicon compound which may be selected depending on a desired end product. It may be of either high or low molecular weight, straight-chain, cyclic or branched. As to its form, it may be liquid or resinous at room temperature. Typical and commercially widely used examples are organo(poly)siloxanes terminated with a hydroxyl group of the general formula (B): wherein R 6 are substituted or unsubstituted monovalent hydrocarbon groups and m is an integer of from 1 to 10,000. Preferably, R 6 are substituted or unsubstituted monovalent hydrocarbon groups having from 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, for example, alkyl groups such as methyl, ethyl, propyl and butyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl and tolyl; aralkyl groups such as benzyl and 2 - phenylethyl; and substituted ones of these groups in which some or all of the hydrogen atoms are replaced by halogen atoms such as chloromethyl and 3,3,3-trifluoropropyl groups. Several illustrative, non-limiting examples of the hydroxyl-containing organic silicon compound are given below. In the formulae, Me is methyl and Ph is substituted or unsubstituted phenyl. Me 3 SiOH , PhSi(OH) 3 , MePhSiOH , (Me 3 SiO) 3 SiOH , The second reactant used in the process of the present invention is an organic silicon compound or α-alkoxysilyl ester of the general formula (A): wherein R 1 , R 4 , and R 5 , which may be the same or different, are independently selected from substituted or unsubstituted monovalent hydrocarbon groups free of an aliphatic unsaturated bond, R 2 is a substituted or unsubstituted monovalent hydrocarbon group e.g. as above for R 6 , preferably a methyl or vinyl group, R 3 is a hydrogen atom or methyl group, and n is 1, 2 or 3. The monovalent hydrocarbon groups free of an aliphatic unsaturated bond represented by R 1 , R 4 , and R 5 include hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, for example, alkyl groups such as methyl, ethyl, propyl, and butyl; aryl groups such as phenyl and tolyl; aralkyl groups such as benzyl and 2-phenylethyl; and substituted ones of these in which one or more or all of the hydrogen atoms are replaced by halogen atoms such as chloromethyl and 3,3,3-trifluoropropyl groups. Several illustrative, non-limiting examples of the organic silicon compound of formula (A) are given below. In the formulae, Me is methyl, Et is ethyl, Bu is butyl, and Ph is substituted or unsubstituted phenyl. The organic silicon compounds of formula (A) may be readily synthesized by heating an alkoxyhydrosilane and an acrylate ester in the presence of a platinum catalyst to effect addition reaction according to the following reaction scheme. In the practice of the present invention, the first and second reactants, that is, a hydroxyl-containing organic silicon compound and an organic silicon compound of formula (A) are mixed for reaction. The organic silicon compound of formula (A) reacts with a silanol group (1) of the hydroxyl-containing organic silicon compound to form an alkoxysiloxane bond (2) and an ester (3) as a by-product according to the following reaction scheme. This reaction usually proceeds in the absence of a catalyst. That is, effective reaction may occur simply by mixing the first and second reactants. For a stoichiometrical reaction, the reaction requires an organic silicon compound of formula (A) in an at least equimolar amount per mol of the hydroxyl group. Preferably therefore, at least equimolar amount, preferably 1 to 1.5 mol per mol of the hydroxyl group of an organic silicon compound of formula (A) is mixed with the hydroxyl-containing organic silicon compound for reaction to take place. When the hydroxyl-containing organic silicon compound as the first reactant is a compound of formula (B), at least 2 mol of the compound of formula (A) is used per mol of the compound of formula (B). Then there is formed an alkoxy-functional organopolysiloxane having an alkoxysilyl group at either end of the general formula (C): wherein R 1 , R 2 , R 6 , m and n are as defined above. Reaction conditions are not particularly limited. Often, a mixture of the first and second reactants is heated at 50 to 150°C, more preferably 80 to 90°C for about 1 to 20 hours, more preferably about 4 to 5 hours. A reaction medium such as toluene, benzene or xylene may be used. The reaction forms an aster by-product as well as the end product. The may be readily removed by heating or stripping in a conventional manner or may be left in the product as the case may be. There has been described a process enabling efficient preparation of an alkoxy-functional organopolysiloxane having an alkoxysilyl group from an organic silicon compound having a hydroxyl group in a catalyst-free system in high yields. The resulting alkoxy-functional organopolysiloxanes having an alkoxysilyl group are useful as modifiers and surface treating agents for inorganic and organic materials and as source materials for preparing silicone resins and rubbers of dealcoholysis curing type. EXAMPLE Examples of the present invention are given below by way of illustration and not by way of limitation. Example 1 A reactor equipped with a stirrer, thermometer and condenser was charged with 91 grams (0.1 mol) of trimethylsilanol and 22.2 grams (0.1 mol) of ethyl α-trimethoxy-silylpropionate. Reaction was effected under reflux for 3 hours. At the end of reaction, 1,1,1-trimethyl3,3,3-trimethoxydisiloxane having a boiling point of 150 to 152°C at 101.3 kPa (760 mmHg) was collected by distillation in a yield of 95%. The structure of the reaction product was identified by NMR and gas mass spectroscopy. Example 2 A reactor as used in Example 1 was charged with 1,000 grams of dimethylpolysiloxane terminated with a hydroxyl group at either molecular chain end having a viscosity of 5.1×10 -3 m 2 s -1 (5,100 centistokes) at 25°C (OH value 0.0070 mol/100 grams) and 22.2 grams (0.084 mol) of ethyl α-triethoxysilylpropionate. Reaction was effected at 90°C for 5 hours. At the end of reaction, excess ethyl α -triethoxysilylpropionate and ethyl propionate by-product were removed by stripping at 120°C and 267 Pa (2 mmHg), obtaining 980 grams of a colorless clear oily product having a viscosity of 5.3×10 -3 m 2 s -1 (5,300 centistokes) at 25°C. To 100 grams of the oily product was added 0.1 gram of a 50% toluene solution of dibutyltin dioctoate. The oily product cured tack-free within 5 minutes at 20°C and RH 50%. For comparison purposes, 0.1 gram of a 50% toluene solution of dibutyltin dioctoate was added to 100 grams of the starting reactant, hydroxyl-terminated dimethylpolysiloxane having a viscosity of 5.1×10 -3 m 2 s -1 (5,100 centistokes) at 25°C. The material remained tacky after 24 hours. Example 3 A reactor as used in Example 1 was charged with 1,000 grams of a 50% toluene solution of a co-hydrolysate of trimethylchlorosilane and tetraethoxysilane (M/Q = 0.70, OH value 0.011 mol/100 grams of resin) and 8.7 grams (0.033 mol) of ethyl α- triethoxysilylpropionate. Reaction was effected at 90°C for 5 hours. At the end of reaction, 0.1 gram of dibutyltin dimethoxide was added to 100 grams of the reaction solution. The solution was cast on a glass plate to a thickness of about 0.5 mm and cured at room temperature for 24 hours. There was formed a hard film which was insoluble in toluene. For comparison purposes, 0.1 gram of dibutyltin dimethoxide was added to 100 grams of the co-hydrolysate toluene solution. The solution was cast on a glass plate and cured at room temperature for 24 hours. There was formed a hard film which dissolved away when dipped in toluene. Although some preferred embodiments have been described, many modifications and variations may be made thereto in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practised otherwise than as specifically described.

Claims: A process for preparing an alkoxy-functional organopolysiloxane by reacting (i) hydroxyl-containing organic silicon compound with (ii) an at least equimolar amount, per mol of hydroxyl group of said compound (i), of an organic silicon compound according with the general formula (A): wherein R 1 , R 4 , and R 5 are independently selected from substituted and unsubstituted monovalent hydrocarbon groups having from 1 to 10 carbon atoms and free of aliphatic unsaturation R 2 is substituted or unsubstituted monovalent hydrocarbon group having from 1 to 10 carbon atoms, R 3 is a hydrogen atom or methyl group, and n is 1, 2 or 3. A process according to claim 1 wherein said hydroxyl-containing organic silicon compound (i) accords with the general formula (B): wherein R 6 are substituted or unsubstituted monovalent hydrocarbon groups having from 1 to 10 carbon atoms, and m is an integer in the range from 1 to 10,000; whereby an alkoxy-functional organopolysiloxane of the general formula (C): is obtained. A process according to any one of the preceding claims in which the organic silicon compound (ii) is selected from A process according to any one of the preceding claims in which the amount of the organic silicon compound (ii) is from 1 to 1.5 mol per mol hydroxyl group of the organic silicon compound (i). A process according to any one of the preceding claims wherein the reaction is conducted at temperature in the range from 50 to 150°C for from 1 to 20 hours. A process according to any one of the preceding claims wherein the reaction is conducted in the presence of a solvent selected from toluene, benzene and xylene.

Inventors: ARAI MASATOSHI, ARAI, MASATOSHI
Applicants: SHINETSU CHEMICAL CO, SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1991
Main classification: C08G77
IPC codes: C08G77, C07F7