Polysiloxanes and their preparation

Abstract

An amino-functional polysiloxane is prepared by reacting an aminosilane (A) which contains an aminoalkyl group and at least one alkoxy group bonded to Si with a carboxylic acid and a silanol-functional polysiloxane (B). The aminosilane (A) is partially converted into its carboxylate salt which acts as a catalyst for the siloxane condensation polymerization reaction between (A) and (B).

What is claimed is:  
     
         1 . A process for the preparation of an amino-functional polysiloxane comprising reacting an aminosilane (A) which contains an aminoalkyl group and at least one alkoxy group bonded to Si with a carboxylic acid (C) and a silanol-functional polysiloxane (B), the amount of carboxylic acid (C) being such that the molar ratio of carboxylic acid groups of (C) to amino groups of aminosilane (A) is less than 1:1 and the amount of silanol-functional polysiloxane (B) being such that the molar ratio of silanol groups of (B) to Si-bonded alkoxy groups of aminosilane (A) is greater than 1:1, whereby the aminosilane (A) is partially converted into its carboxylate salt which acts as a catalyst for the siloxane condensation polymerization reaction between (A) and (B).  
     
     
         2 . A process according to  claim 1 , wherein the aminosilane (A) has the formula  
       
         
           
           
               
               
           
         
       
       wherein A and A′ are each independently a linear or branched alkylene group having 1 to 6 carbon atoms; q=0 to 4; R is selected from the group consisting of hydrogen, an alkyl group, and a hydroxyalkyl group having 1 to 4 carbon atoms; R′ is selected from the group consisting of an alkyl group and an alkoxyalkyl group having 1 to 6 carbon atoms; and Y and Y′ are each independently selected from the group consisting of a group —OR′, substituted alkyl groups, substituted aryl groups, unsubstituted alkyl groups, and unsubstituted aryl groups.  
     
     
         3 . A process according to  claim 2 , wherein the group Y of aminosilane (A) is an unsubstituted alkyl group and the group Y′ is of the formula —OR′.  
     
     
         4 . A process according to  claim 2  wherein the linkages A and A′ of aminosilane (A) are each independently a linear or branched alkylene group having 2 to 4 carbon atoms; q=1; and R is hydrogen.  
     
     
         5 . A process according to claims  1  wherein the silanol-functional polysiloxane (B) is a linear hydroxyl endblocked polydimethylsiloxane of degree of polymerisation 4 to 1000.  
     
     
         6 . A process according to  claim 1  wherein the silanol-functional polysiloxane (B) is a linear hydroxyl endblocked polydiorganosiloxane containing methyl groups and 2 to 30 carbon atom containing groups selected from the group consisting of alkyl groups, alkenyl groups, aryl groups and aralkyl groups  
     
     
         7 . A process according to  claim 1  wherein the carboxylic acid (C) is substituted by an electron-withdrawing moiety.  
     
     
         8 . A process according to  claim 7  wherein the carboxylic acid (C) is selected from the group consisting of lactic acid and fluoroalkanoic acids.  
     
     
         9 . A process according to  claim 1  wherein the carboxylic acid is an aliphatic carboxylic acid having 6 to 20 carbon atoms.  
     
     
         10 . A process according to  claim 1  wherein the amount of carboxylic acid (C) is such that the molar ratio of carboxylic acid groups of (C) to amino groups of aminosilane (A) is 0.002-0.25:1  
     
     
         11 . A process according to  claim 1  wherein the amount of silanol-functional polysiloxane (B) is such that the molar ratio of silanol groups of (B) to Si-bonded alkoxy groups of aminosilane (A) is 1.2-2.0:1.  
     
     
         12 . A process according to  claim 1  wherein an alcohol is co-reacted with the aminosilane (A), carboxylic acid and silanol-functional polysiloxane (B).  
     
     
         13 . A process according to  claim 12  wherein the alcohol is an aliphatic alcohol having 8 to 30 carbon atoms.  
     
     
         14 . A process according to  claim 12  wherein the alcohol is selected from the groups consisting of an ether alcohol and hydroxy-terminated polyethers.  
     
     
         15 . A process according to  claim 16  wherein the carboxylic acid (C) is selected from the group consisting of an alkanoic acid having 1 to 3 carbon atoms and a hydroxy-substituted carboxylic acid, and the alcohol is selected from the group consisting of linear alkanols having 2 to 4 carbon atoms and branched alkanols having 2 to 4 carbon atoms.  
     
     
         16 . A process according to  claim 1  wherein the condensation reaction between (A) and (B) is carried out at a temperature in the range 60-140° C.  
     
     
         17 . A process according to  claim 1  wherein the aminosilane (A), the carboxylic acid and the silanol-functional polysiloxane (B) are mixed with a surfactant and water to form an emulsion, and the condensation reaction between (A) and (B) is carried out in the emulsion, thereby forming an emulsion of an amino-functional polysiloxane.  
     
     
         18 . A process according to  claim 17  wherein the aminosilane (A), carboxylic acid, silanol-functional polysiloxane (B), surfactant and water are mixed to form an emulsion at a temperature below 50° C. and the emulsion is heated to a temperature in the range 60-140° C. to effect the condensation reaction.  
     
     
         19 . A process according to  claim 1  wherein a material selected from the group consisting of water and an alcohol endblocker is added to the reagents after a desired reaction time in order to quench the reaction.  
     
     
         20 . A process according to  claim 1  wherein a non-reactive polysiloxane having a viscosity of less than 375 mPas is added to the reagents and reaction is continued in the non-reactive polysiloxane as diluent, thereby forming a solution of amino-functional polysiloxane in the non-reactive polysiloxane.  
     
     
         21 . A process according to  claim 20  in which the non-reactive polysiloxane is a cyclic polysiloxane having at least 5 silicon atoms.  
     
     
         22 . A process according to  claim 20  in which the non-reactive polysiloxane is a trimethylsilyl-terminated polydimethylsiloxane.  
     
     
         23 . An amino-functional polysiloxane of the formula  
       
         
           
           
               
               
           
         
       
       where A, A′, R and q are defined as in  claim 2;  Y is selected from the group consisting of substituted alkyl groups, unsubstituted alkyl groups, substituted aryl groups and unsubstituted aryl groups; Z and Z′, which can be the same or different, are each selected from the group consisting of substituted alkyl groups, unsubstituted alkyl groups, substituted aryl groups, and unsubstituted aryl groups; wherein in each group X is selected from the group consisting of hydrogen, an aliphatic group and aliphatic groups containing one or more ether linkages, at least one group X being an aliphatic group having 8 to 30 carbon atoms; m=4-100; and n is 1-1000.  
     
     
         24 . An amino-functional polysiloxane according to  claim 23  wherein 0.2-25% of the amino groups are in carboxylate salt form.  
     
     
         25 . A polysiloxane composition comprising a substantially linear amino-functional polydiorganosiloxane having at least one group of the formula R—(NH-A′) q -NH-A- bonded to silicon, wherein A and A′ are each independently a linear or branched alkylene group having 1 to 6 carbon atoms; q=0-4; R is selected from the group consisting of hydrogen, alkyl groups having 1 to 4 carbon atoms, and hydroxyalkyl groups having 1 to 4 carbon atoms, and having a viscosity of at least 10 Pa.s, dissolved in a non-reactive cyclic polysiloxane having at least 5 silicon atoms and having a viscosity of less than 375 mPa.s.  
     
     
         26 . A polysiloxane composition according to  claim 25  wherein the content of octamethyltetrasiloxane is less than 0.25% by weight.