Method for making an amino-functional polydiorganosiloxane using a removable solid catalyst
A method for preparing an amino-functional polydiorganosiloxane employs a removable catalyst. The method differs from previous methods in the selection of catalyst, order of addition of catalyst with respect to other starting materials, and catalyst removal.
1. A method for preparing an amino-functional polydiorganosiloxane comprising:
1) mixing and heating, at a temperature of 50° C. to 160° C., starting materials comprising
A) a silanol functional polydiorganosiloxane,
B) an aminoalkyl-functional alkoxysilane, where amounts of starting materials A) and B) are such that a molar excess of silanol groups with respect to alkoxy groups is present, and
C) 0 to 0.5%, based on combined weights of all starting materials, of an endblocker having triorganosilyl groups; and thereafter
2) providing starting material D) 0.01% to 5%, based on weight of starting material B), of a solid (at conditions of 20° C. to 25° C. and 101 kPa) precatalyst selected from the group consisting of a carboxylic acid, an acid anhydride, and a combination of both the carboxylic acid and the acid anhydride under conditions permitting the precatalyst to react to form a catalyst; thereby forming a reaction mixture; and
3) mixing and heating the reaction mixture under conditions to form a reaction product; and
4) removing all or a portion of residual acid by a technique comprising cooling the reaction product, thereby reducing amount of the residual acid to 0 to <500 ppm, based on the weight of the amino-functional polydiorganosiloxane, where step 4) further comprises filtering and/or centrifuging the reaction product after cooling.
2. The method of claim 1 , where in step 4) the amount of the residual acid is reduced to 0 to <300 ppm, based on the weight of the amino-functional polydiorganosiloxane.
3. The method of claim 1 , where starting material A) is selected from the group consisting of
A1) a silanol end-blocked polydimethylsiloxane with a viscosity of 30 cP to 70 cP at room temperature, and
A2) a silanol end-blocked polydimethylsiloxane with a degree of polymerization of 4 to 1000.
4. The method of claim 1 , where starting material B) is selected from the group consisting of:
B1) 3-aminopropylmethyl dimethoxysilane,
B2) 3-aminopropylmethyl diethoxysilane,
B3) aminoethyl-aminoisobutyl methyl dimethoxy silane,
B4) aminoethyl-aminoisobutyl methyl diethoxysilane
B5) 3-aminopropyldimethyl ethoxysilane,
B6) 3-aminopropyldimethyl methoxysilane,
B7) 3-(2-aminoethylamino)propyl-dimethoxymethylsilane,
B8) 3-(2-aminoethylamino)propyl-diethoxymethylsilane,
B9) aminopropyl methyl dimethoxy silane,
B10) aminopropyl methyl diethoxysilane, and
B11) a combination of two or more of B1) to B10).
5. The method of claim 1 , where starting material C) is present in an amount of at least 0.1% and starting material C) is selected from the group consisting of:
C1) hexamethyldisilazane,
C2) trimethylmethoxysilane,
C3) trimethylethoxysilane, and
C4) a combination of two or more of C1), C2) and C3).
6. The method of claim 1 , where the solid carboxylic acid has a pKa value of 1 to 7 and a melting temperature of 40° C. to 170° C. at 101 kPa.
7. The method of claim 6 , where the carboxylic acid is selected from the group consisting of: D2) benzoic acid, D3) citric acid, D4) maleic acid, D5) myristic acid, D6) salicylic acid, and D7) a combination of two or more of D2), D3), D4), D5), and D6).
8. The method of claim 1 , where the precatalyst comprises the acid anhydride, and the method further comprises combining the acid anhydride with water.
9. The method of claim 8 , where the solid acid anhydride is selected from the group consisting of: D7) succinic anhydride, D8) maleic anhydride, and both D8) and D9).
10. The method of claim 8 , where the water is present in-situ.
11. The method of claim 1 , where: i) all or a portion of starting material C) is added in step 1), ii) all or a portion of starting material D) is added in step 2), or both i) and ii).
12. The method of claim 11 , where: i) a portion of starting material C) is added in step 1), ii) a portion of starting material D) is added in step 2), or both i) and ii); and the method further comprises iii) adding a second portion of starting material C), iv) adding a second portion of starting material D), or both iii) and iv), in an additional step added to the method before step 4).
13. The method of claim 11 , where all of starting material C) is added in step 1), and all of starting material D) is added in step 2).
14. The method of claim 1 , where starting materials A) and B) are present in amounts such that a molar ratio of silanol groups to respect alkoxy groups is at least 1.1:1.
15. The method of claim 14 , where the molar ratio ranges from 1.2:1 to 2.0:1.
16. The method of claim 1 , where the catalyst is benzoic acid, and step 3) is performed by heating the reaction product at a temperature of at least 80° C. at a pressure <50 mmHg for at least 2 hours.
17. The method of claim 16 , where step 3) is performed by heating the reaction product at a temperature of 90° C. to 110° C. at a pressure of 0 to <50 mmHg for 2 to 8 hours.
18. The method of claim 1 , where water is present as a by-product in starting material A), and optionally the carboxylic acid is added in step 2), and the acid anhydride is added after the carboxylic acid has been added and after water has formed as a by-product.