Amino alkoxy-modified silsesquioxanes and method of preparation
An amino alkoxy-modified silsesquioxane (AMS) comprising one or more compounds selected from the group consisting of an amino AMS, an amino/mercaptan co-AMS, an amino/blocked mercaptan co-AMS, mixtures thereof, and a weak acid-neutralized solid or aqueous solution thereof, and a method of making the amino AMS, are presented. The compounds are useful in compounding, processing, cure and storage of silica-reinforced rubbers because they contain low levels of volatile organic compounds (VOC).
1. A method of making a weak acid-neutralized solid or a weak acid-neutralized aqueous solution thereof of an amino-alkoxy-modified silsesquioxane (amino AMS), an amino/mercaptan co-AMS, amino/blocked mercaptan co-AMS or mixtures thereof, and having the formula
wherein w, x, y and z represent mole fractions, z does not equal zero, at least one of w, x or y must also be present, and w+x+y+z=1.00;
wherein at least one of R 1 , R 2 , R 3 and R 4 must be present and selected from the group consisting of R 6 Z, wherein Z is selected from the group consisting of NH 2 , HNR 7 and NR 7 2 ; and the remaining R 1 , R 2 , R 3 or R 4 are the same or different and selected from the group consisting of (i) H or an alkyl group having one to about 20 carbon atoms, (ii) cycloalkyl groups having 3 to about 20 carbon atoms, (iii) alkylaryl groups having 7 to about 20 carbon atoms, (iv) R 6 X, wherein X is selected from the group consisting of Cl, Br, SH, S a R 7 , NR 7 2 , OR 7 , CO 2 H, SCOR 7 , CO 2 R 7 , OH, olefins, epoxides, amino groups, vinyl groups, acrylates and methacrylates, wherein a=1 to about 8, and (v) R 6 YR 8 X, wherein Y is selected from the group consisting of O, S, NH and NR 7 ; wherein R 6 and R 8 are selected from the group consisting of alkylene groups having one to about 20 carbon atoms, cycloalkylene groups having 3 to about 20 carbon atoms, and a single bond; and R 5 and R 7 are selected from the group consisting of alkyl groups having one to about 20 carbon atoms, cycloalkyl groups having 3 to about 20 carbon atoms, and alkylaryl groups having 7 to about 20 carbon atoms,
the method comprising the steps of:
(a) combining as a reaction mixture:
(i) water,
(ii) a solvent for the water,
(iii) a hydrolysis and condensation catalyst,
(iv) a weak acid having a pK a of about 3.5 to about 6.5,
(v) an aminotrialkoxysilane, and
(vi) an optional selection from the group consisting of a mercaptoalklytrialkoxysilane, a blocked mercaptoalkyl-trialkoxysilane, or another silane with a substituent corresponding to R 1 , R 2 , R 3 and R 4 , and mixtures thereof;
b) allowing the reaction mixture to react for about 0.5 hours to about 200 hours to form an amino alkoxysilane-modified silsesquioxane; and
(c) recovering the amino alkoxysilane-modified silsesquioxane from the reaction mixture;
(d) optionally adding a weak acid having a pK a of about 3.5 to about 6.5 to the recovered silsesquioxane,
wherein the amino alkoxy-modified silsesquioxanes consist essentially of a mixture of amino alkoxy-modified silsesquioxanes, each having an open structure and a reactive alkoxysilyl group and being essentially free of closed caged polyhedral organosilsesquioxanes,
and wherein the mixture of the amino alkoxy-modified silsesquioxanes liberates about 0.05% to about 10% by weight alcohol when treated by substantially total acid hydrolysis.
2. The method of claim 1 , wherein the reaction mixture includes an aminotrialkoxysilane and a selection from the group consisting of a mercaptoalkyl-trialkoxysilane, a blocked mercaptoalkyltrialkoxysilane, and mixtures thereof.
3. The method of claim 2 , wherein the reaction mixture includes an aminotrialkoxysilane and a mercaptoalkyltrialkoxysilane, and wherein the hydrolysis and condensation catalyst comprises a selection from the group consisting of a strong base, a strong organic base, and mixtures thereof, and the method further comprises the substep of adding an S—S bond reducing agent to the reaction mixture in step (a), or to the amino alkoxysilane-modified silsesquioxane recovered in step (c), or to both steps (a) and (c).
4. The method of claim 3 , wherein the reducing agent is present in an amount sufficient to form a clear aqueous stable solution of the amino AMS.
5. The method of claim 3 , wherein the reducing agent comprises sodium borohydride.
6. The method of claim 1 , wherein the hydrolysis and condensation catalyst is selected from the group consisting of a strong acid, a strong base, a strong organic acid, a strong organic base, a solid strong cationic resin, and mixtures thereof.
7. The method of claim 6 , wherein the hydrolysis and condensation catalyst is selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, toluenesulfonic acid, sodium hydroxide, potassium hydroxide, lithium hydroxide, DBU (1,8-diazabicyclo[5.4.0] undec-7-ene), DBN (1,5-diazabicylo[4.3.0] non-5-ene), imidazoles, guanidines, and mixtures thereof.
8. The method of claim 6 , wherein the hydrolysis and condensation catalyst comprises a selection from the group consisting of a strong acid, a strong organic acid, a solid strong cationic resin, and mixtures thereof, and the combining as a reaction mixture step (a) includes the substep of adding a sufficient amount of the optional weak acid (iv) to the reaction mixture to substantially neutralize the amine functionality of the aminotrialkoxysilane.
9. The method of claim 6 , wherein the hydrolysis and condensation catalyst comprises a selection from the group consisting of a strong acid, a strong organic acid, a strong base, and a strong organic base, and mixtures thereof, and the recovering step (c) includes the substep of adding the optional weak acid (iv) to the amino alkoxysilane-modified silsesquioxane in an amount sufficient to stabilize the silsesquioxane.
10. The method of claim 6 , wherein the hydrolysis and condensation catalyst is selected from the group consisting of a strong acid, a strong organic acid and a solid strong cationic resin, and the catalyst is present in the reaction mixture (a) in an amount sufficient to neutralize the amino portion of the aminotrialkoxysilane and to catalyze hydrolysis and condensation of the aminotrialkoxysilane.
11. The method of claim 1 , wherein the optional weak acid comprises a weak carboxylic acid.
12. The method of claim 11 , wherein the weak carboxylic acid is selected from the group consisting of acetic acid, ascorbic acid, itaconic acid, lactic acid, malic acid, naphthalic acid, benzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, and mixtures thereof.
13. The method of claim 1 , wherein the solvent for the water is selected from the group consisting of a polar protic solvent, a polar aprotic solvent, an aprotic solvent, and mixtures thereof.
14. The method of claim 13 , wherein the polar protic solvent comprises an alcohol or a mixture of alcohols.
15. The method of claim 13 , wherein the aprotic solvent comprises a hydrocarbon solvent for the mixture of amino alkoxy-modified silsesquioxanes.
16. The method of claim 13 , wherein the aprotic solvent is selected from the group consisting of ether, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, acetone, acetonitrile, ethyl acetate, and mixtures thereof.
17. The method of claim 1 , wherein the mixture of amino alkoxy-modified silsesquioxanes liberates about 0.5% to about 8% by weight alcohol when treated by substantially total acid hydrolysis.