Estolide compositions exhibiting high oxidative stability
Provided herein are estolide compositions having high oxidative stability, said compositions comprising at least one compound of formula: in which n is an integer equal to or greater than 0; m is an integer equal to or greater than 1; R 1 , independently for each occurrence, is selected from optionally substituted alkyl that is saturated or unsaturated, and branched or unbranched; R 2 is selected from hydrogen and optionally substituted alkyl that is saturated or unsaturated, and branched or unbranched; and R 3 and R 4 , independently for each occurrence, are selected from optionally substituted alkyl that is saturated or unsaturated, and branched or unbranched. Also provided herein are uses for the compositions and methods of preparing the same.
1. A method of preparing an oxidatively stable estolide base oil, said method comprising
selecting a first estolide base oil having an initial acid value;
reducing the initial acid value of the first estolide base oil to provide a second estolide base oil having an acid value of equal to or less than 0.5 mg KOH/g; and
combining the second estolide base oil with at least one amine antioxidant to provide the oxidatively stable estolide base oil, wherein said oxidatively stable estolide base oil has a time of at least 700 minutes when tested in a rotating pressurized vessel oxidation test using ASTM Method 2272-11.
2. The method according to claim 1 , wherein reducing the acid value of the first estolide base oil to provide the second estolide base oil comprises contacting said first estolide base oil with at least one acid-reducing agent.
3. The method according to claim 2 , wherein the at least one acid-reducing agent is selected from one or more of activated carbon, magnesium silicate, aluminum oxide, silicon dioxide, a zeolite, a basic resin, or an anionic exchange resin.
4. The method according to claim 1 , wherein the second estolide base oil has an acid value of equal to or less than 0.2 mg KOH/g.
5. The method according to claim 4 , wherein the second estolide base oil has an acid value of equal to or less than 0.1 mg KOH/g.
6. The method according to claim 1 , wherein the oxidatively stable estolide base oil has a time of at least 1000 minutes when tested in a rotating pressurized vessel oxidation test using ASTM Method 2272-11.
7. The method according to claim 1 , wherein the second estolide base oil comprises at least one estolide compound selected from compounds of Formula I:
wherein
x is, independently for each occurrence, an integer selected from 0 to 20;
y is, independently for each occurrence, an integer selected from 0 to 20;
n is an integer greater than or equal to 0;
R 1 is an optionally substituted alkyl that is saturated or unsaturated, and branched or unbranched; and
R 2 is an optionally substituted alkyl that is saturated or unsaturated, and branched or unbranched,
wherein each fatty acid chain residue of said at least one estolide compound is independently optionally substituted.
8. The method according to claim 7 , wherein
x is, independently for each occurrence, an integer selected from 1 to 10;
y is, independently for each occurrence, an integer selected from 1 to 10;
n is an integer selected from 0 to 8;
R 1 is an optionally substituted C 1 to C 22 alkyl that is saturated or unsaturated, and branched or unbranched; and
R 2 is an optionally substituted C 1 to C 22 alkyl that is saturated or unsaturated, and branched or unbranched,
wherein each fatty acid chain residue is unsubstituted.
9. The method according to claim 8 , wherein
x+y is, independently for each chain, an integer selected from 13 to 15; and
n is an integer selected from 0 to 6.
10. The method according to claim 9 , wherein x is, independently for each occurrence, an integer selected from 7 and 8.
11. The method according to claim 9 , wherein y is, independently for each occurrence, an integer selected from 7 and 8.
12. The method according to claim 7 , wherein R 2 is an unsubstituted alkyl that is saturated or unsaturated, and branched or unbranched.
13. The method according to claim 9 , wherein R 2 is an unsubstituted alkyl that is saturated and branched or unbranched.
14. The method according to claim 13 , wherein R 2 is selected from C 6 to C 12 alkyl.
15. The method according to claim 7 , wherein R 1 is an unsubstituted alkyl that is saturated or unsaturated, and branched or unbranched.
16. The method according to claim 13 , wherein R 1 is an unsubstituted alkyl that is saturated and branched or unbranched.
17. The method according to claim 1 , wherein the at least one amine antioxidant is a diphenylamine antioxidant.
18. The method according to claim 17 , wherein the at least one amine antioxidant is an alkylated diphenylamine antioxidant.
19. The method according to claim 18 , wherein the at least one amine antioxidant is selected from one or more of a nonylated diphenylamine, an octylated diphenylamine, or a butylated diphenylamine.
20. The method according to claim 1 , wherein the oxidatively stable estolide base oil consists essentially of the second estolide base oil and the at least one amine antioxidant.
21. The method according to claim 16 , wherein the second estolide base oil consists essentially of the at least one estolide compound.
22. The method according to claim 21 , wherein the second estolide base oil has an acid value of equal to or less than 0.2 mg KOH/g.
23. The method according to claim 22 , wherein the oxidatively stable estolide base oil consists essentially of the second estolide base oil and the at least one amine antioxidant.
24. The method according to claim 23 , wherein the oxidatively stable estolide base oil has a time of at least 1000 minutes when tested in a rotating pressurized vessel oxidation test using ASTM Method 2272-11.