Porous cross-linked polyimide networks
Porous cross-linked polyimide networks are provided. The networks comprise an anhydride end-capped polyamic acid oligomer. The oligomer (i) comprises a repeating unit of a dianhydride and a diamine and terminal anhydride groups, (ii) has an average degree of polymerization of 10 to 50, (iii) has been cross-linked via a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydride groups, and (iv) has been chemically imidized to yield the porous cross-linked polyimide network. Also provided are porous cross-linked polyimide aerogels comprising a cross-linked and imidized anhydride end-capped polyamic acid oligomer, wherein the oligomer comprises a repeating unit of a dianhydride and a diamine, and the aerogel has a density of 0.10 to 0.333 g/cm 3 and a Young's modulus of 1.7 to 102 MPa. Also provided are thin films comprising aerogels, and methods of making porous cross-linked polyimide networks.
1. A porous cross-linked polyimide network comprising an anhydride end-capped polyamic acid oligomer, wherein the oligomer (i) comprises a repeating unit of a dianhydride and a diamine and terminal anhydride groups, (ii) has an average degree of polymerization of 10 to 50, (iii) has been cross-linked via a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydride groups, and (iv) has been chemically imidized to yield the porous cross-linked polyimide network.
2. The network of claim 1 , wherein the dianhydride is selected from the group consisting of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride and biphenyl-3,3′,4,4′-tetracarboxylic dianhydride.
3. The network of claim 1 , wherein the diamine is selected from the group consisting of 3,4-oxydianiline, 4,4′-oxydianiline, p-phenylene diamine, 2,2′-dimethylbenzidine, bisaniline-p-xylidene, 4,4′-bis(4-aminophenoxy)biphenyl, and 2,2′-bis[4-(4-aminophenoxyl)phenyl]propane.
4. The network of claim 1 , wherein the diamine comprises (i) 4,4′-oxydianiline and (ii) p-phenylene diamine or 2,2′-dimethylbenzidine.
5. The network of claim 1 , wherein the average degree of polymerization is 20 to 30.
6. The network of claim 1 , wherein the cross-linking agent is selected from the group consisting of a triamine, an aliphatic amine comprising three or more amines, an aliphatic triamine, an aromatic amine comprising three or more amine groups, an aromatic triamine, 1,3,5-tri(aminophenoxy)benzene, a silica cage structure decorated with three or more amines, octa(aminophenyl)silsesquioxane, octa(aminophenyl)silsesquioxane as a mixture of isomers having the ratio meta:ortho:para of 60:30:10, and para-octa(aminophenyl)silsesquioxane.
7. The network of claim 1 , wherein the oligomer has been chemically imidized to completion.
8. A wet gel comprising the network of claim 1 .
9. An aerogel comprising the network of claim 1 .
10. An aerogel comprising the network of claim 1 , wherein the aerogel was obtained by supercritical fluid extraction.
11. An aerogel comprising the network of claim 1 , wherein the aerogel has a density of 0.10 to 0.333 g/cm 3 .
12. An aerogel comprising the network of claim 1 , wherein the aerogel has a porosity of 80 to 95%.
13. An aerogel comprising the network of claim 1 , wherein the aerogel has a peak pore diameter of 5 to 60 nm.
14. An aerogel comprising the network of claim 1 , wherein the aerogel has a surface area of 200 to 600 m 2 /g.
15. An aerogel comprising the network of claim 1 , wherein the aerogel has a thermal conductivity of 13 to 16 mw/(m-K) at room temperature and 760 Torr.
16. An aerogel comprising the network of claim 1 , wherein the aerogel has a Young's modulus of 0.9 to 102 MPa.
17. An aerogel comprising the network of claim 1 , wherein the aerogel has a higher Young's modulus than a polymer reinforced silica aerogel of similar density.
18. An aerogel comprising the network of claim 1 , wherein the aerogel has a glass transition temperature of at least 270° C. and an onset of decomposition of at least 460° C.
19. An aerogel comprising the network of claim 1 , wherein the weight loss of the aerogel following heating of the network at 400° C. for 24 hours is less than 5%.
20. A monolith comprising the network of claim 1 .
21. A monolith comprising the network of claim 1 , wherein the monolith is 2 to 5 times stronger than a monolith of a polymer reinforced silica aerogel of similar density.
22. A thin film comprising the network of claim 1 .
23. A thin film comprising the network of claim 1 , wherein the average degree of polymerization is 20 to 30.
24. A thin film comprising the network of claim 1 , wherein the thin film has sufficient flexibility to be rolled or folded and then recover completely without cracking or flaking.
25. A thin film comprising the network of claim 1 , wherein the thin film has a tensile strength of 4-9 MPa.
26. A coating comprising the network of claim 1 .
27. A matting comprising the network of claim 1 .
28. A method of making a porous cross-linked polyimide network comprising:
(i) polymerizing a dianhydride and a diamine in a solution to form an anhydride end-capped polyamic acid oligomer comprising terminal anhydrides and having an average degree of polymerization of 10 to 50;
(ii) cross-linking the oligomer with a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydrides; and
(iii) mixing an imidization catalyst into the solution, before phase separation occurs in the solution, to chemically imidize the cross-linked oligomer to form the network.
29. The method of claim 28 , wherein the dianhydride is selected from the group consisting of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride and biphenyl-3,3′,4,4′-tetracarboxylic dianhydride.
30. The method of claim 28 , wherein the diamine is selected from the group consisting of 3,4-oxydianiline, 4,4′-oxydianiline, p-phenylene diamine, 2,2′-dimethylbenzidine, bisaniline-p-xylidene, 4,4′-bis(4-aminophenoxy)biphenyl, and 2,2′-bis[4-(4-aminophenoxyl)phenyl]propane.
31. The method of claim 28 , wherein the diamine comprises (i) 4,4′-oxydianiline and (ii) p-phenylene diamine or 2,2′-dimethylbenzidine.
32. The method of claim 28 , wherein the average degree of polymerization is 20 to 30.
33. The method of claim 28 , wherein the cross-linking agent is selected from the group consisting of a triamine, an aliphatic amine comprising three or more amines, an aliphatic triamine, an aromatic amine comprising three or more amine groups, an aromatic triamine, 1,3,5-tri(aminophenoxy)benzene, a silica cage structure decorated with three or more amines, octa(aminophenyl)silsesquioxane, octa(aminophenyl)silsesquioxane as a mixture of isomers having the ratio meta:ortho:para of 60:30:10, and para-octa(aminophenyl)silsesquioxane.
34. The method of claim 28 , wherein the cross-linked oligomer has been chemically imidized to completion.
35. The method of claim 28 , wherein the imidization catalyst is selected from the group consisting of 1,4-diazabicyclo[2.2.2]-octane, triethylamine, and pyridine.
36. The method of claim 28 , wherein the mixing results in a homogeneous distribution of the imidization catalyst in the solution.
37. The method of claim 28 , wherein the sum of the concentrations of the dianhydride, the diamine, and the cross-linking agent dissolved into the solution is 5 to 20 w/w % of the solution.
38. The method of claim 28 , wherein the solution comprises a solvent selected from the group consisting of N-methyl-2-pyrrolidinone, dimethylformamide, and dimethylacetamide.
39. A porous cross-linked polyimide network formed by the method of claim 28 .