Multifunctional porous aramids (aerogels) and fabrication thereof
The present disclosure provides a series of new and improved porous polyamide aerogels derived from multifunctional aromatics that combine the high mechanical strength of aramids with the pore structure of aerogels. The polyamide aerogels have a hyperbranched structure, relatively low density, high porosity and are derived from functionalized monomers having more aromatic groups than functional groups. The present disclosure also provides a new method for producing the porous polyamide aerogels by polymerizing an aromatic multifunctional carboxylic acid with an isocyanate at moderate reaction condition followed by drying with liquid CO 2 .
1. A porous polyamide aerogel comprising the following repeating units:
2. The porous polyamide aerogel of claim 1 having a hyperbranched structure.
3. The porous polyamide aerogel of claim 1 , wherein the aerogel has a bulk density that is ≦0.4 g/cc, a porosity ≧69%, a Young's modulus ≦50 MPa, a specific energy absorption ≦37 J/g, a speed of sound ≧47 m/s, and a thermal conductivity ≧0.028 W/m·K.
4. The porous polyamide aerogel of claim 1 , wherein at least 10% of the surface area is included in micropores.
5. A hyperbranched porous polyamide aerogel represented by the central formula:
wherein:
(a) A is:
(b) B is:
(Y) m NH b ;
(c) X and Y are aromatic groups;
(d) units A and B are linked through an amide group; and
(e) the ratio of (a+b):(n+m) is at least about 1:1.5.
6. A hyperbranched porous polyamide aerogel of claim 5 wherein A is:
and B is:
7. The hyperbranched porous polyamide aerogel of claim 5 , wherein the aerogel exhibits at least four properties selected from the group consisting of a bulk density that is ≦0.4 g/cc, a porosity ≧69%, a Young's modulus ≦50 MPa, a specific energy absorption ≦37 J/g, a speed of sound ≧47 m/s, and a thermal conductivity ≧0.028 W/m·K.
8. The hyperbranched porous polyamide aerogel of claim 5 , wherein the aerogel exhibits at least two properties selected from the group consisting of a bulk density that is ≦0.4 g/cc, a porosity ≧69%, a Young's modulus ≦50 MPa, a specific energy absorption ≦37 J/g, a speed of sound ≧47 m/s, and a thermal conductivity ≧0.028 W/m·K.
9. The hyperbranched porous polyamide aerogel of claim 5 , wherein at least about 10% of the surface area is attributed to micropores.
10. A method for producing a porous polyamide hydrogel comprising:
combining a polyfunctional aromatic carboxylic acid and a polyfunctional aromatic isocyanate in an aprotic solvent to form a reaction mixture, and
heating the reaction mixture to a temperature ≦135° C. to form a wet gel.
11. The method of claim 10 , wherein heating the reaction mixture involves heating the reaction mixture to a temperature ≦90° C.
12. The method of claim 10 , wherein the polyfunctional aromatic carboxylic acid is trimesic acid, and the polyfunctional aromatic isocyanate is selected from the group consisting of tris(4-isocyanatophenyl)methane, methylene biphenyl diisocyanate, 1,3-phenylene diisocyanate, 1,1′-biphenyl diisocyanate and 1,1′oxy-bis-(isocyanatobenzene).
13. The method of claim 12 , wherein the polyfunctional aromatic isocyanate is tris(4-isocyanatophenyl)methane.
14. The method of claim 12 , wherein the aprotic solvent is DMF.
15. The method of claim 14 , further including:
adding a solvent miscible with supercritical CO 2 ; and
drying the wet gel with supercritical CO 2 .
16. The method of claim 14 , wherein adding a solvent miscible with supercritical CO 2 involves adding acetone.
17. The method of claim 10 , wherein the polyfunctional aromatic carboxylic acid and the polyfunctional aromatic isocyanate include functional groups and aromatic rings having a ratio, and the ratio of functional groups to aromatic rings is at least about 1:1.5.
18. The method of claim 10 , wherein combining a polyfunctional aromatic carboxylic acid and a polyfunctional aromatic isocyanate in an aprotic solvent to form a reaction mixture involves combining proportions of polyfunctional carboxylic acid, polyfunctional aromatic isocyanate and an aprotic solvent in amounts to provide a polymer slurry containing between 5 and 25 wt. % solid.
19. The method of claim 18 , wherein combining a polyfunctional aromatic carboxylic acid and a polyfunctional aromatic isocyanate in an aprotic solvent to form a reaction mixture involves combining proportions of polyfunctional carboxylic acid, polyfunctional aromatic isocyanate and an aprotic solvent in amounts to provide a polymer slurry containing between 10 and 25 wt. % solid.
20. The method of claim 18 , wherein combining a polyfunctional aromatic carboxylic acid and a polyfunctional aromatic isocyanate in an aprotic solvent to form a reaction mixture involves combining proportions of polyfunctional carboxylic acid, polyfunctional aromatic isocyanate and an aprotic solvent in amounts to provide a polymer slurry containing between 10 and 15 wt. % solid.