Mechanically Strong Nanoporous Polyimides (Aerogels) from Anhydrides and Isocyanates: A Structure-Property Study
Among engineering plastics, polyimides demonstrate excellent mechanical properties and high temperature stability. By combining those with inherent aerogel properties, one should realize ideal materials for high temperature thermal insulation. Following our successful synthesis of polyimide aerogels via the underutilized reaction of diisocyanates and dianhydrides, here we correlate bulk mechanical properties with the structure of the monomers. Thus, realizing the importance of multifunctional monomers in terms of imparting mechanical strength, we resort into a trifunctional isocyanate (tris(4-isocyanatophenylmethane): Desmodur RE; courtesy of Bayer, Corp. USA) with two different dianhydrides, pyromellitic dianhydride (PMDA) and benzophenone tetracarboxylic dianhydride (BTDA). The resulting polyimide aerogels, PI-PMDA and PI-BTDA, are stable up to 400 ⁰C (by TGA), as expected. Despite relatively high bulk densities by aerogel standards (up to 0.6-0.7 g cm-3) and a decrease in porosity (down to ~50% v/v) PI-PMDA remain mesoporous and have high surface area (up to 435 m2 g-1). On the other hand, with the same primary particle sizes, PI-BTDA shrink less, have lower bulk densities and higher porosities (up to 80%). Clearly, decreasing the molecular rigidity of the dianhydride (from PMDA to BTDA ) has an immediate impact on the material properties of the resulting aerogels. Both kinds of PI aerogels are extremely robust materials with high energy absorption capabilities (e.g., PI-PMDA : 82±4 J g-1 at 0.68 g cm-3; PI-BTDA : 47±1 J g-1 at 0.37 g cm-3. Upon pyrolysis at 800 ⁰C under Ar, both types of PI aerogels are converted to carbon aerogels in high yields (60-62 % w/w).
C. Chidambareswarapattar et al., "Mechanically Strong Nanoporous Polyimides (Aerogels) from Anhydrides and Isocyanates: A Structure-Property Study," Abstracts of Papers of the American Chemical Society, American Chemical Society (ACS), Mar 2012.
243rd ACS National Meeting and Exposition (2012: Mar. 25-29, San Diego, CA)
Article - Conference proceedings
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01 Mar 2012