Multifunctional porous aramids (aerogels) by efficient reaction of carboxylic acids and isocyanates

Abstract

Polymerization of trifunctional polyaromatic carboxylic acids and isocyanates in dilute DMF solutions using the rather underutilized reaction of the carboxylic acid group (–COOH) with isocyanates (–NCO) towards amides (–NH(CO)–) induces early phase separation of surface-active aramid nanoparticles that form a solvent-filled 3D network stabilized against collapse by the chemical energy of the interparticle covalent bridges (crosslinks). Those wet-gels can be dried with liquid CO2 taken out at the end as a supercritical fluid into lightweight (bulk density ∼0.3 g cm−3) highly porous (77% v/v) multifunctional materials classified as aerogels with high specific energy absorption (37 J g−1), open-air speed of sound (338 m s−1) and Styrofoam-like thermal conductivity (0.028 W m−1 K−1).