Nanoporous Polyurea from a Triisocyanate and Boric Acid: A Paradigm of a General Reaction Pathway for Isocyanates and Mineral Acids

Abstract

Isocyanates react with carboxylic acids and yield amides. As reported herewith, however, transferring that reaction to a range of mineral acids (anhydrous H3BO3, H3PO4, H3PO3, H2SeO3, H6TeO6, H5IO6, and H3AuO3) yields urea. The model system for this study was a triisocyanate, tris(4-isocyanatophenyl)methane (TIPM), reacting with boric acid in DMF at room temperature, yielding nanoporous polyurea networks that were dried with supercritical fluid CO2 to robust aerogels (referred to as BPUA-xx). BPUA-xx were structurally (CHN, solid-state 13C NMR) and nanoscopically (SEM, SAXS, N2-sorption) identical to the reaction product of the same triisocyanate (TIPM) and water (referred to as PUA-yy). Minute differences were detected in the primary particle radius (6.2–7.5 nm for BPUA-xx versus 7.0–9.0 nm for PUA-yy), the micropore size within primary particles (6.0–8.5 A for BPUA-xx versus 8.0–10 A for PUA-yy), and the solid-state 15N NMR whereas PUA-yy showed some dangling −NH2. All data together were consistent with...