CO₂ in Supramolecular Chemistry: Preparation of Switchable Supramolecular Polymers

AbstractCO2 gas was used to construct novel types of supramolecular polymers. Self‐assembling nanostructures 11 and 13 were prepared, which employ both hydrogen bonding and dynamic, thermally reversible carbamate bonds. As precursors, calixarene ureas 1 and 2 were synthesized, which strongly aggregate/dimerize (KD≥106 M−1 per capsule) in apolar solution with the formation of self‐assembling capsules 7 and linear polymeric chains 8, respectively, and also possess “CO2‐philic” primary amino groups on the periphery. CO2 effectively reacts with molecules 7 and 8 in apolar solvents and cross‐links them with the formation of multiple carbamate salt bridges. Oligomeric aggregate 11 and three‐dimensional polymeric network 13 were prepared and characterized by 1H and 13C NMR spectroscopy. The morphology of supramolecular gel 13 was studied by scanning electron microscopy. Addition of a competitive solvent destroyed the hydrogen bonding in assembling structures 11 and 13, but did not influence the carbamate linkers; carbamate salts 12 and 14, respectively, were obtained. On the other hand, thermal release of CO2 from 11 and 13 was easily accomplished (1 h, 100 °C) while retaining the hydroge