CO_2 in Supramolecular Chemistry:Preparation of Switchable Supramolecular Polymers

摘要

CO_2 gas was used to construct novel types of supramolecular polymers.Self-assembling nanostruc-tures 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 (K_D>=10~6M~(-1) per capsule) in apolar solution with the formation of self-assembling capsules 7 and linear polymeric chains 8,respectively,and also possess "CO_2-philic" primary amino groups on the periphery.CO_2 effectively reacts with molecules 7 and 8 in apolar solvents and cross-links them with the formation of multiple carbamate salt bridges.Oligo-meric aggregate 11 and three-dimensional polymeric network 13 were prepared and characterized by ~1H and ~(13)C 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 CO_2 from 11 and 13 was easily accomplished (1 h,100 deg C) while retaining the hydrogen-bonding capsules.Thus,three-dimensional polymeric network 13 was transformed back to linear polymeric chain 8 without breaking up.Encapsulation and storage of solvent molecules by 11 and 13 was demonstrated.This opens the way for switchable materials,which re-versibly trap,store,and then release guest molecules.A two-parameter switch and control over hydrogen bonding and CO_2-amine adducts was established.