From Supramolecular Polymers to Supramolecular Materials

Design of Hydrogen-bonded Supramolecular Materials by Hierarchical Control of Structural Dimensions

Abstract

Appropriately designed low-molecular-weight organic compounds can form self-assembled nano-to mesoscopic-scale supramolecular polymers having a variety of structures by non-covalent intermolecular interactions. To fabricate macro-scale supramolecular materials, the supramolecular polymers have to be assembled further into macro-scale ordered structures. For this purpose, we adopted the molecular design to use non-polar and soft segments as molecular-level cushions in order to assist the assembling process and also applied external mechanical forces in order to induce macro-scale ordering of the supramolecular polymers. Based on this strategy, the supramolecular fibers,, gels, and films were successfully fabricated hierarchically. Molecular design to cover the hydrogen-bonded linear chains by the soft segments and use of the melt-or heat-spinning process allowed fabrication of the flexible supramolecular fibers, in which the one-dimensional hydrogen-bonded polymer chains were aligned along the fiber axis. Two-dimensional hydrogen-bond networks were formed by additional hydrogen-bonds between the linear hydrogen-bonded polymer chains, and molecular design to sandwich this networks by soft segments led to formation of two-dimensional sheet-like structures which induced organogelation by trapping the solvent molecules in between the sheets. Self-supporting and flexible supramolecular films were also fabricated by introduction of polar groups at the surface of the sheet-like structures. These results demonstrate that the molecular design to use soft segments is the efficient method to fabricate supramolecular materials.