Supramolecular polymer

Supramolecular polymers are a subset of polymers where the monomeric units are connected by reversible and highly directional secondary interactions–that is, non-covalent bonds. These non-covalent interactions include van der Waals interactions, hydrogen bonding, Coulomb or ionic interactions, π-π stacking, metal coordination, halogen bonding, chalcogen bonding, and host–guest interaction. Their behavior can be described by the theories of polymer physics in dilute and concentrated solution, as well as in the bulk.

Additionally, some supramolecular polymers have distinctive characteristics, such as the ability to self-heal. Covalent polymers can be difficult to recycle, but supramolecular polymers may address this problem.

History

The preamble of the field of supramolecular polymers can be considered dye-aggregates and host-guest complexes. In early 19th century, it was noticed that dyes aggregate via "a special kind of polymerization". In 1988, Takuzo Aida, a Japanese polymer chemist, reported the concept of cofacial assembly wherein the amphiphilic porphyrin monomers are connected via van der Waals interaction forming one-dimensional architectures in solution, which can be considered as a prototype of supramolecular polymers. Soon thereafter, one-dimensional aggregates were described based on hydrogen bonding interaction in the crystalline state. With a different strategy using hydrogen bonds, Jean M. J. Fréchet showed in 1989 that mesogenic molecules with carboxylic acid and pyridyl motifs, upon mixing in bulk, heterotropically dimerize to form a stable liquid crystalline structure.