Recent Advances in Supramolecular Polymers

Abstract

Typically polymers are defined as a long string of ''mers'' arranged linearly or in a variety of branched configurations and connected by strong covalent bonds. These materials are produced by the ton and account for billions of dollars annually. Clearly these materials have extremely important properties and price/performance ratio. Despite their amaz-ing success there are some properties which are difficult or impossible to obtain from traditional polymers. These in-clude the ability to form and disassemble under specific environmental conditions, the ability to accurately control molecular and nanostructure at multiple level of size hier-archy and generally to be ''smart'', responsive materials. One approach to achieve there desirable properties is to make polymer whose mers are held together by multiple weak noncovalent bonds that can be formed and broken in a predictable, controllable and reversible fashion. These supramolecular polymers are stabilized by nonco-valent forces like hydrogen bonding, pi–pi interactions, metal complexation, and the hydrophobic effect. They have unique properties of reversibility and stabilization by additive directional forces, which although not so strong on their own, give rise to stable systems by summation of all the forces. Natural systems like the DNA double helix and protein folding are a result of the ''bottom-up'' self-assembly of small biomolecules like DNA bases, amino acids in a specific fashion and orientation. Protein structure is maintained by interplay of supramolecular interactions like hydrogen bonding and hydrophobic effect. Fibrillin, main component of microfibrils, is stretchy because of the presence of folded beta-sheet domains, which fold in re-laxed state and unfold when they are stretched [1]. These natural systems, with their complex architecture and diverse functions, have always fascinated and inspired people to prepare materials with novel properties. Design of structures trying to mimic self-assembly of protein units in TMV is one such example. Supramolecular forces play an important role in defining the properties of covalent systems too. For example, the presence of hydrogen bonding in covalent polymers like nylons greatly improves their material prop-erties. Unlike conventional polymers in which the ''mers'' are bound together by string covalent bonds, the supramolecular polymers are assembled together by the process of self-assembly, thereby leading to the formation of a multicom-ponen…