Nanostructuring and functionalizing polymers with cyclodextrins

We summarize our recent studies employing the cyclic starches called cyclodextrins (CDs) to both nanostructure and functionalize polymers. Two important structural characteristics of CDs are taken as advantages to achieve these goals. First the ability of CDs to form non-covalent inclusion complexes (ICs) with a variety of guest molecules, including many polymers, by threading and inclusion into their relatively hydrophobic interior cavities, which are roughly cylindrical with diameters of ∼0.5 to 1.0 nm for α-, β-, and γ-CD containing 6, 7, and 8 α-1,4-linked glucose units, respectively. When guest polymers are coalesced from the CD-ICs by removing their host CDs, they are observed to solidify with structures, morphologies, and even conformations that are distinct from bulk samples made from their solutions and melts. Molecularly mixed, intimate blends of two or more polymers that are normally immiscible can be obtained from their common CD-ICs, and the phase segregation of incompatible blocks can be controlled (suppressed or increased) in CD-IC coalesced block copolymers. In addition, additives may be more effectively delivered to polymers in the form of their soluble or crystalline CD-ICs or rotaxanes. Secondly, many -OH groups attached to the exterior rims of CDs, in addition to conferring water solubility, provide an opportunity to covalently bond them to polymers either during their syntheses or via post-polymerization reactions. Polymers containing CDs in their backbones or attached to their side chains are observed to more readily accept and retain additives, such as dyes, fragrances, etc. They may also be further reacted or treated through their CDs to cross-link and form networks or to form blends with other polymers having a propensity to thread through their attached CD cavities.