Cyclodextrin in polymer synthesis: a green way to polymers

摘要

Cyclodextrins (CDs) and their chemically modified derivatives have been subject of numerous investigations [1-8]. These compounds have found a large number of applications in many areas, since they hve become available in high quantities, e.g. food chemistry as well as cosmetic and pharmaceutical industries. Furthermore, they can be used in organic chemistry or in polymer chemistry as well. Cyclodextrins are obtained by degradation of starch. They are cyclic oligosaccharides consisting of 6 (alpha), 7(beta), or 8(gamma) glucopyranose units, which are joined together by alpha(1->4)-linkage forming a torus-shaped ring structure. The primary hydroxy groups in 6-position are located at the narrow side of the torus, whereas the secondary glucopyranose OH-groups are located at the wider side of the torus (Fig. 1). Due to their polar hydrophilic outer shell and relatively hydrophobic cavity, they are able to build up host-guest complexes by inclusion of suitable hydrophobic molecules (Fig. 2). The formation of these complexes leads to significant changes of the solubility and reactivity of the guest molecules, but without any chemical modification. Thus, water insolutions of native CD or CD-derivatives, e.g. methylated or hydroxypropylated CD. Hydrogen bonds or hydrophobic interactions are responsible for the stability of the complexes. Based on this knowledgen we were encouraged to investigate the behavior of CD-complexes of various monomers, e.g. of methacrylates or methacrylamides. The formation of the complexes can be verified by FT-IR, ~1H NMR, or 2D-ROESY NMR spectroscopy.As an example, the X-ray structure of isoboronyl acrylate (5a)/beta-DMCD complex (beta-DMCD: Heptakis (2,6-di-O-mehyl beta-cyclodextrin) show that the monomeric guest first into the cavity of 2,6-dimethyl beta-cyclodextrin (Fig 3), whereby the double bonds are located on the narrow side of the conical shaped CD [9].