ALPHA-CYCLODEXTRIN POLYETHYLENE GLYCOLPOLYROTAXANE - A STUDY OF THE THREADING PROCESS/

Aqueous solutions of alpha-cyclodextrin (alpha-CD) and polyethylene gl ycol (PEG) form interesting complexes, where several alpha-CD units ar e penetrated by the linear polymeric PEG chain and produce a so-called ''polyrotaxane''. This supramolecular structure is stabilized by stro ng interactions between the alpha-CD hydrophobic internal cavity and t he -CH2OCH2- moieties of PEG. When cyclodextrins have occupied the who le PEG chain, the polyrotaxanes aggregate and precipitate, forming a t hick solid gel. Turbidity measurements at lambda = 400 nm were used to study the threading phenomenon. The temperature of the solution and t he composition of the solvent affect the formation of polyrotaxanes in a significant way. We propose a molecular model to explain the experi mental findings in terms of a multistep threading process. The Gibbs f ree energy related to the formation of polyrotaxanes is calculated acc ording to the transition state theory.