Sol–Gel Transition during Inclusion Complex Formation between α-Cyclodextrin and High Molecular Weight Poly(ethylene glycol)s in Aqueous Solution

Abstract

Poly(ethylene glycol)s (PEG) of high molecular weights were found to form complexes with α-cyclodextrin (α-CD) in aqueous solutions to give gels in a wide range of concentrations. The time of gelation decreases with increase in α-CD and PEG concentrations, indicating that the gels formed during complex formation between α-CD and PEG chains. The time of gelation increases with increase in the molecular weight of PEG, indicating that the PEG chains penetrate α-CD cavities from the ends of PEG and are included by α-CDs. X-Ray powder diffraction studies showed that the gel consists of both complexed α-CD and uncomplexed α-CD, indicating partial inclusion of PEG chains by α-CD. The configuration of the gels and mechanism for the gelation are discussed, and it is suggested that α-CD-PEG complexes act as physical cross-links during gelation. The gel-melting temperature increases with increase in PEG molecular weights and α-CD concentrations, and decreases with increase in PEG concentrations, suggesting that gelation results from the formation of longer or shorter domains of α-CD–PEG inclusion complexes, respectively.