α-Cyclodextrin/Polyethylene Glycol Polyrotaxane:  A Study of the Threading Process

Aqueous solutions of α-cyclodextrin (α-CD) and polyethylene glycol (PEG) form interesting complexes, where several α-CD units are penetrated by the linear polymeric PEG chain and produce a so-called “polyrotaxane”. This supramolecular structure is stabilized by strong interactions between the α-CD h...

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Bibliographic Details
Published in:Langmuir 1997-04, Vol.13 (9), p.2436-2439
Main Authors: Ceccato, Massimo, Lo Nostro, Pierandrea, Baglioni, Piero
Format: Article
Language:English
Subjects:
Applied sciences
Exact sciences and technology
Organic polymers
Physicochemistry of polymers
Polymers with particular structures
Preparation, kinetics, thermodynamics, mechanism and catalysts
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Summary:Aqueous solutions of α-cyclodextrin (α-CD) and polyethylene glycol (PEG) form interesting complexes, where several α-CD units are penetrated by the linear polymeric PEG chain and produce a so-called “polyrotaxane”. This supramolecular structure is stabilized by strong interactions between the α-CD hydrophobic internal cavity and the −CH2OCH2− moieties of PEG. When cyclodextrins have occupied the whole PEG chain, the polyrotaxanes aggregate and precipitate, forming a thick solid gel. Turbidity measurements at λ = 400 nm were used to study the threading phenomenon. The temperature of the solution and the composition of the solvent affect the formation of polyrotaxanes in a significant way. We propose a molecular model to explain the experimental findings in terms of a multistep threading process. The Gibbs free energy related to the formation of polyrotaxanes is calculated according to the transition state theory.
ISSN:0743-7463
1520-5827
DOI:10.1021/la9609231