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a-Cyclodextrin (a-CD) was found to form inclusion complexes with poly (ethylene glycol) (PEG) of various molecular weights to give stoichiometric compounds in a crystalline state in high yields. -CD does not form complexes with the low molecular weight analogs, ethylene glycol, diethylene glycol, and triethylene glycol. The rate of the complex formation depends on the molecular weight of PEG. PEG of molecular weight 1000 forms complexes most rapidly. The complexes were characterized by IR, NMR, 13C NMR, and 13C CP/MAS NMR spectra and X-ray (powder), thermal, and elemental analyses. The NMR spectra of the complexes show that the stoichiometry of the complexes is 2:1 (two ethylene glycol units and one a-CD). X-ray powder patterns of the PEG-a-CD complex show that -CDs form channels. The 13C CP/MAS NMR spectrum of the complex suggests that a PEG chain is included in the channel formed by -CDs. a-CD formed complexes with PEG having small end groups, such as methyl, dimethyl, and amino groups, but did not form complexes with PEG carrying large substituents, such as 2,4-dinitrophenyl and 3,5-dinitrobenzoyl groups. 0-CD did not form complexes with polyethylene glycol) of any molecular weight. The modes of the complexes are discussed.

3-Cyclodextrin (/3-CD) and y-cyclodextrin (y-CD) form inclusion complexes with polypropylene glycol)s (PPG) of various molecular weights to give stoichiometric compounds in crystalline states. -Cyclodextrin (a-CD) did not form complexes with PPG of any molecular weight, ß-and y-CD did not form complexes with the low molecular weight analogs, such as propylene glycol, di(propylene glycol), and tri(propylene glycol). The yields of the complexes of ß-and y-CD with PPG increased with increasing molecular weight (MW) of the PPG and reached a maximum at about MW 1000; yield decreased with a further increase in the MW. They were isolated and found to be 2:1 (monomer unit:CD). The complexes were characterized by IR, NMR, 13C NMR, 13C CP/MAS NMR, and 13C PST/MAS NMR spectra and X-ray (powder), thermal, and elemental analyses. Complex formation of CDs with PPG derivatives has also been studied. The structures of the complexes are discussed. Complex formation of /3-CD with atactic and isotactic PPG has been compared.

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ABSTRACT:Poly(ethylene glycol)s (PEG) of high molecular weights were found to form complexes with ix-cyclodextrin (ix-CD) in aqueous solutions to give gels in a wide range of concentrations. The time of gelation decreases with increase in ix-CD and PEG concentrations, indicating that the gels formed during complex formation between ix-CD and PEG chains. The time of gelation increases with increase in the molecular weight of PEG, indicating that the PEG chains penetrate ix-CD cavities from the ends of PEG and are included by ix-CDs. X-Ray powder diffraction studies showed that the gel consists of both complexed ix-CD and uncomplexed ix-CD, indicating partial inclusion of PEG chains by ix-CD. The configuration of the gels and mechanism for the gelation are discussed, and it is suggested that ix-CD-PEG complexes act as physical cross-links during gelation. The gel-melting temperature increases with increase in PEG molecular weights and ix-CD concentrations, and decreases with increase in PEG concentrations, suggesting that gelation results from the formation of longer or shorter domains of ix-CD-PEG inclusion complexes, respectively.KEY WORDS Sol-Gel Transition/ ix-Cyclodextrin / High Molecular Weight Poly(ethylene glycol)/ Inclusion Complex/ X-Ray Diffraction Pattern/ Cyclodextrins (a-CD, {3-CD, and y-CD) (Figure la) are cyclic oligosaccharides with internal cavities capable of forming inclusion complexes with small organic or inorganic compounds in aqueous solutions and a great number of inclusion complexes have been prepared and characterized.

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