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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 thecomplex 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 stoichiometryof the complexes is 2: 1 (two ethylene glycol units and one a-CD). X-ray powder patternsof the PEG-a-CD complexshow that-CDs form channels. The 13C CP/MAS NMR spectrum of the complex suggests that a PEG chain is included in the channel formed …