PREPARATION AND PROPERTIES OF INCLUSION COMPLEXES OF POLY(ETHYLENE GLYCOL) WITH ALPHA-CYCLODEXTRIN

Alpha-cyclodextrin (alpha-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. Alpha-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, H-1 NMR, C-13 NMR, and C-13 CP/MAS NMR spectra and X-ray (powder), thermal, and elemental analyses. The H-1 NMR spectra of the complexes show that the stoichiometry of the complexes is 2:1 (two ethylene glycol units and one alpha-CD). X-ray powder patterns of the PEG-alpha-CD complex show that alpha-CDs form channels. The C-13 CP/MAS NMR spectrum of the complex suggests that a PEG chain is included in the channel formed by alpha-CDs. Alpha-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. beta-CD did not form complexes with poly(ethylene glycol) of any molecular weight. The modes of the complexes are discussed.