Preparation and Characterization of Inclusion Complexes of Poly(propylene glycol) with Methylated Cyclodextrins

The complex formation between methylated cyclodextrins (CDs) and poly(propylene glycol) (PPG) in water is described. PPG diamine (Mw = 4000) (PPGN4000) was solubilized in the water phase in the presence of 2,6- O -dimethyl-β-CD (DM-β-CD). 2,3,6-Trimethyl- O -α-CD (TM-α-CD), DM-α-CD, and TM-β-CD did not solubilize PPGN and did not give any precipitated complexes. The effects of DM-β-CD on the solubility of PPG were dependent on the Mw of PPG. The interactions between DM-β-CD and PPG were studied by NMR relaxation spectroscopy in D 2 O. The 1 H resonance of C(3)H at the inner wall of DM-β-CD shifted upfield on addition of PPG. The 1 H spin−lattice relaxation times of C(3)H and C(5)H of DM-β-CD markedly increased on addition of PPG. These results show that a PPG chain is included in the cavities of DM-β-CD in an aqueous solution. When PPGN4000 was vigorously stirred with a saturated aqueous solution over 2 days, the mixture became turbid to give precipitated complexes. The DM-β-CD−PPGN4000 complexes were characterized by 1 H NMR, solid-state 13 C NMR, powder X-ray diffraction, atomic force microscopy, and FT-IR techniques. The complex formation between DM-β-CD and PPG was found to consist of two processes: the solubilization of PPG and the precipitation of complexes. The complexation phenomena between poly(ethylene glycol) (PEG) and methylated CDs were also studied in a similar manner. The interaction of PEG with DM-β-CD is much weaker than that of PPG.