Formation and characterization of the inclusion compounds between poly(?-caprolactone)-poly(ethylene oxide)-poly(?-caprolactone) triblock copolymer and ?- and ?-cyclodextrin

Document Type

Article

Publication Date

4-21-2000

Abstract

We report the formation of crystalline inclusion compounds (ICs) between poly(?-caprolactone)-poly(ethylene oxide)-poly(?-caprolactone) triblock copolymer guest and the small-molecule hosts ?-cyclodextrin (?-CD), and ?-cyclodextrin (?-CD). The triblock copolymer-CDs-ICs are formed by cocrystallization from saturated solutions of CDs, and each of them was observed with TGA, DSC, X-ray diffraction, and FTIR and 13C NMR spectroscopes. It was found that the ICs have higher temperature stability than the pure CDs The absence of a melting peak for the crystalline PCL blocks in the heating scan of triblock-CDs-ICs indicates that there is no free crystalline block copolymer. The X-ray powder diffraction patterns of triblock-?CD-IC and triblock-?CD-IC were similar to that of valeric acid-?CD-IC and 1-propanol-?CD-IC, which were confirmed to be a channel crystal structures by single crystal X-ray diffraction. In FTIR studies, new bands appeared at 1737 cm-1 for triblock-?CD-IC and 1730 cm-1 for triblock-?CD-IC compared with the pure cyclodextrins, which confirms the formation of IC. CP/MAS/DD 13C NMR spectra of triblock-CDs-ICs indicate that CDs adopt a more symmetrical conformation in the triblock-CDs-ICs, while pure CDs assume a less symmetrical conformation in the crystal when they do not include a guest block copolymer inside their cavities. One pulse 13C NMR spectra were observed to confirm that crystalline triblock-CDs-ICs have channel structures, with CDs forming the crystal frame of the inclusion compound.

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