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

We report the formation of crystalline inclusion compounds (ICs) between poly(epsilon-caprolactone)-poly(ethylene oxide)-poly(epsilon-caprolactone) triblock copolymer guest and the small-molecule hosts alpha-cyclodextrin (alpha-CD), and gamma-cyclodextrin (gamma-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 C-13 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-alpha CD-IC and triblock-gamma CD-IC were similar to that of valeric acid-alpha CD-IC and 1-propanol-gamma 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-alpha CD-IC and 1730 cm(-1) for triblock-gamma CD-IC compared with the pure cyclodextrins, which confirms the formation of IC. CP/MAS/DD C-13 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 C-13 NMR spectra were observed to confirm that crystalline triblock-CDs-ICs have channel structures, with CDs forming the crystal frame of the inclusion compound. (C) 2000 Elsevier Science Ltd. All rights reserved.