Preparation and characterization of inclusion complexes formed by biodegradable poly(ε-caprolactone)–poly(tetrahydrofuran)–poly(ε-caprolactone) triblock copolymer and cyclodextrins

Inclusion complexes (ICs) formed with cyclodextrins (CDs) and polymers have been an interesting topic over the past decade. Recently, more focus has been shifted to the ICs with biodegradable polymers or copolymers because of their potential applications as novel biomaterials. This work reports the IC formation between CDs and biodegradable poly(ε-caprolactone)–poly(tetrahydrofuran)–poly(ε-caprolactone) (PCL–PTHF–PCL) triblock copolymer and the characterization of the ICs. The PCL–PTHF–PCL triblock copolymer was found to form crystalline ICs with all α-, β-, and γ-CDs. All the three ICs were prepared in high yields from aqueous medium. The ICs were characterized by X-ray diffraction (XRD), 13C CP/MAS NMR, 1H NMR, Fourier transform infrared, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The XRD studies demonstrated that all the ICs assumed a channel-type structure similar to the necklace-like ICs formed by α-CD and poly(ethylene glycol) homopolymers. Solid-state CP/MAS 13C NMR studies showed that the CD molecules in the ICs adopted a symmetrical conformation due to the threading onto a polymer chain. The compositions of the ICs were studied by using 1H NMR spectroscopy. From the 1H NMR and DSC results, it was proposed that only the two flanking PCL blocks are included and covered by α-CD in the α-CD–PCL–PTHF–PCL IC, while the two PCL blocks as well as the middle PTHF block are included and covered by β-CD in the β-CD–PCL–PTHF–PCL IC. On the other hand, it was proposed that the PCL–PTHF–PCL copolymer is probably included and covered by γ-CD in a double-stranded mode in the γ-CD–PCL–PTHF–PCL IC. Finally, The TGA analysis revealed that the ICs had better thermal stability than their free components due to the inclusion complexation, suggesting that the complexation stabilized the copolymer included in the CD channels.