| Due to unique structural and superior properties of carbon nanotubes(CNT), it has been investigated for both in the theoretical understanding and in practical applications. To expand the application of carbon nanotubes, functionalized CNT, including noncovalent modification and covalent modification is necessary.In this thesis, Water-soluble Poly(ethylene glycol)(PEG) grafted multi-walled carbon nanotubes (MWNT-g-PEG) was prepared first, and then fabricate functional nanohybrids with as-modified CNT as templates or nano-supporters in order to overcome the existed problems in this area. The main contributions are as follows:1. MWNT-g-PEG was synthesized by MWNT containing carboxyl groups (MWNT-COOH) with PEG in the presence of N,N-dicyclohexylcarbodiimide (DCC) and 4-N,N-dimethylaminopyridine (DMAP). We first succeeded in constructing MWNT-g-PEG/a-CD hybrid hydrogels based on the complexes of a-cyclodextrins (a-CD) and PEG. The polypseudorotaxane structures of the as-obtained hydrogels were confirmed by 1HNMR, X-ray diffraction, TGA and DSC analyses. As a result, the stoichiometric ratios of EG:a-CD is higher than the theoretical values 2:1 due to the repulsion of the MWNT. It can therefore be suggested that two conditions must exist for the formation of MWNT-g-PEG/a-CD hybrid hydrogels:1) long enough PEG chains must be available for the threading of a-CD and long enough uncomplexed PEG must exist for physical cross-linking; 2) a high graft density must provide enough physical cross-links. The introduction of MWNT nanoparticles positively affected the strength and viscosity of the hydrogels. More importantly, the hybrid hydrogels also showed a shear thinning effect attributed to the supramolecular physical nature of the supra-cross-links. Moreover, it was observed that a disrupted sol phase could be turned reversibly into a gel after shearing and allowing to stand for a certain period of time. It could be concluded that the gels were thixotropic and reversible, and potentially suitable for use as an injectable drug delivery matrix through fine needles.Thermal analysis showed that the thermal stability of the hybrid hydrogel was substantially improved by up to 100℃higher than that of native hydrogel.2. MWNT-g-PEG enclosed by petal-like zinc oxide (ZnO) particles were prepared by sol-gel method at ambient pressure and low temperature (T=70℃). The hybrid nanocomposites were characterized using XRD, FTIR, TEM and SEM. The results obtained exhibited intimate contact between the ZnO nanoparticles and MWNT-g-PEG and ZnO crystallites had a very uniform size distribution of 80-150 nm. It was suggested that the PEG chains on MWNT surface act as the active sites for the in-situ growth of ZnO.3. MWNT-TEMPO-PEG was synthesized by atom transfer nitroxide radical coupling chemistry (ATNRC). MWNT with 2,2,6,6-tetramethylpiperidine-l-oxy (MWNT-TEMPO) groups was prepared first by esterification of 4-hydroxy-2,2,6,6-tetramethylpiperidine-l-oxy (HO-TEMPO) and carboxylic acid group on the surface of MWNT, and then PEG with bromide end group (PEG-Br) were obtained by esterification of PEG and ethyl 2-bromoisobutyryl bromide. When the MWNT-TEMPO was mixed with PEG-Br and heated to 90℃in the presence of CuBr/PMDETA, the formed secondary carbon radicals at the PEG chain ends were quickly trapped by the nitroxide radicalson MWNT-TEMPO to form graft copolymer in which the alkoxyamines were at the conjunction points. The product was characterized by FTIR, NMR, TGA, and TEM. Nevertheless, the efficiency of coupling reaction in MWNT-TEMPO/PEG-Br was 41%, which showed the lower coupling efficiency than that of MWNT-TEMPO/PS-Br system of our previous work. Usually, the higher activity for PEG-Br would lead to the easier termination via disproportionation during the ATNRC procedure. It means that once the radical generated from-C(CH3)2Br, it might not be trapped by TEMPO immediately through the ATNRC (ktc), the radicals would prefer to terminate by disproportionation (ktd) instead of forming the dormant radical. |
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