碳纳米管的有机共价修饰及其性能研究

【作者】 高耸；

【导师】 隋坤艳；

【作者基本信息】 青岛大学 ， 材料加工工程， 2010， 硕士

【摘要】 碳纳米管(CNT)具有优良的力学、电学、热学性能,在理论研究和实际应用方面引起了广泛的关注。为拓展CNT的应用范围,对CNT进行功能化是十分必要的。本论文主要采用有机共价键修饰在多壁碳纳米管(MWNT)上接枝水溶性的聚合物聚乙二醇(PEG),并利用得到的带有官能团的MWNT作为载体或者模板来构建功能化的纳米杂化材料,主要工作如下：1.利用酸化的MWNT在二环己基碳二亚胺／4-二甲氨基吡啶(DCC/DMAP)存在的条件下,同PEG发生酯化反应得到了PEG功能化的碳纳米管(MWNT-g-PEG)。利用PEG与α-环糊精(α-CD)之间的包合作用,首次制备了MWNT-g-PEG/a-CD超分子杂化纳米凝胶。通过X射线衍射、核磁、差示扫描量热法、热失重、流变等测试手段对得到的包合物进行了表征。结果表明,由于MWNT的阻碍作用,包合物中EG：α-CD的单元比大于理论值2：1；研究还表明,MWNT-g-PEG/a-CD杂化凝胶的形成取决于两个条件：1)MWNT上的PEG具有足够高的接枝密度,2)PEG链具有足够的长度。流变学特性分析表明,MWNT-g-PEG/a-CD杂化凝胶的强度远远大于PEG/a-CD凝胶的强度,分析原因是在凝胶的形成过程中,MWNT由于强烈的疏水作用会自组装发生聚集,这种聚集作用的结果使MWNT作为凝胶的超级交联点促进了凝胶网络的形成,因而提高了凝胶的强度。并且,MWNT-g-PEG/a-CD杂化凝胶具有触变性和可逆性,使其在药物注射方面具有潜在的应用。热性能的研究表明,MWNT的引入显著改善了凝胶的热稳定性,并使其热分解温度提高了大约100℃,远远高于目前的有关文献报道。2.利用MWNT-g-PEG作为介质,在低温下,通过溶胶凝胶法制备了MWNT表面负载花瓣状的氧化锌(ZnO)纳米复合材料。通过X射线衍射、红外波谱、扫描电镜和透射电镜对杂化复合材料进行表征。结果表明,ZnO纳米粒子和MWNT之间结合紧密,ZnO的尺寸比较均一。另外,研究表明,MWNT表面的PEG对ZnO的负载起着重要的作用,它是ZnO原位生长的活性点,推测了其生长机理。3.通过原子转移自由基-氮氧自由基偶合的方法(ATNRC)成功制备了MWNT-TEMPO-PEG。首先,通过4-羟基-2,2,6,6-四甲基吡啶氮氧自由基与酸化后MWNT表面的羧基的脱水缩合反应,制备了表面带有氮氧自由基的MWNT (MWNT-TEMPO);另一方面,利用PEG的羟基与2-溴异丁酰溴发生酯化反应得到了末端带有溴原子的PEG (PEG-Br)ATRP引发剂；然后将MWNT-TEMPO和PEG-Br在溴化亚酮／五甲基二乙烯基三胺(CuBr/PMDETA)存在的条件下,进行自由基偶和反应,得到了MWNT-TEMPO-PEG。所得的产物通过红外、核磁、热分析、透射电子显微镜等进行了表征。研究表明,通过ATNRC方法得到MWNT-TEMPO-PEG上的PEG接枝密度为41%,与我们前期做可达54%的MWNT-g-PS的接枝密度相比,降低了很多,分析原因为PEG-Br在ATNRC体系中会发生去质子化而自我终止,从而降低了反应活性。更多还原

【Abstract】 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.更多还原