【作者】 谢龙；

【导师】 杨玉良；

【作者基本信息】 复旦大学 ， 高分子化学与物理， 2007， 博士

【摘要】 到目前为止，在纳米碳管相关的溶液或基体树脂中处理、控制及组装等功能性领域中，共价键合方式修饰纳米碳管已经成为最有效的手段之一。然而对纳米碳管进行聚合物修饰的方法中仍然存在着难以克服的困难——“grafting to”接枝方式中较大分子量聚合物(＞20 000g／mol)的接枝密度低、反应条件要求高(高温、长时间)和制备过程相对繁琐，以及现有改性方式用于工业化生产的可实施性较差等。本课题内容主要围绕上述问题展开，并且成功实现将部分聚合物改性纳米碳管的方式应用于高性能纳米复合材料的制备。以下为主要内容：(1)利用TEMPO活性聚合方式制备含有较高反应活性苄氯基团的两嵌段共聚物，并在相对温和的条件下通过Pschorr-type芳基化法在单壁纳米碳管表面引入苯炔基团。利用苄氯与苯炔基团之间的偶合反应，成功地采用“grafting to”方式将分子量高达47 600 g／mol的两嵌段共聚物接枝到单壁纳米碳管表面，实现了以多点键合方式对单壁纳米碳管的表面改性，并在碳管表面形成了致密均匀聚合物接枝层。通过拉曼和FTIR表征了一步法接枝到碳管表面的苯炔基团；HR-TEM的表征结果证实了此接枝反应的高效性——厚而且均匀的聚合物层包覆在单壁纳米碳管的表面；在TGA上81 wt％的热失重与HR-TEM的结果相一致；同时，~1H NMR证实了随着反应时间的延长聚合物与碳管的键合密度呈逐渐增加的趋势。这一界面层的设计和实现改善了以采用“grafting to”方式进行较大分子量聚合物对纳米碳管表面接枝不均匀的状况，不仅为较大分子量的功能性聚合物修饰纳米碳管开辟了新的途径，也为优化聚合物／单壁碳管纳米复合材料开辟了一种新颖有效思路，并且有利于系统地研究聚合物／纳米碳管界面层的键合密度与复合材料最终力学性能的相关性。(2)少壁纳米碳管的物理和化学性质非常接近于单壁纳米碳管，其特殊的管层结构也赋予它独特的应用领域。我们采用“grafting to”接枝方法并以多点键合的方式对少壁纳米碳管进行聚合物表面修饰，通过两嵌段共聚物上的多个苄氯基团与碳管表面的苯炔基团的偶合反应，得到在碳管表面高键合密度的聚合物接枝层。据理论预测，聚合物／碳管界面的多点键合方式能有效改善聚合物基复合材料的应力传输效率及相关性能。我们把利用上述改性方式修饰的纳米碳管通过溶剂、超声的辅助，并借助旋转涂膜的方法与工业级聚苯乙烯(PS)树脂复合制成了高性能的纳米复合薄膜。针对薄膜平面、液氮脆断面以及拉伸断面的SEM进行了表征，结果证明改性后的纳米碳管能在PS树脂中得到非常良好的分散效果。碳管的净含量仅为0.06 wt％的复合薄膜即可在拉伸强度和拉伸模量方面分别提高了约82％和78％。热性能方面也得到明显增强，相对于纯PS树脂，在纳米碳管含量少于0.06 wt％时其复合薄膜的玻璃化温度几乎没有变化，但是当碳管含量继续增大至0.50 wt％复合薄膜的玻璃化温度则被提高了接近10℃。碳管含量继续增加却会阻碍复合薄膜的力学性能的进一步提高，并且其玻璃化温度的进一步提升也不再明显。(3)便捷、高效是对纳米碳管进行聚合物修饰领域的发展追求。我们通过常规方式进行聚苯乙烯的制备：采用(2，2，6，6-四甲基)-哌啶氮氧自由基(TEMPO)调控并采用偶氮二异丁腈(AIBN)引发制备聚苯乙烯(PS)。通过将对炔基苯胺(APA)嫁接到少壁和单壁纳米碳管(CNT)的表面，得到表面带有苯炔基团的功能化纳米碳管(APA-CNT)。在三氟甲基磺酸存在的情况下，利用苯乙烯分子链末端AIBN残留段端基上的氰基与APA-SWNT的苯炔基在室温条件下进行反应，得到聚苯乙烯包覆且在溶剂中有着良好溶解性能的纳米碳管。通过TEM、AFM和TGA等表征了聚合物功能化纳米碳管的结构形态和接枝效果；Raman和UV-vis表征结果证实了纳米碳管在接枝上聚合物前后相关性能的差异。该方法首次实现了在室温条件下进行聚合物对碳管的修饰；同时，实现了一步法制备带功能性基团的聚合物，完全避免了传统“grafting to”方式修饰碳管的过程中需要对聚合物进行功能化的繁琐步骤。(4)由于苯乙烯单体可以与多种乙烯基单体进行共聚制备聚合物，且适合于多种引发方式，因此我们介绍一种便捷的方式在纳米碳管表面引入大量苯乙烯单体，以便实现聚合物对碳管表面的修饰和简化碳管填充的复合材料的制备工艺。首先通过在SWNTs表面引入苯炔基团，并利用苯炔与苄氯基团的偶合反应将对氯甲基苯乙烯接枝到SWNTs表面，形成富含苯乙烯单体的SWNTs。表面包含大量苯乙烯单体的SWNTs可以通过与乙烯基单体进行原位聚合的方式进行聚合物对SWNTs表面共价键接枝。HR-TEM和SEM对聚合物接枝修饰后的SWNTs表征结果证实了聚合物对SWNTs表面的接枝效果。仅仅通过对氯甲基苯乙烯对其表面修饰后的SWNTs即可在溶剂中得到一定的溶解分散效果，通过进一步与聚苯乙烯接枝修饰后的SWNTs在溶剂中的溶解效果更明显地得到改善。这种通过先在SWNTs表面引入苯乙烯单体来修饰纳米碳管的方法，既可以使修饰后的碳管与乙烯基单体原位聚合实现聚合物对纳米碳管的修饰，也可将富含苯乙烯单体的SWNTs通过熔体混合方式直接与聚合物树脂制备高性能复合材料。更多还原

【Abstract】 Covalent functionalization of carbon nanotubes (CNTs) is currently developing as one of the most powerful tools enabling their processing, manipulation, and assembly from solution and polymer matrices. There are still some problems necessary to overcome in this area, for example, in the existing "grafting to" approaches one needs to balance the molecular weight and grafting density of polymers, and harsh conditions (high temperature and long reaction time) and fussy procedures in polymer functionalizations. The purpose of our investigations is to find some possible routes to overcome the above difficulties. Meanwhile, we hope to explore possible applications of these functionalized CNTs in high-performance polymer nanocomposites. The primary contents of this dissertation are outlined as follows:Single-walled carbon nanotubes (SWNTs) with high covalent bonding density of polymer layers were prepared by "grafting to" approach, where the benzyl chloride groups of styrene copolymers (M_n = 47 600) reacted with the phenyl alkyne groups on SWNTs under relatively mild conditions. This resulted in a grafting efficiency as high as 81 wt % in TGA. Microscopic observations displayed the uniform, thick polymer layers on the SWNT surface. The high density of covalent bonding between polymer and nanotubes was confirmed by Raman, ~1H NMR and FTIR, which makes them well dissolved in organic solvents and homogeneously dispersed in the polymer matrix. The in situ UV-vis observations during the dissolution indicated that for such a multifunctional system almost no cross-links occurred between SWNTs due to the physical absorption and steric hindrance of polymer chains during the functionalization of SWNTs. The current method suggests a possibility to control the covalent bonding density at the interface and to tune the thickness of polymer layers by altering the molecular weights of functional blocks and whole copolymer molecules. It should be helpful for systematically studying the effect of interfacial bonding density on macroscopic properties and further optimizing the properties of SWNT-based nanocmposites.Few-walled carbon nanotubes (FWNTs) have attracted much attention due to their unique structure that may be potential in solving some existing problems associated with SWNTs and multi-walled carbon nanotubes (MWNTs). We here extended the method applied in the first section to the FWNT-polymer interface, in which the pre-synthesized multi-functional diblock copolymers, and then uniform thick polymer layers were coated on the FWNT surface. From the recent molecular simulations and experimental observations, it was recognized that the interfacial shear strength between SWNTs and amorphous/crystalline polymers could be increased with increasing interfacial chemical cross-links. This opinion was further confirmed in our work It was shown that the polymer grafted CNTs with higher bonding density exhibited a pronounced reinforcement effect on the mechanical properties of polymer nanocomposites. The addition of only 0.06 wt % SWNTs resulted in 82% and 78% of increases in tensile strength and elastic modulus of the composites, respectively. This reflects an efficient interfacial stress transfer between SWNTs and polymer. The same increase appeared in thermal property of nanocompostes.The facility and efficiency is important in considering of polymer funcionalization of CNTs. We here report an easy method to functionalize CNTs with polystyrene (PS). We first prepared PS in which 2, 2 -Azobis (isobutyronitrile) (AIBN) was used as an initiator and 2,2,6,6-Tetramethyl-1-piperidineoxy (TEMPO) as a modulator. After the decomposition of AIBN to initiate the polymerization, cyanic groups are left at the PS chain ends. Subsequently, CNTs were functionalized with p-aminophenylalkyne (APA). With the assistance of trifluoromethane sulphonic acid, the coupling reaction between cyanic and phenyl alkyne groups was completed at room temperature, resulting in a 32 wt % grafting efficiency in TGA. The details of PS-grafted CNTs were further characterized by TEM, AFM, Raman and UV-vis. To the best of our knowledge, it is for the first time exhibited that the PS functionalization of CNTs was able to be completed at room temperature and moreover, the grafting polymer (PS) did not require additional incorporation of reactive groups (only the residual cyanic groups at the PS ends were utilized). This is in contrast with the strategies adopted in other "grafting to" methods, and thus simplifies the functionalization procedure of CNTs.Styrene can copolymerize with many vinyl monomers, and adapt to any polymerization initiated methods. We here propose a facile method to introduce lots of styrene monomers to the SWNT surface so that the polymer modification can be realized by means of in-situ polymerization of those styrene monomers covalently linked on SWNTs. To achieve this, phenyl alkyne groups were first grafted to the SWNT surface, followed by the coupling reaction between phenyl alkyne and benzyl chloride of p-chloromethylstyrene. The polymer layers were then formed on the SWNT surface via in-situ polymerization initiated by AIBN and modulated by TEMPO. The results from HR-TEM and SEM proved the micro-configuration of the polymer-grafted SWNTs. Because of introduction of lots of monomers onto the SWNT surface, the solubility of SWNTs was improved and can be dispersed in various organic solvents. The method presented not only affords a chance to copolymerize SWNTs with extensive vinyl monomers, but also can prepare directly nanocomposites by melt-mixing with polymers.更多还原