【作者】 魏坤；

【导师】 黎华明；

【作者基本信息】 湘潭大学 ， 高分子化学与物理， 2009， 硕士

【摘要】 自从碳纳米管被发现以来,由于其独特的结构引起了人们的广泛关注。碳纳米管具有优越的力学性能,优良的化学稳定性和热稳定性,良好的电性能和生物相容性。由于碳纳米管间较强的相互作用及不溶于任何溶剂,极大地制约了其应用。因此,对碳纳米管进行改性以提高其在溶剂及基材中的分散性,具有十分重要的意义。目前为止,已报道多种碳纳米管修饰方法,通常分为物理修饰与化学修饰。本论文采用化学方法中的“向碳纳米管接枝”方法,通过硼酸酯化反应,将双羟基封端的聚苯乙烯(PS)接枝到硼酸功能化的多壁碳纳米管(MWNTs)表面,实现对碳纳米管修饰。该修饰方法的特点在于接枝的可逆性,可以劈下-接上多次重复。此外,本文对碳纳米管凝胶的合成也进行了探索,首先合成含二羟基丙烯酸酯单体和硼酸酯类单体,并将二羟基丙烯酸酯聚合物接枝到碳纳米管上,再与含硼酸单元的共聚物混合,利用硼酸酯化反应合成碳纳米管凝胶。主要研究工作包括以下几个方面:聚合物对MWNTs可逆修饰。先以含二羟基的三硫代碳酸酯[EMP-(OH)2]为链转移剂,采用可逆加成-断裂链转移(RAFT)聚合方法合成双羟基封端的聚合物[PS-(OH)2]。而后利用二溴丁烷将对羟基苯硼酸频哪醇酯接枝到MWNTs表面,去保护后得到硼酸修饰的MWNTs[MWNT-B(OH)2]。通过MWNTs表面的硼酸基团和聚合物链端的双羟基之间的酯化反应,即可将PS接枝到MWNTs表面,同时在酸作用下又能将聚合物“劈”下,实现聚合物对MWNTs的可逆修饰。采用红外光谱(FTIR)和热重分析(TGA)对小分子和聚合物修饰的MWNTs进行了表征。TGA结果表明硼酸的接枝率可达到0.222 mmol/g,聚合物的接枝率为0.041 mmol/g。此外,采用紫外光谱法研究了PS-(OH)2对[MWNT-B(OH)2]的可逆修饰效果,实验结果表明可逆修饰重复5次以后,聚合物修饰的MWNTs的溶解度基本不变,说明聚合物接枝量基本稳定。另外,MWNTs表面接枝聚合物的“劈”下速率与体系中酸浓度有关。MWNT凝胶的合成。采用羟基保护和硼酸基团保护的方法,先分别合成(2,2,5-三甲基-1,3-二氧己烷)丙烯酸甲酯(TDMA)和4-乙烯基苄基-4-(1,3,2-二氧杂己硼烷-2-基)苯甲酸酯(VBDB)两种新型单体。随后将RAFT试剂键接到MWNTs表明,并通过RAFT聚合反应将PTDMA接枝到MWNTs表面,去保护后即得到聚(3-羟基-2-(羟甲基)-2-甲基丙基)丙烯酸酯(PHHMA)修饰的碳纳米管(MWNT-PHHMA)。同样以EMP-(OH)2为链转移剂,采用RAFT聚合方法合成PVBDB-co-PS,去保护后得到含硼酸单元的共聚物(PVPA-co-PS)。将PVPA-co-PS和PHHMA修饰的MWNTs按一定的比例在溶剂中混合后,通过硼酸酯化反应即可得到MWNTs凝胶。更多还原

【Abstract】 Since the discovery of carbon nanotubes (CNTs) in 1991, they have attracted great attentions in recent years. CNTs have excellent mechanical properties, good chemical and thermal stabilities, predominant electric properties and biocompatibility. However, the inherent insolubility of CNTs in most organic and aqueous solvents has hindered their applications. Therefore, it is very important to functionalize CNTs with polymers in order to improve their dispersibility in solvents and matrices. Recently, various functionalization methods have been investigated, including physical adsorption and chemical binding. In this thesis, we have presented a scheme for the functionalization of multiwalled carbon nanotubes (MWNTs) by reversible binding polymer to their surface via boronic acid chemistry. Specially synthesized bifunctional polystyrene carrying a diol on the end was bound to the boronic moieties on the MWNT surface via the diol group, enabling attachment of polymer to the nanotubes. The tube-bound polymers could be released back to solution by cleaving the boronate ester groups, leaving a few polymer molecules on the MWNTs. The released polymer molecules could be rebound to the surface of boronic acid functionalized MWNTs. In addition, MWNT based gel was prepared via boronic acid chemistry by mixing PDHMA functionalized MWNTs and the random copolymer of VBDB and styrene.Reversible binding of polymer to MWNT surface. Polystyrenes carrying a diol on the end [PS-(OH)2] with different molecular weight were synthesized through RAFT polymerization using trimethylolpropane modified trithiocarbonate [EMP-(OH)2] as chain transfer agent. Additionally, the hydroxyl-functionalized MWNTs was firstly treated with 1,4-dibromobutane followed by pinacol 4-hydroxyphenyl boronate to produce boronate-functionalized MWNTs. After deprotection of pinacol group by hydrolysis, the resulting boronic acid-functionalized MWNTs [MWNT-B(OH)2] were used to react with PS-(OH)2. Polystyrene carrying a diol group on the end was bound to the boronic moieties on the MWNT surface via boronic acid chemistry, enabling attachment of polymer to the nanotube surfaces. The MWNT-bound polymers could be released back to solution by cleaving the boronate ester groups. Again, the released polymer molecules could be rebound to the surface of MWNT-B(OH)2. This process of reversible binding polymer to MWNTs is studied here in detail. Several polymer samples with different molecular weight were prepared and investigated. Furthermore, the chemical conditions for cleavage of the boronate ester were also studied in this thesis. The MWNT-B(OH)2 as well as PS-functionalized MWNTs were characterized by TGA analysis and FTIR spectroscopy. Reversible polymer binding to MWNT surfaces was also investigated by UV spectroscopy. The results indicated that the solubility of polymer functionalized MWNTs were almost unchanged after five cycles of binding and rebinding processes. The cleavage of the boronate ester were found to be depended on the acid concentrations of the reaction system.Preparation of MWNT gel. Novel monomers, (2,2,5-trimethyl-1,3-dioxan-5-yl) methyl acrylate (TDMA) and 4-vinylbenzyl 4-(1,3,2-dioxaborinan-2-yl)benzoate (VBDB), were synthesized using hydroxyl and boronic group protection method, respectively. Subsequently, reversible addition-fragmentation chain transfer (RAFT) agent was covalently attached onto the surface of MWNTs, which was used to polymerize TDMA, yielding polymer functionalized MWNTs. After that the dioxolane functional groups were deprotected to form 1,2-diol groups, yielding PHHMA functionalized MWNTs (MWNT-PHHMA). Similiarly, random copolymer of VBDB and styrene (PVBDB-co-PS) was also prepared via RAFT polymerization using EMP-(OH)2 as agent. After deprotection, PVPA-co-PS cpolymer was obtained. The MWNT gel was formed through mixing MWNT-PHHMA and PVPA-co-PS in toluene via borinic acid chemistry.更多还原