Surface modification of carbon nanotubes (CNTs) via click reactions

Carbon nanomaterials have crucial importance in the science and commercial applications. Carbon-based materials like diamond, fullerene, graphite, nanotubes and nanowires are used in some applications such as electronic, optic-electronic, biomedical engineering, tissue engineering, medical implants, medical devices and sensors. New nano-hydrids obtained by hybridization of carbon-based materials with materials having different properties like metals, metal oxides and polymers have increased their area of usage. CNTs can be defined as simply rolled graphite and can be grouped based on their layer numbers as; single walled, double walled and multi walled CNTs. Their circular curve structure is the main reason for quantum restrictions and σ-π re-hybridization. After re-hybridization, three σ bonds slightly move out of the plane and increase the elbowroom of π orbitals. These special characteristics makes CNTs to have better mechanical strength, electrical and thermal conductivity, and chemical and biological activity when it's compared to graphite. However, their area utilization is limited because of their handling restrictions, one of which is their low solubility especially in organic solvents. This results as disadvantage when they need to be purified or be treated so their usage cannot be possible unless they have been pre-modified. Small molecules or polymers can be grafted via covalently or non-covalently approach to the surface of CNTs to increase its dispersion. Frequently used sidewall halogenation reactions, hydrogenation, Diels-alder cycloaddition, [2+1] nitrene addition, thiol-ene reaction can be examples for grafting onto the surface of the π-conjugated skeleton by covalent modification. Surface of carbon nanotubes are non-covalently functionalized by the way of adsorption of polynuclear aromatic compounds having functional groups such as anthracene, naphthalene, pyrene or porphyrin. Small aromatic molecules are attached onto the surface of CNTs via π-π stacking in non-covalent strategy. This strategy has an advantage in terms of preserving mechanical and electronic properties of CNTs' surface after modification. In this study, increasing the usage area of hybrit materials that are obtained by the application of different click chemistries onto the surface of single and multi walled CNTs that increase their solubility in many organic solvents.The first two parts of the stu The walls (surfaces) of carbon nano tubes are modified by different reactions that have significant importance for green chemistry applications. For direct covalent modification, methodologies that does not require any metal ligand complexes are choosen such as Diels-Alder, [2+1] nitrene cycloaddition and thiol-ene reactions whereas for indirect covalent modification, active ester reactions are used dy are focused on the modification of the sidewalls of carbon nanotubes by the covalent approach. In the first part of the thesis, four model reactions between CNTs and small molecules having functional groups such as furan, maleimide, anthracene and azide were carried out to evaluate efficiency of Diels-Alder and nitrene cycloaddition reactions. Positive results obtained from model reactions proceeded the study to the next step which is mono modification of carbon nanotubes with the polymers having suitable functional groups. So, firstly, polymers having an end group (PMMA, PtBA, PS, PEG etc.) such as furan, maleimide, anthracene, azide and thiol were synthesized and characterization of them were supported by the NMR, FT-IR and GPC measurements. Diels-Alder, nitrene cycloaddition and thiol-ene click reactions were performed between these polymers and SWCNTs, MWCNTs, and MWCNT-COOH. In accordance with the results obtained from experiments, second modification methodologies such as Diels-Alder, nitrene cycloaddition and thiol-ene reaction was applied to mono-modified carbon nanotubes, which have positive results from the previous step in the presence of polymers having suitable functional groups. Besides sequential double modification, sequentially one-pot double modification methodology was applied to unmodified CNTs. Double combinations of these chemistries such as nitrene addition - thiol-ene click reaction, Diels-Alder cycloaddition - thiol-ene click reaction, nitrene addition - Diels-Alder cycloaddition were used for double modification of carbon nanotubes sequentially. And, combinations of nitrene addition - Diels-Alder cycloaddition, thiol-ene click reaction - nitrene addition and Diels-Alder cycloaddition - nitrene addition were used for one-pot double modification of CNTs by sequential approach. Thermal gravimetric analysis of the performing experiments from both approaches showed that carbon nanotubes can be functionalized with these approaches. In the second part of the thesis, firstly grafting of amine-terminated PEG to the surface of multi walled CNTs by active ester reaction is performed. This is further followed by the grafting of azide-terminated PS polymers by nitrene reaction. Firstly, acid functions of commercially available carbon nanotubes (MWCNT-COOH) were changed to acid chloride (MWCNT-OCCl). This reaction can be performed by the presence of thionyl chloride or oxalyl chloride together with a catalytic amount of DMF once the optimum reaction temperatures are obtained (0 °C to 60 °C). Then, pentaflourophenyl ester of MWCNTs (MWCNT-COOC5F6) was synthesized by the presence of MWCNT-OCCl pentaflourophenol and pyridine. MWCNT-COOC5F6 were very active against amines and its reaction with amine-terminated PEG (PEG-NH2) completed the first modification reaction of the surface. For the second surface modification, MWCNT-CONHPEG which have been obtained in the first step was dispersed in o-dichlorobenzene. Afterwards, PS-g-MWCNT-CONHPEG was obtained via nitrene addition in the presence of PS-N3 on high temperatures (130 °C). In the last part of the thesis, surface of carbon nanotubes was functionalized by polyesters containing pyren via non-covalent adsorption interaction which is an advantageous method in terms of preserving mechanical, electronic properties of CNTs. Polymers having polynuclear aromatic group were attached onto the surface of CNTs via π-π stacking in non-covalent strategy. So firstly, five different of polyesters (P1-P5) containing electron deficient internal alkyne units derived from acetylene dicarboxylic acid in the main backbone were sythesized. Afterwards, firstly, polyesters gave Huisgen type 1,3-dipolar copper free cycloaddition reaction with pyrene-1-ylmethyl 3-azidopropanoate. One of the choosen polyester backbone (P2) which was previously synthesized gave Huisgen type 1,3-dipolar copper free cycloaddition reaction with pyrene-1-ylmethyl 3-azidopropanoate and the second molecule which had azide function (2-azidoethanol, 3-azidopropionic acid, prop-2-yn-1-yl 3-azidopropanoate). Eight polyesters having pyrene which is a polynuclear aromatic compound were employed as a polymeric platform in the non-covalent modification of carbon nanotubes. The 1,3-dipolar cycloaddition reactions were performed at 40 °C in 1,4-dioxane for 4 hours. Characterization of polymers was supported by the NMR and GPC measurements. Synthesized polyesters were adsorbed into the sidewalls of MWCNTs for 10 days reaction time by non-covalent approach. Characterization of polyester modified MWCNTs were performed with TGA, UV and HR-TEM measurements.