Synthesis Of Nano-Composite Materials Via Bergman Cyclization

Diradicals can be generated through enediyne-containing compounds via Bergman cyclization, which can either be used to cleavage DNA in cancer cells or form polyarylene through radical coupling reaction. Bergman cyclization has attracted tremendous interests due to its applications in antitumor medicine and composite materials. Carbon nanotubes (CNTs) are widely concerned due to their unique optical, electrical, chemical and mechanical properties. However, the great tendency of pristine CNTs to establish strong van der Waals and?-?interactions cause them to form tight bundles, which make them insoluble and indispersible in common solvents and seriously restrict their applications. Consequently, many physical and chemical modification methods have emerged in recent years and greatly improved CNTs' solubility and dispersibility. As a kind of special compounds with unique structure, brush polymers have attracted enormous interesting in many fields such as biomedicine, chemical sensor, smart materials, etc. Furthermore, Brush polymers with conjugated backbone have drawn more attention because of their unique optical and electrical properties. And the further functionalization allows conjugated polymers to be competitive candidates for transistors, solar cells, molecular motors and sensors.In this dissertation, derivatives of enedyine with containing certain functional groups were firstly synthesized, and then the fictionalization of carbon nanotubes and synthesis of Brush polymer were studied utilizing aforementioned compounds via Bergman cylization. The specific contents discussed in this dissertation are as follows:(1) First of all,4-(2-(2-(trimethylsilyl) ethynyl) phenyl) but-3-yn-1-ol was synthesized using 1-bromo-2-iodobenzene as starting material. Secondly, two generations of Frechet type dendrimers with peripheral benzyloxy groups and hexadecane long chains were synthesized. Then, these dendrimers were allowed to react with 4-(2-(2-(trimethylsilyl) ethynyl) phenyl) but-3-yn-1-ol. Subsequently, the trimethylsilyl groups of enediyne units were removed by deprotection to give desired new compounds for the following research.(2) Four brush polymers with rigid conjugated backbone were prepared by "grafting through" method. The aforementioned dendritic enediyne compounds were heated at 282?under vacuum to perform Bergman cyclization polymerization and to form brush polymers. These new brush polymers were characterized with various techniques such as GPC, IR, UV-vis, NMR spectroscopy and wide angle laser light scattering. Furthermore, the "rod-like" morphology of brushes was supported by atomic force microscopy. (3) A new covalent functionalization method for pristine multi-walled carbon nanotubes (MWCNTs) was developed by utilizing the free diradicals generated through Bergman cyclization of enediyne-containing compounds in (1). In N-methyl-2-pyrrolidinone (NMP) at elevated temperature under nitrogen, the unsaturated double-bonds on the sidewall of MWCNTs were attacked by diradicals via "grafting to" method. The strategy, namely slow addition method, was explored. The structure and morphology of resulting products were characterized with a variety of techniques, including TGA, UV-vis, TEM, IR and Raman spectroscopy. The dendrimers functionalized MWCNTs showed good solubility/dispersibility in common organic solvents such as tetrahydrofuran, NMP, N,N-dimethylformamide, methylene dichloride and so on. They were successfully applied to formation of polymer nanocomposites through electrospinning with polycaprolactone. The results confirmed the surface functionalization of carbon nanotubes were successful.(4) Pristine multi-walled carbon nanotubes (MWCNTs) were functionalized by utilizing the free radicals generated through Bergman cyclization of enediyne containing compounds 4-(2-ethynylphenyl)but-3-ynyl acetate. Subsequently, polyesters were grafted from the surface of MWCNTs through ring opening polymerization of?-caprolactone or lactide initiated by free hydroxy groups generated after hydrolysis of ester groups on the surface of MWCNTs. Functionalized MWCNTs were characterized with various techniques such as TGA, NMR, IR, UV-vis, TEM and Raman spectroscopy, etc. After surface modification, MWCNTs showed good solubility in common organic solvents and polymer solutions. Fabrication of MWCNTs polymer nanocomposites was revealed through electrospinning with polycaprolactone.