Free Radical Reactions In Polymer Chemistry Of Fullerenes And Carbon Nanotubes Modified

In recent years, the materialization of fullerenes and their application have been a (?) point of the research on chemistry and physics of fullerenes, especially for the design and preparation of fullerene-derived macromolecules. Carbon nanotubes, whose structure is correlative with that of fullerene, have attracted particular attention for their unique structural, mechanical, optical, and electrical properties. The composite materials obtained by the covalent attachment of specific polymer to carbon nanotubes may be a concernful field in material chemistry. Based on previous investigation work of our research group and the development trend of interrelated fields at home and abroad, this thesis was focused on the synthesis and characterization of polymer modified fullerene and carbon nanotubes by free radical reaction. At the same time, the optical limiting properties of the products obtained were also determined and discussed. The contents of this thesis include six chapters.In chapter 1, the advanced development in the research of fullerene modified polymer derivatives and polymer grafted carbon nanotubes by free radical reactions was summarized. The research envisagement for the whole thesis was also proposed.In chapter 2, telechelic C₆₀-end capped polymers and C₆₀ end-capped four-arm polymer derivatives were synthesized via atom transfer radical addition (ATRA) reaction. Bromo-double-terminated polystyrene (Br-PSt-Br) and poly(methyl methacrylate) (Br-PMMA-Br) with predesigned molecular weight and narrow polydispersity, prepared by atom transter radical polymerization (ATRP) using the initiating system α,α'-dibromo-p-xylene(DBX)/CuBr/2,2'-bipyridine(bipy), were applied to react with C₆₀ using CuBr/bipy as catalyst system under conventional heating process or microwave irradiation(MI). The structure of final telechelic C₆₀ end-capped polymer derivatives were confirmed by a variety of characterization techniques such as gel permeation chromatography (GPC), UV-vis, FT-IR, thermal gravimetric analyses (TGA), DSC, ¹H NMR and ¹³C NMR. The results showed that microwave irradiation could significantly increase the rate of fullerenation reaction, and the physical properties and structure of the C₆₀ end-capped polymers are not modified by the use of microwave. One telechelic C₆₀ end-capped polystyrene product and its corresponding bromo-double-terminated polystyrene precursor synthesized with conventional heating process were applied as the MALDI coating materials for a novel hydrophobic polymer micro-contact printing protocol which can achieveone-step desalting and sample concentration. The average signal-to-noise ratios (S/N) for molecular ion signals obtained with this one-step method are found to be 5 times better than that obtained using traditional metal plate method for the BSA digests under the optimizing condition. The C₆₀ end-capped four-arm polymer derivatives were prepared via the ATRA reaction of C₆₀ and bromo-terminated four-arm polymer (PSt or PMMA) using CuBr/bipy as the catalyst system. The structure of C₆₀ end-capped four-arm polymer derivatives were also characterized and discussed. Another technique of synthesizing C₆₀ end-capped four-arm polymers from azide functional polymers was also applied for comparison. All telechelic C₆₀ end-capped polymers and C₆₀ end-capped four-arm polymer derivatives can easily dissolve in common organic solvents such as THF, toluene and trichloromethane. Their optical limiting properties were measured in THF solution at 532 nm. All the fullerene functionalized polymer samples showed optical limiting response close to that of C₆₀.In chapter 3, fullerenation of polycarbonate (PC) was achieved by direct reaction of C₆₀ and PC in the presence of azo-bis-isobutyronitrile (AIBN) using 1,1,2,2-tetrachloroethane as the solvent under microwave irradiation (MI). Comparing with conventional heating process (CH), microwave irradiation could significantly enhance the rate of the fullerenation under identical reaction conditions. The C₆₀ content of the fullerene-functionalized polycarbonate (C₆₀-PC) could be controlled via varying the C₆₀/PC feed ratio and the reaction time. The C₆₀-PCs are soluble in common organic solvents such as THF and chloroform. The products were characterized by GPC, UV-Vis, FT-IR, TGA, DSC, ¹H NMR and ¹³C NMR. The reaction of C₆₀ with PC under MI was monitored by electron spin resonance (ESR) spectrum, the fullerene radicals were detected in reaction solutions and also in the solid product polymers, indicating the radical mechanism of the reaction. The nonlinear optical property of C₆₀-PCs in THF was investigated by the open-aperture z-scan technique at 527nm, and its nonlinear absorption coefficient was found to be in the same order as that of C₆₀. Considering the improvement of solubility, the C₆₀-PCs synthesized under MI can be applied as effective nonlinear optical materials. In additon, we also studied the reaction of C₆₀ and polystyrene (or poly(N-vinyl carbazole)) under MI using AIBN as radical initiator. The structure and optical properties of these products were also studied. The above results prove the versatility of microwave irradiation technique for the AIBN-initiated fullerenation.In chapter4, a specific fullerene derivative, C₆₀(CHCOOH)₂, was introduced intothe matrix network of well-ordered hexagonal mesoporous silica (SBA-15) via a chemical bond interaction. The methods included aminiosilylation of the surface silanols within SBA-15 channels by 3-aminopropyl triethoxysilane (APTS), and subsequently amide reaction between amino groups of APTS/SBA-15 and carboxylic acids of C₆₀(CHCOOH)₂. The final material, C₆₀(CHCOOH)₂/APTS/SBA-15, was confirmed by XRD, TEM and BET technique, FT-IR and UV-vis spectra. The [60]fullerene carboxylic derivative molecules are uniformly distributed in channels of SBA-15, and while the pure [60]fullerene molecules maintain clusters or larger aggregates state. The photoluminescence properties of C₆₀(CHCOOH)₂/APTS/ SBA-15 indicate that the surface modified SBA-15 maintains the photoluminescence activity of the guest fullerene derivative for longer times and SBA-15 is an effective carrier for fullerene derivatives.In chapter 5, The linear polystyrene (PSt) was grafted onto the convex surfaces of multiwalled carbon nanotubes (MWNTs) via a ATRA reaction method. Bromine-terminated polystyrene synthesized by ATRP was allowed to react directly with MWNTs under ATRP conditions using CuBr/bipy as catalyst. The PSt-grafted MWNT samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR spectra, Raman spectra, ¹H NMR, UV-vis spectra, TGA, and X-ray diffraction. In comparison, another technique was also applied to synthesize PSt-grafted MWNTs via the reaction of azide functional linear polystyrene with MWNTs. The products can dissolve in 1,2-dichlorobenzene, tetrahydrofuran and chloroform to form well-dispersed solutions. Optical limiting property measurements in chloroform were carried out at 532nm using the open-aperture z-scan technique. The results demonstrate that the samples preserve good optical limiting properties when the polymer is covalently attached to the carbon nanotube. Both nonlinear scattering and nonlinear absorption play dominant role in optical limiting performance of these stable solutions.In chapter 6, polymer-grafted multiwalled carbon nanotubes were prepared through free radical reaction. Microwave irradiation was applied to in situ emulsion polymerization of styrene or methyl methacrylate in the presence of MWNTs. The emulsion polymerization under microwave irradiation was accomplished in less than half-hour. The purified samples, in which the free polymer were removed, were characterized by TEM, TGA, FTIR, Raman and UV-vis spetra. From the characterization results, it was confirmed that PSt and PMMA were successfullygrafted onto carbon nanotubes. Another free radical reaction for preparing polymer-grafted MWNTs was also studied. The ready-made poly(N-vinyl carbazole)(PVK) was allowed to react directly with MWNTs at 70℃ for 52 hours in the presence of AIBN. The purified deep grey products, which can dissolve in toluene, trichloromethane and 1,2-dichlorobenzene, were then characterized by FTIR spectra, SEM, TGA, elemental analysis, XPS, UV-vis spectra and Raman spectra. It was confirmed that poly(N-vinyl carbazole) was grafted onto the surface of the carbon nanotubes. The optical limiting properties of the polymer grafted MWNTs samples prepared via these two free radical reactons were investigated by open-aperture z-scan method. All of the samples of PSt, PMMA or PVK modified carbon nanotubes in trichloromethane showed optical limiting behavior better than that of C₆₀ in toluene.