Preparation And Properties Of Polypyrrole Derivatives And Their Nanocomposites

Polypyrrole (PPy) is one of the more important functional polymer materials duo to its excellent optical and electronic properties, and has many potential applications in sensors, supercapacitors, solar cell, composites and nonlinear optical materials, etc.. However, unsubstituted polypyrrole has some disadvantages, such as insoluble, nonmelting, poor ductility and difficulty in processing. In order to improve the properties, the polymer can be prepared by introducing a flexible substituent to pyrrole molecule or copolymerization with other monomer.3-Acylpyrroles with different substituent length, including 3-acetylpyrrole, 3-valerylpyrroIe and 3-dodecanoylpyrrole, are synthesized by introducing an acyl to pyrrole molecule in 3-position. p-Alkoxybenzaldehydes including p-butyloxyben-zaldehyde and p-octyloxybenzaldehyde are prepared by one step reaction method, using p-hydroxybenzaldehyde as raw materials. FTIR and 1H NMR spectra indicate that synthesized monomers are the target products.In this article, three polypyrrole derivatives-poly(3-acylpyrrole), including PAPy, PVPy and PDPy, are prepared using FeCl3 as an oxidant. Then five poly(pyrrolyl methine) derivatives-poly{(3-acyl)pyrrole-[2,5-diyl(p-alkoxybenzyli-dene)]}, including PAPDMOBE, PAPDBOBE, PAPDOOBE, PVPDBOBE and PDPDBOBE, are prepared by polycondensation between 3-acylpyrrole and p-alkoxybenzaldehydes in acidic condition. The synthesized poly(pyrrolyl methine) derivatives are novel soluble, narrow band gap and% conjugated polypyrrole derivatives with electron donor/acceptor groups. The structure and properties of the polypyrrole derivatives are investigated via FTIR,1H NMR, UV-Vis-NIR, PL, CV, TGA and XRD. In addition, we discuss the relationship between substituent structure and properties of the polypyrrole derivatives. The results indicate that thermal decomposition temperatures and optical band gap of poly(3-acylpyrrole) and poly(pyrrolyl methine) derivatives are about 210℃ and 2.2eV,160℃ and 1.5eV, respectively. Especially, the poly(pyrrolyl methine) derivatives belong to narrow band gap and π conjugated polymers. Photoluminescence spectra suggest that the poly(3-acylpyrrole) and poly(pyrrolyl methine) derivatives both are good blue fluorescence materials. Furthermore, the solubility of poly(3-acylpyrrole) and poly(pyrrolyl methine) exhibits that the former is only partially soluble in strong polar organic solvents, while the latter can be completely dissolved in a suitable solvent.Carbon nanotube is an one-dimensional nano carbon materials, which exhibits excellent mechanical, electrical and thermal properties because of its unique hollow tubular structure, nanometer size, large specific surface area and aspect ratio. Graphene (GR) is a new type of two-dimensional carbon material composed of monolayer carbon atoms by sp2 hybridization, and it has honeycomb lattice structure. Graphene displays some excellent properties, such as mechanical, electrical, thermal and optical properties, owing to its unique structure. Among the polypyrrole derivatives, carbon nanotubes and graphene have similar π-π conjugate electronic structure. So the polypyrrole derivatives are good materials with the incorporation of carbon nanotubes and graphene. Thus, the properties of polypyrrole derivatives, such as optical, electrical and thermal properties, can be significantly improved by in situ composite with carbon nanotubes and graphene due to their unique structure and excellent properties.Polypyrrole derivatives/carbon nanotubes and polypyrrole derivatives/graphite oxide (or graphene) composites are fabricated by in situ chemical polymeriation, using pyrrole,3-acylpyrrole and p-methoxybenzaldehyde as raw materials, and carbon nanotubes and graphite oxide (GO) as templates of polymeriation of monomers. The structure, morphology, thermal stability, electrical and electro-chemical properties of the resulting composites are investigated by FTIR, XRD, FESEM, TEM, TGA, CV, GCD, EIS and a four-probe method. In addition, we discuss the properties of the composites influenced by the structure and content of the polymers. Lastly, electrical energy storage mechanism, specific capacitance, solution resistance, charge transfer resistance and electrode process dynamics of the electrode materials are systemically studied by CV, GCD and EIS technologies.FTIR spectra show that carbon nanotubes and graphite oxide only serve as templates of polymeriation of monomers. FESEM and TEM images present polypyrrole derivatives are quite uniformly coated on the surface of carbon nanotubes and graphite oxide (or graphene), and the coating thickness of polypyrrole derivatives increases with the increasing feed ratios. XRD patterns indicate that poly(3-acylpyrrole) and their nanocomposites are partly crystalline, while PPy, PPDMOBA and their nanocomposites are completely amorphous. The electrical conductivity of the materials are measured at room temperature, the results show that carbon nanotubes are remarkably able to enhance the conductivity of their composites. The conductivity of graphite oxide exhibits a very low value, while that of graphene reachs 16.7S/cm. Furthermore, the conductivity of PPy/GO composites significantly increases with the increasing feed ratio of pyrrole to graphite oxide. As the feed ratios are 3/1 and 5/1, the conductivities of the composites reach 1.27 and 6.25S/cm, respectively, which are larger than that of pour PPy and GO, indicating that the existence of a synergistic effect between PPy and GO.The electrochemical performance of the polypyrrole derivatives nanocomposites is investigated in detail, the results suggest that all the fabricated poly(3-acylpyrrole)/ MWNTs, PPy/MWNTs, PPDMOBA/MWNTs,PPy/GO, PPy/GR and PPDMOBA/ GO composites have good charateristics of electrical double-layer capacitance and low charge transfer resistance. Among them,pPy/MWNTs, PPy/GO and PPy/GR composites have higher specific capacitance and good cycle stability, which are close to ideal capacitors, and they can be used for the development of new application for supercapacitors.