Polymer Polyparaphenylene Research Articles

A gap opening in graphene covered by a conducting polymer: The role of many-body effects

We study the adsorption of the conducting polymer poly-para-phenylene (PPP) on graphene using first-principles electronic structure calculations. In this article, we decided to investigate the role of polarization of the polymer on the band gap renormalization of the graphene sheet. For this purpose, we supposed that the polymer is lying flat on the sheet of graphene. The polymer adsorption has caused the polarization of graphene and vice versa. We demonstrate the anisotropic polarization of the polymer significantly affects the energy band structure of graphene by opening a gap at the Dirac point. Upon polymer adsorption, the conical shape of the graphene at the Dirac point is partially transformed and leads to opening the band gap about 260 meV at this point. This finding can change the metallic property of the graphene and created semiconducting property inside the compound. This result can only be explained by many-body effects which are treated within the G0W0 quasi-particle approximation while the Kohn-Sham single-particle band structure of graphene is hardly modified by the presence of the polymer. Our findings can be understood as a renormalization due to image charge effects on the anisotropic polymer chain.

Raising the thermoelectric performance of PbS with low-content polyparaphenylene

Lead sulfide (PbS), a promising medium-temperature thermoelectric material, is a cheap and excellent substitute for lead pyride. However, its high thermal conductivity limits its thermoelectric properties strongly. In this paper, the nanocomposites with PbS matrix and organic conducting polymer polyparaphenylene (PPP) supplement are introduced to decrease the thermal conductivity by mechanical mixing method. The experimental results show that the thermal conductivity of PbS–PPP nanocomposites significantly decreases and the minimum thermal conductivity is 0.43 W m−1 K−1, which can be obtained when the mass ratio of the PPP is 3% at 773 K. Consequently, the figure of merit (ZT) of PbS–PPP nanocomposites reaches as large as 0.5, which is 52.40% of magnitude higher than that of pure PbS. Therefore, it is an effective way to improve the thermoelectric properties of PbS by introducing the organic conducting polymer PPP. This work may shed light on developing high-performance thermoelectric materials via organic–inorganic nanocomposites at the intermediate temperature range.

Synthesis and characterization of polyparaphenylene from cis‐dihydrocatechol

AbstractConducting polymer polyparaphenylene (PPP) was synthesized from cis‐dihydrocatechol (DHCD) obtained from bacterial transformation of benzene. Results showed that the DHCD to DHCD‐DA (diacetate) synthesis process produced some byproducts as impurities including trace amounts of phenol, quinone, and phenyl acetate derived from phenol. These impurities played a negative role in the polymerization process of DHCD‐DA to P(DHCD‐DA). In this study, a distillation fractionation method was employed to obtain monomer DHCD‐DA with high purity and high yield. Four different polymerization methods using the purified DHCD‐DA, including bulk polymerization initiated by different catalyst systems, solution polymerization as well as emulsion polymerization, were compared. A very high P(DHCD‐DA) yield of 92% with a molecular weight of 84,500 was obtained under an optimized condition using the bulk polymerization process initiated by (di)benzoyl peroxide (BPO) and ferrous sulfate. A standard curve was established to evaluate the aromatization degree of P(DHCD‐DA) to PPP under different temperatures based on the intensity of FTIR absorption and functional groups on the PPP. The glass transition temperature and the crystallinity of PPP increased with the degree of aromatization of the prepolymer P(DHCD‐DA). Thermal analysis indicated that the PPP possessed high thermal stability both in nitrogen and in air atmospheres. All these results would help the synthesis of PPP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Influence of polyparaphenylene on the magnetotransport of manganite/polymer composites

The ferromagnetic, polycrystalline manganese oxide La 0.7Sr 0.3MnO 3 (LSMO) and the conjugated polymer polyparaphenylene (PPP) were prepared by conventional solid-state reaction processing in air and synthesis by cationic polarization of benzene, respectively. The so-obtained compounds were individually characterized after their electrical, magnetic, structural or thermal properties by using conventional analysis methods. By mixing the pre-prepared LSMO and PPP powders, [LSMO] 1− x [PPP] x ( x stands for the weigh fraction of PPP) two-phase manganite/polymer granular composites were obtained and their microstructural, transport and magnetic features carefully investigated. The resistance of composites calcined at 400 °C for 1 h in air atmosphere increased with x on the whole temperature range. In turn, these samples displayed a pronounced low-field magnetoresistance (LFMR) effect within a wide temperature range. Spin-polarized tunneling of conduction electrons across interfaces or grain boundaries was invoked as the dominant mechanism controlling this effect. The addition of the polymer may modify the LSMO grain surfaces adjusting the conduction carrier's spin-dependent tunneling distance, which sensitively depends on the nature of the interface or on interface-related disorder. Concretely, the PPP should provoke spin disorder at the LSMO interface.

Study of the overtones and combination bands in the Raman spectra of polyparaphenylene-based carbons

A detailed study of the second-order Raman spectrum of the polymer polyparaphenylene (PPP) prepared according to the Kovacic method and heat treated at temperatures THT between 650 and 750 °C is presented. The Raman experiments have been performed with five different laser excitation energies in the visible range between 1.92 and 3.05 eV. Several Raman bands in the region between 2400 and 3400 cm−1 have been detected and assigned to the overtones and combination bands of the two conformations of the PPP polymer (benzenoid and quinoid) that co-exist in our samples. Due to the carbonization process, these bands broaden and decrease in intensity with increasing heat treatment temperature, as is also observed for the corresponding first-order Raman features. The complete absence of these high-frequency Raman bands for PPP with heat treatment temperatures in excess of 750 °C indicates complete transformation of the polymer into a disordered carbon material.

Resonant Raman Characterization of Polyparaphenylene Based Carbon Materials

ABSTRACTThe structure of the polymer polyparaphenylene (PPP), heat-treated at temperatures (THT) between 650°C≤ THT ≤750°C and prepared according to either the Kovacic or the Yamamoto methods, is studied by the resonant Raman technique using five laser excitation energies Elaer in the range 1.92–3.05 eV. The resonant Raman analysis allows identification of the benzenoid and quinoid forms of PPP as well as the amorphous material associated with the onset of the carbonization process. The results enable us to follow the evolution of the PPP polymer with heat-treatment temperature and to determine the differences between the materials prepared using the two different methods.