Search Results
Abstract
The thermal stability of polypyrrole (PPy) samples has been studied by thermogravimetry/mass spectrometry and pyrolysis-gas chromatography/mass spectrometry in inert atmospheres. PPy has been prepared by chemical oxidative polymerization using ferric sulfate as an oxidant and anionic surfactants, such as dodecylbenzenesulfonic acid and sodium dodecylbenzenesulfonate as co-dopants. For comparison we have studied polypyrrole (PPy-SO4) prepared without any additive. It was found that the presence of anionic surfactants improved the thermal stability of PPy. The decomposition of PPy doped with ferric sulfate and anionic surfactants occurs at relatively high temperature indicating that chemical interactions exist between the polymer and the surfactants.
Abstract
Electro-conducting doped polypyrrole was deposited by in situ oxidative polymerisation on PET non-wovens. Thermal properties were evaluated by means of DSC and TG in nitrogen and air. Flame resistance tests reveal that coated PET fibres resist to direct contact with fire. By thermal analysis, it was found that PPy reduces the temperature at which thermo-oxidative degradation of PET occurs. Polypyrrole-coated PET non-wovens were heated above the melting point of PET for 30 min. After the heating the fibres become brittle and frail, but SEM observations revealed that they maintained their fibrous shape. A loss of chlorine was found because of intense heating.
Abstract
Chemical polymerization of pyrrole (Py) was carried out in a reaction calorimeter by using FeCl3 or CuCl2 as an oxidant in an acetonitrile medium. The formation heat of polypyrrole (PPy), determined under a wide range of reactant concentrations and reaction temperatures, is directly related to the PPy yields and to the degree of polymerization. Due to the negative values of both the entropy and enthalpy of the reaction the gravimetric yield is inversely related to the temperature and directly to the Py concentration. The yields to the PPy and the related reaction heats, are close to zero when the 
ceiling temperatures
are reached (T
ceil=348 K for Fe-doped and T
ceil=313 K for Cu-doped PPys). It was observed that a ceiling concentration corresponds to each ceiling temperature and only light oligomers are formed if Py concentration is too low. The electric conductivity values of the products were also determined and a direct relationship to the yields was found as well. The highest electric conductivity value (C=0.6 S cm–1) was related to the PPy fresh synthesized from a 0.017 M Py solution.
Abstract
We have studied the synthesis of polypyrrole-clay nanocomposites by the in situ oxidative polymerization of pyrrole in the interlayer space of vermiculites with different layer charges from Santa Olalla and Ojén, Spain. Moreover, the influence of different interlayer cations (Na+, Mg2+, Fe3+) on the interaction between pyrrole and the vermiculties was studied. The resulting materials were characterized by means of DTA-TG, XRD, FTIR and Mössbauer spectroscopy. In all samples polymerization of pyrrole was observed, presumably triggered by the structural iron. In most cases it was found to be externally deposited. An uptake of pyrrole in the interlayer space and PPy formation is observed in the case of the Fe3+-intercalated Ojén vermiculite, which has a lower layer charge than the Santa Olalla vermiculite.
Abstract
The ability to electrochemically control the binding of uranium ions by redox active polypyrrole resins has been studied. The optimization of the conditions for the fixation of uranium has been defined while taking in account the nature of the fixed species, the nature of the resin and the nature of the solutions.
Abstract
The thermal behavior of different synthesized polypyrrole (Ppy) composites was studied in order to obtain quantitative information about the synthesis process and qualitative information about thermal stability of composites. An inorganic anion has been used as dopant (PW12O40 3−), and this has allowed obtaining a complete analysis of Ppy degradation process, since this anion does not degrade in the range of temperature used. In order to validate the quantitative information obtained by thermogravimetric analysis (TG), the work was completed with X-ray photoelectron spectroscopy (XPS) study, since the use of the N+/N or W/N ratios are useful to measure the doping level reached by the synthesis process. Also pyrolysis/gas chromatography/mass spectrometry (py–GC–MS) and differential scanning calorimetry (DSC) were used to obtain information of the products generated as a consequence of the degradation process. FTIR-ATR has been used to characterize Ppy powders.
The calorimetric determination of the ceiling temperature for the chemical polymerization of pyrrole
Implications on the electrical conductivity
Abstract
The previously found strong dependence of the polymerization enthalpy on the reaction temperature has been rationalized. The temperature dependence is to be ascribed to the existence of a ‘ceiling temperature’ for the polymerization process of the pyrrole monomer. The determined ceiling temperature has beenT≊350 K when FeCl3 was used as the oxidizing agent in CH3CN solution. The existence of a ceiling temperature together with its already determined exoenthalpic nature allows to classify the polymerization reaction as an exoentropic one. From the dependence of the yield of insoluble polymer on the reaction temperature, the trend of the relative mean numeral molecular massM n for the different obtained polymers has been determined. Measurements of electrical conductivity on pressed pellets of the different polymers allowed to establish a correlation between theM n value and the conductivities The dependence of the conductivity on the exposition time to the air allowed to do some essays on the aging behaviour of the obtained polypyrrole. By making some assumptions, an absolute calorimetric determination of the value ofM n of polypyrrole was tempted together with that of the related poly-N-vinilpyrrole.
Oxidative chemical polymerization of pyrrole
Calorimetric and kinetic measurements
A reaction calorimeter has been used to determine at three different temperatures the enthalpy values for the polymerization of pyrrole dissolved in acetonitrile, by using FeCl3 as the oxidative agent. From the calorimetric data it has been found that the reaction is first-order with respect to the pyrrole. The rate constants at the same temperatures have also been determined. By using the Arrhenius equation we have obtained the activation energy for the formation of this electroconducting polymer.
Abstract
Secondary ion mass spectrometry (SIMS) is a well-established technique that permits rapid detection of stable and radioactive nuclides. Its resolving mass power provides an efficient analytical method and, in particular, it makes possible accurate isotopic ratio determination. Tests were carried out to evaluate the performance of this technique for the assessment of trace concentrations of uranium and plutonium in urine samples prepared in thin sources. Special attention has been paid to the preparation of the specimens which represents a critical step for the employment of this technique due to the erosion process used by SIMS. Fixation of the matrix in Polypyrrole films have been proved to be suitable. Present results show that concentrations in the order of 10–10 g·1–1 of238U (10–6 Bq·1–1) and 10–11 g·1–1 of239Pu (10–2 Bq·1–1) can be rapidly measured.
]. Polypyrrole (PPy) is a conducting polymer with unique properties, namely, high electrical conductivity, relatively good environmental stability, nontoxicity, relatively low cost, and ease of preparation, which are favorable for various types of application in
