Chemical Polymerization Of Pyrrole Research Articles

Polypyrrole overoxidation during its chemical synthesis

The composition of the synthesis medium was investigated by high-performance liquid chromatography during the chemical polymerization of pyrrole with FeCl 3 in water. It is shown that the polypyrrole is simultaneously degraded during the synthesis in short soluble maleimide molecules. This degradation process may be attributed to the polymer ‘overoxidation’ which is described as a gradual polymer oxidation by water in the presence of FeCl 3. Such a degradation is strongly enhanced at the beginning of the synthesis and leads to poor conductivity products. Moreover, such a degradation appears to be strongly amplified in low FeCl 3 concentration solutions. Quantitative measurements confirm that polymerization is second-order kinetics with respect to FeCl 3 while overoxidation appears to be only first order. A consistent overoxidation mechanism is discussed.

Interaction of collagen with polypyrrole in the production of hybrid materials

AbstractA series of collagen–polypyrrole hybrid materials have been synthesized by the chemical polymerization of pyrrole using FeCl3 as initiator in the presence of soluble collagen. The black color of the resulting materials indicates the presence of polypyrrole while collagen was verified by amino acid analysis of the hybrids. Collagen incorporation into the hybrid was found to be a function of pyrrole concentration used in the polymerization. When the concentrationof pyrrole was high, the collagen loading was low and vice versa. This inverse relationship was also found in the hybrids' electrical conductivity. A 26% collagen content in the hybrid gave a conductivity of 1.4 S cm−1 while a 4% collagen gave a higher value of 62.4 S cm−1. Thermogravimetric data suggest that the two polymers exist in the hybrid as a blend. The nature of the interaction of the components in the hybrid is believed to be strong since collagen could not be extracted despite denaturation with sodium dodecylsulfate.

Sensing properties of polypyrrole-polytetrafluoroethylene composite thin films from granular metal-polymer precursors

A newl class of sensor-oriented composite conducting thin films was grown utilizing an original method. The technique is based on the chemical polymerization of pyrrole (PY) vapours onto an oxidizing salt pattern obtained via chlorination of a co-sputtered granular metal thin film. Time stability of the samples realized with this technological approach and their response to exposure to different atmospheres were studied; the behaviour of the material subjected to mechanical strain was also investigated.

Electrically conducting ionomers

The preparation and physical properties of conducting ionomers have been investigated. A two-step process was used to prepare a polyethylene-based film grafted with poly(styrenesulphonic acid). A pre-irradiation technique was applied to carry out the grafting of polystyrene on various polyethylene films. The grafted films were then sulphonated to yield the ionomer. Chemical polymerization of pyrrole into the ionomer was carried out in aqueous solutions and caused a four orders of magnitude increase in the conductivity of the film. Better conductivities were obtained when 1,1,2-trichloroethane was used as the chain transfer reagent during grafting of polyethylene with styrene. The conductivity, structure, composition and mechanical properties of the electrically conducting ionomers were evaluated. Films having high conductivities and improved mechanical properties were obtained.

Electrically conducting polyethylene/polypyrrole films

The preparation and physical properties of conducting ionomers were investigated. A two-step process was used to prepared polyethylene based film grafted with polystyrene sulphonic acid. Two methods, both based on chemical polymerization of pyrrole using ferric chloride, were conducted to form the conducting ionomers in aqueous solutions. In one method the polymerization agent was electrochemically recycled. The conductivity, structure, composition and mechanical properties of the conducting ionomers prepared in the two methods were evaluated and compared. Films having high conductivities and improved mechanical properties were obtained.

Microstructure and charge transport in electrically conducting polypyrrole/poly(p-phenylene terephthalamide) composite fibers

Electrically conducting composite polypyrrole/poly(p-phenylene terephthalamide) (PPTA or Kevlar R) fibers have been prepared by chemical polymerization of pyrrole within the void structure of never-dried PPTA fibers. The composite morphology has been examined by scanning electron microscopy (SEM) and wide angle x-ray diffraction techniques, which indicate the existence within the fiber interior of a dispersed polypyrrole phase having no preferred direction of orientation. The d.c. conductivity exhibits a temperature dependence characteristic of three-dimensional variable-range hopping in the limit of low temperature; however it begins to diverge from this law at higher temperatures for the more conductive samples. The temperature dependence of the composite fiber thermopower can be understood in terms of the model proposed by Kaiser.

Effective Doping of Polymer Anion during Chemical Polymerization of Pyrrole Using Fe(OH)3 Oxidant

Abstract Polypyrroles were prepared by the chemical polymerization of pyrrole using various combinations of Fe3+ oxidants and electrolytes. The morphology and yield of the resulting polymers were affected by the property of the electrolyte anion in the oxidative solution. The size of the particles of the resulting polymers was decreased by using a high-molecular-weight polymer anion as the electrolyte anion. Both the polymer anion and Cl− were incorporated as a dopant into the polypyrrole matrix during the chemical polymerization of pyrrole, using an aqueous solution containing both FeCl3 and the polymer anion. On the contrary, the polymer anion was effectively incorporated as a dopant into the polypyrrole matrix during the chemical polymerization of pyrrole, using an aqueous solution containing both Fe(OH)3 and the polymer acid. A novel type of chemical preparation of the polypyrrole-polymer anion composite using the Fe(OH)3 oxidant and the polymer acid was developed.

Vicrostructure and Electrical Properties of Kevlar/Polypyrrole Composite Fibers

AbstractElectrically conducting composite polypyrrole/poly(p-phenyleneterephthalamide) (PPTA or KEVLAR) fibers have been prepared by chemical polymerization of pyrrole within the interstices of the hydrogen-bonded gel structure of never-dried PPTA fibers. The resultant fibers contain a uniform dispersion of polypyrrole, as evidenced by scanning electron microscopy. The temperature dependence of the electrical conductivity of these hybrid fibers is presented. The conductivity is well described by the fluctuation-induced charge transport model over the entire temperature range of interest. However, the low temperature electrical conductivity also exhibits a hoppinglike temperature dependence, and an Arrhenius-like temperature dependence is observed in the high temperature limit. Measurements of the temperaturedependent tbermopower are indicative of a p-type carrier.

Highly electroconductive polypyrrole composites

Following up our pioneering works on polypyrrole (PP) [1, 2], one of the few synthetic metals having a fairly good stability in air, we have tried to overcome some of the limits of its synthesis and handling. It was known that PP may be synthesized by oxidative polymerization with chemicals, giving black substances having a high molecular weight and insulating properties [3, 4]; on the contrary the electrochemical oxidation produces highly conducting materials (up to 1 to 5 x 102Scm ~) [2], but it is limited by the shape and nature of the electrode; PP films prepared in this way are brittle and generally show poor mechanical properties; the preparation of PP plastics composites, always by anodic oxidation, is at the moment being actively investigated [5, 6] and appears to be the best way to combined mechanical and electrical characteristics of both partners; however, it is somewhat intriguing and does not solve the problem of obtaining large specimens. We thought that many of the previous problems might be solved by finding a general method of producing highly conducting PP by oxidative polymerization by chemicals, directly on a suitable matrix, thus attaining most requirements mentioned above with few disadvantages. In the course of our study on the chemical polymerization of pyrrole to highly conducting PP [7], we have found that by supporting the monomer on a porous substrate before contacting it with an oxidant solution, it was possible to improve the volumic conductivity of the polymer formed. In terms of conductivity per gram of electroactive material, an improvement by a factor of up to 3 or 4 was found. Good conductivities, very close to those from electrochemical oxidation, were obtained by a careful testing of experimental conditions. The most suitable supporting material to date seems to be an ordinary filter paper (for instance Whatman no. 91 filter paper), but also wood, clothes, glass fibres, polystyrene and silica gel granules may give interesting results as far as both mechanical properties and the conductivity of the composite materials are concerned. Among various oxidants tested we found that ferric salts show the best performance. Thus many paper strips (50 mm × 5 ram) were charged with pyrrole and

A functionalized polypyrrole film prepared by chemical polymerization at a vapour–liquid interface

Thin conducting polypyrrole films doped with negatively-charged functional molecules were prepared by chemical polymerization of pyrrole at a vapour–liquid interface.