Mieczyslaw Lapkowski

Polypyrrole and poly(N-methylpyrrole) films doped with Keggin-type heteropolyanions: preparation and properties

Abstract Solutions of pyrrole in acetonitrile in the presence of Keggin-type heteropolyacids (HPA) such as (SiW12O40)4− and PW12O3−40 yield soluble complexes. Oxidation of the complexes gives polypyrrole films doped by the HPA. The electrochemical behaviour of the HPA immobilized in several film thicknesses is described. It is different for HPA alone in solution because of the lack of conductivity of the polypyrrole and poly(N-methylpyrrole) in the potential range of reduction and in the range of molecular dispersion of HPA in the polymer matrix. The levels of doping of the polymers by HPA are similar to those with classical anions, but here the HPA are retained in the films rather better even upon cycling.

Vibrational spectroscopic studies of the isotope effects in polyaniline

Comparative Raman spectroscopy studies of nondeuterated polyaniline and polyaniline deuterated on the ring and on the nitrogen enabled us to confirm the assignments of principal Raman modes. Spectroelectrochemical studies carried out for these two isotopically different polymers indicate the creation of two types of structures upon electrochemical doping, namely polaron lattice and bipolaronic structure.

One-step electrochemical immobilization of keggin-type heteropolyanions in poly(3-methylthiophene) film at an alectrode surface: Electrochemical and electrocatalytic properties

Abstract Immobilization of Keggin-type heteropolyanions (HPA), such as PW 12 O 40 −3 , SiW 12 O 40 4− and PMo 12 O 40 3− , in poly(3-methylthiophene is performed by electropolymerization of the thiophene derivative in the presence of the corresponding HPA acid. The polymerization was possible even in the presence of a large amount of water because of the formation of a complex between the HPA and the 3-methylthiophene. The cyclic voltammetry curves in acetonitrile during polymerization are described and also of the polymer films doped with HPA. In the case of the phosphomolybdate anions, we observed in addition to the redox system of the polymer, six monoelectronic transfer from the HPA. These multiple electron transfers can explain the possibilities of such modified electrodes in electrocatalysis. Effectively, we observe an electrocatalytic reduction of oxygen in acetonitrile (0.5 M HClO 4 ) by comparison with an unmodified bare glassy carbon electrode.

UV–VIS–NIR and Raman spectroelectrochemistry of regioregular poly(3-octylthiophene): comparison with its non-regioregular analogue

Spectroelectrochemical behaviour of regioregular poly(3-octylthiophene) has been investigated using UV–VIS–NIR and Raman spectroscopies. Static and dynamic UV–VIS–NIR spectroelectrochemical experiments combined with cyclic voltammetry show that oxidative doping of the regioregular polymer is a two-step process in which polarons (radical cations) are first created which then recombine to bipolarons (dications). This two-step oxidative doping mechanism is corroborated by FT Raman spectroelectrochemical studies which show significant changes in the positions and intensities of the Raman bands coinciding with the first and second oxidation peaks in cyclic voltammetry. These changes can be interpreted in terms of the doping induced formation of quinoid sequence of bands in the oxidized polymer. Vibrational calculations carried out for undoped and doped poly(3-octylthiophene) gave a very good agreement between the calculated Raman band frequencies and those recorded experimentally for the regioregular polymer.

Electrochemical behaviour of polyaniline films doped with heteropolyanions of Keggin structure

Abstract Electrically conducting polyaniline (PANI) doped with heteropolyanions (HPA) of Keggin structure was synthesised by electrochemical polymerisation. Cyclic voltammetry showed reversible redox systems from the polymer itself and from the immobilised HPA. The electrocatalytic investigations of PANI electrode modified by HPa in reaction of electroreduction of bromate have been performed.

Radical Cation of Helical, Cross-Conjugated β-Oligothiophene

The radical cation of carbon-sulfur [7]helicene is configurationally stable in solution at room temperature. In contrast to the radical cations of alpha-oligothiophenes, which form diamagnetic pi-dimers at low temperature, the radical cation of this helical, cross-conjugated beta-oligothiophene shows a low propensity toward dimerization.

In situ EPR spectroelectrochemical studies of paramagnetic centres in poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-butylenedioxythiophene) (PBuDOT) films

In situ EPR spectroelectrochemical studies of two members of poly(3,4-alkylenedioxythiophene) family of polymers, namely poly(3,4-ethylenedioxythiophene) – PEDOT and poly(3,4-butylenedioxythiophene) – PBuDOT have been performed with an aim to investigate the effect of doping and subsequent dedoping on charge carriers in these polymers. The objectives of investigations were to characterise the type of paramagnetic centres appearing in the polymer and to observe the influence of doping on their concentration and other spectroscopic properties. It was found that the evolution of spins in both polymers upon doping follows a trend similar to that observed for other thiophene-based polymers. The characteristic points of these curves are different however for each polymer. The maximum spin concentration in PEDOT takes place at 0.2 V and for PBuDOT it is at 0.35 V. While generally similar in behaviour during doping, the behaviour of these two polymers upon dedoping is markedly different. For PBuDOT the concentration of spins follows a more or less reverse path of the doping curve whereas in PEDOT a hysteresis of concentration of spins appears. Similar trends are observed for the signals’ ΔBpp widths. Both polymers display distinct narrow EPR lines at the end of the reduction half-cycle suggesting that a noteworthy concentration of spins exist in them even in the fully reduced (dedoped) state. Analysis of the EPR spectra of the polymers in their doped states revealed their complex character. It was found that these complex spectra could be decomposed into two separate components – one Gaussian and one Lorentzian. Based on EPR microwave saturation studies the Gaussian component was attributed to highly mobile polarons which are confined in isolated spin packets and the Lorentzian one to delocalised less mobile polarons, homogeneously distributed within the material, which thus could be associated with the electrons of conductivity.

Behaviour of some poly(pyrrole-anthraquinone) films in DMSO electrolytes

Abstract Several films of poly(pyrrole-anthraquinone) have been prepared by the electropolymerization in organic media of anthraquinones adequately substituted by some N-alkylpyrroles. These films have been studied mainly by electrochemical methods in DMSO with either TEAFB or LiClO4 as the supporting salt. Bonded anthraquinones can be reversibly reduced to their radical anions or dianions with a fair yield, except on slow or prolonged cycling where the protonation effect modifies this behaviour. Spectroelectrochemical studies confirm these facts and additionally allow the probable complex formations in fully reduced films to be detected.

In situ self hardening bioactive composite for bone and dental surgery.

A new biomaterial is presented which consists of a cellulose derivative - silanised hydroxyethylcellulose (HEC-SIL) and biphasic calcium phosphate (BCP). Rheological properties of the polymer itself and its mixture with BCP are pH-dependent. At pH 10-12 HEC-SIL is liquid and undergoes quick gellation at pH < 9. Similarly, the paste of HEC-SIL and BCP is fluid and injectable at higher pH and solidifies in biological solutions. The rate of this solidification can be easily controlled by the degree of substitution of hydroxyethylcellulose with silicoalkoxy groups.

Carbazole electrochemistry: a short review

Carbazole and its derivatives have become important materials for optoelectronic applications in recent years. In this work, we have collated information on the oxidation of carbazole and its derivatives. Knowledge of their electrochemical properties affords insight into the mechanisms for their oxidation and reduction as well as possible subsequent reactions. This knowledge therefore provides the basis for evaluating the stabilities of these materials and for designing novel carbazole-derived materials with desired properties as well as new devices.