M. Zagórska

Polyaniline based optical pH sensor

Abstract Thin layers of polyaniline are suitable to measure optically the pH in the range of 2–12 in the near infrared region. The deposition of such layers is strongly facilitated by the use of solution-processable polyaniline. Previously unconsidered hysteresis effects are observed in the titration curves. Testing the sensor layers over a period of 300xa0h and up to 500 titration cycles revealed excellent reproducibility and stability. An absorbance drift lower than 1% per day (corresponding to about 30 titration) was observed.

Thermally processable conducting polyaniline

Abstract Protonation of polyemeraldine base with aryl phosphoric acid diesters have been studied with the main goal to obtain thermally processable conducting polymers. Polyaniline protonated with aryl diesters exhibits excellent thermal properties. Since diesters plasticize polyaniline in addition to its protonation conductive blends of PANI and plasticized PVC with low (ca. 6 wt%) percolation threshold can be prepared by hot pressing.

Processable conducting polyaniline

Abstract It has been found that diesters of phosphoric acid with branched alkyl substituents solubilize polyaniline in its protonated (conducting) state. Polyaniline protonated with bis(2-ethylhexyl)phosphate or bis(2-methylpropyl)phosphate is highly soluble in common organic solvents such as toluene, decaline, THF and chlorinated hydrocarbons. Conducting blends with poly(methylmethacrylate) or poly(acylonitrile-butadiene-styrene) (ABS) can be prepared showing high conductivity for very low electroactive component content. Protonation of polyemeraldine base with neat esters results in a heavily plastisized mixture which can be thermally processed to give free standing films with conductivities exceeding 10 S/cm. Depending on the content of the protonating agent, time and temperature of pressing films with different Young modulus, tensile strength and elongation at break can be prepared. Similarly, conducting blends with excellent mechanical properties can be prepared from diester plasticized polyaniline and plasticized polyvinyl chloride.

Efficient photo and electroluminescence of regioregular poly(alkylthiophene)s

We report absolute photoluminescence (PL) and electroluminescence quantum efficiencies for thin films and polymer light-emitting diodes prepared with regioregular (that is, exclusively head-to-head/tail-to-tail conformation and/or exclusively head-to-tail conformation) poly(alkylthiophenes). In particular, we find a maximum PL quantum efficiency of ∼11% for the head-to-head/tail-to-tail conformers, an order of magnitude higher than for the head-to-tail conformers. The results show that chemical conformation plays a crucial role in determining the material electronic structure and, hence, the relevant optical properties. The results are significant to the wide field of conjugated, synthetic, light-emitting materials, and hence to the development of large-area organic displays.

Spectroscopic properties of poly(3-alkylthiophenes) and their ‘head-to-head’, ‘tail-to-tail’ coupled analogues poly(4,4′-dialkyl-2,2′-bithiophenes)

Abstract Electrochemical doping of new soluble conducting polymers, namely, poly(4,4′-dialkyl-2,2′-bithiophenes), has been studied ‘in situ’ and ‘ex situ’ by various spectroscopic methods. These compounds represent the ‘head-to-head’ and ‘tail-to-tail’ analogues of poly(3-alkylthiophenes). The π→π ∗ transition in poly(4,4′-dialkyl-2,2′-bithiophenes) is blue shifted with respect to that characteristic of poly(3-alkylthiophenes) suggesting a higher torsion angle between the adjacent substituted thiophene rings. The doping-induced bipolaronic bands (Vis-NIR) are, however, located in essentially the same positions as the doping-induced ones in poly(3-alkylthiophenes). This observation may suggest that during doping, more twisted poly(4,4′-dialkyl-2,2′-bithiophenes) adopt a structure more similar to that of doped poly(3-alkylthiophenes). The changes in FT-IR spectra are also consistent with the bipolaron model since all the five expected doping-induced modes appear with the onset of the oxidation peak and grow in intensity with increasing potential.

Heteropolyanion-doped polypyrrole as catalyst for ethyl alcohol conversion

Abstract Heteropolyanion-doped polypyrrole can serve as a catalyst for ethyl alcohol conversion. The insertion of 12-molybdophosphoric anions into the polymer matrix significantly changes the selectivity of the catalyst with respect to unsupported crystalline H 3 PMo 12 O 40 . For example catalytic conversion of ethyl alcohol carried out on polypyrrole containing 75.5 wt.% of 12-molybdophosphoric anions and standardized by heating in helium, gives acetaldehyde as the main product (51%). On the acid-base centers ethylene (45%) and small amounts of diethyl ether (3.5%) are formed. Standardization of the catalyst by heating in air leads to heavy crosslinking of the polymer with simultaneous restoration of acid molecules. As a result, the selectivity and activity of this catalyst are similar to those of unsupported H 3 PMo 12 O 40 .

Highly conductive composites of polyaniline with plasticized cellulose acetate

Abstract Highly transparent, conductive blends can be prepared from plasticized cellulose acetate and polyaniline protonated with sulphonic acids, phosphonic acids and phosphoric acid diesters. Films cast from m-cresol solution exhibit percolation threshold below 0.5 wt% and excellent mechanical properties of plasticized cellulose acetate.

Poly(3-alkylthiophenes) and poly(4,4′-dialkyl-2,2′-bithiophenes): a comparative study by impedance spectroscopy and cyclic voltammetry

Abstract We have studied the electrochemical behaviour of two families of substituted polymers, poly(3-alkylthiophenes) (PATs) and poly(4,4′-dialkyl-2,2′-bithiophenes) (PDABTs), by impedance spectroscopy and cyclic voltammetry. In the PAT family the redox mechanism separates into two reversible redox reactions intervening at two different potentials. In the case of PDABTs, probably because of better stereoregularity due to the coupling mode between monomers, the redox reaction was found unique. In both cases as for nonsubstituted polymers the total doping charge was decomposed into a faradaic charge resulting from the diffusion of doping ions into small aggregates of compact polymer and a ‘capacitive’ charge due probably to the formation of a double layer around the small aggregates. The diffusion coefficient D was measured and the relation L 2 / D was found to be independent of the polymer thickness L . A relation connecting the capacitive charge to the faradaic charge was derived. In general the ratio between capacitive charge and faradaic charge was found to be lower in polydialkylbithiophenes than in polyalkylthiophenes which present a capacitive effect smaller that nonsubstituted polymers.

Spectroscopic studies of poly(4,4′-dialkyl-2,2′-bithiophenes) — the ‘head-to-head’ analogues of poly(3-alkylthiophenes)

Abstract Poly(4,4′-dialkyl-2,2′-bithiophenes) prepared by chemical polymerizatiok of 4,4′-dialkyl-2,2′-bithiophenes show highly regular structure. Due to different coupling patterns (equivalent to ‘head-to-head’ and ‘tail-to-tail’ coupled rings), their spectroscopic features are different to corresponding, mainly ‘head-to-tail’ coupled poly(3-alkylthiophenes). In particular, their π−π ∗ transition occurs at much shorter wavelengths due to lower conjugation caused by close vicinity of alkyl chains in adjacent thiophene rings. On the basis of the comparative investigation of poly(4,4′-dialkyl-2,2′-bithiophenes) and poly(3-alkylthiophenes) we discuss 13C solid state NMR and FT-IR spectra.

Spectroelectrochemical properties of poly(4,4'-dialkyl-2,2'-bithiophenes) and poly( 3-alkylthiophenes): A comparative study

The influence of alkyl side chain distribution patterns on the Spectroelectrochemical properties of poly(alkylthiophenes) has been studied. Two types of compounds were studied as representing different coupling patterns: n n(i) poly(4,4-dialkyl-2,2-bithiophenes), which represent head-to-head and tail-to-tail coupled poly(al-kylthiophene) chains; and n n(ii) poly(3-alkylthiophenes), which represent head-to-tail coupled poly(alkylthiophene) chains. n nBoth types of polymers can be obtained chemically or electrochemically by the constant potential method or the potential scanning method. Poly(4,4-dialkyl-2,2-bithiophenes) differ significantly from poly(3-alkylthiophenes) in their voltammetric and spectroelectrocheinical properties. The oxidative doping of these compounds occurs in a very narrow potential range (35 mV as determined by static Spectroelectrochemical studies) and is significantly retarded in dynamic measurements. Analysis of the changes in absorption in the 500 nm spectral region and the observation of an induction period in the oxidation at constant potential seem to indicate that the oxidative doping is preceded by structural changes which facilitate the oxidation. n nAlthough in the neutral state poly(4,4-dialkyl-2,2-bithiophenes) absorb at 390 nm, i.e. their π→π* transition is blue-shifted as compared to poly(3-alkylthiophenes), the polaronic states included by doping are located in the same spectral region for both families of polymers. This observation is consistent with the postulate of significant changes induced by doping in poly(4,4-dialkyl-2,2-bithiophenes). The more twisted head-to-head and tail-to-tail coupled poly(alkylthiophene) chains must adopt a more planar structure, similar to poly(3-alkylthiophenes), in order to create polaronic states and accommodate the charge-compensating anions.