Jukka Laakso

Thermochromic and solvatochromic effects in poly(3-hexylthiophene)

Abstract We report thermochromic and solvatochromic effects in the soluble conductive polymer poly(3-hexylthiophene). Thin solid films of the polymer change colour at higher temperatures. The colour of solutions of the polymer can be changed by varying the composition of the solvent. Optical absorption in good solvents is similar to that of thin solid films at higher temperatures, while in poor solvents, absorption features similar to those found in solid films at low temperatures are observed. We discuss these effects with reference to the existence of a hitherto disregarded type of conformational defect, conformons. These are rotational defects on the polymer chain, leading to loss of planarity. High vacuum studies of the thermochromic effect in thin films using X-ray photoemission spectroscopy support this interpretation. The standard series of defects in conductive polymers, solitons, polarons and bipolarons, may have to be extended to include conformons.

Counter-ion induced processibility of polyaniline: conducting melt-processible polymer blends

Summary form only given. Conducting polymer blends made by blending thermoplastic bulk polymers with Polarene/sup TM/, a proprietary conducting polyaniline composition, using conventional melt-processing techniques are reported. The percolation threshold for conductivity is observed at astonishingly low weight fractions of the conjugated conducting polyaniline indicating the formation of a unique morphology. Results on electrical and mechanical properties of these blends will be presented and discussed.

Melt and solution processable poly(3-alkylthiophenes) and their blends

Abstract We report on the properties of melt and solution processable poly(3-alkylthiophenes), P3AT, and on the fabrication of electrically conducting polymer blends consisting of P3AT, specifically poly(3-octylthiophene), POT, and a thermoplastic matrix polymer made using ordinary melt processing techniques. The POT used in this work was synthesized using two different chemical polymerization techniques. Films made from as-synthesized POT powder, either by solution casting or melt processing techniques were found to be easily doped by electron acceptors to conductivities of 20–30 S/cm. Blending of POT with thermoplastics such as ethylenevinylacetate copolymer, EVA, in the molten state yields polymer blends with excellent mechanical properties that might be doped to conductivities exceeding 1 S/cm.

Thermochromism in thin films of poly(3-alkylthiophenes)

Abstract We report spectroscopic studies fo the thermochromic effect in poly(3-alkylthiophenes). Thin solid films of poly(3-butylthiophene), poly(3-hexylthiophene), poly(3-octylthiophene) and poly(3-decylthiophene) undergo a reversible color transition when going from low to high temperature. The optical absorption shifts to higher photon energies with higher temperature. The transition, which occurs over a broad temperature range, occurs at lower temperatures for polymers of longer alkyl side chains. The colour change can be interpreted assuming a change of polymer conformation from a rigid rod geometry at low temperatures to a random coil conformation at higher temperatures. We discuss the physics of this transition.

Electrically conductive compositions based on processible polyanilines — PANEPOL TM

Abstract Truly melt- and solution processible electrically conductive polyaniline (PANI) compositions can be produced commercially utilizing the technology originally developed some years ago in a joint-effort between Neste Oy and UNIAX Corporation. This technology, PANIPOL TM , utilizes PANI protonated by functionalized protonic acids in combination with proprietary plasticizers. Neste has now further developed this technology and reached semi-industrial scale production capabilities. We briefly discuss some features of fusible, conductive PANIPOL TM compositions developed specifically for use in conductive products such as injection molded articles, extruded films and fibers.

Conducting polymer blends

Abstract We report the production and properties of electrically conducting polymer blends utilizing the melt-processability properties of high molecular weight poly(3-octylthiophene), POT. We have found that polymer blends produced by mixing appropriate amounts of POT with a variety of thermoplastic matrix polymers have excellent mechanical properties and that they can be doped to yield electrically conducting polymer blends with conductivities exceeding 1 S/cm.

X-ray diffraction and infra-red spectroscopy studies of oriented poly(3-alkylthiophenes)

Poly(3-octylthiophene) was stretched at 100°C to a final length up to five times the initial length. The degree of orientation in the crystalline and amorphous phases has been determined by means of X-ray diffraction and polarized infra-red spectroscopy. The value of the orientation function in the crystalline region was 0.72, which is comparable to the value 0.81 predicted from a theoretical calculation based on the draw ratio. The orientation of the amorphous phase was considerably lower, 0.47. Based on X-ray diffraction data from poly(3-alkylthiophenes) with different lengths of the side-chain, a tentative crystal structure for the poly(3-alkylthiophenes) is proposed

Processable Conducting Poly(3-Alkylthiopenes)

The poly(3-alkylthiophenes) represent a new generation of conducting polymers, that exhibit both solution and melt processability. These properties open new possibilities for the utilization of conducting polymers in practical applications. Furthermore, the solubility of these polymers enables the characterization of the physical and chemical structure in greater detail than hitherto have been possible. In this chapter we give a brief review of the synthetic routes to the poly(3-alkylthiophenes) as well as an overview of some of the recent results on the physical and chemical characterization of this class of materials. In this overview we include results on stability properties, transport properties, thermo- and solvatochromism. We also discuss some aspects of the utilization of the poly(3-alkylthiophenes) in applications.

Doping and dedoping processes in poly (3-alkylthiophenes)

Abstract Doping, thermal dedoping and degradation processes in poly(3-octylthiophene) and poly(3-decylthiophene) have been studied. The doped state is unstable. The dedoping decay rate of conductivity depends on the dopant, dedoping degree (or conductivity) and temperature. The temperature dependence follows the Arrhenius law. The most stable dopant studied was FeCl3. Other dopants, I2, PF6− and organic acid anions had orders of magnitude higher conductivity decay rates. Dedoping is associated with degradation of the polymer, especially when doped with FeCl3.

Conductivity and structure of DBSA-protonated polyaniline

Abstract The discovery of a processable and conducting polyaniline complexes including functionalized sulphonic acids is an important discovery in the field of conjugated polymers. The conductivity, electronic and crystalline structure properties of polyaniline protonated with dodecylbenzenesulphonic acid are proportional to the molar concentration of the acid. The protonation leads to a layer structure evident in X-ray diffraction patterns and the crystallinity follows a growth as a function of the acid concentration similar to the conductivity increase. The electronic structure measured by UV-VIS spectroscopy shows an increase in the polaron concentration up to an acid concentration of 0.35 after which a broadening of the peak indicates the formation of a polaron band.