High pressure conductivity and morphology of conducting polymer colloids

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29333/1/0000400.pd

Effect of chain rigidity on conductivity of conjugated polymers

There are several ways to introduce processability to conjugated polymers, and one of them is discussed here. The basic approach involves the introduction of flexible centers in a conjugated backbone with a periodicity that allows the existence of conjugated sequences characterized by an electron mobility high enough to result in electronic conduction upon oxidation or reduction. The process consists of the use of AsF/sub 5/ as a polymerization catalyst, and AsF/sub 3/ as a non-conventional medium for the reaction. The Lewis acid coupling reactions, via which the polymerization occurs, result in soluble materials. Characteristics of the materials obtained by polymerizing acetylene and some aromatic compounds are discussed

Advances in inherently conducting polymers

The discovery of polyacetylene as the prototype material led to extensive research on its synythesis and characterization. The techniques that emerged as the most important and promising ones are those that dealt with molecular orientation and that resulted in conductivities almost as high as that of copper. The study of dozens of other materials followed. Interest in conducting polymers stems from their nonclassical optical and electronic properties as well as their potential technological applications. However, some of the factors currently limiting their use are the lack of long-term stability and the need to develop conventional low-cost techniques for easy processing. Therefore, research was extended toward solving these problems, and progress has been recently made in that direction. The synthesis of new materials such as stable and easily processable alkylthiophenes, water-soluble polymers, and multicomponent systems, including copolymers and composites, constitutes an important step forward in the area of synthetic metals. However, a full understanding of materials chemistry and properties requires more work in the years to come. Although, few small-scale applications have proven to be successful, long-term stability and applicability tests are needed before their commercial use becomes reality

Molecular and supramolecular orientation in conducting polymers

Intrinsic anisotropy in electrical and optical properties of conducting polymers constitutes a unique aspect that derives ..pi..-electron delocalization along the polymer backbone and from the weak inter-chain interaction. To acquire such an intrinsic property, conducting polymers have to be oriented macroscopically and microscopically (at the chain level). A review of the various techniques, including stretch-alignment of the polymer and of precursor polymers, polymerization in ordered media, i.e., in a liquid crystal solvent, and synthesis of liquid crystalline conducting polymers will be given. 29 refs

Resonance Raman excitation profiles of polyacetylene/polyisoprene block co-polymers in toluene

We have measured the resonance Raman spectra and excitation profiles of a soluble polyacetylene/polyisoprene block-copolymer in toluene solution. These are the first reported excitation profiles that have been referenced to an internal solvent standard, the toluene Raman bands. We find that this copolymer exhibits the same two bands in the C=C stretch region, i.e., 1463 and 1519 cm/sup /minus/1/, that have been attributed to a bimodal distribution in conjugation length for polyacetylene thin films. The 1519 cm/sup /minus/1/ peak has been associated with short chain segments of polyacetylene and we assign it to an average chain length of N=11 C=C's based on the frequency of the peak of its excitation profile. The excitation profile of the 1463 cm/sup /minus/1/ mode peaks at 2.15 eV corresponding to a chain length of 31 C=C's. Based on the relative integrated intensities of these two excitation profiles, our block copolymer contains a 35% mole fraction of long chain segments to short chain segments. In contrast to previous results, we find that the 1294 cm/sup /minus/1/ band, which is a mode with a mixture of C-C stretch and C-H deformation, is resonance enhanced, with an excitation profile that peaks at 2.6 eV, the same energy as the 1519 cm/sup /minus/1/ mode's profile. 2 figs

The thermal isomerization of polyacetylene studied by Raman scattering

A study of the thermal isomerization of cis-(CH)x films has been carried out by means of Raman scattering spectroscopy. It is found that the Raman band profiles, induced by trans-(CH)x films, are dependent both on the temperature and on the isomerization time. The trans sequences first increase in length to a maximum length occurring at the maximum of the d.c. conductivity as measured in similar samples. A degradation of the films is then observed as punctual defects alter the carbon-carbon bond conjugation.Nous présentons une étude, par diffusion Raman, de l'isomérisation thermique de films de polyacétylène. Pour différents temps et températures d'isomérisation, nous montrons que le profil des bandes Raman induites par le trans-(CH)x est modifié. Dans un premier stade, nous observons que les séquences trans augmentent en longueur jusqu'à un maximum qui correspond au maximum de conductivité électrique mesuré sur des échantillons similaires. Ensuite, une dégradation des films est observée, correspondant à la formation de défauts ponctuels altérant l'alternance des liaisons carbone-carbone

Poly(vinyl pyridine)-based stabilizers for aqueous polypyrrole latices

The preparation and characterization of sub-micronic polypyrrole latex particles using polymeric stabilizers based on poly(vinyl pyridine) is described. These novel colloidal dispersions enhance the usually limited processability of the electroactive component, and in addition exhibit usefully high solid-state conductivity, despite the presence of the insulating stabilizer component. Furthermore, these latices exhibit reversible base/acid induced flocculation-stabilization behavior. The latter phenomenon is of fundamental interest and is expected to have commercial applications. The latices were characterized by transmission electron microscopy, visible absorption spectroscopy, FTIR and Raman spectroscopy, microanalysis, and compressed pellet dc conductivity. Base-induced particle flocculation was studied as a function of latex particle concentration. 24 refs., 4 figs., 2 tabs

EPR study of the cis-trans isomerization process in polyacetylene films

Using EPR we have studied the isomerization process converting cis-(CH) x films to the trans form upon thermal treatment. Following the measured linewidth and number of spins versus time and temperature, it is shown that for the lowest temperatures (T ∼ 200 °C) degradation becomes more and more efficient. There exists a small temperature range ( T ∼ 140-150 °C) where optimal characteristics (total isomerization + small degradation) can be achieved.En utilisant la RPE nous avons étudié le processus d'isomérisation qui conduit, par traitement thermique, des films de cis-(CH)x à la configuration trans. En suivant les comportements avec le temps et la température des largeurs de raie et nombre de spins mesurés, nous avons montré que pour les températures les plus basses (T ∼ 200 °C) la dégradation du système devient de plus en plus efficace. Il existe un étroit domaine de température (T ∼ 140 à 150 °C) où des caractéristiques optimales (isomérisation totale + faible dégradation) peuvent être obtenues