Methods for significantly increasing the molecular weight of polyaniline are described. The conductivity of doped polyaniline is shown to be more directly dependent on its degree of alignment/crystallinity than on its molecular weight. The tensile strength of polyanilines films and fibers increases with increasing stretch alignment. An interpenetrating polymer system involving polyaniline which shows greatly enhanced conductivity at pH values where polyaniline has negligible conductivity is described. The doping level of polyaniline is shown to be dependent not only on the pH of the dopant medium but also on the presence of dissolved neutral salts. This new phenomenon is explained in terms of Donnan equilibrium effects.

The optimized molecular structures of doped polyacetylene model compounds are studied by the ab initio SCF MO method. The calculated structures are assigned to polaron, charged soliton and poison unit. The one dimensional energy band structures of the charged soliton-antisoliton and the polson-antipolson lattices are investigated. The latter one gives a quasi-metallic energy band. The results of the energy band calculation are consistent with the electrical properties and ultraviolet photoemission spectra of the doped polyacetylene.

We develop a new model for heavily doped metallic polyacetylene. An electron and a hole injected in a doped chain make localized defects called superpolarons (SP's) in the electronic order parameters (OP) in a charged soliton lattice. The SP's can make quantum intrachain translational motion and interchain transfer via dopant ions. They are stabilized by their quantum motions and SP pairs are spontaneously produced in a high doping regime. The SP's are Fermions and can be a Fermi liquid in the doping regime. Some metallic properties of the Fermi liquid of the SP' s are studied.

Recent structural studies of the polyaniline family of electronic polymers in the base and salt forms are reviewed. We describe the crystalline and amorphous structures of the two classes of emeraldine. The structural evolution with HC1 doping and ring substitutions are also discussed in relationship with the electronic properties of these materials. Implications for charge transport phenomena are also considered.

In acidic medium, polyaniline has positive charges on its molecular backbone. These charges come from either protonation at the nitrogen atom sites or polarons in its β-electronic system [1]. Although polyaniline, due to its positive charges, is a polycation, yet its physical properties are quite different from the classical polyelectrolytes. For example, the polycation vinylbenzyltrimethylammonium chloride is soluble in water but polyaniline molecules (and other conducting polymers too) tends to aggregate into intractable solid. Conducting polymers aggregate into intractable solid because of their stiff molecular backbone and the strong short range attractive forces between βclouds of adjacent polyaniline chains. The insolubility of polyaniline poses problem for solution processing of polymers. There have been a heavy effort towards the resolution of this problem [2].

(2-Methoxy)ethoxy substituted anilines have been polymerized by chemical and electrochemical methods in hydrochloric acid (HC1) and p-toluenesulphonic acid(TsOH). Electrical conductivity, optical properties, solubility and charge capacity of these polymers are discussed.

The electrochromic responses for two kinds of polypyrrole (PPy) films, PPy/inorganic anion and PPy/polyanion composite films, were studied by electromodulation technique. Analyses of electrical and optical responses show that electrochromic responses in conducting state were nearly the same for the both films, however, those in redox active state were characteristic of the two films. The differences in the responses of the two films seem to arise from the differences of both the morphologies of the films and charge transport properties in the films.

According to the “spacer” strategy we have previously proposed the monomers candidate for providing conductive polymers endowed with special properties should contain the polymerogenic rings (pyrrole or thiophene), as terminal units, linked to a central π-conjugatively active frame; we describe how it is possible in this way to control the redox potentials E of the polymers derived from such monomers. This control is beneficial because it is possible to increase the E° value of polypyrrole-type systems and decreases the E° value of polythiophene-type systems. Also, the “spacer”may be further functionalised and, being remote from the polymerisation site, cannot alter the conductivity characteristics typical of the polymer derived from the parent heterocycle (pyrrole or thiophene): such a functionalisation may provide the final, tailored, conductive polymer with special properties (e.g. solubility). If the central ring, acting as a spacer, is formed linking two positions of a di-heterocycle with a saturated chain, it is possible to partially control the twist angle between the heterocyclic units. Crystal and molecular structures have shown that dipyrrole units further linked through the nitrogen atoms are quite sensitive to the central ring size. With respect to the conductivity of unsubstituted polypyrrolc, the conductivity of the polymers derived from such monomers is dependent from the twist angle between the rings. This result is relevant to describe conditions of conjugation between the heterocyclic units of a monomer required to produce upon doping a conductive polymer.

The oxidizing power of clays is put to use for the polymerization of heterocycles (pyrrole- and thiophene- types) in the 2D-interfoliar space and on the external surface of the clay particles. A mechanism is proposed for the oxidative polymerization.

A brief overview is presented of the electrical and linear optical properties of conjugated polymers in their electrically insulating forms. Topics discussed include electronic structure and optical spectroscopy, thermochromism, and device applications, particularly electroluminescence. Structure-property relationships are stressed. Particular emphasis is placed on the properties of polydiacetylenes as they are available as macroscopic single crystals and, hence, are the best defined class of conjugated polymers.

Based on theoretical calculations Polyarenemethylidenes (PAM) 1 have been predicted to be low gap polymers with good semiconducting and photoelectrical properties. The preparation of such a polymer with a well defined structure affords the synthesis of suitable precursors. We have been able to synthesize and characterize a variety of monomers in which the inner quinonoid system is present. Also more extended systems containing one or two additional benzene rings at the quinonoid system have been prepared. The chemical and electrochemical polymerization of the precursors is reported, leading to polymers 1 in a great structural variety.

Studies of the effect of different electrode combinations on the device characteristics of simple three layer light-emitting diodes (LEDs) prepared with poly(ρ-phenylenevinylene) (PPV) as the emissive layer sandwiched between two metal contacts have shown that it is generally more difficult to inject electrons than holes. In order to improve the efficiency of such devices it is, therefore, necessary to develop methods to enhance the injection of electrons and we illustrate here one example where we have successfully achieved this by the introduction of a further, electron transport, layer. The result is an eight fold increase in efficiency over our best three layer PPV devices. The efficiency is also dependent on the details of the polymer electronic structure and using a family of copolymers we have been able to produce enhancements in efficiency to values of up to 30 times that of the corresponding PPV devices. Variations in the polymer electronic structure also affect the colour of emission and the same family of copolymers allow control of emission colour from blue/green to orange/red. Supramolecular control of the copolymer electronic structure can be achieved by lithographic patterning and we show that it is possible to produce regions within a single polymer film that possess different π-π* energy gaps.

We have studied charge carrier generation by photons in thin films of poly(di-n-hexylsilane) over the photon energy range 3.15 to 6 eV and find that it is nonlinear in light intensity to above 4.5 eV. We show that the generation mechanism is exciton-exciton annihilation.

Using 632.8, 514.5, 488.0, and 457.9 nm as wavelengths of excitation, Raman spectra have been observed for single crystals of the polydiacetylene of - (CH2)4OCONHCH(CH3) 2 (Poly-IPUDO). The hysteresis effect observed for the thermochromic shift in the Raman spectra is supported by data from repetitive temperature cycling in differential scanning calorimetry.

We report a study of the near infrared photoinduced absorption of a series of poly -3-decylthiophene with different supermolecular organization as solution cast films, good solvent and aggregated bad solvent solutions.

Photoinduced subgap electronic states are detected both in the solid and in solutions independently from the presence of polymer aggregates. The study of the photoinduced activity Δ/T on the laser intensity I indicate a I0.6 dependence for the films and a I0.95 dependence for the solutions. This is the evidence that the photoinduced states are generated in the solid via an inter-chain mechanism while in the solution via an intra-chain mechanism.

A possible role of the solvent into the photoexcitation pathway is discussed.

Propylmethylpolyazine, [N=C(R1)-C(R2)=N]X (R1=CH3, R2=CH2CH2CH3), is an organic-soluble linear conjugated polymer. The ultraviolet spectrum of thin films of this material shows two peaks at about 280 nm and 320 nm. These absorptions are ascribed to transitions from different filled valence bands to the same empty conduction band. Oxidative doping of this polymer with iodine gives spectra that are consistent with the generation of bipolarons. Irradiation of pristine thin films with 300 nm light causes a two step photoprocess to occur. The first step happens during the first hour of irradiation and if the film is left in the dark is completely reversible. The second step takes considerably longer to complete (more than 12 hr of irradiation) and is irreversible. The UV spectrum and FTIR spectrum of the step one photoproduct suggest that the imine bond is undergoing an E to Z isomerization photochem-ically which reverses in the dark. The step two product is probably due to a cycloaddition reaction.

Alkyl substituted poly(2, 5-thienylenevinylene)s were produced with a new synthesis. The polymers are soluble and processable and show a strong electrochromic effect in the visible spectral range.

A series of highly conductive, environmentally and thermally stable polyanilines was synthesized. These polymers, which are obtained by employing careful synthetic conditions, purification procedures, and dopant variations, show interesting morphological structures and high temperature stability. Thermal studies by TGA, DSC and DMTA show a glass transition temperature (Tg) for neutral polyaniline around 185°C. This is the same temperature at which the conductivity and crystallinity decrease. Isothermal heatings of the polyaniline tosylate at 200 and 250°C in air show significant amounts of weight loss. This is due to dopant loss through irreversible chain rearrangements and air oxidation at temperatures above Tg.

The aqueous polymerization of pyrrole and aniline by ferricyanide and persulfate, respectively, was monitored by Raman scattering and potentiometry. Raman scattering gave well-resolved signals for monomer and oxidizer. The kinetics of polypyrrole formation could be determined by both techniques, whereas only Raman scattering was suitable for the aniline system. The stoichiometry of the pyrrole polymerization remained constant at 2.5 oxidant molecules per pyrrole consumed. The aniline reaction showed an accelerated region with aniline consumption lagging persulfate use.

The modification of the mechanical properties of polypyrrole(PPy) by electrochemical preparation of conductive composite film from pyrrole(Py) and two kinds of liquid crystalline copolyamide of poly(p-phenylene-terephthal- amide)(PPTA) poly(p-phenyleneterephthalamide/diphenyl ether terephthal- amide) (PPTA[0]) and poly(p-phenyleneterephthalamide/diphenyl methane tere-phthalamide) (PPTA[C]) are presented.

The electrical conductivity of the PPTA[0]/PPy and PPTA[C]/PPy composites are the same order of magnitude as PPy or PPTA/PPy. The mechanical properties of the composite films are better than that of pure PPy. and the composite films have good electroactivlty and thermalstability.