J.G. Masters

A simple method to estimate the oxidation state of polyanilines

Abstract The electrical conductivity and other properties of polyaniline (PANI) and its derivatives are highly dependent on its oxidation states. In order to obtain a simple method to determine the oxidation state, a systematic study was performed to investigate the interconversion between pernigraniline (PB) PANI form to emeraldine (EB) one, and from EB to leucoemeraldine (LEB), by ultraviolet/visible (UV/Vis) spectroscopy. UV/Vis spectra were carried out for different oxidation degrees of PANI/N-methyl-2-pyrrolidinone (NMP) solutions. The redox states interconversion was made in NMP solutions in ambient air and/or inert atmosphere. LEB base presents only one peak in the absorbance spectra, associated with the π–π* transition, while the other two forms, EB and PB, exhibit another peak of lower energy. This second peak, related to a molecular exciton in EB, has its maximum intensity diminished as the EB is reduced or oxidized. By plotting the relative intensity of these peaks vs. the oxidation degree, it was possible to identify, with a reasonable accuracy, the oxidation state of PANIs. This method was also applied to poly(o-methoxyaniline) (POMA).

Polyaniline: Allowed oxidation states

Abstract The interconversion of different oxidation states of polyanilines has been studied. It is concluded that the polyaniline bases (NMP solution) exist only in three discrete oxidation states at the molecular level.

Polyaniline: Oriented Films and Fibers

Abstract The dependency of the conductivity of polyaniline (emeraldine oxidation state) on its molecular weight has been determined. Uni- and biaxially oriented films and uniaxially oriented fibers of emeraldine base have been studied and the dependency of their degree of crystallinity, tensile strength, and conductivity (after doping) on draw ratio has been determined.

Polyaniline: Synthesis and properties of pernigraniline base

Abstract The most highly oxidized polyaniline, in the form of pernigraniline base, can be synthesized as an analytically and oxidatively pure solid (powder or large free-standing films) by the controlled oxidation of emeraldine base by m -chloroperbenzoic acid or directly from aniline by oxidative polymerization with (NH 4 ) 2 S 2 O 8 . In the first method, the emeraldine oxidation state is converted directly to the pernigraniline oxidation state without passing through any intermediate discrete oxidation state at the molecular level. Treatment of perigraniline base with aqueous HCl results not in a protonated form of pernigraniline but in reductive ring chlorination to give the emeraldine oxidation state.

Thermochromism in the insulating forms of polyaniline: Role of ring‐torsional conformation

The temperature‐dependent optical spectra of the major insulating forms of polyaniline—the fully reduced leucoemeraldine base, half‐oxidized emeraldine base (EB), and fully oxidized pernigraniline base (PNB)—and of two oligomeric model compounds for polyaniline are reported. All three forms of the polymer possess a ∼3.8 eV optical absorption assigned to a transition from the valence band to a narrow π* conduction band; in all cases this transition shifts to higher energy and weakens with increasing temperature, T. The oxidized forms also exhibit transitions at ∼2 eV; in EB, this absorption feature has previously been assigned to a ‘‘molecular exciton’’ and is found to increase in energy with increasing T. In PNB, the observed ∼2.3 eV transition is correlated with the expectation of a Peierls dimerization gap in this half‐filled band system; in contrast to the ∼2 eV transition in EB, this optical transition energy decreases with increasing T in PNB. These observations are for the most part understood by a ...

X-ray structure of polyanilines

Abstract We describe two classes of the emeraldine form of polyaniline, Class I exhibits ES-I crystal structure in the HCl salt form and in the base form it is amorphous EB-I. Class II materials form partially crystalline structures EB-II and ES-II in base and HCl salt forms, respectively. We compare structural results on emeraldine with data for partially crystalline leucoemeraldine base (LEB) and pernigraniline base (PNB) — the fully reduced and oxidized forms of polyaniline, respectively. We contrast our studies of the EB-I/ES-I system with results for poly( o -toluidine) base, POT-EB and hydrochloride, POT-ES.

Time-resolved fluorescence of polyaniline

Abstract We report the time-resolved fluorescence of polyaniline in NMP solution as a function of its average oxidation state which is continuously varied from the fully reduced leucoemeraldine base to the half-oxidized emeraldine base form of the polymer.

Vibrational analysis of the reduced form of polyaniline: the leucoemeraldine base

Abstract Extensive studies have been carried out on the different forms of polyaniline. In this paper, we present a study of the vibrational properties of the leucoemeraldine base, the reduced form of polyaniline. Infrared absorption and resonant Raman scattering (RRS) spectra are presented for the polymer, together with those obtained in model compounds such as diphenylamine and N , N ′-diphenyl-1,4-phenylenediamine. The Raman spectrum of the leucoemeraldine base exhibits mainly bands at 1181, 1219, 1597 and 1618 cm −1 . By the use of a valence-force-field model, we have assigned these vibrational modes, including those of the model compounds. Calculations are in rather good agreement with previous assignments and the main force constants, which are determined from the fit of the experimental IR and Raman bands, are physically reasonable compared to what is found in other polymers.

Photoinduced Absorption and Erasable Optical Information Storage in Polyanilines

Abstract Photoinduced absorption spectroscopy has been used to study a variety of forms of polyaniline. Experiments on emeraldine base and leucoemeraldine base have led to a picture of the photoproduction and decay of massive, long-lived defect states that can be described in terms of conformational changes involving rotations of the C 6 H 4 rings. Photoexcitation spectra of other polyanilines, such as pernigraniline base and poly( o -toluidine), exhibit similar features including relatively weak photoinduced infrared vibrations and a relatively strong photoinduced absorption peak near 1.4–1.5 eV. In several of these materials, the photoinduced changes are very long-lived, leading to an investigation of the polyanilines as media for erasable optical information storage.

Vibrational analysis of reduced and oxidized forms of polyaniline

Abstract In this paper, we present dynamic calculations of vibrational modes of two forms of polyaniline: the fully reduced form (Leucoemeraldine Base) and the fully oxidized form (Permigraniline Base). Our model is based on the use of force constants to provide an interpretation of experimental frequencies obtained by Resonant Raman Scattering and infrared absorption. In order to obtain the best set of parameters, we have performed calculations on both polymers and model compounds. Our model leads to a good fit between experimental and calculated frequencies, also we present the main force constants which are in agreement with previous works performed on similar armatic structures.