Richard V. Gregory

Kinetic study of the chemical polymerization of aniline in aqueous solutions

Abstract The oxidative chemical polymerization kinetics of aniline (AN) with ammonium peroxydisulfate (APS) in aqueous acid solutions with and without the presence of initial substrates is reported. A semi-empirical kinetic equation, − d [ AN ] dt = k 1 [ AN ][ APS ] + k 2 ′[ AN ][ P ] , where [P] = equivalent concentration of polymer, is proposed for this autoaccelerated reaction. The value obtained for k2′ depends primarily on acid concentration and the presence of substrate surfaces; k1 is affected by the presence of catalyst and the initial reactant concentrations. In general, k2′ has a value about two to three orders of magnitude higher than k1. A mechanism similar to the electrochemical polymerization is proposed for the autoacceleration reaction which involves the oxidation of aniline by highly oxidized polyaniline with the incorporation of acid.

THERMAL PROPERTIES OF CHEMICALLY SYNTHESIZED POLYANILINE (EB) POWDER

Abstract Thermal characteristics of chemically synthesized polyaniline (EB) powder have been investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), modulated DSC (MDSC), wide angle X-ray diffraction (WAXD), FTIR spectra, solid MS spectrum, and solubility tests. The exothermic peak measured both in conventional DSC and MDSC was a non-reversing chemical cross-linking reaction and was further confirmed by wide angle X-ray, FTIR, and solubility tests. Two glass transitions ( T g ), ∼70°C and ∼250°C, in polyaniline (EB) powder, were observed for the first time using MDSC during the process of heat treatment. These results clearly demonstrate that the morphology of polyaniline (EB) powder is changed by thermal treatment in the range of 185–350°C.

A method to prepare soluble polyaniline salt solutions : in situ doping of PANI base with organic dopants in polar solvents

Abstract Soluble PANI salt solutions can be prepared by mixing PANI base solutions with organic doping solutions in select polar solvents such as NMP and DMSO. Dopants containing carboxylate or amino groups, such as sulfosalicylic and m -sulfanic acids, yield soluble salt solutions. Free-standing films prepared from these solutions have a conductivity close to the value obtained in a pressed pellet doped with the identical dopant. UV-Vis spectra demonstrate the co-existence of highly doped and undoped phases in the partially doped solutions indicating that the doping process may not be a homogeneous one.

Improved solution stability and spinnability of concentrated polyaniline solutions using N,N′-dimethyl propylene urea as the spin bath solvent

Abstract It is widely known that the intrinsically conductive polymer (ICP) polyaniline is soluble in NMP solvent in its nonconducting base form. However a concentrated polyaniline/NMP solution (>5%) is unstable and rapidly forms gels at room temperatures. We have found that the gelation time and solution stability of polyaniline in DMPU is greatly increased and that this solvent may be suitable for use as a spin bath for the wet spinning of polyaniline fibers in the base form. We report in this paper some initial rheology data on solutions of PANI using NMP, NMP/LiCl, and DMPU as the solvent. All examined PANI solutions showed a similar rheological behavior in that the solutions became more shear dependent with increasing concentrations or increased aging time. The spinnability of PANI solutions was superior when DMPU is used as the spin bath solvent. NMP/LiCl was also examine since this solution tends to prohibit coagulation of PANI in solution.

Influence of the doping conditions on the surface energies of conducting polymers

Abstract The surface energies and polarities of the conducting polymers, polyaniline, polypyrrole and poly(3-hexylthiophene), dedoped and doped, were investigated by the harmonic-mean equation based on contact angle measurements. The values of the surface energies and polarities of dedoped conducting polymers are similar to those of conventional polymers. However, the surface energies of the doped conducting polymers vary greatly depending on the choice of the dopants and doping level. The results reveal that the change in surface energy of conducting polymers may result from the contribution of the polar components, depending on the types and concentration of the dopants, since the dispersion components of the measured surface energies of the examined conducting polymers do not change significantly from doping to dedoping.

Spectral studies and thermal properties of a urethane-substituted polythiophene

Abstract A new polythiophene containing a urethane side chain in the β-position was chemically polymerized in chloroform using FeCl 3 as the oxidant. The urethane-substituted polythiophene is soluble not only in common organic solvents, such as chloroform and tetrahydrofuran, but also in strong polar solvents such as N,N -dimethylformamide, N,N -dimethylacetamide and N -methyl-2-pyrrolidinone. This allows the polymer to be blended with conventional polymers, such as polyurethane, polyacrylonitrile, polyamide, polycarbonate and polyester, in solution while maintaining good electrical conductivity. The structures of the monomer and polymer were characterized using NMR, IR, molecular weight and elemental analysis. The spectral results suggest that the chain order of this polymer is quite regular. M w and M n of this polymer obtained by gel permeation chromatography are 169 284 and 63 557, respectively. This polythiophene containing a urethane side chain also demonstrates solvatochromic behavior which was characterized by UV-Vis absorption spectroscopy. Glass transition temperatures obtained by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) studies are 62 and 73 °C, respectively, and the melting point of this polymer measured by DSC is 265 °C. Thermogravimetric analysis results indicate that this polymer is a thermally stable material.

Solubility and rheological characterization of polyaniline base in N-methyl-2-pyrrolidinone and N,N′-dimethylpropylene urea

Abstract The thermodynamic ‘goodness’ of N-methyl-2-pyrrolidinone (NMP) and N,N′-dimethylpropylene urea (DMPU) as solvents for polyaniline (PANI) (emeraldine base) were compared by studying the dilute solution viscometry of solutions of PANI in NMP and DMPU. The intrinsic viscosity of PANI polymer in NMP was found to be 0.71 dl g−1, whereas the same polymer in DMPU had an intrinsic viscosity of 0.77 dl g−1, which indicates that DMPU is a ‘better’ solvent for PANI. The rheology and rheological stability of solutions of PANI in NMP and DMPU were studied by cone and plate rheometry. A 10% PANI solution in NMP gelled within 60 min, whereas a 17.5% solution in DMPU did not show any change in its viscosity for as long as 400 min. Solutions of PANI (10–17.5%) in DMPU displayed prominent shear thinning behaviour at lower shear rates (below 3 s−1 and Newtonian behaviour at higher shear rates (3–15 s−1). A solution of 10% PANI in NMP showed a similar prominent shear thinning followed by a gradual decrease in viscosity with an increase in shear rates, presumably due to breaking of the ‘weak’ thixotropic gel.

Electronic properties of polyaniline/carbon nanotube composites

Composites of high molecular weight polyaniline and carbon nanotubes are investigated for electronic device applications. Physical characterization by Thermogravimetric analysis and atomic force microscopy indicates that polyaniline containing 1% Carbon Nanotubes is suitable for organic devices. Measured electrical characteristics of Schottky diodes fabricated using these materials exhibit current levels in the polyaniline/carbon nanotube composite devices nearly an order of magnitude higher than in the polyaniline devices.

Mechanical and Electrical Properties of Solution-Processed Polyaniline/Multiwalled Carbon Nanotube Composite Films

Mechanical and electrical properties of high molecular weight polyaniline/multiwalled carbon nanotube composite films were investigated. Addition of carbon nanotubes to polyaniline films was accomplished by solution processing. Physical characterization of these composites by thermogravimetric analysis, tensile testing, dynamic thermal mechanical analysis, and atomic force microscopy measurements indicate that polyaniline containing 1% carbon nanotubes is more mechanically and thermally stable than neat polyaniline. Rectifying aluminum contacts were fabricated using this composition of the composite material, along with neat polyaniline for comparison. The measured electrical characteristics indicate that the current levels of the polyaniline/carbon nanotube composite devices are nearly an order of magnitude higher than those of the polyaniline devices; thus, this composite material has the potential for applications in organic electronics.

Mechanically strong, flexible highly conducting polyaniline structures formed from polyaniline gels

Abstract Strong and highly conductive films up to 0.6 mm thick can be prepared from polyaniline gels. Concentrated emeraldine base solutions (>6 wt%) in NMP are found able to form these gels. Films obtained from these gels have better mechanical properties than those obtained from typical dilute solutions (1 wt%). Doping of the gel films in different dopant/solvent solutions are studied. Films doped in EtSO3H/acetic acid can be cold drawn to a draw ratio of 3.5 to 1 and have conductivities of 103 S/cm or better. Dopant and moisture content are found to have a large influence on the mechanical properties of the films.