Emeraldine base molecular weight

Results and Discussion. The 2-ethyl polyaniline concentration in the silica gel film was determined by constructing a Beer s law calibration curve from solutions of known concentration. Assuming an average molecular weight of 5000, the 2-Et PANi concentration in the silica gel was found to be 9.6 x 10 4 M. The refractive indices of CS2 and 2-Et PANi SiC>2 were estimated to be 1.6 and 1.4 at 1.06 im, respectively. The emeraldine base doped silica gel was found to have low losses due to scatter, and exhibited good transparency at 1.06 im. Spectrophotometric measurements at 1.06 fim yielded absorption coefficients of 0.1 cm-1 (> 99% T over 1 mm pathlength) for the CS2 reference and 4 cm 1 (96% T over 1 mm pathlength) for the 2-Et PANi doped silica film. 

There are, however, some problems with this method. First, high molecular weight fractions are not soluble in the strongest solvent, A-methyl pyrroli-done, for emeraldine base. Second, Wessling has shown by membrane filtration and photon correlation spectroscopy that these transparent, clear blue liquids are in fact dispersions and not solutions. 

Chemical polymerizations of aniline with (NH4)2S208 were initially performed at room temperature. However, later studies showed that the PAn obtained was of relatively low molecular weight and contained significant defect sites such as undesirable branching due to ortho-coupling.5960 Subsequently, the most widely employed temperature for chemical polymerization of aniline monomers has been ca. 1-5°C, as described by MacDiarmid and coworkers,61 providing a PAn whose emeraldine base (EB) forms have molecular weights (Mw) of 30,000-60,000 g mol-1. 

When solutions of several wt% emeraldine base PANI in NMP are left standing at room temperature, they gel spontaneously. In this process, small crystallites grow at entanglement sites and a network based on physical crosslinks is formed. The gelation time depends strongly on concentration and molecular weight, since gelation relies on chain overlap. 

From these as yet incomplete and on-going studies it is apparent that neither the extent of crosslinking in the emeraldine base films used or the molecular weight of the polyaniline employed in their preparation have any obvious major effect on their behavior on stretching. 

A solution of the amorphous "processed" emeraldine base in NMP exhibits a bimodal molecular weight distribution (by g.p.c monodispersed polystyrene standard), the maximum molecular weight fraction corresponding to approximately 325,000,35,37 consistent with earlier studies. 37,39 Lower molecular weights, in concentrated H2SO4 solution of emeraldine base/ synthesized in a slightly different manner, have... 

The absorption spectra of polyaniline films cast from sulfuric acid are strongly dependent on the molecular weight (viscosity). Figure 2 shows spectra of three thin films spin-cast from sulfuric acid solution, and subsequently treated by 0.5M HCl solution to achieve full protonation. To study the effect of molecular weight on the absorption spectrum, we used emeraldine base samples fractionated from the same preparation batch (polymerization and compensation) as described in the previous section. This procedure prevents any uncertainty in the viscosity value, and avoids slight variations in the preparation procedure. 

TFA Trifluoroacetic acid TFE Trifluoroethanol HA Hydroxyapatite filler PEO Poly(ethylene oxide) PANi Polyaniline (emeraldine base) BDI Diisocyanatobutane DCM Dichloromethane DMAC Dimethylacetamide THE Tetrahydrofuran HEA Hexafluoroacetone HEP l,l,l,3,3,3-Hexafluoro-2-Propanol D Eiber diameter. The silk is isolated from cocoons of silkworm B. mori and degummed. The silk derived has an average molecular weight of around 9 x 10 (g/mol). 

We have prepared a series of nylon / poly aniline blends using the solvent hexafluoroisdpropanol (HFIP), which is an excellent solvent for polyaniline emeraldine base (PANI-EB), polyaniline doped with various sulfonic acids (PANI-ES) and for hi molecular weight nylon 6 and nylon 12. It was observed that conductivity and morphology of the blends varied with the compatibility of the sulfonic acid anion with the nylon. Methanesulfonic acid, butane sulfonic acid dodecylbenzene sulfonic acid and camphor sulfonic acid were used as PANI dopants and the PANI-ES / nylon blends were characterized by electrical conductivity (room and low temperature) and transmission electron microscopy. The results of these various measurements and the conclusions which can be drawn regarding morphology and conductivity of Ihe blends, will be reported. 

A small number of studies have investigated the molecular weight of polyaniline as prepared by standard methods. In early work, MacDiarmid and Epsteini reported that the normal gel permeation chromatography (GPC) techniques could be used to determine molecular weight distributions of polyaniline. The emeraldine base form of the polyaniline was dissolved in... 

Mattes et al. also determined the Mark-Houwink constants for polyaniline emeraldine base in NMP. The Mark-Houwink equation relates the intrinsic viscosity (solution viscosity at infinite dilution) to the polymer molecular weight ... 

Most fibers and films of PAn have been prepared from a solution of emeraldine base and converted to the emeraldine salt by acid doping. The choice of dopant acid has a profound effect on mechanical properties. In fact, MacDiarmid et al. have shown that the mechanical properties depend in a complex way on dopant, casting solvent and polymer molecular weight. Full details of the effects of polymer structure (as influenced by dopant and solvent) on the mechanical properties are yet to be eludicated. 

When two molecular weights of an aromatic monoamine were allowed to condense with one molecular weight of DHDHTA, a -phenylenediamine was produced. Thus, Ph-NH-Ph-NH-Ph-NH-Ph-NH2 ("emeraldine base") afforded "COA blue", a material with an unknown number of Q s which could be reduced to COA (white, leuco) with phenyl hydrazine. 

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