John R. Reynolds

A quartz microbalance study of the electrosynthesis of polypyrrole

Abstract An electrochemical quartz crystal microbalance has been used to study the anodic electropolymerization of pyrrole and concurrent deposition of polypyrrole onto gold in acetonitrile and propylene carbonate using tetraethylammonium tosylate, tetrabutylammonium tetrafluoroborate, and lithium perchlorate. Simultaneous dynamic measurements of charge and mass have been used to monitor the efficiency of the polymerization/deposition process as a function of film thickness and electrodeposition rate. This work demonstrates that the early stages of film formation are affected by the solubility of the oligomers formed and that the ultimate efficiency is electrolyte dependent. Additionally, it is shown that the polymerization process exhibits second-order reaction kinetics with respect to monomer concentration.

Self-doped conducting copolymers: a charge and mass transport study of poly{pyrrole-CO[3-(pyrrol-1-YL)propanesulfonate]}

Abstract A self-doped copolymer of pyrrole, poly{pyrrole-co-[3-(pyrrol-1-yl)propanesulfonate]}, in which the charge compensating counterion is bound covalently to the polymer main chain, has been prepared and the charge and mass transport in the polymer during redox switching has been investigated using chronocoulometry and microgravimetry as a function of the supporting electrolyte The results are compared with the behavior of polypyrrole under similar conditions It is shown that within this new family of materials, called “self-doped conductive polymers”, ion mobility is restricted to cationic species and thus the polymer can be viewed as an ion-specific membrane This is in contrast to the case of polypyrrole, where a more complex behavior prevails The charge passed during the chronocoulometric experiment varies as tα where 0.2

Electrochemistry of some β‐Substituted Polythiophenes Anodic Oxidation, Electrochromism, and Electrochemical Deactivation

The anodic electrochemistry of the soluble poly(3-ethylmercaptothiophene) (PEMT) and poly[3,4-bis(ethylmercapto)thiophene] (PBEMT), is compared with the behavior of polythiophene (PT), poly(3-methylthiophene) (PMT), and poly(3-hexylthiophene) (PHT). In all five cases, the first anodic oxidation was reversible and was accompanied by reversible electrochromic behavior. When the polymers were driven to more positive potentials, there was immediate loss of electroactivity and concomitant color change to black. An electrochemical cross-linking/chain extension technique is discussed for PEMT as a means of growing smooth polymer films on electrode substrates starting from soluble oligomers in solution

Aqueous electrochemistry of tellurium at glassy carbon and gold. A combined voltammetry-oscillating quartz crystal microgravimetry study

The electrochemistry of tellurium was studied in an aqueous H2SO4 matrix using glassy carbon and Au working electrodes. Cyclic voltammetry was used in conjunction with oscillating quartz crystal microgravimetry to delineate features in the voltammograms accompanied by mass loss or gain at the electrode surface, from those attributable to the solution phase. The voltammetry profiles for Te showed a remarkable degree of sensitivity to the electrode surface. Thus, a set of waves attributable to the direct 6 e− reduction of HTeO2+ to H2Te, and a cathodic pre-wave associated with the catalytic deposition of Te0, were noted at the Au surface. These features were conspicuously absent at the glassy carbon surface. On the other hand, the 2 e− reduction of Te0 to H2Te manifested in a similar fashion at the two electrode surfaces. Evidence for follow-up homogeneous reaction chemistry involving HTeO2+ and H2Te is presented. Using a combination of the voltammetry and microgravimetry data, an internally consistent mechanistic scheme is presented for Te aqueous electrochemistry, and discussed within the framework of previous work at other electrode surfaces including Pt.

Processable polymers and copolymers of 3-alkylthiophenes and their blends

Abstract Poly(3-alkylthiophenes) have been prepared using anhydrous FeCl 3 in CHCl 3 while dry air was bubbled through the reaction mixture. Molecular weight studies via GPC, using polystyrene standards in conjunction with RI and UV detection along with absolute determinations using a multiangle laser light scattering (MALLS) detector, have shown these materials are of high molecular weight (M w of up to 400,000) and relatively low polydispersity ( M w M n ). Further, the MALLS detector (absolute molecular weights) provides weight average molecular weights 2–5 times larger than those obtained using polystyrene standards showing that polystyrene is a rather poor standard for these materials. A series of copolymers of the 3-alkylthiophenes was prepared using a 1:1 molar feed ratio of the two monomers and the molecular weights of the materials decreased with decreasing side chain length. Poly(3-alkylthiophenes) were processable via a variety of methods, including melt spinning to form soft fibers. The films and fibers were dopable with typical oxidants to conductivities of up to 5 Ω −1 cm −1 . The solution pulled fibers were observed to be birefringent with considerable orientation along the fiber axis. EDAX studies have shown that the doping of melt-spun Fibers was quite uniform. Blends of poly(3-decylthiophene) with low density polyethylene have been prepared and melt-spun into fibers. Blends prepared by melt-blending the components were seen by electron microscopy to be phase separated into large domains while those prepared from xylene solution were much more uniform. Spinning was easier with the blends and the fibers spun from the blend prepared from xylene solution was seen to be birefringent with considerable orientation along the fiber axis. Doping of the melt spun fibers obtained from xylene solution formed blends gave conductivities of ca. 10 −1 − 1 Ω −1 cm −1 while those produced from the melt formed blends were non-conducting.

The physical and electrical properties of copolymers of polypyrrole

Abstract A series of copolymers of pyrrole with N-substituted monomers have been synthesized and their electrical properties investigated. Varying the nitrogen substituent on the pyrrole ring between methyl, phenyl and (3-bromophenyl) substituted monomers was found to strongly affect the copolymer composition. The reactivity difference can be attributed to the differences in the oxidation potentials of the monomers. These pyrrole copolymers are the first in which a direct analysis has been made of composition.

Use of the quartz microbalance in the study of polyheterocycle electrosynthesis

Abstract An electrochemical quartz crystal microbalance has been used to study the anodic electropolymerization and concurrent deposition of polypyrrole onto gold in acetonitrile and propylene carbonate using tetraethylammonium tosylate, tetrabutylammonium fluoroborate, and lithium perchlorate. Simultaneous dynamic measurements of charge and mass have been used to monitor the efficiency of the polymerization/deposition process as a function of film thickness and electrodeposition rate. This work demonstrates that the early stages of film formation is affected by the solubility of the oligomers formed and that the ultimate efficiency is electrolyte dependent.

Poly (metal tetrathiooxalates): A structural and charge-transport study

Abstract A family of highly conducting transition metal complex polymers, poly(metal tetrathiooxalates) of Ni(II), Cu(II), and Cu(I), have been synthesized and characterized. Pressed pellets of these compounds exhibit typical semiconducting behavior, with room-temperature conductivities of 10 0 to 10 +2 ω −1 cm −1 . Thermoelectric power measurements indicate that the materials behave as metals with electrons as the charge carriers. Large angle X-ray scattering (LAXS) experiments show the compounds to fit a model of a planar ribbon-like structure with a square planar geometry around the metal and dithiolene metal-ligand linkages as opposed to dithiocarbamate linkages.

Conductive amorphous metal-tetrathiolato polymers: Synthesis of a new precursor C6O2S8 and its derived polymers and laxs structural studies

Abstract Octathio-1,3,4,5,6,8,9,10-dicyclopenta [a,e] cyclooctene dione-2,7, C 6 O 2 S 8 , has been obtained by UV irradiation of 1,3,4,6-tetrathiapentalene-2,5-dione and characterized by elemental analysis, IR and mass spectroscopy. Upon treatment of C 6 O 2 S 8 with sodium methoxide, the corresponding tetrathiolato-salt C 4 S 8 4− is generated and can be reacted with a nickel salt to give conductive [(NiC 4 S 8 )C x ] n polymers with different C cations. Structural LAXS investigation on these polymers as well as on other nickel tetrathiolato polymers, (NiC 2 S 4 ) n , (NiC 6 S 8 ) n , [(NiC 2 S 4 )Ni 0.15 ] n and on tetrathiooxalato polymers, [M{C 2 S 4 }(NEt 4 ) x ] n (M=Ni,Cu), are reported.

The effect of structural modification on the physical and electronic properties of polythiophenes

Abstract Conductive polymers of β-ethylmercapto substituted thiophenes have been synthesized to obtain soluble materials. Structural analyses of the conducting polymers indicate that a well-defined β-substituted 2,5-thienylene polymeric structure is formed. Electronic absorption spectra of oxidized polymer films or solutions exhibit formation of bipolaronic species. Conductivities in the semiconductor range have been obtained for the oxidized polymers. Theoretical calculations have been carried out, using PRDDO method, to demonstrate radicalion reactivities for the thiophene monomers and minimum conformations for substituted polymers. Heterogeneous blends have been made by co-casting these polymers with typical thermoplastic materials and studied by optical microscopy and thermal analysis.