A comparative study about cross-linking in electrogenerated polypyrrole and poly(N-methylpyrrole) is presented. Experimental studies on polymer films prepared under a constant potential of 1.4V but ...considering different polymerization times as well as quantum mechanical calculations on model oligomers indicated that cross-linking is very low in polypyrrole, while cross-links are frequently formed by poly(N-methylpyrrole) chains. These behaviors have been attributed to the architecture of the molecular chains, which is completely different for the two systems under study. Thus, polypyrrole forms linear chains with some irregularities in the inter-ring linkages, while branched molecules with many irregularities are the most stable for poly(N-methylpyrrole). These remarkable differences are fundamentally due to the steric repulsions induced by the methyl groups of poly(N-methylpyrrole).
The electrochemical behavior of 2,5-di-(-2-thienyl)-pyrrole (SNS) on Pt has been studied from a 10 mM monomer solution in 0.2 M LiClO
4+ethanol or in 0.2 M LiCl+ethanol by cyclic voltammetry, ...chronopotentiometry and chronoamperometry. The monomer exhibits two similar consecutive oxidation processes. Uniform, adherent and electroactive films of dark-blue poly(SNS) doped with ClO
4
− or with Cl
− are obtained at low potentials related to the first process. Reproducible film weights are found at 0.700 V versus Ag|AgCl during 360 s. The increase in transport rate of reactants by stirring the solution with a magnetic bar at 150 rpm accelerates the SNS electropolymerization, allowing to collect much more polymer weight than from the quiescent solution. The productivity of poly(SNS) doped with Cl
− determined by ‘ex situ’ ultramicrogravimetry increases notably under stirring, although its percentage in Cl
− is similar to that found under quiescent conditions. This is ascribed to the production of a major proportion of longer linear molecules in polymer, consistent with its higher conductivity when it is synthesized under stirring. This effect is not so clear for the poly(SNS) doped with ClO
4
− due to the little influence of stirring upon its productivity and conductivity. The detection of short linear oligomers in the soluble fractions of polymers in thioglycerol by mass spectrometry-fast atom bombardment allows to propose a radical polycondensation as initial electropolymerization mechanism.
Hereditary xerocytosis is a rare hemolytic anemia in which erythrocytes are dehydrated due to a loss of potassium and water through their cell wall membrane. In adults, this condition leads to a ...mild-to-moderate hemolysis. We report a case of hydrops fetalis secondary to hereditary xerocytosis. Management with intrauterine erythrocyte and albumin transfusions resulted in a favorable postnatal course.
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