José I. Iribarren

Optically active polyamides containing 1,3-dioxolane cycles in the backbone

Abstract The structure in the solid state of two optically active polyamides obtained from 2,3- O -methylene- l -tartaric acid and linear α,ω-alkanediamines with 9 and 12 carbon atoms, abbreviated P9MLT and P12MLT respectively, was investigated. Two ordered phases, one of smectic liquid crystal-type and another showing crystalline order, were characterized for P12MLT. Crystallization of the former into the second was induced by annealing. Infrared spectroscopy showed that hydrogen bonds are intermolecularly set in both phases and that they are weaker in the crystal phase. Quantum mechanical calculations found the O–C–C O sequence of the tartaric unit to be in a gauche conformation. CP-MAS 13 C NMR revealed that the dioxolane ring is a mixture of the C 2 - exo and C 2 - endo puckered forms in equal amounts and that the polymethylene segment crystallizes in the all- trans conformation. X-ray diffraction of fibers and electron microscopy of solution grown single crystals afforded data consistent with a crystal lattice with orthorhombic geometry and parameters a=7.8 A , b=5.8 A , c=20.0 A . Experimental data obtained from P9MLT indicated a similar behavior for this system.

Poly(3,4-ethylenedioxythiophene) on self-assembled alkanethiol monolayers for corrosion protection

Self-assembled monolayers (SAMs) of octanethiol and dodecanethiol were used to modify the stainless steel substrates for electrodepositing poly(3,4-ethyledioxythiophene) (PEDOT), a well known polythiophene derivative. Although the influence of the alkanethiol monolayers on the morphology and topology of micrometric (thickness: 2.25–2.35 μm) PEDOT films is practically negligible, they increase significantly the ability to store charge and the adherence. In contrast, treated substrates not only enhance the electrochemical properties of ultra-thin PEDOT films (thickness: 150–350 nm) but also affect significantly the thickness, roughness, porosity, morphology and topology. Such changes depend on both the length of the alkyl chain in the alkanethiol and the incubation period used for the preparation of the SAMs. Finally, the protection against corrosion imparted by PEDOT films deposited on treated substrates has been examined and compared with that obtained using PEDOT deposited on bare stainless steel electrodes. Inhibition of the corrosion in a 3.5% NaCl solution was found to be considerably higher when PEDOT is deposited on treated electrodes, which has been attributed, in addition to the barrier effect produced by the SAMs, to the structural changes induced at the first stages of the electropolymerization.

New insights into the characterization of poly(3-chlorothiophene) for electrochromic devices

Poly(3-chlorothiophene) has been prepared by anodic polymerization in boron trifluoride diethyl etherate with 0.1 M tetrabutylammonium tetrafluoroborate. The potential applied for the generation of the polymer has been found to affect considerably both physical (e.g. the thickness and roughness of the films, and the current efficiency) and electrochemical properties (e.g. the electroactivity, the doping level and the specific capacitance) whereas the density and the electrical conductivity remain practically unaltered in the interval ranging from 1.60 to 1.90 V. The dependence of the electrochemical behaviour with the generation potential has been explained by the morphological and topographical characteristics of the material, which have been investigated not only using scanning electron microscopy and atomic force microscopy but also electrochemical impedance spectroscopy. On the other hand, experimentally determined electronic properties have been reproduced by quantum mechanical calculations on model oligomers formed by up to 16 chemical repeating units that were arranged through a repetitive sequence of head-to-tail linkages. Oxidized and reduced poly(3-chlorothiophene) were found to be blue and Bordeaux red, respectively, the intensity of such two colors depending on the potential used for the generation of the film. Moreover, morphological changes induced by oxidation–reduction processes indicated that this polymer is a potential candidate for the fabrication of very stable electrochromic devices. Accordingly, an all-thiophene electrochromic device made of poly(3,4-ethylenedioxythiophene) and poly(3-chlorothiophene) has been successfully fabricated. This device has been proved to exhibit very remarkable redox stability: the loss of electroactivity is 65% of the initial value after 390 cycles and remains stable at such a value for more than 500 cycles.

La modelización molecular como herramienta para el diseño de nuevos polímeros conductores

The ability of molecular modeling techniques based on quantum chemical methods to predict the molecular and electronic structure of organic conducting polymers is examined. More specifically, we report on the applicability of these computational tools to study different aspects of polythiophene and its derivatives: molecular geometry and planarity, the structural changes induced by the doping process, the electronic properties and the design of new conducting materials.

Preparation, Surface Characterization and Anticorrosive Behavior of Polyaniline and Poly(3,4-ethylenedioxythiophene) Deposited on Aluminum Alloy AA2024-T3

This work is focused on studying the preparation and characterization of two different conducting polymers, polyaniline and poly(3,4-ethylenedioxythiophene), on aluminum alloy AA2024-T3. In addition to the direct electrochemical deposition of the conducting polymers onto an untreated aluminum substrate, the alloy surface pre-treatments based on single chemical acid pickling or chemical acid pickling followed by application of self-assembled monolayers have been also considered before the coating application. Coatings electrochemically deposited onto both untreated and pre-treated substrates have been characterized by physicochemical and electrochemical techniques, whereas their protective performance has been evaluated by means of polarization electrochemical techniques and accelerated corrosion tests. Although conducting polymers are widely used as protective coatings for steel substrates, the results obtained in this work indicate that their protective effect is not improved when deposited onto aluminum.