F. R. Díaz

Synthesis, characterization and electrical properties of polyimines derived from selenophene

Abstract Polyimines derived from 2,5-di-(oxophenyl)selenophene (I) were synthesized by reacting (I) with different diamines in suitable mixtures of solvents. All the diamines obtained were black and highly insoluble. The polymers were characterized by IR Spectroscopy and Elemental Analysis. NMR was not intended in view of the insolubility of the compounds. Differential scanning calorimetry was utilized to determine the thermal parameters (Tg and Tm) of these polymers. Electrical properties of the doped (doping agents: iodine, antimony pentafluoride, aluminum and ferric chloride) and undoped polymers were determined at room temperature and atmospheric pressure. No variation in conductivity was observed when AlCl3 or FeCl3 was used as dopant. This behavior has been ascribed to the poor electron-acceptor properties of these salts, inhibiting thus the doping process. On the other hand, an important increase of the conductivity was attained when iodine was employed as doping agent; conversely, when the polymers were exposed to AsF5, only a moderate increase in conductivity was observed for all the polymers surveyed. The increase in conductivity of these polymers after doping is due to the presence of nitrogen, a very electronegative element, in their structures that promotes the oxidation of the polymeric chain.

Polythiophene, polyaniline and polypyrrole electrodes modified by electrodeposition of Pt and Pt+Pb for formic acid electrooxidation

The electrosynthesis of polythiophene (PTh), polyaniline (PANI) and polypyrrole (PPy) films modified by dispersion of Pt or Pt+Pb and its employment in the electrocatalytic oxidation of HCOOH are studied and compared. The influence of parameters such as polymer film thickness, the number of dispersed Pt particles, the amount of Pb deposited and the presence of Pb2+ in the electrolyte on the electrooxidation of HCOOH is investigated. Electrode systems including the polymer and a mixture of Pt and Pb particles show a better electrocatalytic activity than electrodes having a polymer–Pt combination or bulk Pt electrodes. Furthermore, during the electrooxidation of HCOOH using polymer–(Pt+Pb) electrodes the presence of fewer poisoning species is observed, indicating that the role of Pb in these electrode systems is in agreement with the Pb adatom effect observed when bulk Pt electrodes are used. However, the presence of Pb(ii) in the electrolyte is not required for the PTh–(Pt+Pb) electrode system and, in addition, a better electrocatalytic effect is obtained in this case. With application of an appropriate E/t program the activity is unchanged over a long time.

Synthesis and characterization of poly(esters) derived from diacids and diphenols containing silicon and germanium

Abstract Poly(esters) containing two heteroatoms, Si or Ge, in the main chain, derived from diphenols bis(4-hydroxyphenyl)-dimethyl-germane, bis(4-hydroxyphenyl)-diphenyl-germane, bis(4-hydroxyphenyl)-dimethyl-silane and bis(4-hydroxyphenyl)-diphenyl-silane, and the acid dichlorides bis(4-chloroformyl-phenyl)-dimethyl-germane, bis(4-chloroformyl-phenyl)-diphenyl-germane, bis(4-chloroformyl-phenyl)-dimethyl-silane and bis(4-chloroformyl-phenyl)-diphenyl-silane, were synthesized under phase transfer conditions using two phase transfer catalysts, and characterized by spectroscopic methods. This technique showed low effectivity for the synthesis of these kinds of polymers, showing a low increase of the yields and η inh values in comparison with the interphasial process. In these experimental conditions there were no important differences neither in the studied parameters between the monomers with Si or Ge, nor between the catalysts.

Effect of the side chain structure on the glass transition temperatures of some poly(thiocarbonate)S

Abstract A series of poly(thiocarbonate)s with aliphatic, aromatic and cycloaliphatic side groups has been prepared and the glass transition temperatures ( T g )s of these polymers were measured by differential scanning calorimetry (DSC). The magnitude of the T g was related to the bulkiness, flexibility, and polarity of the pendant groups attached to the polymer main chain. A general decrease in T g values is observed when these polymers are compared with the corresponding poly(carbonate)s analogues. Theoretical calculation of T g for some of the polymers were carried out using the method described by Van Krevelen et al. These values are in fair agreement with the experimental values. The critical value of the chain length at which T g becomes constant ( T g −8 was calculated for all the polymers using the relation proposed by Cowie. It was found that the molecular weights of the polymers are too low for T g to become independent of the chain length.

Electroluminescent polycarbazole thin films obtained by electrochemical polymerization

Abstract Polycarbazole (PCZ) thin films have been electrochemically synthesized on SnO 2 coated glass substrates. The electrolyte used was the anhydric LiClO 4 . It is shown that, after optimization of the potential scanning domain, PCZ films are systematically obtained. The physical and morphological properties of films are described. The films obtained with LiClO 4 as electrolyte are homogeneous and their coverage efficiency on the SnO 2 underlayer is very high. Films are exempt of pinholes, cracks and other morphological defaults as shown by scanning electron microscopy. Cyclic voltammograms are reversible, attesting the high quality of the structural properties of the films. Moreover these films are photoluminescent. After deposition of an aluminum upper layer, the structures SnO 2 /PCZ/Al behave like diodes with a forward polarization when the SnO 2 electrode is positively biased. Also these structures exhibit electroluminescent properties.

Thermogravimetric analysis of polythiocarbonates: thermal decomposition temperatures and kinetic parameters

Abstract The thermal stability and the kinetic parameters of a series of polythiocarbonates with aliphatic, aromatic, and cycloaliphatic side groups were studied. The thermal decomposition temperatures (TDT) are influenced by the structure of the polythiocarbonate because when the bulk of the side group increases the TDT values also increase. The activation energies were determined using the Arrhenius relationship and obey first-order kinetics, except for one polythiocarbonate which corresponds to zero-order kinetics. The activation energies are also related to the structure of the side groups. The activation energy of the polythiocarbonate from bisphenol A is very similar to that of the respective polycarbonate.

Polycarbazole obtained by electrochemical polymerization of monomers either in solution or in thin film form

Polycarbazole has been synthesized by electrochemistry. The carbazole monomer source consists either in carbazole in solution in the electrolyte or in carbazole deposited in thin film form onto the working electrode. The two families of polymers have been studied by infrared absorption, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, electron spin resonance, and electrical conductivity measurements. It is shown that the polycarbazole films obtained with carbazole deposited in the thin film form exhibit a better polymerization efficiency and an electrical conductivity one order of magnitude higher. This result is in good accordance with a higher spin density and homogeneity. It is proposed that not only are some monomers activated during the evaporation but also that the physical contact between the working electrode and the continuous carbazole films induces the growth of homogenous highly polymerized polycarbazole films. In agreement with this suggestion, the SEM study shows that this type of polycarbazole thin films keep in memory the morphology of the SnO2 under layer.

Synthesis, characterization and electrical properties of poly[bis-(2-aminophenyl)disulfide] and poly[bis-(2-aminophenyl)diselenide]: Part II. XPS, ESR, SEM and conductivity study

Abstract Poly[bis(2-aminophenyl)disulfide] (DSDA) and poly[bis(2-aminophenyl)diselenide] (DSeDA) were synthesized by monomer oxidation with ammonium persulphate at different polymerization times, in 0.5 M H2SO4 and 1 M HCl media. X-ray photoelectron spectroscopy (XPS) analysis of DSDA shows similar percentage of imine and amine groups in the polymer, like emeraldine. DSeDA shows different percentages of imine and amine groups, which corresponds to a state different of emeraldine. When the time of polymerization of DSDA is increased, a small change in the oxidation state is detected, but in DSeDA the number of imine groups decreases. When polymerization is carried out in HCl media, both polymers present a minimum percentage of chlorine unit with covalent linkage to macromolecule. Moreover, electron spin resonance (ESR) study shows the presence of nitrogen and carbon radicals in the structure, and both radicals should be associated to chlorine or sulfate ions. The two polymers present low level of conductivity related to low level of doping. The macromolecules present a granular structure, but DSeDA is more pulverulent.

Synthesis, characterization and electrical properties of poly[bis-(2-aminophenyl)disulfide] and poly[bis(2-aminophenyl)diselenide]

Abstract Polybis(2-aminophenyl)diselenide and polybis(2-aminophenyl)disulfide were chemically synthesized by oxidation of the monomers with ammonium persulphate in 0.5 M H 2 SO 4 and 1 M HCl media, at variable polymerization times. Synthesis of polybis(2-aminophenyl)diselenide for 4.5 h afforded a product with the spectroscopic properties (FT-IR and UV–Vis) similar to those of poly emeraldine. On the other hand, the synthesis of polybis(2-aminophenyl)disulfide with these spectroscopic properties was not so straight forward and, consequently, conditions such as medium, oxidizing agent, temperature, concentration of monomer and oxidizing agent, and polymerization time had to be throughly surveyed. Both emeraldine dichalcogenide polymers proved to be insoluble in common organic solvents, but they dissolve well in concentrated sulphuric acid, yielding blue solutions and PANI-like spectra. They get doped by iodine vapor, but very little doping is obtained in acid aqueous media. Their conductivities attained those of semiconduction.

Some aspects of the solution properties and chain flexibility of poly[2,2-propane-bis(4-phenylthiocarbonate)]

Abstract The dilute solution properties of poly[2,2-propane-bis (4-phenylthiocarbonate)] (PPhTC) in various solvents have been studied by viscosity, osmotic pressure and gel permeation chromatography measurements. The unperturbed dimensions were determined, and the viscometric relationships were established. The information obtained was used to compare the conformational properties of PPhTC with those of other polycarbonates and related polymers containing benzene rings as main-chain segments.