J. L. Acosta

Studies of sulfonated block copolymer and its blends

Abstract This paper reports the synthesis and characterization of a sulfonated polymer based on hydrogenated poly(styrene–butadiene) block copolymer (HPBS). Block copolymer ionomers were prepared through sulfonation of part of the polystyrene blocks. The free acid samples (HPBS–SH), and their blends with the non-sulfonated polymer (HPBS) and polypropylene (PP) were studied. FTIR was used to confirm sulfonation. DMA and DSC analyses have shown that Tg (HPB) remains constant for all the samples studied. Glass transition temperatures of polystyrene (PS) measured through DMA present an increase of about 30°C after sulfonation, diminution (up to 13°C) when the amount of HPBS increases in HPBS–SH/HPBS blends and augmentation (up to 28°C) as the PP content in HPBS–SH/PP blends increases. Complex impedance measurements have shown that proton conductivity of HPBS–SH was about 8×10 −3 Ω −1 cm −1 , lower values were observed generally in the case of blends. Non-isothermal crystallization of PP was studied using Avrami analysis.

Carbon black effect on the microstructure of incompatible polymer blends

Abstract This work reports on a study of the effects exerted by carbon black (CB) on the microstructure of the incompatible polymer blend polyvinylidene fluoride/polyamide (PVDF/PA) by means of calorimetric and dynamic mechanical determinations of the glass transition temperatures, as well as the isothermal crystallization kinetics. The results demonstrate partial polymer compatibilization to take place in the PVDF-rich phase, as a consequence of an improvement in component adhesion at the CB–PVDF interface. In addition, CB is shown to modify the isothermal crystallization kinetic parameters.

Characterization of polymer systems based on sulfonated poly(2,6-dimethyl-1,4-phenylene oxide)

The sulfonation reaction of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been carried out, incorporating the resulting product into pure PPO to study, in forthcoming research, the electrical and mechanical features of the composites with regard to their performance in fuel cells. Pure sulfonated polymers and their blends have been characterized from a microstructural and electrical point of view, by means of X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and complex impedance spectroscopy. Membranes have been manufactured with excellent ionic conductivity at room temperature. © 2000 Society of Chemical Industry

Extrinsic conducting and superconducting polymer systems: 1. Analysis of the structure of PVDF/PS blends containing copper and carbon black fillers

Abstract This paper reports on the obtention of two extrinsic conducting polymer systems by means of copper and carbon black filler incorporation into a polymer system consisting of a poly(vinylidene fluoride)/polystyrene (PVDF/PS) blend. With the aim of analysing the influence exerted by copper and carbon black on the morphology, microstructure and compatibility of the systems under study, the glass transition temperatures as well as isothermal and non-isothermal crystallization kinetics were determined for the different systems. The dynamic mechanical and calorimetric results demonstrated on the one hand that carbon black produces partial compatibilization of the PVDF/PS system, while on the other hand they prove both copper and carbon black to be capable of modifying the microstructure and morphology of the initial system.

Nucleation and growth of LiCF3SO3-doped polyalkylthiophenes

Abstract The effect of monomer and electrolyte (LiCF 3 SO 3 ) concentrations on the nucleation and growth processes of polythiophene, poly(3-methythiophene) and poly(3-hexylthiophene) electrogenerated on a platinum electrode in an acetonitrile media were studied. The current transients were fitted using a mathematical equation that considers up to seven contributions, each of them representing a different classical nucleation and growth mechanism. The results indicate that the electrogeneration of polythiophene and poly(3-methylthiophene) films follow a similar mechanism, two-dimensional processes being detected at short reaction times, the overall processes being governed at longer reaction time by an instantaneous three-dimensional nucleation under charge control mechanism. The electrogeneration of poly(3-hexylthiophene) films, however, takes place without overlapping of nuclei, the process now being governed by an instantaneous nucleation three-dimensional diffusion control mechanism.

Applications of a statistical model to the analysis of the kinetic parameters in isothermal and non-isothermal crystallization of polymer blends based on PVDF

In this work the classical Scheffe model is applied to the study of isothermal and non-isothermal crystallization of blends based on the systems PVDF, PMMA and PVA. In the light of the results obtained the validity of the model proposed is assessed. The authors endeavour to contribute to the discussion on the compatibility of these materials, which latter aspect is of utmost relevance when interpreting the properties presented by these polymer blends.

Heterogeneous sulfonation of blend systems based on hydrogenated poly(butadiene-styrene) block copolymer. Electrical and structural characterization

Abstract Conducting membranes of hydrogenated poly(butadiene–styrene) block copolymer (HPBS) were obtained by heterogeneous sulfonation and then their electrical properties were studied. In addition, the effects of PP content on the morphology of these blends, as well as their conducting properties, were considered. The degree of sulfonation was determined by means of photoelectron spectroscopy (XPS) and the structural characterization was carried out using differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA). The results show that sulfonated HPBS has difficulties to be made into membranes besides reduced conductivity while the polymer blends with PP have high conductivity values and good dimensional stability. In this work, we find that increasing the PP content in the blend improves mechanical aspects, but on the other hand, conductivity decreases as the PP does not participate in the sulfonation process. The sample of composition 70% HPBS/30% PP sulfonated for 12 h with HClSO3 0.1 M (AMP-13S) was seen to be adequate as fuel cell membrane, especially due to the high conductivity properties and excellent dimensional stability.

Electrochemical synthesis of poly(3‐methylthiophene): A kinetic study

Poly(3-methylthiophene) (P3MT) films were electrogenerated on both platinum and carbon-felt working electrodes. The kinetic equation was determined by the monomer and electrolyte concentrations being changed for different reaction times. For each sample, the weight of the polymer obtained was measured along with the polymerization charge, the oxidation charge, the ratio (R) between the two magnitudes, the charge storage efficiency (SE), and the doping level. The results obtained from the kinetic study indicate significant electrolyte participation in the electropolymerization process. The SE and the doping level decreased inversely proportionately to both the reaction time and the concentrations of the monomer and electrolyte. The ratio R increased with reaction time as well as with monomer or electrolyte concentrations for all P3MTs generated on the carbon-felt electrodes, whereas for those films generated on platinum electrodes, the highest values were obtained for the lowest monomer and electrolyte concentrations.

Determination of the interaction parameter of partially or totally compatible systems through glass transition temperature measurements

Abstract A compatibility study was conducted on the system poly(vinylidene fluoride)/polystyrene in the presence of carbon black, metallic copper, YBaCuO ceramics and poly(vinyl acetate). From T g measurements the volume fractions of the respective minority polymer in either phase were calculated, and applying an expression proposed by Kim and Burns, the Flory-Huggins polymer-polymer interaction parameters χ 12 were determined. The results show that a greater portion of polystyrene is dissolved in the poly(vinylidene fluoride)-rich phase than vice versa, the dissolution level being a function of the nature of the third component added to the blend.

Compatibility of binary and ternary blends from their thermal and dielectric properties. A comparative study

Abstract Thermal and dielectric measurements were carried out in order to obtain the values corresponding to the glass transition temperature for different blends on the basis of polyvinylidene fluoride/polyvinyl acetate/polymethyl methacrylate. From these results their compatibility was analyzed. It was found that there is no agreement between the results of both techniques. Also the single T g criterion is discussed.