Robson Pacheco Pereira

Miscibility, crystallinity and morphological behavior of binary blends of poly(ethylene oxide) and poly(methyl vinyl ether–maleic acid)

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(methyl vinyl ether–co–maleic acid) (PMVE–MAc). Single Tg was observed for all blends, indicating miscibility. The dependence of Tg on the weight per cent of PEO presents a negative deviation from linearity at high PEO content, associated to a greater blend free volume, mobility and flexibility than in pure PEO. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites as the PMVE–MAc is added is observed. FTIR provided evidence of specific interaction between the polymers.

Blends of poly(ethylene oxide) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate): thermal analysis, morphological behaviour and specific interactions

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM). A single glass transition temperature was observed for all blends, indicating miscibility. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites is observed, as PVPh-HEM is added. FTIR was used to probe the intermolecular specific interactions of the blends and the miscibility of the blend is mainly attributed to PVPh-HEM/PEO intermolecular interactions via hydrogen bonding.

Synthesis and properties of bis(1,3-dithiole-2-thione-4,5-dithiolato)bismuthate(1-) salts, [Q][Bi(dmit)2]. Crystal structure of [AsPh4][Bi(dmit)2]·1/2DMSO: comparison of the solid state structures of [Q][Bi(dmit)2] and [Q][Sb(dmit)2]

Abstract Ionic complexes, [Q][Bi(dmit)2] (5:QNEt4, NBu4, 1,4-Me2-pyridinium and AsPh4), have been obtained from BiBr3 and [Q]2[Zn(dmit)2] [H2–dmit4,5-dimercapto-1,3-dithiole-2-thione]. As established by the crystal structure determination of [(5:QAsPh4)·1/2DMSO], the cations have near tetrahedral geometries and are well separated from the anions. The anions, containing chelating dmit ligands, are linked into chains via Bi–thiolato–S inter-anion bonds: Bi2S2 rings are formed within the chains, with Bi⋯Bi distances alternating between 3.7760(3) and 3.9092(3) A. The bismuth atoms are six-coordinate, arising from two inter-anion Bi–S [Bi–S=3.0391(13) and 3.1643(14) A] and four intra-anion Bi–S bonds [between 2.6680(13) and 2.8370(13) A], with stereochemistries, including the equatorial-sited stereochemically active lone pair, of distorted pentagonal bipyramids. There are no S⋯S contacts between the anions less than the sum of the van der Waals radii. Comparisons are made between the structure of [(5:QAsPh4)·1/2DMSO] and those reported previously for (5:QNEt4), [(5:QNEt4)·1/2Et2O] and [(5:QNBu4) as well as those for [Q][Sb(dmit)2] (4).

Specific interactions in blends of poly(ethylene oxide) and poly(bisphenol A-co-epichlorohydrin): FTIR and thermal study

Blends of poly(ethylene oxide) (PEO) of high molecular weight with poly(bisphenol A-co-epichlorohydrin) (PBE) with high epoxy equivalent were studied spectroscopically, thermally and morphologically. As similar systems of low molecular weight, a single Tg was observed for all blends, indicating miscibility. A progressive decrease in the degree of crystallinity and in the size of the PEO spherulites as the PBE is added is also observed. Quantitative analysis from FTIR spectra provided determination of specific interactions between the constituents and their variation with PEO content. Simulations were performed utilising the spectra of the pure polymers to confirm that the observed changes in the experimental spectra of the blends were due to interaction between the polymers. 2003 Elsevier Ltd. All rights reserved.

New Proton Conductive Membranes Based on Acid-doped Interpenetrating Polymer Networks

Semi-interpenetrating polymer network (SIPN) membranes were synthesized from polyethyleneimine (PEI) and DGEBA (diglycidyl ether of bisphenol A) and immersed in H3PO4 solutions in order to obtain proton conductive membranes. The SIPN membranes were characterized by vibrational spectroscopy and thermogravimetric analysis, while the SIPN/H3PO4 systems were studied by electrochemical impedance spectroscopy. Membranes retained water up to 210 o C, with thermal stability higher than 270 o C. Conductivity values were found between 10 -4 and 10 -3 Ω -1 cm -1 , increasing for a temperature range between 20 and 80 o C. Activation energy values evidenced the predominance of a vehicular mechanism of proton conduction in the systems and the overall properties of the membranes point to a promising material for application in Fuel Cells.