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Solution polycondensations of 3,3′-diaminobenzidine with two dicarboxylic acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid) to obtain two different polybenzimidazoles, OPBI and CF3PBI, correspondingly, were studied in terms of formation of processable polymers and insoluble crosslinked gel. The syntheses were conducted in Eaton's reagent using conventional heating (CH) at 100, 140 and 180 °C and microwave irradiation (MW) at 90 and 100 °C. The content of gel fraction was lesser using high temperature conditions under CH. The MW-assisted syntheses resulted in acceleration of polycondensations, but an abrupt growth of the insoluble gel was also observed under these conditions. The FTIR data showed that MW irradiation stimulated the side acylation reactions, and OPBI suffered more from the side acylation than CF3PBI. [ABSTRACT FROM AUTHOR]

The polycondensations of 3,3′-diaminobenzidine with two acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid), were conducted in Eaton’s reagent at the unusually high temperature of 180°C and under microwave irradiation at 90°C. Both protocols resulted in soluble polybenzimidazoles, OPBI and CF3PBI, of high molecular weights in very short reaction times. The synthesized polybenzimidazoles exhibited high thermostability and excellent mechanical properties. The influence of the reaction conditions on the polymer structure and molecular weights was studied. The “microwave effect” was demonstrated by comparison of the polycondensations conducted under microwave irradiation and conventional heating. [ABSTRACT FROM AUTHOR]

A kinetic model for the redox-initiated radical telomerization of vinyl acetate activated by microwave irradiation is presented. Four approaches based on the “microwave” or “thermal” effects were used to study the cases under microwave irradiation. One of the models assumes microwave-induced generation of radicals from monomer. The second model considers higher reaction temperatures than those reported in the experiments. The third model assumes that microwave radiation affects specifically catalyst-involved reactions. The fourth model is a combination of the second and third ones. The kinetic model captures well the effect of initiator, catalyst and solvent contents, as well as absence or presence of microwave irradiation, on polymerization rate and molecular weight development. Limiting monomer conversions and fairly constant values of number average molecular weight and molar mass dispersity were predicted by the model, which agrees with experimental observations. [ABSTRACT FROM PUBLISHER]

The rapid increasing of the population in combination with the emergence of new energy-consuming technologies has risen worldwide total energy consumption towards unprecedent values. Furthermore, fossil fuel reserves are running out very quickly and the polluting greenhouse gases emitted during their utilization need to be reduced. In this scenario, a few alternative energy sources have been proposed and, among these, proton exchange membrane (PEM) fuel cells are promising. Recently, polybenzimidazole-based polymers, featuring high chemical and thermal stability, in combination with fillers that can regulate the proton mobility, have attracted tremendous attention for their roles as PEMs in fuel cells. Recent advances in composite membranes based on polybenzimidazole (PBI) for high temperature PEM fuel cell applications are summarized and highlighted in this review. In addition, the challenges, future trends, and prospects of composite membranes based on PBI for solid electrolytes are also discussed. [ABSTRACT FROM AUTHOR]