N-substitution of polybenzimidazoles: Synthesis and evaluation of physical properties

Regulating Molecular Interactions in Polybenzimidazole Membrane for Efficient Vanadium Redox Flow Battery

The tightly bonded structure of polybenzimidazole (PBI) membrane is the origin of its poor proton conductivity, which severely hinders achieving a cost-effective membrane for vanadium redox flow battery (VRFB). It desires a strategy to relax the membrane structure to significantly improve the proton conductivity and maintain its structure stability. Therefore, this work proposes a novel strategy through regulating molecular interactions within PBI membrane to loosen up the structure of PBI membrane and dramatically enhance the proton conductivity. The interactions in PBI membrane are switched by DMSO/water and acid through sequentially treating membrane with these solutions. The efficient PBI membrane prepared using this strategy demonstrates an outstanding performance for VRFB, with the proton conductivity enhanced by 3850 % (from 1.9 to 76.3 mS cm-1), and VRFB achieves a high energy efficiency of 80.5 % under 200 mA cm-2. More importantly, this work shed lights on the structure-property relationship of PBI membrane, and the mechanism in enhancing proton conductivity is unraveled, which is of great significance for the development of VRFB membranes.

Effect of the Acid Medium on the Synthesis of Polybenzimidazoles Using Eaton's Reagent

The influence of trifluoromethanesulfonic (TFSA) superacid on conditions of the synthesis of polybenzimidazoles, such as OPBI and CF₃PBI, was studied. It was shown that the polycondensations proceeded smoother and at lower temperatures in the presence of the TFSA in Eaton's Reagent and that polymers of high molecular weights, and readily soluble in organic solvents, were obtained. The effect was more pronounced for CF₃PBI, where the low reactivity monomer, 4,4' (hexafluoroisoproylidene)bis (benzoic acid), was used. CF₃PBI was obtained at a moderate temperature of 140 °C with no gel fraction and exhibited an inherent viscosity twice higher than the one obtained by the traditional method. In fact, the addition of TFSA allows the obtention of soluble N-phenyl substituted CF₃PBI by direct synthesis, which had not been obtained otherwise. Thus, the use of TFSA is a good media for the synthesis of N-substituted PBIs under relatively mild conditions.

Influence of Polymer Composition and Substrate on the Performance of Bioinspired Coatings with Antibacterial Activity

A series of methacrylic copolymers bearing thiazolium cationic groups and catechol moieties were evaluated as antibacterial coatings on a variety of materials including aluminum and plastics such as polycarbonate, poly(methyl methacrylate), and silicone rubber. The thermal properties of the copolymers were first studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The cationic copolymers were thermally stable up to 200 °C and presented glass transition temperatures values well above 100 °C; thus, an acceptable thermal behavior for typical biomedical applications. The cationic copolymers with variable content of the adhesive anchoring N-(3,4-dihydroxyphenethyl) methacrylamide (DOMA) units were coated onto the metal and polymeric substrates by drop casting and the adhesive properties of the obtained coatings were further evaluated as a function of DOMA content and substrate. Optical profilometry, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra, and antimicrobial studies reveal that the coatings adhere stronger to metal substrates than to the polymeric substrates. The copolymers with higher content of DOMA, 24 mol.%, resist solvent erosion treatment when coated onto all substrates and exhibit antimicrobial activity against Gram-positive S. aureus bacteria after this erosion treatment. In contrast, copolymers with low content, 9 mol.% of DOMA, only remain attached onto the aluminum metal substrate after solvent treatment, while on polymeric substrates the coatings are almost removed and do not show any efficacy against S. aureus bacteria.

Novel reverse-selective poly(2,5-benzimidazole) derivatives for membrane-based gas separation

Three novel polymers were synthesized by introducing hexyl, dodecyl, and octadecyl groups to the side chains of poly (2,5-benzimidazole) (ABPBI). Fourier transform infrared, thermal stability, and mechanical strength tests were applied to characterize the three polymers. Elemental analysis was also carried out to determine the degree of substitution. Gas permeation behavior of the three derivative membranes was investigated with pure gas, including hydrogen (H2), nitrogen (N2), oxygen, methane, and carbon dioxide (CO2). The results show that except the hexyl-substituted ABPBI the other two polymers are reverse selective because in both polymers CO2 has a higher permeability than H2. Among the three derivatives, octadecyl-modified ABPBI shows the best permselectivity of gas pairs, such as CO2/N2 (approximately 13) and CO2/H2 (approximately 2.8), with a quite high CO2 permeability (approximately 100 barrer) at 35°C and 3.0 atm.