Abstract

Polyimides (PIs) based on 3,3′,4,4′-tetracarboxylicdiphenyl ether dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 4,4′-diaminodiphenylsulfone and 4,4′-methylenedianiline were synthesized. They are easily dissolved in many strong and polar solvents like dimethylformamide, N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone, and dimethylsulfoxide. A new kind of anhydrous proton conducting system based on PI/H₃PO₄ and PI/H₃PO₄/imidazole (Imi) blends was prepared. The chemical oxidation stability of the composite membranes was studied. The flexible PIs have better chemical oxidation stability. The addition of phosphoric acid can accelerate the degradation process of PIs, while the addition of Imi in PI/H₃PO₄ blends can greatly improve their chemical oxidation stability, which becomes much better than that of pure PIs. The proton conductivity of PI/H₃PO₄ blends is still lower compared with that of polybenzimidazole/H₃PO₄ blends. After the addition of Imi, the anhydrous proton conductivity of PI/H₃PO₄ blends increases significantly with increasing Imi content. Copyright © 2006 Society of Chemical Industry

Magnetorheological (MR) fluids based on glycol, iron powder, polyvinylpyrrolidone (PVP), and carbon nanotubes (CNTs) were prepared. Effects of polyvinylpyrrolidone and carbon nanotubes on sedimentation stability and magnetorheological properties were studied. It is found that the synergetic effects of PVP and CNTs improve the sedimentation stability significantly, and the addition of CNTs reduces the sedimentation velocity and increases the equilibrium sedimentation ratio of the magnetizable particles in MR fluids remarkably. The addition of PVP can reduce the sedimentation velocity of the magnetizable particles, but cannot increase the equilibrium sedimentation ratio and will not change the up trend of apparent viscosity with the increasing intensity of the external magnetic field. When the PVP content is lower, the increment of original apparent viscosity of the MR fluids at zero-intensity of magnetic field is inconspicuous, and their values of apparent viscosity under magnetic field are similar. However, the apparent viscosity of the MR fluids increases tremendously when the contents of PVP increase to certain degree. The results show that the synergetic effects of PVP and CNTs not only improve the sedimentation stability of the MR fluid but also promote its magnetorheological effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1653–1657, 2006

Summary: Styrene-maleic imide copolymer with benzimidazole side group was prepared from 2-amino-benzimidazole and styrene-maleic anhydride copolymer. The structures of the new styrene-maleic imide copolymers from both random and alternating styrene-maleic anhydride copolymer were characterized by FTIR, DSC, and gel permeation chromatography (GPC). Styrene-maleic imide copolymer has good solubility, excellent film forming ability, and is easy to prepare, though the solubility of styrene-maleic imide copolymer decreases a little with increasing maleic imide. The proton conductivity of phosphoric acid doped styrene-maleic imide copolymer was studied. The temperature dependence of proton conductivity in H₃PO₄ doped a-styrene-maleic imide copolymer can be fitted by a simple Arrhenius equation very well, while H₃PO₄ doped r-styrene-maleic imide copolymer has somewhat deviation from Arrhenius equation. The structure of alternating copolymer is more favorable for proton transport contributed by hopping mechanism. The proton conductivity of phosphoric acid doped styrene-maleic imide copolymer can be improved by increasing the acid doping level or the imidazole content.

In this paper, synthesis of poly(N-methylbenzimidazole) (PNMBI) and poly(N-ethylbenzimidazole) (PNEBI) with various alkylation degrees was achieved by adding enough LiH and controlling the amount of substituting reactant. The degree of substituted methyl or ethyl was determined by elemental analysis. Changes in infrared spectroscopy due to nature and degree of substitution can clearly be found. With the modification of PBI, the solubility of PNMBI and PNEBI is improved significantly. There is no significant change of chemical structure of PNMBI after 0.5 h thermal treatment in both N₂ and air at a temperature lower than 250 °C. Compared with PBI, the methanol permeability of PNMBI and PNEBI is a little higher but still of the same order of magnitude. Copyright © 2004 Society of Chemical Industry

Polybenzimidazole (PBI)/polyimide (PI) and PBI/polyvinylpyrrolidone (PVP) blends were prepared. All of these polymers are suitable for acid doping as a matrix because of the existence of the N-heterocycle in the polymers, which can eventually be used as proton conductors. The miscibility of PBI/PVP blend is confirmed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM), while the miscibility of PBI/PI is already reported in references. Temperature dependence of proton conductivity of acid doped PBI/PI and PBI/PVP blends are studied. As the temperature increases, proton conductivity of H₃PO₄ doped PBI/PVP blends increases. Temperature dependence of proton conductivity of the blends can still be fitted by a simple Arrhenius relation. The proton transport of the blend is similar to that of PBI. The methanol permeability of PBI/PI blends is also studied. Methanol permeability in PBI/PI, PI, and PBI membranes decreases with increasing methanol concentration. POLYM. ENG. SCI., 45:1395–1400, 2005. © 2005 Society of Plastics Engineers

To increase the solubility and film forming ability of polybenzimidazole (PBI), poly(N-methylbenzimidazole) (PNMBI) with different degrees of methylation was synthesized. Chemical structure, degree of substitution, and solubility of PNMBI was studied. PNMBI is easier to be doped with acid than PBI. The basicity of PNMBI was improved with the introduction of methyl groups on the imidazole moiety. Effects of methylation degree, H₃PO₄ content and temperature on proton conductivity of PNMBI doped H₃PO₄ was studied. Proton conductivity of H₃PO₄ doped PNMBI-1.2 membranes increases with increasing doping level. Temperature dependence of proton conductivity of H₃PO₄ doped PNMBI-1.2 membranes follows the Arrhenius law. With an increase in the degree of substitution, proton conductivity of H₃PO₄ doped PNMBI decreases dramatically. The proton transport mechanism was also discussed. The proton conductivity of PNMBI/H₃PO₄ is mainly contributed by proton hopping or Grotthuss mechanism. Copyright © 2004 John Wiley & Sons, Ltd.

The preparation of sulfonated polybenzimidazole (sPBI) by the grafting of (4-bromomethyl) benzenesulfonate onto polybenzimidazole (PBI) has been investigated. The methanol permeability and proton conductivity of PBI and sPBI have been studied, and the effects of methanol concentration and temperature on the methanol permeability of PBI and sPBI membranes are discussed. The results showed that the PBI membrane is a good methanol barrier. Methanol permeability in this membrane decreases with increasing methanol concentration and increases with increasing temperature. The temperature-dependence of methanol permeability of PBI and sPBI membranes is of the ‘Arrhenius type’. Methanol permeation of sPBI is less sensitive to temperature than that of PBI. However, sPBI is a poorer methanol barrier when compared to PBI. Methanol permeability in sPBI membranes increases with increasing methanol concentration and temperature. The proton conductivity of sPBI is 4.69 × 10⁻⁴ S cm⁻¹ at room temperature in the hydrated state. The DC conductivity of sPBI–H₃PO₄ increases with increasing temperature. Proton transport in sPBI–H₃PO₄ is less sensitive to temperature than that in PBI–H₃PO₄. Copyright © 2004 Society of Chemical Industry