No abstract

In this study, new monomers having siloxane groups were synthesized as an intermediate for preparation of siloxane modified polyimide polymers. Then with these monomers, the synthesis of uncrosslinked and crosslinked polyimide–siloxane hybrid polymer membranes were achieved. The purposes of the preparation of modified polyimides were to modify the thermal and chemical stability, and mechanical strength of polyimides, and to improve the gas separation properties of polymers. The new diamine monomer having siloxane groups was prepared from 3,5‐diaminobenzoic acid (3,5‐DABA) and 3‐aminopropyltrimethoxysilane (3‐APTMS) in N‐methyl‐2‐pyrollidone (NMP) at 180°C. The modified polyimide membranes having different amount of siloxane groups were synthesized from pyromellitic dianhydride (PMDA), 4,4‐oxydianiline (ODA), and 3,5‐diaminobenzamido‐N‐propyltrimethoxy silane (DABA/PTMS) in NMP using a two‐step thermal imidization process. The synthesis of modified polyimide membranes were characterized by Fourier transform infrared spectroscopy (FTIR). The thermal analysis of the polyimides were carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Water absorption and swelling experiments were also carried out for the investigation of structural properties of polymers. FTIR observations confirmed that the polyimide membranes with new diamine intermediate were successfully obtained. Thermal analysis showed that the uncrosslinked copolyimides exhibited two glass transition temperatures, indicating that they were separated microphases and it was found that all the modified copolyimides had showed higher glass transition temperature (Tg) than unmodified polyimides. The separation properties of the prepared polyimide membranes were also characterized by permeability for O2 and N2 gases and ideal selectivity values were calculated. Copyright © 2009 John Wiley & Sons, Ltd.

No abstract

No abstract

Abstract.A proton-exchange membrane for a direct methanol fuel cell was prepared by modifying the chemical structure of poly(vinyl alcohol) (PVA) by means of sulfonation. We report the synthesis of a new proton-conducting polymer membrane with poly (vinyl alcohol) and diamine-containing organic molecules immobilized to PVA. The sulfonation was carried out by using 4,4-diaminodiphenyl ether-2,2-disulfonic acid (ODADS). A sulfonated diamine monomer, ODADS, was successfully synthesized by direct sulfonation of a commercially available diamine, 4,4-diaminodiphenyl ether (ODA), using fuming sulfuric acid as the sulfonating reagent. The chemical structure and thermal stability of the sulfonated PVA were studied by using FTIR and thermogravimetric analysis techniques, respectively. The proton conductivities of membranes were investigated as a function of ODADS content. The thermal decomposition of PVA-ODADS membranes started at 220°C. Differential scanning calorimetry (DSC) results indicated the homogeneity of the blends. Proton conductivity values of the sulfonated PVA membranes ranged between 8.25 and 16.53 mS/cm and the conductivities of PVA-ODADS membranes increased with the increasing ODADS content.