CROSSLINKED SULFONATED POLYIMIDE-INORGANIC OXIDE NANOCOMPOSITE MEMBANES WITH STRONG RESISTANCE TO FREE RADICAL ATTACK

摘要

Proton conductive composites have been highlighted as one of potential proton exchange membranes (PEMs). The composite type PEMs are expected to substitute or modify commercial Nafion~R membranes. For fabrication of the composite membranes, there have been trials to add inorganic oxides such as silica (SiO_2), alumina (A1_2O_3), zirconium oxide (ZrO_2) and titanium oxide (TiO_2) into polymer matrix [1-3]. In most of cases, inorganic oxide particles are incorporated in-situ into polymer matrix via sol-gel synthetic route using alkoxide precursors such as tetraethyl orthosilicate (TEOS). In spite of homogenous distribution of SiO_2 phase, sol-gel process was affected by a lot of factors including kinds of alkoxide precursors, Ph in the reaction medium, solvents, reaction temperature and pressure, which lead to different morphologies and physico-chemical properties in the resulting hybrid membranes. On the other hand, direct mixing of SiO_2 particles can be simple and convenient approach to fabricate composite membranes on the assumption that the inorganic nanoparticles are homogenously distributed in the polymer matrix [4.5]. In the present study, an approach to improve membrane resistances to hydrolytic and peroxide radical attack was investigated via incorporation of functional inorganic fillers including SiO_2. Pluronics~R, commercial surfactant, were used as dispersants to induce nano-dispersed inorganic phase and as crosslinkers to form polymer networks at the same time. As a result, dispersants accompanied by inorganic oxide particles, so called organometallic complexes, were expected to cause peculiar microstructure depending on polymer matrix and inorganic fillers. The influences of the organometallic complexes on the membrane durability as well as other membrane performances were discussed considering the availability of inorganic fillers.