• Macromolecular Research
• /
• v.16 no.4
• /
• pp.360-366
• /
• 2008

Poly(dialkoxyphenylene 1,3,4-oxadiazole)s were conveniently synthesized to compare their material properties of solvent solubility, thermal stability and molecular alignment with respect to alkyl chain length and meta/para-phenylene structure. All prepared polymers exhibited good solubility in co-solvents containing various volume levels of chloroform to trifluoroacetic acid. Meta-polymers showed slightly better solubility than para-polymers. All polymers produced were thermally stable up to $320^{\circ}C$. Photoluminescence of polymer films was observed with blue light emission at around 450 nm. X-ray diffraction patterns of all polymers indicated that they were composed of stacked molecular sheets with the same layer-to-layer distance of $3.4\;{\AA}$. However, side chain-to-side chain and main chain-to-main distances within the layers increased with increasing alkyl chain lengths. The meta-polymer chains were separated more than the para-polymer chains.

• Proceedings of the Membrane Society of Korea Conference
• /
• 2003.11a
• /
• pp.61-63
• /
• 2003

A major research objective related to proton exchange membrane(PEM) for DMFC is to achieve high proton conductivity over 10$^{-2}$ S/cm, high hydrolytic stability and low methanol permeability with low cost base materials. for the purpose, a lot of thermoplastic polymers such as polysulfones, polyethersulfone, polyetherketones, polyimides, polyoxadiazole, polyphosphazene and polybenzimidazol have been investigated. Amongst those polymers, polyimides have been suggested as a potential PEM due to their excellent thermal, chemical stability and good mechanical properties. Generally, polyimides are synthesized by polycondensation with numerious diamines and dianhydriedes. In our study, polyimide was prepared using non-sulfonated diamine, sulfonated diamine directly synthesized by fuming sulfuric acid, and naphthalenic dianhydride to improve the hydrolysis stability under acidic condition. Through monomer sulfonation-subsequent polymerization method, the high proton conducting capability and the desired sulfonation level were effectively controlled at the same time. To reduce severe methanol transport through the membrane, the chemical crosslinking among polymer chains was introduced using various crosslinking agents with different chain lengths. The crosslinked sulfonated polyimide membranes showed high proton conductivity up to 8.09$\times$10$^{-2}$ S/cm and from crosslinking effect methanol transport through the membranes was considerably reduced as compared with unmodified membranes. For increase of chain length of crosslinker, methanol permeability was adversely reduced to 10$^{-8}$ $\textrm{cm}^2$/s due to decrease of IEC and increase of crosslinking desity.