Synthesis and Changes of Conductivities and Thermal Stabilities of 4,4′-Oxybis [N-(3,4-Dihydroxybenzilidene) Aniline] Chelate Polymers
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In this study novel metal coordination polymers were synthesized such as poly-4,4′-oxybis[N-(3,4-dihydroxybenzilidene)aniline] (P-3,4-HBA) containing Cu, Co, Pb, Ni, Zn, Cd, Cr, Mn and Zr metals in the polymer backbone. The polymers are abbreviated as P-3,4-HBA-Cu, P-3,4-HBA-Co, P-3,4-HBA-Pb, P-3,4-HBA-Ni, P-3,4-HBA-Zn, P-3,4-HBA-Cd, P-3,4-HBA-Cr, P-3,4-HBA-Mn and P-3,4-HBA-Zr, respectively. To confirm the structures FT-IR, UV-vis, 1H and 13C-NMR spectral techniques were used. Additional characterization of the polymers was made by size exclusion chromatography (SEC), TGA-DTA and solubility tests. By TGA analysis, P-3,4-HBA-Zr was the most stable polymer against thermal degradation among those synthesized. In addition, it was found that, with exception of P-3,4-HBA-Cr, the other synthesized polymers have little solubility in many organic solvents and water. According to SEC results, P-3,4-HBA-Cr has a single fraction containing 21–22 mer units. Electrical conductivities of the monomer and polymers were measured by the four-point probe technique. The polymers were semiconductors; and, some of their conductivities can be increased via doping with iodine. According to the electrical conductivities of the undoped P-3,4-HBA-Cr and P-3,4-HBA-Zr polymers have nearly ten-times higher conductivities in comparison to the others. From UV-vis measurements, the optical band gaps (E g ) of 3,4-HBA and P-3,4-HBA-Cr were 2.58 and 2.39 eV, respectively. This result indicates that P-3,4-HBA-Cr has a lower band gap and consequently higher electrical conductivity than 3,4-HBA. Thus, with good solubility, high electrical conductivity and high thermal stability P-3,4-HBA-Cr may be considered as the most useful metal coordination polymer among those synthesized.