Preparation, Characterization And Properties Of Poly(2,3-dimethylaniline) Doped With Different Acids

Polyaniline（PANI） has been extensively considered as one of the best usefulorganic conducting materials because of its good environmental stability, highconducting and optical properties, especially the protective properties against corrosion.However, owing to the stiffness of its backbone, the PANI is difficult to be processedthrough a traditional method because it is both unstable at melt-processing temperaturesand insoluble in most organic solvents except for N-methylpyrrolidone（NMP）, greatlylimiting its further wide practical application. So several modifying ways have beendeveloped to improve its solubility. Among them, alkyl, alkoxy, and aminoring-substituted and N-substituted PANIs have caught great interest because of theirmuch better solubility in many common solvents and, therefore, relatively goodprocessibility. The ring-substituted PANI were the one of the effective methods toimprove the dissolvability and the processability of PANI.2,3-dimethylaniline is one kind of the derivatives of aniline, has been extensivelyused as the intermediate of medicine and pesticides. But the reports about P（2,3-DMA）were few. So in this study, The P（2,3-DMA） was synthesized by chemicalpolymerization using phosphoric acid, hydrochloric acid, sulfuric acid and camphorsulfonic acid as protonic acid media respectively. The effects of the mole ratio of dopedacid to2,3-dimethylaniline and oxidant （ammonium persulfate, APS） on theelectrochemical properties （cyclic voltammogram, tafel） of P（2,3-DMA） were discussedusing the carbon paper loaded P（2,3-DMA） as working electrode, and the yield ofP（2,3-DMA） was also investigated. The molecular structure of P（2,3-DMA） wascharacterized by FT-IR and UV-vis spectroscopies, and X-ray diffraction technique. Thedissolvability and the anticorrosion properties were of P（2,3-DMA） were compared withPANI, and the anticorrosion properties of P（2,3-DMA） was studied by Tafel technique.The experimental results show that:â‘ The optimized H₃PO₄/monomer ratio, oxidant/monomer ratio, temperature andreaction time for the preparation with a high yield, better electrochemical properties are2.5/1,2/1,30℃and9h, respectively. When the mole ration of CSA to2,3-DMA was1.25, the mole ration of APS to2,3-DMA was2, the temperature was30℃and thereaction time was9h, the P（2,3-DMA） doped with CSA has the best electrochemicalproperties and the highest polymerization yield. The optimized H₂SO₄/monomer ratio, oxidant/monomer ratio, temperature and reaction time for the preparation ofP（2,3-DMA） doped with H₂SO₄are0.5/1,2/1,30℃and9h. The optimizedHCl/monomer ratio, oxidant/monomer ratio, temperature and reaction time for thepreparation of P（2,3-DMA） doped with HCl are2.5/1,2/1,30℃and9h, respectively.The P（2,3-DMA） has the best electrochemical properties and the highest yield.â‘¡The experimental results show that the main chain of polymers doped withdifferent acids were similar, but in the UV-Vis spectra of H₃PO₄doped P（2,3-DMA）, theÏ€-Ï€*electronic transition absorption peak of the quinoid ring shows a largebathochromic shift indicates the higher conjugation degree and electron delocalizationthan the other polymers. A hypocrystalline structure was observed in all the samplesexcept for CSA doped P（2,3-DMA） under XRD. H₃PO₄doped P（2,3-DMA） shows thebest crystallinity, and its intermolecular regularity and orderliness were the best. Anincrease in solubility was observed in the CSA doped polymer. Cyclic voltammetry testresults show that P（2,3-DMA） has redox reversibility. Anticorrosion performance wasinvestigated with the help of polarization curves （Tafel） analysis for P（2,3-DMA）,compared with the EB, the anticorrosion of P（2,3-DAM） were better, especially theH₃PO₄doped P（2,3-DMA） is found to be better as compared with other polymers,which has the highest corrosion potential and the lowest corrosion current.