Preparation And Anticorrosive Properties Of Poly(2,3-dimethylaniline) And Its Composites With Nano Inorganic Particles

Despite the large amount of literature has demonstrated that polyaniline has goodcorrosion resistance of mild steel, the poor solubility and processing properties of PANIcaused by its high rigidity of molecular chain backbone and large intermolecularinteractions restricted its commercial applications greatly. One of a certain chemicalmodifications of polyaniline, such as the introduction of certain substituents generatepolyaniline derivatives can effectively improve the insolubility and difficultprocessability of PANI. Poly(2,3-dimethylaniline)(P(2,3-DMA)) is a major derivativesof polyaniline, which was substituted by two methyl groups on the same side of benzenering. The stiffness of PANI backbone was effectively decreased due to the high sterichindrance between the molecular chains so that the solubility of PANI could beimproved. P(2,3-DMA) has a good application prospect in terms of corrosion. Thepolymer–nano-inorganic materials-based composites may combine the advantages ofpolymers like flexibility, processability, durability, load bearing capability, etc. and ofinorganic nanofillers like selectivity, thermal stability, high melting and boiling points,and densities. So we prepared a series of poly(2,3-dimethylaniline)/nano-inorganiccomposite materials in order to improve the corrosion resistance and thermal stability ofP(2,3-DMA). Details are as follows:P(2,3-DMA) was synthesized by emulsion polymerization using dodecyl benzenesulfonic acid as emulsifier and dopant. Effects of the two methyl substituents on thestructure and morphology of polyaniline were characterized by Fourier TransformationInfrared spectroscopy (FTIR), Wide-angle X-ray diffraction (WXRD), Field emissionscanning electron microscopy (FESEM). Cyclic voltammetry measurements (CV) andthermogravimetric analysis (TGA) was used to study the electrochemical and thermalstability. Epoxy resin coating containing P(2,3-DMA) and PANI respectively werepainted on mild steel and accelerated immersion tests were performed to evaluate theanticorrosion property of the coatings in3.5%NaCl solution.Poly(2,3-dimethylaniline)-TiO2composite (PTC) was prepared by oxidativepolymerization of2,3-dimethylaniline in phosphoric acid medium with ammoniumpersulphate as oxidant for the first time. Carbon papers loaded PTC were used asworking electrode for electrochemical tests to study the effects of TiO2on the propertiesof the composite. The results showed that the property was best when the content of TiO2was15%. The composite was characterized by Fourier transformation infrared(FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM).Suitable coating with PTC was formed on steel using epoxy resin, and its corrosionresistance behavior was studied by open circuit potential (OCP) and electrochemicalimpendence spectroscopy (EIS) in3.5%NaCl solution.Poly(2,3-dimethylaniline)/nano-Al2O3composite (PAC) was synthesized byemulsion polymerization using dodecyl benzene sulfonic acid as emulsifier and dopant.The structure of PAC was characterized by Fourier fransformation infrared spectroscopy,UV–visible adsorption spectroscopy, and field emission scanning electron microscopy.The thermal stability was studied by thermogravimetric analysis, and theelectrochemical performances were studied by cyclic voltammetry measurements.Epoxy coatings containing PAC and P(2,3-DMA) respectively, were painted on steel,and accelerated immersion tests were performed to evaluate the anticorrosion propertyof the coatings in3.5%NaCl solution.The results showed that:(1) P(2,3-DMA) was successfully prepared by emulsion polymerization usingdodecyl benzene sulfonic acid (DBSA) as emulsifier and dopant. The results indicatedthat the structure of P(2,3-DMA) was similar with that of PANI. The high sterichindrance between the molecular chains caused by the two methyl group substitutionseffectively decreased the stiffness of PANI backbone so that the solubility of PANI wassignificantly improved. The coatings of P(2,3-DMA) were found to offer good corrosionprotection and showed a better anticorrosion performance than conventional polyanilinecoating according to the results of EIS, OCP and TAF measurements in3.5%NaClsolution, which shows a promising prospect for P(2,3-DMA) in the field of corrosionprotection and more suitable for the industrialization.(2) P(2,3-DMA)-TiO2composite was successfully prepared by chemicalpolymerization of2,3-DMA and TiO2in the presence of phosphoric acid usingammonium persulfate as oxidant. The FTIR spectra show that there is an interactionexists at the interface of P(2,3-DMA) and TiO2particles. The interaction may beassociated with the interaction of titanic and nitrogen atom in P(2,3-DMA)macromolecule. Titanium is a transition metal, has intense tendency to formcoordination compound with nitrogen atom in P(2,3-DMA) macromolecule. XRDpattern of PTC indicates that the crystallinity of TiO2is not altered by P(2,3-DMA)polymer. The SEM study of PTC clearly shows that TiO2particles are fully covered by P(2,3-DMA). Open circuit potentials and impedance studies of coated samples in3.5%NaCl immersion test have shown that coating containing PTC has got higher corrosionresistant property than that of P(2,3-DMA) and PANI. The higher corrosion protectionability of coating containing PTC has been associated with the increase in barrier todiffusion, redox properties of P(2,3-DMA) as well as very large surface area availablefor the liberation of dopant due to the addition of nano-TiO2particles.(3) PAC was successfully prepared by emulsion polymerization using DBSA asemulsifier and dopant. The structure characterization shows that there is an interactionbetween the Al2O3nanoparticles and P(2,3-DMA) macromolecules. The TGA indicatesthat the thermal stability of PAC is much better than that of P(2,3-DMA). Theelectrochemical behavior of the PAC is reversible and stable, and its anticorrosionperformance is better than that of P(2,3-DMA) in3.5%NaCl solution.(4) P(2,3-DMA) and its inorganic nanoparticles composites have good solubilityand corrosion resistance, is expected to replace the massive use of PANI in the field ofanticorrosion of metals.