Preparation Of Polyaniline Derivatives And Their Corrosion Protection Performance In Composite Coatings

Corrosion will impair the performance of metal materials,increase maintenance costs of equipment,and even cause safety accidents,which is a severe factor restricting the application of metal materials.Polyaniline has excellent potential in metal surface protection due to its oxidation-reduction reversibility.However,theπ-πconjugated structure of the molecular skeleton endows polyaniline with strong rigidity.The use of polyaniline needs to solve the problem of the agglomeration in epoxy matrix,and improve the barrier property and long-term corrosion resistance of the coating.The tunable properties of polyaniline are mainly ascribed to the benzene ring and amino structure,which could be modified by simple chemical method.Herein,a series of polyaniline derivatives and composite materials have been designed and synthesized.The main research content is as follows:（1）Trimethylsilyl-substituted polyaniline（PSi An）was synthesized and characterized by FTIR and SEM-EDS.Results showed that silanes were successfully linked onto the polyaniline chain.The fabricated filler exhibits high hydrophobicity and good compatibility in the epoxy matrix.Incorporating PSi An into epoxy coating has a significant influence to the barrier property,effectively reducing the porosity of coating and interrupting the permeation pathway of aggressive substance.The results of electrochemical impedance spectroscopy showed that the|Z|_0.01Hz of PSi An/epoxy composite coatings still reached 10¹⁰Ω·cm² after 60-day immersion in 3.5 wt.%Na Cl solution,which was almost three orders higher than that of the pristine coating.XPS and EIS confirmed the formation of dense complex on alloy surface.It turned out that the synergy between impermeability and passivation effect endowed epoxy coating with excellent corrosion resistance.The long-term effectiveness of anti-corrosion epoxy coating was significantly improved,and a novel approach to preparing a highly hydrophobic filler was proposed.（2）Poly（aniline-co-pyrrole）wrapped titanium dioxide composites were synthesized via situ oxidative polymerization and dispersed into epoxy matrix to improve the corrosion resistance of EP coating.Electrochemical impedance spectroscopy（EIS）demonstrates that composite coating hybrid Ph An-PPy/Ti O₂ filled possesses the better impermeability than other EP-based coatings in neutral and acidic media.Furthermore,Ti O₂ enhanced the oxygen reduction catalytic activity of copolymer,thereby inducing the formation of a denser complex.A novel hybrid functional filler was proposed to enhance the self-healing property of the coating.（3）A novel conjugated poly（aniline-co-3-amino-9-ethyl-carbazole）（PAn Cz）copolymer was synthesized by chemical oxidative copolymerization and used as corrosion protection additives.Composite coatings with different PAn Cz contents（1 wt.%,2 wt.%,3 wt.%）were prepared,and its protective properties on Al alloys in 1 M H₂SO₄solution were studied.The EIS results show that the epoxy varnish coating loses the protective properties after immersion for 18 h,and its impedance modulus drops below 10⁵Ω·cm².In contrast,the PAn Cz composite coatings have better acid resistance,whose low-frequency impedance remains around 10⁶Ω·cm² even after immersion for 30 h.XPS confirmed that PAn Cz not only adsorbed on the substrate to form a protective polymeric layer through coordination bonds,but also induced the formation of oxide film.This work indicates that the prepared PAn Cz filler has great potential in improving the acid resistance of epoxy coating.