Anti-corrosive Behavior Of Well-dispersible Aniline/p-phenylenediamine Copolymers And Copolymer/epoxy Composite Coatings

Polyaniline(PANI)anti-corrosive coatings have attracted much attention due to environment-friendly,long-term efficacy and self-healing.Solving the aggregation of PANI in conventional solvents is the key problem recently.This paper is focused on the development of well-dispersible aniline/p-phenylenediamine copolymers(P(ANI-co-p-PDA))and excellent anti-corrosive composite coatings.The main results are as follows:Well-dispersible P(ANI-co-p-PDA)copolymers were synthesized by chemical oxidative polymerization in the presence of non-ionic surfactant nonylphenol ethoxylates(TX-8)with the HLB value of 10-11.The influence of TX-8 adding modes and monomer feed ratios on the structure and dispersion stability was investigated.Meanwhile,the anti-corrosive properties of medium-carbon steel coated by P(ANI-co-p-PDA)and P(ANI-co-p-PDA)/Epoxy were evaluated by electrochemical methods.FE-SEM images and stability analysis showed that the particle diameter of P(ANI-co-p-PDA)adding TX-8 in initial stage of reaction(P(ANI-co-p-PDA)-2-F1)is much smaller,the dispersion stability of P(ANI-co-p-PDA)-2-F1 in toluene was much more better than that of P(ANI-co-p-PDA)with other TX-8 adding modes and modified PANI.Electrochemical corrosion tests showed that P(ANI-co-p-PDA)-2-F1/Epoxy on carbon steel possessed good corrosion resistance,and composite coatings containing 7 wt.%P(ANI-co-p-PDA)-2-F1 exhibited best anti-corrosive performance.Raman spectroscopy analysis indicated that the passivated layer was formed in the surface of carbon steel coated with composite coatings,which was composed of Fe3O4 and?-Fe2O3.Nano/micro scale P(ANI-co-p-PDA)were synthesized by the combination of rapidly-mixed reaction and copolymerization technique.The influence of monomer feed ratios on the morphology and dispersion stability was studied.Moreover,the anti-corrosive properties of self-dispersing P(ANI-co-p-PDA)with nano/micro scale/Epoxy coatings were evaluated.The results indicated that PANI synthesized by rapidly-mixed reaction had nanofiber-like structure,which was gradually destroyed with adding p-PDA to copolymers,and finally turned out the irregular sheet structure with a wide distribution.Because of the influence of morphology and molecular weight,copolymer with ANI/p-PDA molar feed ratio of 2/1(P(ANI-co-p-PDA)-NS21)had good dispersion stability in toluene.P(ANI-co-p-PDA)-NS21/Epoxy composite coatings exhibited the highest corrosion potential,membrane resistance,and lowest corrosion current,which leaded to the best anti-corrosive effect to the carbon steel.