Study On Aniline Copolymerization And Its Composite

The conducting polymer polyaniline (PANI) have attracted increasing interest due to its simple structure, low price and super stability in recent years. Especially in the aspect of metal corrosion and protection, Polyaniline as a non-toxic and anti-corrosive pigment become the most promising applications. A large number of literature reports, the anticorrosion performance of polyaniline strongly depends on its electrochemical properties, Only have enough redox activity can exert its long-term anti-corrosion ability. Generally, the redox activity of PANI can only be retained in acidic media at pH<4, because the occurrence of deprotonation of the nitrogen atoms in the PANI backbone at high pH values may result in the loss of conductivity and electroactivity in neutral or alkaline solutions, which has become a major obstacle in the application of anti-corrosion. In this reseach, special emphasis is placed on the synthetic methods and electrochemical features for the self-doped, polymer acid-doped and graphene-doped PANI, including their underlying mechanisms for achieving good electroactivity. The application of doped PANI in anti-corrosion coatings are also discussed.(1) Based on the polymer acid-doped mechanism, acrylic ester grafting epoxy with carboxyl groups (A-g-EP) was firstly prepared using solution polymerization, the complex of polyaniline (PANI) and A-g-EP (PANI-A-g-EP) was then prepared by in-situ chemical oxidative polymerization of aniline which pre-reacted with the carboxyl groups on A-g-EP. Infrared spectroscopy(FTIR), ultraviolet-visible spectroscopy (UV-Vis), differential scanning calorimetry(DSC), thermogravimetric analysis (TGA), surface resistance measurement and electrochemical test were carried out to characterize the properties of the PANI-A-g-EP complex. The results show that PANI can be doped by carboxyl groups on A-g-EP and it has delocalized bipolaron and a unique self-crosslinking structure, the effects of PANI content have a great impact on its conductivity. PANI-A-g-EP complex coating demonstrates excellent antistatic properties, however poor preservative effect due to the low molecular weight.(2) Based on the protonic acid doping mechanism, to improve the pH dependence of redox activity of polyaniline, the copolymerization (PAASA) of aniline and 5-aminosalicylic acid (ASA) in H2SO4 solution was carried out through chemical oxidative polymerization. The negatively charged functional groups on polymer chain can directly dope polymer to achieve self-doping copolymer. Infrared spectroscopy(FTIR), ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning eletron microscopy(SEM), transmission electron microscopy(TEM), electrochemical test and salt spray test were carried out to characterize the structure and the properties of the copolymer. The results show that the comonomer ratio of ANI/ASA have a great effect on the yield, conductvity and morphology. When ASA/ANI monomer ratio isl6:l, regular continuous uniform nanofibers can be obtained and electrochemical activity has been improved because there is still a pair of redox peaks in neutral medium.(3) Based on the charge transfer mechanism, the graphene oxide was introduced into polymerization system to prepare the complex of PAASA and graphene (GPA) using one-step solution method. Infrared spectroscopy(FTIR), ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy (Raman), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning eletron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical test were carried out to characterize the structure and properties. The results show that graphene oxide can be reducted by comonomer and the copolymer fibers are uniformly supported on the surface of graphene. When the mass ratio of PAASA and graphene oxide was 8:1, the two largest and the most obvious pairs of redox peaks still remained in neutral medium, which indicates the electrochemical activity has been greatly improved.When the coating of water born acrylate grafted epoxy (EMA/A) containing 1.5 wt% GPA8 was immersed in 3.5% NaCl solution, the corrosion current reduced two orders of magnitude after eight days, which indicats excellent anticorrosion properity.