The synthesis and characterization of poly(parabanic acid) polymer precursor (polyurea), were investigated in the present study, by considering factors such as the chemical structure of the monomers, the reaction temperature, and the reaction media. Furthermore, the aforementioned polyurea was also used to successfully cast films and coatings. Electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, dilute solution viscometry, thermal gravimetric analysis and shear viscometer were employed to characterize polymers and coatings.
It was shown that condensation polymerization is strongly dependent on the conductive effect of the functional groups. The yield of condensation reactions was very high, around 95%. The cyclization of polyurea to poly(parabanic acid) was partially completed and two different kinds of poly(parabanic acid)s were obtained: soluble and insoluble. In addition, copolymerization using two different diamines with diisocyanate was used to prepare copolyurea. Polyurea gel based on the polyurea discussed above was also made.
FTIR analysis showed the disappearance of NCO absorption bands at 2280 cm-1 and appearance of the absorption band for urea linkage, -CO-NH-, indicating the successful synthesis of polymers. Dilute solution viscometry was employed to estimate the intrinsic viscosity and the molecular weight of the polyurea synthesized in the present work.
Electrochemical impedance spectroscopy was used to measure the electrochemical performance of all coatings developed. From the Nyquist and Bode plots, it was found that the polyurea coatings developed in the present case showed high impedance, about 108. However, the parameters obtained from fitting EIS plots to Randles cell model did not show obvious dependence on the time for immersion. Acid was also embedded into the coatings to investigate the influence of acid on corrosion behavior. The corrosion performance of doped systems was complicated owing to the incorporation of the acid into the coating and was improved after 3 days of immersion due to the fact that crosslinking reaction might happen in the coating and therefore influence of catalysis was weakened. The doped systems failed after the third day due to the acid in the environment, based on the Nyquist plots. The diffusion coefficient of polyurea films was also calculated based on the capacitance of the films. It was revealed that incorporation of another component, silicon rubber, could lead to decrease in diffusion coefficient because of possible crosslinking reaction between the polyurea and silicon rubber.
Thermal gravimetric analysis revealed that the polyurea B, the major component of all coating developed in the present work, is thermally stable. The decomposition temperature of this polyurea B is around 374°C.