## 4 Nanoparticles-Promoted Polymer Hybrid Coatings
### Polyimide (PI) Based Hybrid Coatings  
Polyimide (PI) is a kind of polymer with an amide ring in the main chain, among which the polymer with phthalimide structure is more important [101; 102]. According to the structural unit of the molecule, they can generally be divided into aliphatic PIs and aromatic PIs. Because of the poor practicability of aliphatic PIs, polymers with aromatic PIs are particularly important. PI, as a kind of special engineering plastic with excellent performance, is also one of the polymer materials with the highest heat resistance rating so far. Because of its excellent performance, it is widely used in high-tech fields such as microelectronics, separation membranes, aerospace, and so on. PI has strong high-temperature resistance, its glass transition temperature is generally above 200 \({}^{\circ}\)C, and the most important feature of all aromatic PI is its good heat resistance, its thermal decomposition temperature can often reach 500 \({}^{\circ}\)C, and brittle behavior will not occur at ultra-low temperatures. In addition, it has very high mechanical strength and a low thermal expansion coefficient, which means that PI film can maintain good physical protection performance in a hot and humid environment. Furthermore, PI has excellent dielectric properties, and its dielectric constant is about 3.4. When fluorine is introduced into PI, its dielectric constant can be reduced to ca. 2.5. This makes it widely used in the electrical insulation industry, as the outer coating of insulated wire or direct coating. Due to the self-lubricating property of PI, it can resist aging and electrical breakdown.  
Due to the excellent properties of PI, it has a great prospect in the application of high corrosion resistance coatings, especially in corrosion protection under harsh chemical media and mechanical damage conditions. [PERSON] et al. [103; 104] (Figure 7) prepared TRGO/PI nanocomposite corrosion-resistant coatings with different mass fractions by adding high-temperature thermally reduced graphene oxide (TRGO) as a two-dimensional nanofiller to the PI polymer matrix and evaluated the electrochemical corrosion behavior of the coating in simulated seawater (3.5 wt% NaCl solution) using alternating current impedance spectroscopy and potentiodynamic polarization curves. The results showed that the addition of TRGO could significantly improve the resistance and corrosion protection efficiency of  
Figure 6: **(a)** The TEM image of dopamine@BCZT powders, the coating layer is about 15 nm; **(b)** FTIR spectra of ceramic powders before and after dopamine modification. **(c)** The XRD patterns of ceramic/epoxy resin composites with different volume fractions of dopamine@BCZT powders. **(d)** The dielectric constant and dielectric loss tangent of dopamine@BCZT/epoxy resin composites with various concentrations of dopamine@BCZT powders at 1000 Hz and room temperature [100].  
the coating. When the TRGO content was 0.3 wt%, the corrosion resistance of the coating was best enhanced, and the maximum coating resistance was 1.3176 \(\times\) 10\({}^{6}\)\(\Omega\), the highest corrosion protection efficiency reached 99.65%, and its corrosion protection gain was related to the excellent physical and chemical properties of PI and the physical barrier performance of TRGO.