**2. Synthesis of polyimide**

When one monomer reacts with other monomers, it forms a carbon chain of the polymer. In case of polyimide, the monomers such as diamine (ODA) react with another monomer such as dianhydride (PMDA) to form polyamic acid solution (PAA). In this reaction, an oxygen atom of diamine reacts with the hydrogen atom of dianhydride, and the hydrogen of dianhydride reacts with the carbon of diamine to give a repeated unit of polyamic acid. To obtain polyimide film, thermal heat is applied for several hours to evaporate DMAC solvent. The chemistry and the properties of polyimides can vary due to the availability of several monomers.

*Synthesis Process Optimization of Polyimide Nanocomposite Multilayer Films, Their Dielectric… DOI: http://dx.doi.org/10.5772/intechopen.91206*

**Figure 5.** *Generalized reaction mechanism of aromatic imide formation.*

The ratio of monomers can affect the molecular weight of PAA and change the molar mass of the final PI film [6, 18] (**Figure 5**).
