**2.4 Synthesis of PAA/nanoparticle composite solution**

The PAA/SiO2 nanocomposite solution was synthesized by applying the in-situ polymerization method, as elaborated in **Figure 7**. For the better link between PI and nanoparticles, SiO2 was treated with a KH-550 coupling agent to modify its surface. Altered surface SiO2 nanoparticles and dimethylacetamide (DMAC) were dispersed by applying ultrasonication and high-speed stirring, then oxy dianiline (ODA) was added into the solution and mixed for 1 h. After that pyromellitic dianhydride (PMDA) was added into two portions. For the first portion, almost 90% PMDA was added and mixed for 30 min, then the remaining 10% PMDA was added and mixed for 2–6 h until yellowish color high molecular weight PAA solution was obtained.

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

**Figure 7.** *Polyimide film synthesis process.*
