Preparation method of polyimide film based on high modulus and low thermal expansion coefficient

The invention discloses a preparation method of a polyimide film based on high modulus and low thermal expansion coefficient, polyimide precursor resin is polyamide acid, and is obtained by introducing diamine containing nitrogen-containing heteroaromatic rings on the basis of dianhydrides containing two different structures for condensation polymerization. By optimizing the proportion of rigid units and flexible units of polyimide, the polyimide precursor resin with high modulus and low thermal expansion coefficient is obtained. The preparation process and the operation process are simple, and the elastic modulus of polyimide presented after salivation and imidization of the synthesized polyamide acid resin can reach 8 GPa or above; and the thermal expansion coefficient can reach 17 ppm/DEG C or below at the temperature of 50-200 DEG C, and the material has excellent thermal stability and mechanical properties and can be used in the fields of chip packaging, chip-on-film, ultra-high-temperature cable insulat