Polyamide-imide resin adhesive, preparation method thereof and temporary adhesive film for packaging semiconductor element

The preparation method comprises the following steps: under the protection of inert gas, dissolving a flexible long-chain diamine monomer in a polar organic solvent, adding a catalyst and an activating agent in an ice bath, uniformly stirring and mixing, adding 1, 2, 4-trimethyl-1, 3-pentanedione, and uniformly stirring, so as to obtain the polyamide-imide resin adhesive. The preparation method comprises the following steps: adding 1, 2, 4-trimellitic anhydride acyl chloride or a mixture of 1, 2, 4-trimellitic anhydride acyl chloride and a flexible long-chain aromatic dianhydride monomer into a reaction kettle, stirring and reacting at 0-40 DEG C for 10-14 hours, then adding an end-capping reagent for end capping, diluting until the solid content is 5-10% after end capping, and carrying out imidization treatment on the diluted reaction liquid to obtain the polyamide-imide resin adhesive. The polyamide-imide resin adhesive controlled by the preparation method disclosed by the invention has excellent heat resis