A block copolymer of polyamide acid includes a first polyamide acid and a second polyamide acid alternately connected. The first polyamide acid is made by first dianhydride monomers and second diamine monomers. The second polyamide acid is made by second dianhydride monomers and first diamine monomers. Each first dianhydride monomer is or comprises a liquid crystal structure. Each second dianhydride monomer and each second diamine monomer respectively include a first flexible structure. Each first diamine monomer includes a liquid crystal structure. Each liquid crystal structure includes a cyclic group selected from a chemical structural formula of and intermediate groups selected from a chemical structural formula of Each flexible structure includes a group selected from a group consist of ether bond, ketone group, sulphone group, aliphatic hydrocarbon group, and any combination thereof.