4-Aminobenzoic acid 4-aminophenyl ester (APAB) acts as a polymer monomer to synthesise a series of polyesterimide (PEsI) copolymers with 4,4′-BPDA and TFMB. The average interchain distances of these polymers ranged from 4.6 to 5.7 ?, which increased with the increase of TFMB content.The glass transition temperatures (Tg) of PEsI-0.3 and PEsI-0.4 were 445°C and 455°C, respectively, whereas there was no significant change in the glass transition temperatures (Tg) of PEsI copolymers when APAB content was greater than 50 mol%. These PEsI copolymers have coefficients of thermal expansion (CTE): 3.8 ~ 24.2 ppm K-1, modulus: 5.7-7.8 GPa, tensile strength: 282-332 MPa, elongation at break: 10.2%-23.3%, and dielectric constants: 2.53-2.76. These PEsI copolymers can be used as novel base film materials for flexible printed circuit boards (FPCs).
