Molecular weight controlled poly(amic acid) resins end‐capped with phenylethynyl groups for manufacturing advanced polyimide films

To investigate the effect of reactive end‐capping groups on film‐forming quality and processability, a series of molecular weight‐controlled aromatic poly(amic acid) (PAA) resins functionalized with phenylethynyl end groups were prepared via the polycondensation of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), para ‐phenylenediamine (PDA), and 4‐phenylethynyl phthalic anhydride (PEPA) served as molecular‐weight‐controlling and reactive end capping agent. The PAA resins with relatively high concentrations endow enhanced wetting/spreading ability to form PAA gel films by solution‐cast method which were thermally converted to the fully‐cured polyimide (PI) films. The mechanical and thermal properties of PI films were investigated as a function of PAA molecular weights (M_n ) and thermal‐curing parameters. Mechanical property, dimensional stability and heat resistance of the fully‐cured PI films with PAA M_n > 20 ×10³ g mol^?1 are found to be better than that of their unreactive phthalic end‐capped counterparts. The covalent incorporation of chain‐extension structures in the backbones, induced by thermal curing of phenylethynyl groups, might facilitate yielding a higher degree of polymer chain order and consequently improved resistance strength and elongation at break to tensile plastic deformation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45168.