Ultrahigh thermal-stability polyimides with low CTE and required flexibility by formation of hydrogen bonds between poly(amic acid)s

•The diphenylpyridine and diphenylpyrimidine moiety were introduced into PI chains.•The ultralow CTE (< 5 ppm K−1), high Tg (> 450 °C) and good flexibility were achieved.•Effect of chain rigidity, chain packing and in-plane orientation on CTE was studied.•The impact of hydrogen bonds formed at the PAAs stage on CTE was discussed.