9‐diarylfluorene (DAF)‐based polymers with high performances, 9,9‐(4‐hydroxyphenyl)‐4,5‐diazafluorene (N‐BPF) was designed as a new cardo structure and the properties of poly(ether ketone)s (N‐PEKs) containing N‐BPF skeletons were examined in detail. N‐PEKs were synthesized in high yields via polycondensation of N‐BPF with difluoroarenes. N‐PEKs showed cardopolymer‐specific properties such as high thermal