AbstractA series of novel semi‐ladder polymers containing 7H‐benzimidazo[2,1‐a]benzo[d,e]isoquinolin‐7‐on‐3,11‐diyl units in the chain was prepared by one‐step high temperature solution polycondensation of 4,4′‐oxy‐,4,4′‐carbonyl‐, and 4,4′‐sulfonyldi‐1,8‐naphthalenedicarboxylic anhydride (1a‐c) with 2,2′‐diamino‐4,4′‐oxydianiline (2) or 2,2′‐diamino‐4,4′‐hexafluoroisopropylidenedianiline (4). The similarity of the IR and UV spectra of the polymers and the model compounds7a‐cconfirms the presence of the benzimidazobenzoisoquinolinone rings in the polymer chain. All the resulting polymers have excellent thermal stability both in argon and in air. The polymers prepared from4are soluble in