A series of cardo poly(ether ketone imide)s (PEKI-C) containing large-volume bulky phthalide groups were prepared by aromatic nucleophilic substitution reaction of commercially available phenolphthalein and 4,4'-bis(4-fluorophthalimido)diphenyl ether/4,4'-difluorobenzophenone. The glass transition temperatures (T(g)s) increased from 221 to 278 degrees C with increasing the content of 4,4'-bis(4-fluorophthalimido) diphenyl ether moiety in the copolymerization. The 5% weight loss temperatures (T-5%) of PEKI-C (a-e) reached up to 472-495 degrees C in nitrogen and 466-481 degrees C in air. Flexible films, which could be easily cast from the polymer solutions, exhibited good mechanical properties with tensile strengths of 73-124 MPa, elongations at break of 9.7-12.8%, and tensile moduli of 2.2-2.8 GPa. Their films with cut-off wavelengths from 336 to 368 nm were transparent and essentially colorless. It is noted that the T-g, T-5%, tensile strengths, elongations at break, and tensile moduli of PEKI-C (a-e) increased with increasing the content of 4,4'-bis(4-fluorophthalimido)diphenyl ether in the copolymerization. (C) 2015 Elsevier Ltd. All rights reserved.