A series of novel poly(thioether ether ketone imide)s (PTEKIs) bearing the thioether and ketone groups with high molecular weights (Mw: 87,800–150,100 g/mol) were synthesized by aromatic nucleophilic substitution reaction. The polymers were characterized by Fourier transform infrared spectra (FT‐IR), 1H NMR, GPC, and elemental analysis. The composition of the copolymers varied systematically in order to study its relation with polymer properties. Increase in the content of 3‐substituted phthalimide moiety in the polymer backbone improves the solubility in tested solvents, and increases the glass transition temperature (Tg), whereas copolymers with high content of 3‐substituted phthalimide demonstrated to be inferior thermal stability. The PTEKI films also exhibited good optical transparency, including the cutoff wavelengths lower than 400 nm and transmittances higher than 77% at 450 nm. Copyright © 2010 John Wiley & Sons, Ltd.