3,3＇-Bis(4-chloro-1,8-naphthalimido)diphenylsulfone (1a) and 4,4＇-bis(4-chloro-1,8-naphthalimido)diphenylsulfone (1b) and model imides have been synthesized and characterized by n.m.r. and i.r. spectroscopies and by d.s.c. The results of the structural investigations indicate that la and Ib are pure naphthalimides, without traces of isoimides. la and Ib were used to generate three series of poly(thioetherimide-sulfones). The polymer synthesis involved a nucleophilic displacement polymerization between 1a or 1b and Li2S or dithiol reactants such as 1,3-benzenedithiol and 2,5-dimercapto-1,3,4-thiadiazole under basic conditions in NMP or DMAc. The copolymers were characterized by i.r., n.m.r. and thermal analysis. Model compounds were synthesized for the correct assignment of C-13 n.m.r. chemical shifts. All the copolymers showed a good thermal stability, exhibiting 10% mass loss in the range 400-500 degrees C. The copolymers containing parasubstituted phenylsulfone units and/or the ones containing thiadiazole units were soluble in common polar solvents such as DMSO, DMF, NMP and DMAc.