New polythioethers containing a 1,4-dithiin-2,3;5,6-tetrayl diimide structure were synthesized by condensation of N-(p-chlorophenyl)-2,3-dichloromaleimide (2) with anhydrous sodium sulfide in molar ratio 2:3 or by condensation of bis(N,N -p-chlorophenyl)-1,4-dithiin-2,3:5,6-tetrayl diimide (3) with various bisphenols. The polyethers were prepared by condensation of 3 with various bisphenols. The monomer 3 was synthesized by nucleophilic substitution of 2 with nonahydrate sodium sulfide. IR and UV spectroscopy, as well as elemental analysis confirmed the structures. The polymers were characterized by viscosimetric measurements, softening points and thermogravimetric data. They showed good solubility in aprotic solvents and high thermal stability.