Poly(ether sulfone) and poly(ether sulfone ketone) copolymers (I-V) were synthesized by the nucleophilic substitution reaction of 4,4＇-dihydroxy diphenyl sulfone (DHDPS, A) with various mole proportions 4,4＇-difluoro benzophenone (DFBP, B) and 4,4＇-difluoro diphenyl sulfone (DFDPS, C) using sulfolane as solvent in the presence of anhydrous K2CO3. The polymers were characterized by physicochemical and spectroscopic techniques. All polymers were found to be amorphous, ana the glass transition temperature (T-g) was found to increase with the sulfonyl content of the polymers. C-13-nuclear magnetic resonance (NMR) spectral data was interpreted in terms of the compositional triads, BAB, BAG, CAC, ABA, and ABB, and indicate that transetherification occurs at high concentration of DFBP units in the polymer (TV). The good agreement between the observed and calculated feed ratios validates the triad analysis. Thermal decomposition studies reveal that the thermal stability of the polymers increases with increase in the carbonyl content in the polymer. Activation energies for thermal decomposition were found to be in the range of 160-203 kJ mol(-1) with the cleavage of phi-SO2 bond being the preponderant mode of decomposition and depended on the block length of the sulfonyl unit.