Poly(ether sulfone) copolymers I-V were synthesized by the nucleophilic substitution reaction of 4,4-dichlorodiphenyl sulfone with varying mole proportions of 4,4-isopropylidene diphenol (bisphenol A) and 4,4-dihydroxydiphenyl sulfone (bisphenol S) using sulfolane as the solvent in the presence of anhydrous K2CO3. The polymers were characterized by different physicochemical techniques. The glass transition temperature was found to decrease with increase in the concentration of bisphenol A units in the polymers, All polymers were found to be amorphous. Thermogravimetric studies showed that all the polymers were stable up to 400 degrees C with a char yield of about 36% at 900 degrees C in a nitrogen atmosphere. C-13-NMR spectral analysis reveals that bisphenol S-based triads are preferentially formed compared to bisphenol-A triads, indicating greater reactivity of bisphenol S toward dichlorodiphenyl sulfone. The overall activation energy for the thermal decomposition of bisphenol A-based polymer (I) is much higher than that of bisphenol S-based polymer (II). This was attributed to the modification of the backbone of polymer I during the initial cleavage of the C-CH3 bond of the isopropyledene group. Polymer II decomposes by cleavage of the C-SO2 bond.