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Four random, differently ended (À ÀCl, À ÀNH 2 , À ÀOH, and À ÀCOO 2 ), polyethersulfone/polyetherethersulfone (PES/ PEES) copolymers were studied to investigate the influence of chain ends on thermal and rheological behaviors. The number average molar mass (M n % 9500 gÁmol 21 ) and the PES/PEES ratio (40/60) of all copolymers investigated were checked by 1 H NMR spectra. Thermal degradations were carried out in the scanning mode and initial decomposition temperatures (T i ) and activation energy values of degradation (E a ) were obtained. Glass transition temperature (T g ) was determined by differential scanning calorimetry and complex viscosity (g*) by rheological measurements in isothermal heating conditions (T ¼ 2708C). All parameters determined were largely affected by copolymer chain ends and decreased according to the same order, À ÀOH > À ÀNH 2 > À ÀCl > À ÀCOO 2 . The results were discussed and interpreted.

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