Triblock copolymers containing polysulfone, poly(alkylene oxide), and poly(dimethylsiloxane) segments were obtained by addition of preformed a,x-bis(hydrogensilyl) poly(dimethylsiloxane) oligomers to alyl end-capped poly(alkylene oxide)-bpolysulfone. Viscometric and UV absorption measurements were carried out in dilute 1,2-dichlorethane solutions, in the temperature range of 20-758C. The specific interactions exhibited by the block copolymers in a selective solvent are influenced by the copolymer composition and temperature. The results point to a conformational transition phenomenon, located around 558C, which is attributed to the transition from a segregated to a pseudo-Gaussian conformation through a compressed-segregated conformation. POLYM. ENG. SCI.,