INFLUENCE OF THE COPOLYMER MOLAR-MASS ON THE PHYSICAL GELATION OF TRIBLOCK COPOLYMERS IN A SELECTIVE SOLVENT OF THE MIDDLE BLOCK

The influence of the copolymer molar mass on the thermoreversible gela tion of the triblock copolymer olystyrene-b-poly(ethylene/butylene)-b- polystyrene in a paraffinic oil was studied. The solvent used is selec tive for the middle poly(ethylene/butylene) block of the copolymer. Th e thermal behavior as a function of copolymer concentration was invest igated. The sol-gel transition temperature increased with the copolyme r concentration and molar mass. The mechanical properties of the gels were examined through oscillatory shear and compressive stress relaxat ion measurements. The concentration dependences of the elastic storage modulus were established and were observed to be similar for the thre e copolymers. The relaxation rates observed were extremely high, indic ating a considerable mobility in the gel over the measurement time. Th e relaxation rate decreased as the copolymer molar mass increased. The swelling behavior has also been examined. All gels swelled significan tly The copolymer concentration dependences of the swelling ratio were linear but their ordinates were not close to unity. Whereas the two c opolymer with higher molar mass show a similar swelling behavior, the copolymer with the lowest molar mass shows a swelling capability marke dly smaller.