Study of the mechanical behavior of thermoreversible gels of PS-b-poly(ethylene/butylene)-b-PS triblock copolymers in a selective solvent for the middle block of the copolymer

The thermoreversible gelation of three triblock copolymers polystyrene-b-po ly(ethylene/butylene)-b-polystyrene, with different molar mass and a simila r chemical composition, in n-octane was studied. The solvent is selective f or the middle poly(ethylene/butylene) block of the copolymers. The influenc e of the molar mass of the three copolymers on the gelation and on the mech anical properties of the gels was analysed. The sol-gel transition temperat ures, T-gel, have been determined and they increase with the copolymer conc entration and the copolymer molar mass. On the other hand, the mechanical p roperties of the different gets were examined through oscillatory shear and compressive stress relaxation measurements. The concentration dependence o f the elastic storage modulus, G' for the three copolymer studied fit a sol e straight line in a double-logarithmic scale and its slope (2.22) is close tu that expected for systems in good solvents (2.25). AS the temperature i s near to the sol-gel transition temperature, the elastic modulus are small er and the relaxation rates, are higher.