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-poly(ethylene/butylene)-b-polystyrene, with different molar mass and a similar chemical composition, in n-octane was studied. The solvent is selective for the middle poly(ethylene/butylene) block of the copolymers. The influence of the molar mass of the three copolymers on the gelation and on the mechanical properties of the gels was analysed. The sol-gel transition temperatures, T-gel, have been determined and they increase with the copolymer concentration and the copolymer molar mass. On the other hand, the mechanical properties of the different gets were examined through oscillatory shear and compressive stress relaxation measurements. The concentration dependence of the elastic storage modulus, G' for the three copolymer studied fit a sole 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 is near to the sol-gel transition temperature, the elastic modulus are smaller and the relaxation rates, are higher.