Thermoreversible Gelation of Polystyrene−b-Poly(ethylene/butylene)−b-Polystyrene Triblock Copolymers in N-Octane

The thermoreversible gelation of three triblock copolymers polystyrene−b-poly(ethylene/butylene)−b-polystyrene, with different molar masses 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 copolymer on the sol−gel transition and on the mechanical properties of the gels was analyzed. The sol−gel transition temperature increased with the copolymer concentration and the copolymer molar mass. The mechanical properties of the different gels were examined through oscillatory shear and compressive stress relaxation measurements. The concentration dependence of the elastic storage modulus was established with an exponent close to that expected for systems in good solvents (2.25) that possess a structure similar to that of chemical networks. The experimental data of the three copolymers fit a sole straight line in a double-logarithmic scale. The relaxation rates observed were high for the copolymers with lower molar masses, indicating a considerable mobility in the gel over the measurement time. The relaxation rate decreased as the copolymer molar mass increased. Some of the copolymer gels examined exhibited some elasticity, allowing reversible deformation. The degree of elastic response of SEBS gels increased the higher the gelation temperature of the gel was, that is, the longer the lifetime of the gel junctions was.