A NOVEL MECHANICAL DISPERSION AND MOLECULAR ORDERING IN STYRENE BUTADIENE STYRENE TRIBLOCK COPOLYMER FILMS

The dynamic mechanical properties were measured for styrene-butadiene-styrene triblock copolymer (SBS) films cast from solution in tetrahydrofuran containing 10% methyl ethyl ketone by volume. On the tan delta-T plots, a novel dispersion was observed around 65-degrees-C. The dispersion became bigger by physical aging, and it disappeared by heat-treating at 60-degrees-C. The similar dispersion was also observed on the films cast from cyclohexane solution. To investigate the origin of the dispersion, the ultrasonic velocity and attenuation coefficient, density, and DSC were measured for as-cast, aged, and heat-treated films. It was suggested that the dispersion can be ascribed to the molecular ordering formed in polystyrene molecules under nonequilibrium circumstances.