Viscoelastic behavior of styrene-butadiene styrene block copolymers in temperature range of glass rubber transition of styrene block

Dynamic mechanical measurements were performed with styrene-butadiene-styrene (SBS) block copolymers, Kraton D-1101 and D-1102. Isochronal data were obtained from -130 to 85 degrees C in the tensile mode at 1 Hz and from 60 to 160 degrees C in the shear mode at 1 rad/s. The isothermal measurements were also performed at 60, 90, 120, 140, and 160 degrees C in the frequency range of 0.0316 to 100 rad/s. The results suggest that the two polymers have different morphologies although the styrene content and the diblock content are about the same for both polymers. Kraton D-1101, which has 1.5 times higher molecular weight, has 3-5 times higher rubbery modulus, compared to D-1102. The lower molecular weight polymer, D-1102, appears to have a larger amount of the mixed phase at the boundary. This is suggest by the lower temperature of the ''domain disruption'', T-dd and the higher magnitude of tan delta at T-dd. This explains the difference in the rubbery moduli of the two polymers.