Viscoelastic relaxation and phase morphology of linear styrene-butadiene-styrene triblock copolymer

Phase behavior and viscoelastic relaxation of styrene-butadiene-styrene triblock copolymer(SBS) were investigated. Through the TEM observation, it can be found that there exist cocontinuous phases in the SBS and the dimension of each phase can be confirmed. The DSC test reveals that the heating history that samples exposed to have a significant effect on SBS phase structure, especially for PS phase with a small mass proportion in SBS. There is an order-disorder transition with temperature increasing, and the transition temperature is considered to be related to the size of PS domain. The dynamic rheological measurements were conducted to evaluate the viscoelastic relaxation behavior of SBS triblock copolymer at different temperatures. Three relaxation peaks appearing on the temperature dispersion curve of dynamic loss tangent at different frequencies is attributed to the relaxation of various motorial unit of SBS. Differing from PS homopolymer, with the increase of temperature, SBS still presents a high elastic modulus because of the interaction between PS and PB phases, and the entanglement of PB chains. Furthermore, an obvious peak as shown in the dynamic frequency sweep curves is involved in the order-disorder transition when the temperature is beyond 98 degrees C.