Viscoelastic relaxation of styrene–butadiene–styrene block copolymers with different topological structures

Abstract

The viscoelastic relaxation of linear styrenebutadiene-styrene triblock copolymer (l-SBS) and star styrene-butadiene-styrene triblock copolymer (s-SBS) with four arms were investigated with differential scanning calorimetry and dynamic rheological measurements. Three characteristic viscoelastic responses of l-SBS and s-SBS in the plot of the loss tangent (tan d) and temperature at different frequencies (x's), which corresponded to the relaxation of the polybutadiene (PB) block (peak I), the glass transition of the polystyrene (PS) phase (peak II), and the mutual diffusion between the PB blocks and PS blocks (peak III), respectively, were observed in the experimental range. Although x was 0.1 rad/s, a noticeable peak III was gained for both l-SBS and s-SBS. The dynamic storage modulus (G 0 ) of l-SBS showed two distinct types of behavior, depending on the temperature. At temperature (T) < T 2 (where T 2 is the temperature corresponding to peak II), G 0 of l-SBS displayed a very weak x dependency. In contrast, at T > T 2 , G 0 decayed much more rapidly. However, G 0 of s-SBS displayed a very weak x dependency at both T < T 2 and T > T 2 . Only near T 2 did s-SBS decay with x a little sharply. These indicated, in contrast to l-SBS, that s-SBS still exhibited more elasticity even at T > T 2 because of its crosslinking point between the PB blocks (the star structure). In the lower x range, l-SBS exhibited a stronger peak III than s-SBS despite the same styrene content for l-SBS and s-SBS. The high tan d value of peak III for l-SBS was considered to be related to the internal friction among the PB blocks or the whole l-SBS chain, not the PS blocks.

Interfacially modified LDPE/GTR composites with non-polar elastomers: From microstructure to macro-behavior

“…It is also evident that incorporation of SBS copolymer (Kraton ® ) in LDPE/GTR composites has shifted the maximum of E 00 towards higher temperatures, which suggests enhancement of interfacial interactions between LDPE and GTR caused by compatibilization. Moreover, LDPE/GTR composites modified with Kraton ® showed second a E 00 maximum when temperature changed from À100 to À60 C, which corresponds to the glass transition temperature of butadiene segments (T g equals À90 C) [29,30]. This temperature was shifted towards higher temperatures in LDPE/GTR/Kraton ® composites, which suggests partial miscibility of butadiene segments with LDPE and GTR.…”

Morphology and microphase separation of star copolymers

“…Yu and coworkers prepared linear PS‐ b ‐PB‐ b ‐PS triblock copolymer and (PB‐ b ‐PS) 4 with the same weight fraction of PS (40 wt %). Figure presents the TEM images of linear and (PB‐ b ‐PS) 4 .…”

Mechanical vs. electrical hysteresis of carbon nanotube/styrene–butadiene–styrene composites and their influence in the electromechanical response

“…Due to the nature of soft and hard domains of SBS composition which show very distinct mechanical properties, the polybutadiene (PB) chains always orienting upon mechanical deformation stronger than the polystyrene (PS) chains, essentially due lower the initial modulus of the soft phase [15]. The block structures of PB and PS domains depend on the different block structure which ranges approximately between 10 and 25 nm [15,16]. The SBS as a matrix for electromechanical sensors, shows higher piezoresistive sensibility than others TPEs [17].…”