Research On Rheological Behavior And Phase Behavior Of SIS

SIS block copolymer refers to a triblock copolymer composed of polystyrenepolyisoprene-polystyrene.It is an important thermoplastic elastomer and has attracted wide attention from the industry since its synthesis.In addition to its excellent physical properties,SIS has a molecular backbone consisting of thermodynamically incompatible PS segments and PI segments.The two blocks maintain their physical and chemical properties due to thermodynamic incompatibility,making the rheological behavior and mechanical relaxation of SIS block copolymers complexity,which greatly enriches the research content of rheology.The diverse microphase separation structure of SIS has also attracted the attention of many scholars.Its rheological performance and various viscoelastic parameters strongly depend on the internal structure of the polymer and the form of molecular movement.Therefore,rheological testing methods are commonly used to study the macroscopic properties and phase behavior of SIS triblock copolymers.This paper mainly used rotational rheometer?capillary rheometer?small angle X-ray scattering and SEM to study the phase separation structure ? steady state rheological behavior and dynamic viscoelasticity of three SIS with different soft-hard block ratios and two SIS blend systems.The SAXS was used to characterize the microphase structure of SIS with three different copolymer compositions(hard and hard block ratios).It is proved that with the increase of PS block content in SIS,the phase morphology of the three SISs appears as spherical phase,hexagonal cylindrical phase and lamellar phase in turn.In rheological test,at low temperatures,when the PS phase entanglement point is not destroyed,the higher the PS block content,the greater the degree of entanglement of the polymer melt network.SIS behaves as high shear stress,high shear viscosity,large entrance pressure drop and large capillary pressure drop;At high temperatures,when the PS phase is in a viscous flow state,the PS phase entanglement point is destroyed,the PS block content contributes less to the degree of network entanglement,and the effect of molecular weight on the degree of entanglement increased.It showed that the larger the molecular weight of SIS,the greater the shear stress,the higher the shear viscosity,the greater the entrance pressure drop and the greater the pressure drop in the capillary.Exploring the effect of temperature on the phase structure and rheological behavior of the three SIS showed that the temperature change has no obvious change on the phase structure of the three SIS,but it has a greater impact on the steady-state rheological properties and dynamic viscoelasticity of the SIS.And the higher the PS block content in SIS,the greater the temperature dependence.The investigation results of the instability of extrusion flow of the three SIS show that with the increase of PS block content in SIS,the instability of extrusion flow of polymer melt at low temperature is gradually improved.The root cause of the unstable extrusion flow of L-S-15 and L-S-29 is the sudden change of the state of the interface between the SIS melt and the inner wall of the capillary,which causes pressure fluctuations and surface distortions.Through the study of SIS/SI system,it is confirmed that the existence of SI twosegment components will not only affect the microphase phase state of SIS triblock system but also affect the steady-state rheology and dynamic viscoelasticity.For SIS whose microphase separation structure is a spherical phase,the presence of SI two-block components will destroy the originally regular spherical phase structure.And when the content of SI diblock component reaches 50%,the phase structure of SIS system showed a hexagonal cylindrical phase structure.The SIS/SI systems with different microphase structures have different steady-state rheological behaviors,and this difference has obvious temperature dependence.At 130 oC,with the increase of SI content in the system,the shear viscosity gradually increased;at 170°C,it shows a completely opposite trend.The SI diblock component presented in the SIS/SI system can significantly lower the storage modulus,loss modulus and complex viscosity of the material.In addition,the SI diblock component in the SIS system had a terminal segment that can relax,which brings additional relaxation time to the SIS system.The research on the SIS/PS system confirmed that the blending system can exhibit the tensile hardening.And two cases could promote the occurrence of tensile hardening earlier and more violently:(1)The content of PS blocks in the SIS matrix increased;(2)The added amount of PS homopolymer increased.