Uniaxial Elongational Viscosity of Poly (Styrene-Block-Butadiene-Block-Styrene) Melts

Abstract

Experimental studies about the effect of block copolymerized structures on the uniaxial elongational viscosity were performed. Two poly (styrene-block-butadiene-block-styrene) (SBS, S/B weight ratio=4/6) samples with linear and star (4arms) structures were used for the elongational viscosity measurement at constant strain rates. The block copolymer samples exhibited the strain-softening elongational viscosity. This property was in contrast to the strain-hardening elongational viscosity which is observed for homopolymer melts. The cause of the strain-softening property was analyzed from the structural change by small angle X-ray (SAX) and transmission electron microscope (TEM). The lamellar structures were more oriented and became longer along the elongational direction e elongation, while the lamellar thickness remained almost constant. he obsrvation inicates that the laellar structures, instead of the SBS molecules, were oriented and stretched. The rheological discussion on the strain-softening elongational viscosity was also carried out by the BKZ model. The damping functions of the block copolymers from step-shear relaxation experiments showed larger decrease than that of the Doi-Edwards prediction. The structural change observation and the BKZ analysis suggested that the largely decreased damping functions are due to the lamellar orientation and cause the strain-softening elongational property.

Shape Memory Polyurethane with Porous Architectures for Potential Applications in Intracranial Aneurysm Treatment

“…Vernon and Vernon published the first thermally-induced SMP in 1941, demonstrating that a dental material made of methacrylic acid ester resin possessed good elastic memory and was able to recover to its original shape after enough heat was applied [15]. By now, thermally-induced SMPs include polyurethanes [8,16], polyetheresters [17,18], polynorbornene [1,19], and poly(styrene-block-butadiene) [20,21]. Nanoparticles, such as carbon nanotubes and graphene oxide, have been dispersed within SMPs to fabricate shape memory nanocomposites for biomedical applications [22,23,24].…”