Polyblends of Poly(Styrene-b-Butadiene-b-Styrene) and Polystyrene. I. Mechanical Properties.
CALIFORNIA UNIV BERKELEY DEPT OF CHEMICAL ENGINEERING
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Kraton 1101, a styrene-butadiene-styrene triblock copolymer SBS, was blended with homopolymers of styrene PS of various molecular weights by dissolving in mutual solvents. All polyblends cast from mixed solvents of tetrahydrofuran and methyl ethyl ketone were found to be plastic-like. Stress-strain curves of these materials all exhibited a yield point, and a flat drawing region. Samples can be stretched beyond 500 strain without fracture. Blends containing high amounts of added PS 40 showed stress-whitening effects. Most samples undergo necking when strained beyond the yield point. However, the necked regions are rubbery and exhibit high elasticity rather than irreversible drawing. Dynamic mechanical data of stretched and unstretched polyblends show that the former have enhanced loss tangent region between the primary glass transition loss peaks of styrene and butadiene blocks. The increased loss tangent is due to the decreased storage modulus values of the stretched samples, while the loss moduli remained unchanged. Stress-strain data of gradient layered polyblends are also presented.
- Elastomers and Rubber