Dynamic Mechanical Properties of Block Copolymer Blends–A Study of the Effects of Terminal Chains in Elastomeric Materials I. Torsion Pendulum Measurements

Blends of well characterized polystyrene-polybutadiene (SB) diblock copolymers and polybutadiene continuous SBS triblocks provide network systems with controlled amounts of terminal chains of known molecular weight. Three different SB diblocks were blended in various amounts with a single SBS triblock. The mechanical properties of these materials were studied in free oscillation at about 0.2 Hz over a temperature range from – 150°C to 100°C. The terminal chains act as an internal plasticizer lowering the storage modulus in the intertransition region. If their molecular weight is sufficiently large, a second, broad maximum appears in the loss modulus curve. Thus, the terminal chains can contribute to secondary loss mechanisms. The appearance of the polybutadiene transition region is unaffected by the amount of terminal chains.