Viscoelastic Properties of Styrene-Butadiene Block Copolymers at Elevated Temperatures

摘要

Dynamic viscoelastic properties of styrene-butadiene block copolymers having different molecular weights and compositions were measured at elevated temperatures. The Phase structure formed in the copolymers is broken by shear flow at high rates. For the samples having molecular weights lower than 105, the broken phase structure recovers completely after heat treatment at 160°C for 1 hr, while for the samples having molecular weights higher than 2.5×105, the recovery of the broken structure is very difficult. Frequency dependence curves of the storage shear modulus, relaxation spectrum, entanglement modulus, and characteristic time for entanglement relaxation are discussed in relation to molecular factors such as the molecular weight and composition of the component blocks in the copolymers. The experimental results are also compared with theological properties of styrene and butadiene homopolymers. It is suggested that the dynamic measurement is very useful for the investigation of phase structure formed in block copolymers.