Molecular Weight Dependence of Zero-Shear Viscosity of Block Copolymers in the Disordered State

The molecular weight dependence of zero-shear viscosity (η0) of polystyrene-block-polyisoprene (SI diblock) copolymer in the disordered state was investigated. For the investigation, a series of lamella-forming, nearly monodisperse SI diblock copolymers were synthesized via sequential anionic polymerization, and order−disorder transition temperatures (TODT) of the block copolymers were determined from isochronal dynamic temperature sweep experiments at an angular frequency (ω) of 0.01 rad/s and also from dynamic frequency sweep experiments over a wide range of temperatures. The η0 of the SI diblock copolymers in the disordered state (at T > TODT) was determined from η0,r = limω→0[| (ω)|], for which logarithmic plots of reduced complex viscosity | (ω)| vs aTω with aT being temperature-dependent shift factor were first prepared, where | (ω)| is defined by | (ω)| = |η*(ω)|(Trρr/Tρ)/aTin which |η*(ω)| is the complex viscosity at ω, T is the measurement temperature, Tr is a reference temperature defined by Tr ...