Reentanglement kinetics in sheared polybutadiene solutions

Interrupted shear measurements were used to follow the reentanglement kinetics and associated molecular weight dependence for solutions of near-monodisperse polybutadiene (PB). The time-dependent recovery of the overshoot in the shear stress was measured for PB having weight-average molecular weights (M-w) equal to 61, 90, 107, and 167 kg/mol, corresponding to a range of 17-47 entanglements per chain in solution. The times for recovery of the stress overshoot were 1.5 decades longer (30 times greater) than the corresponding linear viscoelastic relaxation times, the latter determined from dynamic shear data or from stress relaxation following cessation of flow. Notwithstanding the differing time scales, the M-w dependences for entanglement recovery and linear viscoelastic relaxation were equivalent (power law exponent similar to 3.4).