Viscoelastic Properties of Entangled Polymers. III. The Transient Network Model.

Abstract : The viscoelastic behavior of entangled polymers is modeled by a three dimensional transient network where the entangled points are considered to act as temporary crosslinks. Polymer chains are represented by beads and springs. The effect of entanglements on chain dynamic are introduced by assigning enhanced frictional coefficients to selected beads, and extra elastic couplings between pairs of the entangled beads. The formation and disengagement of the entanglements can be envisioned to be in a dynamic equilibrium. The strength of elastic coupling is set to decrease with increasing the distance between the entangled points. The resulting modified Rouse-Bueche-Zimm matrix is solved for the relaxation times from which the dynamic moduli, relaxation moduli, steady-state shear compliance, and zero-shear viscosity are computed. Results are in excellent agreement with experimental data on monodisperse polystyrene, poly-alpha-methylstyrene, polyvinyl acetate and polybutadiene. (Author)