Viscosity of ring polymer melts

We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η to their ring counterparts η at isofrictional conditions is discussed as function of the number of entanglements Z. In the unentangled regime η is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η. In the entanglement regime, the Z-dependence of rings viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1η ~ Z is weaker than the scaling prediction (η ~ Z ) and the simulations (η ~ Z ). Nevertheless, the present collection of state-of-the- art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year old problem.