Polymer rheology: Influence of molecular weight and polydispersity

Literature data on the non‐Newtonian flow of bulk polymer and of polymer solutions are correlated on the basis of a four‐parameter equation, η = η ∞ + (η 0 − η ∞ )/[1 + (τ D ) m ], η being the viscosity at shear rate D , and η 0 and η ∞ limiting values at D = 0 and D = ∞, respectively. The parameters η 0 , η ∞ , and τ all show dependence on molecular weight, and in general there is good correlation between τ and η 0 . There is evidence that τ is related to a molecular weight higher than the weight‐average. The exponent m shows dependence on molecular weight distribution and approaches an upper limit of unity for a monodisperse linear polymer. For linear unblended polymers it may be expressed empirically by m = ( M̄ n / M̄ w ) 1/5 .