Most polymers with cross-linking attributes are studied as non-Newtonian fluids and they often exhibit viscoelasticity. So, one needs at least three parameters to describe their behavior. Eta (regular constant viscosity), E (elasticity), and the third parameter to address the deviation from the Newtonian properties that may have different roles and different physical interpretation depending on the model used to study the behavior of the polymer. I suggest you to go through this, Article Linking the fractional derivative and the Lomnitz creep law ...

Thank you Vicash for your answer

You may need a ubbelohde viscometer to determine the intrinsic viscosity of cross-linked polymers experimentally.