All else being equal,broadening the molecular-weight distribution generally results in a polymer melt becoming non-Newtonian at lower values of shear rate,so by the time we come to those shear rates relevant to extruding etc.,the polymer is easier to handle with a lower viscosity. A small degree of branching of the polymer chains generally decreases the viscosity of a melt with the same average molecular weight since the branched chain is more compact.However,if the branching is extensive,for a reasonably high molecular weight (-10)the viscosity at low shear rates may be much higher,giv the difficulties for these cor 之netran rtheless,in almost all cases esults in a lower viscosity at h igh shear r rates. Polymer Solutions Solution Viscosity depends on same factors as polymer melts Viscosity also effect by concentration and solvent interaction effects ox 20 10 3.5 10 2 1 0.35 10) 103 10 103103 10 Shear rate,/s The flow curve for 3%w/w polystyrene in toluene, for different molecular weights(shown in millions) 33 Polymer Solutions Viscosity also effect by concentration and solvent interaction effects Solution Viscosity depends on same factors as polymer melts