Rheological properties of polymers such as non-Newtonian viscosity and non-zero normal stress differences during the shear flow of polymeric liquids were interpreted from the point of view of the free volume theory. It was shown that the shear viscosity variations result from the changes of the total free volume, while the normal stress differences stem from the anisotropy of the free volume distribution in a polymer liquid subjected to the shearing flow. Theoretical predictions were compared

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... th literature data for PE-LD melt (known as IUPAC melt A) and polyisobutylene (PIB) solution in 2,6,10,14-tetramethylpentadecane (NIST standard reference material). Good agreement between theory and the experiment was found.