Rheological characteristics of melts of low-molecular-weight branched polyethylene in the region of critical molecular weights

The viscosity and the first difference of the normal stresses have been measured at stationary shear rates from 5.68 to 4500 sec−1 for melts of low-density polyethylenes obtained by thermal degradation of commercial polyethylene in a nitrogen atmosphere. In addition, the complex modulus has been measured on the angular frequency range from 0.396 to 198.5 sec−1. Three regions of molecular weights differing with respect to the value of the exponent in the relation η0 = kMα have been established. At\(\bar M\)>\(\bar M_c \) normal stresses are observed in the region of shear rates corresponding to a linear dependence of the shear rate on the shear stresses.