Elastic and viscous properties of linear and long-chain branched ethene/α-olefin copolymers in the terminal regime

Creep and creep recovery measurements of several mLLDPEs were used to investigate the time dependence and to determine both the zero shear-rate viscosity η₀ and the steady-state elastic recovery compliance J_e⁰. The well-known correlation between the zero shear-rate viscosity η₀ and the molar mass M_w was found to be obeyed by all samples containing comonomer contents up to 29 wt.-%, too. This is somewhat surprising, as such a high comonomer content means that more than 25 wt.-% of the molar mass are not in the main chain and thus the number of entanglements should be significantly reduced. For the linear steady-state elastic compliance J_e⁰ an increase with growing molar mass M_w (for constant molar mass distribution) was observed independent of the kind and content of the comonomer. The reasons for this molar mass dependence of J_e⁰ are not clear, as J _e⁰ independent of M_w was found for linear monodisperse polymers, but might be attributed to intrachain phase separation. However, to our knowledge this is one of the first studies so far for polydisperse polyethylenes with constant MMD.