Evaluation of relaxation spectra of linear, short, and long-chain branched polyethylenes

The frequency dependent rheological data of several different linear, short- and long-chain branched metallocene catalyzed polyethylenes are assessed with respect to the relaxation spectra. For linear mLLDPEs with M_w/M_n≈ 2, a "master spectrum" is established by normalizing on the molar mass. For samples with a distinctly different molar mass distribution, deviations from the "master spectrum" can be observed. It is also demonstrated how the long-chain branches in polyethylenes of different structure influence the spectrum. Depending on the length of branches in long chain branched materials, it is shown that an increasing in the degree of long-chain branching can be clearly observed in the slow relaxation modes, while the fast ones are only affected by high degrees of long-chain branching.