Front Cover: Due to effective shielding of two axial sites around the nickel center, higher activity of o‐benzhydryl di‐substituent pyridine‐imine nickel catalysts and higher Mv of LDPE are obtained. As the catalyst structure reveal a significant effect on the catalyst activity and polymer properties. Further details can be found in the article by Mohsen Mogheiseh, Gholam Hossein Zohuri, and Mostafa Khoshsefat in article number https://doi.org/10.1002/mren.201800006.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/mren.201800006. Pyridine-Imine CatalystA series of pyridine-imine [N-N] ligands are efficiently prepared through the condensation reaction of ketone/aldehyde precursor and synthesized aniline. The ligands (L n , n = 1-4) and corresponding nickel complexes (C n , n = 1-4) are characterized and used for polymerization of ethylene in the presence of modified methylaluminoxane as cocatalyst. The produced low density polyethylenes show at least 21 branches per 1000 carbon atoms with M v values up to 80.0 × 10 4 . Aldimino-based catalyst is more active than the analogue catalyst, although, ketimines result in polyethylene with higher M v . Nevertheless, the product of aldimino-based catalyst indicates the highest melting point of 132.3 °C but ketimine exhibits the highest crystallinity of 32.98% at the same polymerization conditions. Specific morphologies including smooth spherical and irregular porous particles are observed for some polymer samples. However, at high polymerization temperatures and different monomer pressures, different morphologies as well as two melting point peaks are observed in scanning electron microscopy (SEM) images and differential scanning calori meter thermograms, respectively.

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In the presence of modified methylaluminoxane as cocatalyst, the behavior of a binary catalytic system based on pyridineimine nickel (N) and iron (F) catalysts was evaluated in order to reach a proper mixture of polyethylene (PE). A computational study along with kinetic profile suggested that the catalyst F with higher electron affinity (A) and electrophilicity (ω) in the methyl cationic active center and stronger interaction with the monomer led to high integrated monomer consumption and higher activity. In addition, the samples produced by the mixture of catalysts showed a higher value of M v [19.4 × 10 4 g (PE) mol (Fe+Ni) −1 h −1 )], melting point (127.8 C), and crystallinity extent (41.29%) than the samples produced by the single catalysts. The addition of multiwalled carbon nanotubes (MWCNT) into the polymerization media reduced the activity of catalysts [from 7.50 × 10 4 to 0.66 × 10 4 g (PE) mol (Fe+Ni) −1 h −1 ] and the thermal properties of the low-density polyethylene nanocomposite samples. However, the sample containing 2.33% MWCNT 20-30 improved the total thermal stability of the neat polyethylene blend up to 400 C. Scanning electron microscope images of the samples demonstrated irregular to virtually uniform morphologies were obtained through the in situ and solution-mixing techniques.

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