In this paper, using a comprehensive study, we have investigated the effect of various polymerization parameters during the synthesis of bimodal polyethylene resins on their rheological and mechanical properties. Bimodal polyethylene resins were synthesized in two subsequent stages in a lab-scale reactor by manipulating a set of parameters such as C 2 /H 2 ratios in the first and second stages, the split value, and the comonomer type. The results showed that the comonomer type and C 2 /H 2 ratio of the second stage of the polymerization are the most critical parameters that control the final resins' slow crack growth resistance properties. On the other hand, the shear-thinning behavior of the resins is mainly controlled by the first-stage polymers. Although the C 2 /H 2 ratio of the first stage results in a moderate effect on the rheological properties of the final resins, its split value governs the flow characteristics of the final molten polymers under high shear rates.

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Due to the many risks of using chlorinated alkylaluminum cocatalysts (CACs), reducing or omitting their amount in methods used for synthesizing Ziegler–Natta catalysts (ZNCs) has always been a dream of polymer chemists. CACs play a crucial role in the chlorination of Mg­(OR)2 supports, which are the most industrially favorable precursors in ZNCs’ recipes. In this article, using a systematic investigation, an initiative approach has been suggested to chlorinate the supports using halocarbons and chlorine-free alkylaluminum cocatalysts (CFACs). It was evidenced that the successive addition of a CFAC and a halocarbon to a suspension of Mg­(OR)2 is a reliable method for chlorine atom exchange between the halocarbon and Mg­(OR)2. Doing so, a highly active ZNC was produced and characterized mainly by inductively coupled plasma, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. In the next step, the catalyst’s performance in monomodal and bimodal copolymerization reactions of ethylene and 1-butene was investigated, and the produced copolymers were fully characterized. The characterizations were carried out using numerous techniques such as rheometric mechanical spectroscopy (RMS), self-nucleation and annealing, differential scanning calorimetry, mechanical tests, and so forth, and their results were compared with a famous ZNC whose support was chlorinated with a CAC. Finally, a possible mechanistic pathway for the reaction between Mg­(OR)2 and halocarbons using CFACs as a chlorine transporter was described. All in all, it was revealed that the new approach could be relied upon as a promising way to chlorinate Mg­(OR)2 supports without using dangerous and corrosive CACs. The produced copolymers using the new formulation had the same physical and mechanical properties as those made by industrial counterparts.