Kinetic Features of Hexene-1 Polymerization over Supported Titanium-Magnesium Catalyst

Heterogeneity of Active Sites in the Polymer Chain Transfer Reactions at Olefin Polymerization over Multisite Supported Ziegler-Natta Catalysts

In this review, we summarize and discuss our experimental data published in a number of papers on the transfer reactions of polymer chains in the polymerization of ethylene, propylene, and hexene-1, and the copolymerization of ethylene with α-olefins over multisite supported titanium-magnesium catalysts (TMC). Three groups of transfer reactions are discussed in the review: (1) transfer reactions with AlEt3 cocatalyst, (2) transfer reactions with hydrogen, and (3) transfer reactions with participation of α-olefins in the case of ethylene copolymerization with α-olefins. We have found polymerization conditions where it is possible to observe heterogeneity of active sites of TMC for all three groups of the indicated reactions. It is shown that (1) the transfer reaction with AlEt3 proceeds with higher reactivity on the active sites that produce polymers with low molecular weight; (2) the transfer reaction with hydrogen, in the case of α-olefin polymerization and copolymerization of ethylene with α-olefins, proceeds with higher reactivity on the active sites which produce polymers with high molecular weight; (3) the transfer reaction with α-olefins proceed with higher reactivity on the active sites that produce high molecular weight polymers.

Tandem Synthesis of Ultra-High Molecular Weight Drag Reducing Poly-α-Olefins for Low-Temperature Pipeline Transportation

Ultra-high molecular weight poly-α-olefins are widely used as drag reducing agents (DRAs) for pipeline transportation of oil and refined petroleum products. The synthesis of polyolefin DRAs is based on low-temperature Ziegler-Natta (ZN) polymerization of higher α-olefins. 1-Hexene based DRAs, the most effective at room temperature, typically lose DR activity at low temperatures. The use of 1-hexene copolymers with C8-C12 linear α-olefins appears to offer a solution to the problem of low-temperature drag reducing. The present work aims to develop two-stage synthesis of polyolefin DRAs that is based on selective oligomerization of ethylene in the presence of efficient chromium/aminodiphosphine catalysts (Cr-PNP), followed by polymerization of the olefin mixtures, formed at oligomerization stage, using efficient titanium-magnesium ZN catalyst. We have shown that oligomerization of ethylene in α-olefin reaction media proceeds faster than in saturated hydrocarbons, providing the formation of 1-hexene, 1-octene, and branched C10 and C12 olefins; the composition and the ratio of the reaction products depended on the nature of PNP ligand. Oligomerizates were used in ZN polymerization 'as is', without additional treatment. Due to branched character of C10+ hydrocarbons, formed during oligomerization of ethylene, resulting polyolefins demonstrate higher low-temperature DR efficiency at low polymer concentrations (~1 ppm) in comparison with benchmark polymers prepared from the mixtures of linear α-olefins and from pure 1-hexene. We assume that faster solubility and more efficient solvation of the polyolefins, prepared using 'tandem' ethylene-based process, represent an advantage of these type polymers over conventional poly(1-hexene) and linear α-olefin-based polymers when used as 'winter' DRAs.

Study on the synthesis of hexene-1 catalyzed by Ziegler-Natta catalyst and polyhexene-1 applications

This paper presents the synthesis of two aminosilane-based external donors for the Ziegler-Natta catalysis: di(piperidyl) dimethoxysilane (DPPDMS) and dipyrrolyldimethoxysilane (DPRDMS). We compared the electron donation by these two compounds in the MgCl2- supported Ziegler-Natta catalysis of the polymerization of hexene-1 into a polyhexene-1 (PHe) elastomer with that of the common donor cyclohexylmethyldimethoxysilane (CHMMS). The catalytic activity of the system and isotacticity of the polymer (PHe) product improved significantly because of the considerable steric hindrance and strong electronic effects of these aminosilane-based external donors. The effects of different external donors on the catalytic efficiency, polymer isotacticity, molecular weight and molecular weight distribution of the PHe products were investigated. Under the best reaction conditions, the catalyst activity, polymer molecular weight, and glass-transition temperature were determined as 899 g/g Cat·h-1, MW = 252,300 g/mol, and -41.39°C, respectively. The PHe was characterized by FTIR and NMR. This report also describes blending of PHe and low density polyethylene that leads to a significant increase in the impact strength and elongation at breaks.