Preparation of linear low-density polyethylene by the in situ copolymerization of ethylene with an iron oligomerization catalyst and rac-ethylene bis(indenyl) zirconium (IV) dichloride

An iron oligomerization catalyst, [(2-ArN=C(Me))₂C ₅H₃N]FeCl₂ [Ar = 2,6-C₆H ₃(F)₂], was combined with rac-ethylene bis(indenyl)zirconium (IV) dichloride [rac-Et(Ind)₂ZrCl₂] to prepare linear low-density polyethylene (LLDPE) by the in situ copolymerization of ethylene. A series of LLDPEs with different properties were prepared by the alteration of the reaction temperature, Fe/Zr molar ratio, Al(Fe + Zr) molar ratio, and reaction time. The structures of the polymers were characterized with differential scanning calorimetry, ¹³C NMR, gel permeation chromatography (GPC), and so forth. The melting points, crystallizations, and densities of the resulting products increased, and the average branching degree decreased, as the reaction temperature, Al/(Fe + Zr) ratio, and reaction time increased. The melting points, crystallizations, and densities of the polymers decreased, and the average branching degree increased, when the Fe/Zr ratio increased. The ¹³C NMR and GPC results showed that there were no unreacted α-olefins remaining in the resulting polymers because the percentage of low-molar-mass sections (C₄-C ₁₀) of the oligomers obtained with this catalyst was very high (>70%). In addition, the formation of polymers with two melting points under different reaction conditions was examined in detail, and the results indicated that the two melting points of the polymers could be attributed to polyethylene with different branches.