Tailoring Polyethylene Characteristics Using a Combination of Nickelα-Diimine and Zirconocene Catalysts under Reactor Blending Conditions

Abstract

Ethylene was polymerized using a combination of Ni(α-diimine)Cl2 (1) (α-diimine = 1,4-bis(2,6-diisopropylphenyl)acenaphthenediimine) and rac-ethylenebis(IndH4)ZrCl2 (2) (IndH4 = 4,5,6,7-tetrahydro-1-η5-indenyl) compounds, activated with methylaluminoxane in toluene. The polymerizations were performed at three different temperatures (0, 30, and 50°C), and the effect of varying the zirconium loading molar fraction (xZr) was monitored. The polymerization runs carried out at 0 and 50°C show that the productivity increases linearly with xZr. On the other hand, at 30°C the productivity reaches a maximum of 8.19×103 kg of PE/mol[M]·h for xZr = 0.67, indicating a non-linear correlation between the productivity and xZr. The polyethylene characteristics have been evaluated by means of differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and scanning electron microscopy (SEM). The PE produced at 0 and 30°C showed monomodal molecular weight distributions with narrow polydispersities. At higher temperature (50°C), using xZr = 0.10, two different polyethylenes were produced; an amorphous rubbery PE with M̄w of 83×103 g·mol–1 and a linear high density PE with M̄w of 284×103 g·mol–1. DSC thermograms of the PE obtained at 0°C (xZr = 0.25–0.50) showed the presence of two melting points corresponding to branched and linear PE, indicating a low compatibility between the phases. By SEM it was observed that the branched polyethylene obtained at 0°C forms very small aggregates dispersed in the linear polyethylene matrix, but the polymer obtained at 30°C forms larger particles which show low compatibility with the linear polyethylene.