Preparation of linear low-density polyethylene from ethylene by tandem catalysis of iron and titanium non-metallocene catalysts

• A tandem catalytic system consisting of Fe and Ti non-metallocene catalysts.
• In situ copolymerize ethylene to LLDPE with high activity.
• LLDPE with various branches including ethyl, butyl and longer branches.
• The branching degrees can be tuned efficiently from 4.6 to 39.3/1000C.

A non-metallocene titanium complex of β-carbonylenamine derived [O−NS]TiCl3 (2), which can form a tandem catalytic system with difluoro-substituted 2,6-bis(imino)pyridyl iron complex (1), was firstly used as in situ copolymerization catalyst to prepare linear low-density polyethylene (LLDPE) with ethylene as the sole monomer stock and MMAO as the only cocatalyst. During the reaction, 1/MMAO oligomerized ethylene to linear α-olefins with high activity and selectivity, while 2/MMAO copolymerized ethylene with the in situ generated α-olefins to LLDPE with high activity (up to 6 × 106 g/mol Ti h atm). The influences of reaction conditions upon catalytic activity and polymer structures and properties have been researched. The polymers were characterized by differential scanning calorimetry (DSC), high temperature gel permeation chromatography (GPC) and high temperature 13C NMR spectroscopy and proved to be LLDPE with ethyl, butyl as well as longer branches. The branching degrees were tuned efficiently from 4.6 to 39.3/1000C by different reaction conditions such as reaction temperature, Fe/Ti molar ratio and Al/(Fe + Ti) molar ratio. The melting points, degree of crystallinity and molecular weights also changed correspondingly with reaction conditions.

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