Efficient Modulation of Polyethylene Microstructure by Proper Activation of (α-Diimine)Ni(II) Catalysts: Synthesis of Well-Performing Polyethylene Elastomers

Abstract

The activation of a prototypical nickel(II) Brookhart catalyst by either methylalumoxane (MAO) or diethylaluminum chloride (AlEt2Cl) under a variety of conditions showed that a proper choice of the mode of activation is a powerful tool to modulate the polymer microstructure. In particular, use of AlEt2Cl instead of MAO resulted in the production of more branched polyethylenes with a higher content of long chain branches and even some “branches on branches”. Characterization of these materials by NMR, thermal, X-ray diffraction, and mechanical analyses provided insight into the relationships between the microstructure and the crystallization behavior and the elasticity of the polymers. For these branched polyethylenes, a transition from plastomeric toward elastomeric behavior occurs for branch concentrations much lower than for ethylene–propylene copolymers and like those observed for ethylene copolymers with bulkier comonomers. For elastomeric materials, reduction of branch concentration implies two relev...