“Two-in-One” catalysis of broad/bimodal molecular-weight-distribution polypropylene by a combination of Ziegler–Natta and metallocene catalysts
•A metallocene was integrated into a Ziegler–Natta catalyst for polypropylene (PP).•The modified catalyst was best activated by TIBA (not TEA) in conjunction with MAO.•The modified catalyst led to broad/bimodal molecular-weight-distribution PP.
A strategy for combining Ziegler–Natta and metallocene catalysis to synthesize broad/bimodal molecular-weight-distribution polypropylene (PP) is proposed. The chemistry is centered on a fabrication as well as utilization of a modified MgCl2/TiCl4 Ziegler–Natta catalyst with incorporated C2-symmetric ansa-metallocene catalyst capable of promoting isospecific propylene polymerization. A MgCl2/TiCl4 catalyst is prepared in the presence of a 1,3-diether internal electron donor, 9,9-bis(methoxymethyl)fluorene (BMMF), which, with a porous physical architecture, is able to accommodate MAO-encapsulated and protected rac-[methylene(3-tert-butyl-1-indenyl)2]ZrCl2 (rac-CH2(3-t-Bu-1-Ind)2ZrCl2) without impairing its own composition and structure. Activation of the two-piece catalyst is found to be best conducted by pairing triisobutylaluminium (TIBA) instead of triethylaluminium (TEA) with MAO. Polymerization of propylene with TIBA-MAO-activated modified MgCl2/TiCl4 catalyst containing rac-CH2(3-t-Bu-1-Ind)2ZrCl2 produces broad/bimodal molecular-weight-distribution PP with tunable compositions. Moreover, reactor particles of PP thus produced are ensured with good granular morphology, which is crucial for application in modern PP industry with dominant bulk and gas polymerization processes.
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Journal: Applied Catalysis A: General - Volume 484, 22 August 2014, Pages 142–147