Synthesis, molecular structure and catalytic performance of heterocycle-fused cyclopentadienyl-amido CGC of Ti (IV) in ethylene (co)polymerization: The formation and precision rheometry of long-chain branched polyethylenes
Long-chain branching is an efficient tool to design and produce polyolefins with enhanced mechanical characteristics, physical properties, and processability. In the synthesis of long-chain branched polyethylene (LCB PE), constrained geometry complexes (CGCs) of Ti (IV) [(η5-C5Me4)SiMe2NtBu]TiX2 (X = Cl, Ti1; X = alkyl) are highly effective at elevated temperatures. However, further development of polyolefin technologies requires new catalytic approaches to provide LCB formation in broad temperature interval. In the present study, a series of CGCs of Ti (IV) of general formula [Cp#SiMe2NtBu]TiCl2 derived from heterocycle-fused cyclopentadienes Cp# (Ti2–Ti5) were synthesized and characterized by NMR spectroscopy and by X-ray diffraction analysis (XRD). New complexes Ti2–Ti5 along with benchmark precatalysts (n-BuC5H4)2ZrCl2 (Zr1) and Ti1 were supported on MMAO-12/silica and investigated in ethylene homopolymerization and ethylene/hex-1-ene copolymerization. In contrast to benchmark complexes Ti1 and Zr1, Ti2–Ti5 catalyzed formation of LCB PEs even at 80 °C, as confirmed by precision rheology studies of ethylene/hex-1-ene copolymers. The complex Ti2, derivative of 5-methyl-5,10-dihydroindeno[1,2-b]indole, demonstrated the best set of properties.