Long-Chain Branched Polyethylene via Coordinative Tandem Insertion and Chain-Transfer Polymerization Using rac-{EBTHI}ZrCl2/MAO/Al–alkenyl Combinations: An Experimental and Theoretical Study

• DOI: 10.1021/acs.macromol.0c01671
• Publication Date: 2020-10-08T17:08:32Z
• Authors: Orlando Santoro; Lorenzo Piola; Karl Mc Cabe; Olivier Lhost; Katty Den Dauw; Aurélien Vantomme; Alexandre Welle; Laurent Maron; Jean-François Car...; Evgueni Kirillov
• Keywords: Cationic polymerization; Chain transfer; Branching (polymer chemistry)

In situ synthesis of topologically modified linear polyethylenes (PE) using single-site polymerization catalysis is a challenging task, but it can enable the production valuable advanced polymer materials with tailored properties. Described herein an investigation aimed at efficient generation long-chain branches (LCB) in PEs Al–alkenyl species, namely, iBuAl(oct-7-en-1-yl)2 (Al-1), combination homogeneous rac-{EBTHI}ZrCl2 (Zr-1)/MAO or heterogeneous MAO on silica-supported-rac-{EBTHI}ZrCl2 (supp-Zr-1)/TIBAL catalytic systems. As corroborated by extensive rheological studies and 13C NMR spectroscopy, reagent was found to be quite formation LCB, via mechanistic pathway involving both insertion transmetallation reactions. Formation LCB has been rationalized density functional theory (DFT) computations carried out putative [rac-{EBTHI}Zr-R]+ (R = Me, nPr, pentyl) cationic species including solvent model. Of three possible isomers Al/Zr heterobimetallic complexes derived from Al-1, only one identified, kinetic thermodynamic grounds, as key intermediate. The DFT study also unveiled that (i) ethylene into Zr–alkyl bond growing PE chain accompanied reversible decoordination Al-vinyl transfer agent (AVTA), (ii) vinyl 1,2-coordination/insertion alkenyl moieties Al-1 bond, resulting branching, direct competition ethylene, (iii) recoordination AVTA after either step thermodynamically favored mostly responsible for phenomenon.