Abstract
Sterically bulky diarylmethyl-based ligands have received increasing attention in the field of late-transition-metal catalyzed olefin polymerization. Ortho-substituents may have a significant impact on the performance of diarylmethyl-based α-diimine Pd catalysts. In this contribution, a series of α-diimine Pd catalysts bearing ortho-methoxyl/hydroxyl functionalized dibenzhydryl units were prepared, characterized, and investigated in ethylene polymerization and copolymerization with methyl acrylate (MA). The catalytic performances were improved by introducing more ortho-substituents. The catalysts exhibited good thermal stabilities at high temperatures, producing branched polyethylenes. The catalysts bearing hydroxyl groups possessing intramolecular H-bonding, resulted in slightly higher incorporation ratios of MA unit when compared with the catalysts bearing methoxyl groups.
Highlights
Polyolefins have been the world’s largest produced synthetic polymers [1]
Ligands L1 and L2 were synthesized by refluxing 6 with the anilines 2 and 3 in toluene that was catalyzed by p-toluenesulfonic acid (PTSA)
The ligand L3 and L4 were synthesized by heating the mixture of 6 with 4 or 5 in toluene and ethanol (1:1) at 105 ◦ C in the presence of PTSA
Summary
Polyolefins have been the world’s largest produced synthetic polymers [1]. Late-transition-metal catalysts can mediate olefin copolymerization with polar monomers [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21], providing a direct and potentially economic way to access functionalized polyolefins with some improved properties as well as some unique functions [22,23,24,25,26,27,28,29,30,31]. In the 1990s, Brookhart et al reported the studies of α-diimine Pd catalysts for olefin polymerization and copolymerization with polar monomers (Chart 1A) [32,33,34]. These α-diimine Pd catalysts can produce polyolefins with branched even branch-on-branch structures while using ethylene as the only monomer via the “chain-walking” polymerization mechanism [35,36,37,38,39,40], providing a unique approach for modulating the polyolefin microstructures [41].
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