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<p>Nine novel non-metallocene titanium-based catalysts (Z1–Z9) were synthesized and evaluated for ethylene polymerization to produce polyethylene wax (PE-WAX). The polymerization conditions were systematically optimized, and the structure–activity relationships of the catalysts were elucidated. Structural differences among the catalysts significantly influenced their performance: alkoxy catalysts (Z1–Z3), featuring aliphatic ligands, exhibited lower activity compared to aryloxy catalysts (Z4–Z9) with aromatic ligands. Specifically, ortho-substituted aryloxy catalysts Z7 and Z9 demonstrated the highest activity due to optimized steric and electronic effects from their substituent positions. A clear correlation was observed between polymer molecular weight and catalyst burial volume (V<sub>Bur</sub>), where larger V<sub>Bur</sub> values hindered ethylene monomer insertion, promoting chain transfer and resulting in shorter polymer chains. With the highest-activity Z7 catalyst, density functional theory calculations clarified the active center morphology, identifying two distinct Ti-alkyl intermediates existing stably simultaneously. Based on these findings, a mechanistic model for the formation of PE-WAX was proposed, wherein the synergistic effect of dual active centers lowered the chain-transfer energy barrier, enhanced catalytic activity, and allowed the controlled synthesis of low-molecular-weight PE-WAX with high crystallinity and a narrow molecular weight distribution.</p>

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Novel non-metallocene titanium catalysts for controlled synthesis of polyethylene wax: combined experimental and density functional theory studies

  • 期刊论文

  • 发表日期：

    2025年9月3日

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  • Xiao Gui,
  • Qishun Guo,
  • Shijia Wang,
  • Xinpeng Xing,
  • Wei Liu,
  • Tao Jiang,
  • Bing Yan

摘要

Nine novel non-metallocene titanium-based catalysts (Z1–Z9) were synthesized and evaluated for ethylene polymerization to produce polyethylene wax (PE-WAX). The polymerization conditions were systematically optimized, and the structure–activity relationships of the catalysts were elucidated. Structural differences among the catalysts significantly influenced their performance: alkoxy catalysts (Z1–Z3), featuring aliphatic ligands, exhibited lower activity compared to aryloxy catalysts (Z4–Z9) with aromatic ligands. Specifically, ortho-substituted aryloxy catalysts Z7 and Z9 demonstrated the highest activity due to optimized steric and electronic effects from their substituent positions. A clear correlation was observed between polymer molecular weight and catalyst burial volume (VBur), where larger VBur values hindered ethylene monomer insertion, promoting chain transfer and resulting in shorter polymer chains. With the highest-activity Z7 catalyst, density functional theory calculations clarified the active center morphology, identifying two distinct Ti-alkyl intermediates existing stably simultaneously. Based on these findings, a mechanistic model for the formation of PE-WAX was proposed, wherein the synergistic effect of dual active centers lowered the chain-transfer energy barrier, enhanced catalytic activity, and allowed the controlled synthesis of low-molecular-weight PE-WAX with high crystallinity and a narrow molecular weight distribution.