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<p>Developing highly thermostable catalytic systems remains a central objective in the field of late-transition-metal olefin polymerization. In this work, we report a new series of <i>α</i>-diimine Pd(II) catalysts that exhibit remarkable thermal resistance in ethylene polymerization (up to 100 °C). With the aid of concerted effects of both steric blockage and intra-ligand C—H⋯F hydrogen bonding linkage, conformational rotation of the <i>N</i>-aryl groups is substantially restricted, thereby imparting exceptional thermostability to these <i>α</i>-diimine Pd(II) precatalysts. By tuning the chain-walking degrees through the steric influence of ortho-substituent of <i>N</i>-phenyl substituents or by adjusting the polymerization temperature, the branching density of the resulting polyethylenes can be finely modulated from moderately branched to hyperbranched structures (72.7–142.1/1000C). More unexpectedly, these highly thermally robust unsymmetrical <i>α</i>-diimine Pd(II) complexes, stabilized by intra-ligand C—H⋯F hydrogen bonding, are capable of producing polyethylenes with widely adjustable molecular weights, ranging from oligomers to high-molecular-weight polymers (<i>M</i><sub>n</sub>=0.6×10<sup>3</sup>−87.2×10<sup>3</sup> g/mol). Furthermore, ethylene/methylacrylate (E/MA) copolymers were also successfully obtained using these catalysts, achieving MA incorporation levels of up to 4.7%.</p>

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Modulating Molecular Weight of Polyethylenes from Oligomer to Polymer Using Highly Thermal Stable Cationic α-Diimine Palladium Complexes

  • 期刊论文

  • 发表日期：

    2026年5月12日

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  • Feng-Bin Liu,
  • Chun-Yu Zhang,
  • Xue-Quan Zhang,
  • Heng Liu,
  • Xiao-Hua Wang

摘要

Developing highly thermostable catalytic systems remains a central objective in the field of late-transition-metal olefin polymerization. In this work, we report a new series of α-diimine Pd(II) catalysts that exhibit remarkable thermal resistance in ethylene polymerization (up to 100 °C). With the aid of concerted effects of both steric blockage and intra-ligand C—H⋯F hydrogen bonding linkage, conformational rotation of the N-aryl groups is substantially restricted, thereby imparting exceptional thermostability to these α-diimine Pd(II) precatalysts. By tuning the chain-walking degrees through the steric influence of ortho-substituent of N-phenyl substituents or by adjusting the polymerization temperature, the branching density of the resulting polyethylenes can be finely modulated from moderately branched to hyperbranched structures (72.7–142.1/1000C). More unexpectedly, these highly thermally robust unsymmetrical α-diimine Pd(II) complexes, stabilized by intra-ligand C—H⋯F hydrogen bonding, are capable of producing polyethylenes with widely adjustable molecular weights, ranging from oligomers to high-molecular-weight polymers (Mn=0.6×103−87.2×103 g/mol). Furthermore, ethylene/methylacrylate (E/MA) copolymers were also successfully obtained using these catalysts, achieving MA incorporation levels of up to 4.7%.