Achieving Linear α-Macro-olefins in Ethylene Polymerization through Precisely Tuned Bis(imino)pyridylcobalt Precatalysts with Steric and Electronic Parameters.

Abstract

Synthesis of functional polyethylene from ethylene alone is tricky and heavily dependent on both the type and structure of the precatalyst and the choice of cocatalyst used in the polymerization. In the present study, a series of cobalt precatalysts was prepared and investigated for ethylene polymerization under various conditions. By incorporation of strong electron-withdrawing groups (F and NO₂) and a steric component (benzhydryl) into the parent bis(imino)pyridine ligand, the catalytic performance of these precatalysts was optimized. On activation with MAO or MMAO, these precatalysts with relatively open structure achieved unprecedented ethylene polymerization rates at 60 °C (up to 27.6 × 10⁶ g mol^-1 h^-1) and remained effective at temperatures up to 100 °C. Chain growth reactions were moderate, resulting in polyethylene with molecular weights up to 61.0 kg/mol and broad bimodal dispersity index. High crystallinity and melt temperature indicated a strictly linear microstructure, as further confirmed by high-temperature ¹H/¹³C NMR measurements. Of significant note that chain termination predominantly occurred through β-elimination (up to 84.5%), yielding vinyl-terminated long-chain olefins. These functional α-macro-olefins are valuable as precursors for postfunctionalization, expanding the potential applications of polyethylene across various sectors.