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

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.