Star Ultrahigh-Molecular-Weight Polyethylene

Star polymers have attracted immense interest from scientific
and
industrial communities due to their unique properties relative to
linear polymers; however, the synthesis of the long-sought star polyolefins
remains highly challenging because of the lack of desired catalysts.
Herein, we report the synthesis of tri- and tetranuclear neutral salicylaldiminato
nickel(II) catalysts through well-defined multinuclear nickel(II)
precursors rather than multisite ligands. A one-step and clean synthesis
of three-arm and four-arm star polyethylenes without tedious purification
via the core-first approach is accomplished by these nickel(II) catalysts.
These star polyethylenes possess ultrahigh molecular weights of 1432–2370
kDa, very narrow molecular weight distributions of Mw/Mn = 1.30–1.39, substantially
linear arms of 1.7–3.0 branches/1000C, and excellent mechanical
properties. As a result, star ultrahigh-molecular-weight polyethylene
has become a new member of the family of polyolefins.