Designing polyethylenes of complex chain architectures via Pd-diimine-catalyzed "living" ethylene polymerization.

Polymer chain architecture is a critically important chain parameter governing intrinsically the properties and applications of polymers. The rapid developments in "living"/controlled polymerization techniques, particularly the controlled radical polymerization techniques, in the past two decades have enabled the precision synthesis of novel polymers having a great variety of complex yet well-defined chain architectures from various monomer stocks. For polyolefins synthesized via catalytic coordination polymerization, the design of complex chain architectures, however, has only started recently because of the relatively limited advancements in the catalytic "living" olefin polymerization technique. In this regard, the versatile Pd-diimine catalysts have provided some unprecedented opportunities, due to their outstanding features, in rendering successfully a novel class of polyethylenes of various new complex chain architectures through the "living" ethylene polymerization protocol. The complex chain architectures designed to date have included hyperbranched, hybrid hyperbranched-linear, block, gradient and block-gradient, star, telechelic, graft and comb, and surface-tethered polymer brushes. This Feature Article attempts to summarize the recent developments achieved in the area, with an emphasis on the synthetic strategies for the architectural design. These developments demonstrate the great potential for further advancements of this new exciting research area.