Structurally different from existing polyethylene grades, hyperbranched polyethylenes (HBPEs) synthesized by Pd–diimine-catalyzed chain walking polymerization represent a novel class of polyethylene materials with unprecedented chain architectures and unique physical properties. A large number of research investigations have been carried out in the area in the past decade, and have led to the successful synthesis of a broad range HBPEs of various controlled chain topologies, molecular weights, and functionalities by tuning polymerization parameters and/or catalyst structures. Meanwhile, some new specialty applications of these materials have also been demonstrated in various fields ranging from lubricant additives to polymer building blocks to nanoencapsulation, with some interesting performance properties discovered. This review aims to summarize the developments in this area.

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.