Late-transition metal chain-walking polymerization catalysts, because of their abilities to produce various branched polyethylenes (PE) from ethylene alone, were distinctively fascinating. Although numerous studies have been done so far, exploration of how to synthesize PE with desired and specific structure via chain-walking polymerization from ethylene is elusive. In our works, we designed and synthesized a novel rigid chain-walking catalyst [Pd] that successfully produced ultra-highly branched PE with methyl branches (220 Me / 1000 C) exclusively from ethylene alone. However, higher temperature resulted in the decrease of not only branching degree but also selectivity of branches. In order to overcome it and fulfill superior control, we further synthesized a low-cost nickel (II) catalyst [Ni] that enabled the exclusive methyl branch pattern with an ultrahigh number (100 ~ 200 Me / 1000 C) over a particularly broad temperature range of 30 oC~ 90 oC that meets the industrial process. Generally, due to the chain-walking process after polar monomer insertion, chain-end functionalization that polar group is at the chain-end of branches was the major result of copolymerization. Thus main-chain functionalization was hard to realize. In our works, we showed main-chain incorporation of polar monomer using [Pd], key to this strategy was the inverted regioselectivity of polar monomer insertion. Block polymer is an important material in industry, in our works we demonstrated a one-pot reaction that produced block polymers with the sole feedstock of ethylene. Beyond temperature and pressure, we found a new and convenient additive to drastically switch the branching numbers in [Pd] promoted ethylene polymerization. Key features that a polar additive does not induce chain transfer (living mode, PDI &lt; 1.10) readily enabled the preparation of diblock topologies. With polar monomer, functionalized block PE could be produced in the same way.

Precise control of chain-walking polymerization: exclusive branch pattern, main-chain functionalization, block polymer

ACS Spring 2022

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