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The industrial synthesis of functional polyolefins relies on free radical polymerization, which requires high temperature and pressure and offers poor microstructure control. Herein, we report a cation-switching strategy to access ethylene and alkyl acrylate copolymers with made-to-order molecular weight, molecular weight distribution, and polar monomer density, tunable within a catalyst-dependent range. This precision was achieved by exploiting the cation exchange dynamics between M+ and M′+ (where M+, M′+ = Li+, Na+, K+, or Cs+, and M ≠ M′) with our nickel phenoxyphosphine-polyethylene glycol catalyst. Under non-switching conditions, copolymerization of ethylene and methyl acrylate (MA) using our nickel catalyst in the presence of M+ and M′+ salts afforded ethylene-MA copolymers (EMA) with adjustable molecular weight distributions based on the ratio of M+ : M′+ employed. Under dynamic cation switching conditions, this catalyst system yielded monomodal EMA with molecular weight and MA incorporation that can be varied independently. Studies of the EMA revealed that while they retain the thermal and mechanical properties of polyethylene having the same molecular weight, increasing the MA per chain by as few as 1–3 units leads to measurable increase in their wettability and susceptibility toward oxidative cleavage. This work adds to a growing body of evidence suggesting that ethylene-based materials can be designed for improved degradability without compromising their performance. 

Cation tuning is a simple yet powerful strategy to modulate the reactivity of polymerization catalysts but the design rules to achieve maximum cation effects are not well understood. In the present work, it was demonstrated that inserting a methylene spacer between a nickel phenoxyimine complex and an M-polyethylene glycol (PEG) (where M = Li+, Na+, K+, or Cs+) unit led up to >70-fold increase in ethylene polymerization activity and 6-fold higher polymer molecular weight relative to that of the first-generation catalysts. It is hypothesized that these effects are due to the exclusive formation of 1:1 over 2:1 nick-el:alkali species and closer proximity of the M-PEG moiety to the nickel center. These results suggest that the successful creation of cation-responsive catalysts requires an understanding of the cation binding stoichiometry as well as the structural and electronic changes associated with its host-guest interactions. 

A phosgene-free method to prepareN-carboxyanhydrides from amino acids and carbon dioxide has been developed. This method is mild enough to be used in the tandem synthesis of alkaloids tryptanthrin and phaitanthrin A.