Ethylene and alkyl acrylate copolymers made-to-order using dynamic cation switching polymerization and evidence for improved polymer degradability with low polar group density

Abstract

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.