Ultrahigh Molecular Weight Ethylene-Acrylate Copolymers Synthesized with Highly Active Neutral Nickel Catalysts

Abstract

Molecular weight is a crucial parameter in catalytic olefin polymerization to determine the thermomechanical properties of polymers. Elevating the molecular weight of ethylene-acrylate copolymer, a typical polar polyolefin has been a persistent challenge. This study presents the direct synthesis of ultrahigh molecular weight (UHMW) ethylene-acrylate copolymers using a highly active, neutral, single-component phosphine-phenolate nickel catalyst under mild conditions. The coordination-insertion copolymerization of ethylene and various acrylates, such as methyl acrylate, n-butyl acrylate, and t-butyl acrylate, can yield ethylene-acrylate copolymers with UHMWs (M_n) ranging from 1000 to 2700 kDa, with exceptional activities of up to 4.03 × 10⁶ g mol^-1 h^-1. A relatively large-scale synthesis (30-50 g) of UHMW ethylene-acrylate copolymers was notably achieved. The properties of these UHMW ethylene-acrylate copolymers were comprehensively evaluated, demonstrating that these copolymers retained the bulk properties of ultrahigh molecular weight polyethylene (UHMWPE) while exhibiting improved surface and dyeing properties. In particular, the tensile strength of the ethylene-acrylate copolymers significantly increased with higher molecular weights, reaching 44 MPa (147 MPa after a predrawing ratio of 3.1), which is comparable to that of UHMWPE.

Keywords: Ethylene–acrylate copolymer; Nickel catalyst; Polar UHMWPE; Polyolefin; Thermomechanical property.