Recent advances in nickel Catalysis for thermoplastic polyethylene elastomers: Synthesis strategies, properties, and future perspectives

Abstract

Polyolefins, particularly polyethylene (PE), rank among the most significantly applied synthetic polymers due to their exceptional chemical, thermal, and physical properties, which underpin their broad application spectrum. The characteristics of these polymers, such as flexibility, elasticity, and mechanical strength, are largely dictated by the polymerization process, catalyst selection, and polymer molecular architecture. Thermoplastic polyolefin elastomers (POEs) represent a notable subclass, prized for their ease of processing—allowing shaping, molding, and recycling—combined with their characteristic elastic properties. These materials are typically synthesized as branched or block copolymers of ethylene and α-olefins using early transition metal catalysts. The advent of late transition metal catalysts, particularly those based on nickel, has paved the way for a more direct approach to produce thermoplastic elastomers. These catalysts, with their distinctive chain-walking capability, obviate the need for comonomers, enabling the synthesis of branched polyethylene elastomers (PEEs) with the potential to replace traditional POEs. This review delves into the advancements in PEE synthesis via nickel catalysis, focusing on the design principles behind nickel catalysts that facilitate controlled branching. It critically evaluates the interplay between catalyst structure, reaction conditions, and polymer properties, emphasizing how these variables can be optimized to enhance elasticity, strength, and processability of PEE. Additionally, the review compares PEEs with conventional POEs, highlighting the superior balance of elasticity and thermoplasticity that makes PEEs advantageous for specific applications. Finally, the article addresses current challenges in fine-tuning the catalyst design, branching architectures and offers perspectives on future research directions in the development of catalyst design for high-performance PEEs.