SCHEDULED MAINTENANCE
High-performance polyethylene elastomers using a hybrid steric approach in α-diimine nickel precatalysts†
Abstract
The synthesis of polyethylenes with concurrent high mechanical and elastic properties at elevated reaction temperatures using nickel catalysts proves to be challenging, primarily due to excessive chain walking and transfer reactions. In this study, hybrid steric hindrance, involving flexible cycloalkyl and relatively compact benzhydryl groups, was introduced into the α-diimine structure to prepare a set of nickel complexes, aiming to enhance the catalytic performance and polyethylene properties simultaneously for ethylene polymerization. Upon activation with EASC, these precatalysts displayed exceptionally high activity (up to 4.3 × 107 g mol−1 h−1 at 30 °C) and high thermal stability (activity up to 1.8 × 106 g mol−1 h−1 at 110 °C over a period of 30 min). High to ultra-high molecular weights and a moderate to high number of branches (34–145 per 1000C) along with narrow unimodal dispersity (PDI ≤ 2) across various reaction conditions are the characteristics of the obtained polyethylene. Of significant note is that the polyethylene obtained at high reaction temperature using these precatalysts exhibited significantly distinguished mechanical and elastic properties. Particularly, the PE prepared at 80 °C displayed high tensile strength (σ = 25.9 MPa) concurrently with high elastic recovery (SR = 70%), a combination of mechanical and elastic properties rarely reported in polyethylenes prepared at high temperatures. These results highlight the role of the hybrid steric bulk strategy in effectively controlling the ratio of chain walking and chain growth reactions.
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