α-Diimine nickel-catalyzed propylene–diene copolymerization: towards a potential sulfur-crosslinked elastomeric alternative to EPDM

Abstract

The development of sulfur-crosslinkable, main chain-saturated elastomers beyond conventional ethylene–propylene–diene monomer (EPDM) is of long-standing importance in polyolefin chemistry. Herein, we report a series of α-diimine Ni(II) complexes bearing sterically congested cyclopolyarene moieties at the rear position of an acenaphthenyl backbone. In combination with diethylaluminum chloride (AlEt₂Cl) as a cocatalyst, these complexes effectively promoted the copolymerization of propylene with linear, acyclic, nonconjugated α,ω-dienes, affording a new class of hyperbranched, unsaturated elastomers. The influences of key copolymerization parameters, including ligand structure, diene identity, and comonomer concentration, on catalytic activity and comonomer incorporation were systematically investigated, and the resulting hyperbranched poly(propylene–diene) rubbers (BPPDRs) were thoroughly characterized. Structure–property correlations revealed that BPPDRs exhibited pronounced elastomeric behavior and good compatibility with EPDM. Vulcanization and mechanical evaluations further demonstrated that EPDM blends containing 20 wt% BPPDR displayed curing characteristics and tensile properties comparable with those of neat EPDM. Overall, this work establishes a viable nickel-catalyzed strategy for accessing EPDM-like elastomers via propylene/diene copolymerization, and provides new insights into the design of sulfur-crosslinkable, main-chain-saturated rubbers based on hyperbranched polyolefin architectures.