Tandem Catalytic Polymerization of Ethylene toward Long-Chain Branched Polyolefin Elastomers with Predominant 1-Octene Incorporation

Polyolefin elastomers (POEs) achieve enhanced performance through α-olefin incorporation (e.g., 1-octene), yet conventional 1-octene production suffers from limited selectivity, costly separations, and reactor fouling from polyethylene byproducts. Herein, we report an ethylene-exclusive tandem catalytic polymerization (TCP) strategy that integrates a PNP-Cr catalyzed ethylene oligomerization to generate α-olefins enriched in 1-octene, along with trace vinyl-terminated polyethylene (PEM), followed by a CGC-Ti catalyzed in situ copolymerization of ethylene with the α-olefins and PEM. This process affords long-chain branched (LCB) POEs with predominant 1-octene incorporation. The PNP-Cr catalyst achieved activities up to 6.44 × 106 g/(mol Cr·h), producing more than 94 wt % C6+ α-olefins, mainly 1-hexene and 1-octene, along with 0.1–2.2 wt % PEM bearing up to 82% terminal vinyl groups. The resulting POEs contained 6.8–12.5 mol % α-olefin incorporation, achieved weight-average molecular weights up to 146 kg/mol, and displayed melting temperatures as high as 90 °C. A TCP kinetic model based on the method of moments was established, which revealed that higher ethylene pressure promoted 1-octene formation, while accurately predicting molecular weights, dispersity, and copolymer composition of the copolymers. Importantly, the POEs displayed tunable structure–property relationships. The ethylene/α-olefin sequence distributions were controllable by polymerization temperature, pressure, and catalyst ratios, and triple-detector gel permeation chromatography revealed 0–4.5 LCBs per chain. The POEs further demonstrated thermorheological activation energies exceeded 40.8 kJ/mol. Compared with a commercial 1-octene-based POE of comparable molecular weight and α-olefin content, the TCP-derived POEs exhibited higher tensile strength while maintaining comparable elongation at break and elastic recovery. This integrated TCP approach mitigates α-olefin purification and polyethylene fouling challenges, providing an efficient route to directly produce LCB POEs from ethylene.