Recent Advances in Controlled Production of Long-Chain Branched Polyolefins

Polyolefins, composed of carbon and hydrogen atoms, dominate global polymer production. This stems from the wide range of physical and mechanical properties that various polyolefins can cover. Their versatile properties are largely tuned by chain microstructure, including molar mass distribution, comonomer content, and long-chain branching (LCB). Specifically, LCB imparts unique characteristics, notably enhances processability crucial for downstream applications. Tailoring LCB structural features has encouraged academic and industrial efforts, chronicle in this review from a chemistry standpoint. While encompassing post-reaction modification based traditional methods like peroxide grafting, ionizing beam irradiation, and coupling reactions, the main focus is given to catalyst-centric strategies and innovative polymerization schemes. The advent of single-site catalysts-metallocenes and late transition metals catalysts-amplifies interest in tailored chemical methods, but the progress in LCB formation flourishes via tandem catalytic systems and bimetallic catalysts under controlled reaction conditions. Specifically, the breakthrough in coordinative chain transfer polymerization unveils a novel avenue for controlled LCB synthesis by sequential chain propagation, transfer, liberation, and enchainment. This short review highlights recent approaches for the production of LCB polyolefins that can provide a roadmap crucial for researchers in academia and industry, steering their efforts toward further advancements in the production of tailored polyolefin.

Assessing 1,9-Decadiene/Ethylene Copolymerization with Ziegler-Natta Catalyst to Access Long Chain-Branched Polyethylene

1,9-Decadiene/ethylene copolymerization is assessed as a way for Ziegler-Natta catalysts to access long chain-branched polyethylene (PE). A MgCl₂/9,9-bis-(methoxymethyl)fluorine/TiCl₄ catalyst with triethylaluminium as a cocatalyst is exemplified for the task. 1,9-Decadiene was found to induce a substantial comonomer effect on catalyst activity and continuing decreases of PE molecular weight. Both the double bonds of 1,9-decadiene were poorly reactive during polymerization, of which the polymer chain-attached was even much less reactive than the original one. As a consequence, at decreased feeds, 1,9-decadiene gave small amounts (<0.1 mol %) of pendant vinyl groups to PE without prompting the formation of long-chain branches. Long chain-branching was realized at increased 1,9-decadiene feeds, which was however accompanied by proportional gelation.