Assessing 1,9-Decadiene/Propylene Copolymerization with Ziegler-Natta Catalysts to Long-Chain-Branched Polypropylene

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.

Achieving high molecular weight alternating copolymers of 1-octene with methyl acrylate via Lewis acid catalyzed copolymerization

The radical (co)polymerization of long-chain α-olefins (C4+) to produce high molecular weight (Mw) polymers is of great importance. However, this process is currently faced with significant challenges due to the presence of less reactive allylic radicals during radical (co)polymerization, leading to oligomers or polymers with extremely low Mw (less than 1 × 104 g mol-1). Using copolymerization of 1-octene with methyl acrylate (MA) as a proof-of-concept for addressing this challenge, we present a feasible method for synthesizing high Mw α-olefin copolymers via scandium trifluoromethanesulfonate (Sc(OTf)3)-mediated radical copolymerization. In this case, copolymers of 1-octene and MA (poly(1-octene-alt-MA)) with a Mw exceeding 3 × 104 g mol-1 were successfully synthesized in the presence of Sc(OTf)3. Meanwhile, the presence of alternating 1-octene-MA sequential structures was observed. To further enhance the Mw of poly(1-octene-alt-MA), a difunctional comonomer, 1,7-octadiene, was introduced to copolymerize with 1-octene and MA. The results indicate that the incorporation of difunctional comonomer leads to a significant increase in the Mw of the copolymers synthesized. The addition of 1 mol% of 1,7-octadiene resulted in a copolymer with a remarkably high Mw of up to 13.45 × 104 g mol-1 while still maintaining a high degree of the alternating 1-octene-MA sequence (41%). The influence of polymerization parameters on the molecular weight were also investigated. Increasing the monomer concentration, reducing the dosage of initiator, and lowering the polymerization temperature have been found to be advantageous in enhancing the molecular weight. This approach has also been successfully applied to the synthesis of high molecular weight alternating copolymers of other long-chain α-olefins, including 1-hexene, 1-decene and 1-tetradecane, with methyl acrylate. In summary, this study provides a feasible method for converting "less activated" α-olefins into high Mw olefin copolymers. This approach holds significant potential for the production of value-added polyolefins, thus offering promising prospects for future applications.

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.