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Copolymerization of ethylene and methyl acrylate by palladium catalysts bearing IzQO ligands containing methoxyethyl ether moieties and salt effects for polymerization

Polymer Journal volume 53, pages 1057–1060 (2021)Cite this article

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In addition to modification of ligands, the addition of salts or Lewis acids has also been shown to improve catalyst performance. Since 2012, Jordan et al. found that the addition of Lewis acids alters the polymerization activity and molecular weight of the product when catalyzed by palladium complexes bearing phosphine–sulfonate, phosphinite, or phosphonite (Fig. 1, left middle) [6]. Modification of palladium/phosphine–sulfonate complexes by B(C6F5)3 increased the polymerization activity but decreased the molecular weight, while B(C6F5)3 modification of palladium/phosphine–phosphonate increased both the molecular weight of the polymer and polymerization activity. The addition of magnesium chloride to palladium/phosphine–sulfonate–diethylphosphonate resulted in lower polymerization activity but higher-molecular-weight ethylene polymerization [6b]. In 2015, Do et al. reported the introduction of an oligoethylene glycol moiety to nickel polymerization catalysts to locate additional metal cations around the nickel center; an oligoethylene glycol moiety was bound to nickel/salicylaldimine-type catalyst 2 (Fig. 1, left bottom) [7]. Catalyst 2 with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF4) showed 20-fold higher polymerization activity and a threefold higher molecular weight than the obtained polymer. Other BArF4 salts did not affect the catalyst properties. However, it should be noted that all of these studies on the additive effect are limited to ethylene homopolymerization in nonpolar solvents in the absence of any polar functional groups.

In 2017, Chen et al. examined the copolymerization of ethylene and methyl acrylate (E/MA) with palladium/phosphine–sulfonate complexes bearing oligoethylene glycol moieties bound to the diarylphosphine part [3b]. The higher incorporation of MA with the polyethylene moiety was explained by the increase in local polarity around the palladium center, but no further studies on the salt effect have yet been reported for copolymerization. We hypothesized that the addition of salts near the central metal would accelerate the insertion of acrylates by the interaction of polar monomers and cations (Fig. 1, right). As a result, the addition of lithium borate salt increased the polymerization activity and decreased the molecular weight without decreasing the incorporation of MA into the copolymer, as described below.

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Fig. 1
Fig. 2

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Acknowledgements

The authors are grateful to Prof. Shingo Ito (Nanyang Technological University) and Prof. Ryo Nakano (Nagoya University) for helpful discussions.

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  1. Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan

    Shumpei Akita & Kyoko Nozaki

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Akita, S., Nozaki, K. Copolymerization of ethylene and methyl acrylate by palladium catalysts bearing IzQO ligands containing methoxyethyl ether moieties and salt effects for polymerization. Polym J 53, 1057–1060 (2021). https://doi.org/10.1038/s41428-021-00500-3

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