Abstract
Early transition metal catalysts produce high-density and linear low-density polyethylenes with spectacular efficiency. Nevertheless, these catalysts are ineffective in producing low-density polyethylene homopolymers with large –(CH2)xCH3 branch densities (x ≥ 5) or low-molecular-mass (Mn < 1,200 g mol−1) highly branched polyethylenes (HBPEs). The latter are potential alternative synthetic lubricants that have eluded efficient catalytic synthesis. Here we report the synthesis of low-Mn HBPEs with 61–93 branches per 1,000 carbon atoms from abundant ethylene as the primary feedstock using a soluble, highly active ion-paired organozirconium catalyst in a saturated hydrocarbon solvent. The unprecedented activity and branch selectivity reflect previously unrecognized aspects of the cationic catalyst–counteranion pairing in nonpolar media and are characterized spectroscopically and quantum mechanically. The HBPE products are rheologically and tribologically attractive candidates for synthetic lubricants.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 digital issues and online access to articles
$119.00 per year
only $9.92 per issue
Rent or buy this article
Prices vary by article type
from$1.95
to$39.95
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
All other data supporting the findings of this study, including synthesis and characterizations of compounds (Supplementary Methods 1.2), polymerization experimental procedures (Supplementary Methods 1.3, 1.4 and 1.6) and NMR spectra of compounds, HBPE products and PAO4 samples (Supplementary Figs. 3–22) are available in the Supplementary Information. The data that support the plots within this paper are available from the corresponding authors upon reasonable request.
References
Al-Ali AlMa’adeed, M. & Krupa, I. Polyolefin Compounds and Materials: Fundamentals and Industrial Applications (Springer, New York, NY, 2015).
Stürzel, M., Mihan, S. & Mülhaupt, R. From multisite polymerization catalysis to sustainable materials and all-polyolefin composites. Chem. Rev. 116, 1398–1433 (2016).
Baier, M. C., Zuideveld, M. A. & Mecking, S. Post-metallocenes in the industrial production of polyolefins. Angew. Chem. Int. Ed. 53, 9722–9744 (2014).
Nowlin, T. E. Business and Technology of the Global Polyethylene Industry: An In-depth Look at the History, Technology, Catalysts, and Modern Commercial Manufacture of Polyethylene and Its Products (Wiley, New York, NY, 2014).
Chanda, M. Plastics Technology Handbook 5th edn (CRC Press, Boca Raton, FL, 2017).
White, J. L. & Choi, D. D. Polyolefins: Processing, Structure Development, and Properties (Carl Hanser, Munich, 2005).
Xiang, P., Ye, Z. B. & Subramanian, R. Synthesis and characterization of low- and medium-molecular-weight hyperbranched polyethylenes by chain walking ethylene polymerization with Pd-diimine catalysts. Polymer 52, 5027–5039 (2011).
Synthetic Lubricants (Group IV, Group V) Market Analysis by Product (PAO, Esters, PAG), by Application (Engine Oils, HTF, Transmission Fluids, Metalworking Fluids) and Segment Forecasts to 2024 (Grand View Research, 2016).
Falivene, L. et al. Control of chain walking by weak neighboring group interactions in unsymmetrical catalysts. J. Am. Chem. Soc. 140, 1305–1312 (2018).
Guo, L., Dai, S., Sui, X. & Chen, C. Palladium and nickel catalyzed chain walking olefin polymerization and copolymerization. ACS Catal. 6, 428–441 (2016).
Wiedemann, T. et al. Monofunctional hyperbranched ethylene oligomers. J. Am. Chem. Soc. 136, 2078–2085 (2014).
Ittel, S. D., Johnson, L. K. & Brookhart, M. Late-metal catalysts for ethylene homo- and copolymerization. Chem. Rev. 100, 1169–1204 (2000).
Guan, Z., Cotts, P. M., McCord, E. F. & McLain, S. J. Chain walking: a new strategy to control polymer topology. Science 283, 2059–2062 (1999).
Johnson, L. K., Killian, C. M. & Brookhart, M. New Pd(ii)-based and Ni(ii)-based catalysts for polymerization of ethylene and alpha-olefins. J. Am. Chem. Soc. 117, 6414–6415 (1995).
Arriola, D. J. et al. Hyperbranched ethylene-based oligomers. Patent WO2014209927A1 (2014).
Murtuza, S., Harkins, S. B., Long, G. S. & Sen, A. Tantalum- and titanium-based catalytic systems for the synthesis of hyperbranched polyethene. J. Am. Chem. Soc. 122, 1867–1872 (2000).
Mu, H., Pan, L., Song, D. & Li, Y. Neutral nickel catalysts for olefin homo- and copolymerization: relationships between catalyst structures and catalytic properties. Chem. Rev. 115, 12091–12137 (2015).
Li, L. et al. Catalyst/cocatalyst nuclearity effects in single-site polymerization. Enhanced polyethylene branching and α-olefin comonomer enchainment in polymerizations mediated by binuclear catalysts and cocatalysts via a new enchainment pathway. J. Am. Chem. Soc. 124, 12725–12741 (2002).
Bellachioma, G., Ciancaleoni, G., Zuccaccia, C., Zuccaccia, D. & Macchioni, A. NMR investigation of non-covalent aggregation of coordination compounds ranging from dimers and ion pairs up to nano-aggregates. Coord. Chem. Rev. 252, 2224–2238 (2008).
Chen, M.-C., Roberts, J. A. S. & Marks, T. J. Marked counteranion effects on single-site olefin polymerization processes. Correlations of ion pair structure and dynamics with polymerization activity, chain transfer, and syndioselectivity. J. Am. Chem. Soc. 126, 4605–4625 (2004).
Macchioni, A. Ion pairing in transition-metal organometallic chemistry. Chem. Rev. 105, 2039–2074 (2005).
Zuccaccia, C. et al. NOE and PGSE NMR spectroscopic studies of solution structure and aggregation in metallocenium ion-pairs. J. Am. Chem. Soc. 126, 1448–1464 (2004).
Li, H., Stern, C. L. & Marks, T. J. Significant proximity and cocatalyst effects in binuclear catalysis for olefin polymerization. Macromolecules 38, 9015–9027 (2005).
Rocchigiani, L. et al. Synthesis, characterization, interionic structure, and self-aggregation tendency of zirconaaziridinium salts bearing long alkyl chains. Organometallics. 30, 100–114 (2011).
Wohlfahrt, C. in Static Dielectric Constants of Pure Liquids and Binary Liquid Mixtures (ed. Madelung, O.) Ch. 2 (Springer-Verlag, Berlin, 1991).
Motolko, K. S. A., Price, J. S., Emslie, D. J. H., Jenkins, H. A. & Britten, J. F. Zirconium complexes of a rigid, dianionic pincer ligand: alkyl cations, arene coordination, and ethylene polymerization. Organometallics. 36, 3084–3093 (2017).
Stalzer, M. M. et al. Single-face/all-cis arene hydrogenation by a supported single-site d 0 organozirconium catalyst. Angew. Chem. Int. Ed. 55, 5263–5267 (2016).
Gu, W. et al. Benzene selectivity in competitive arene hydrogenation: effects of single-site catalyst···acidic oxide surface binding geometry. J. Am. Chem. Soc. 137, 6770–6780 (2015).
Gillis, D. J. et al. Synthesis and characterization of the series of d 0 arene complexes [Cp*MMe2(η 6-arene)][MeB(C6F5)3] (M = Ti, Zr, Hf). Organometallics 15, 3600–3605 (1996).
Midey, A. J., Williams, S., Miller, T. M. & Viggiano, A. A. Reactions of O2 +, NO+ and H3O+ with methylcyclohexane (C7H14) and cyclooctane (C8H16) from 298 to 700 K. Int. J. Mass Spectrom. 222, 413–430 (2003).
Hunter, E. P. L. & Lias, S. G. Evaluated gas phase basicities and proton affinities of molecules: an update. J. Phys. Chem. Ref. Data 27, 413–656 (1998).
Li, L. et al. Catalyst/cocatalyst nuclearity effects in single-site polymerization. Enhanced polyethylene branching and α-olefin comonomer enchainment in polymerizations mediated by binuclear catalysts and cocatalysts via a new enchainment pathway. J. Am. Chem. Soc. 124, 12725–12741 (2002).
Hayduk, W. IUPAC Solubility Data Series: Ethene Vol. 57 (Oxford Univ. Press, Oxford, 1994).
Galland, G. B., de Souza, R. F., Mauler, R. S. & Nunes, F. F. 13C NMR determination of the composition of linear low-density polyethylene obtained with [η 3-methallyl-nickel-diimine]PF6 complex. Macromolecules 32, 1620–1625 (1999).
McInnis, J. P., Delferro, M. & Marks, T. J. Multinuclear group 4 catalysis: olefin polymerization pathways modified by strong metal–metal cooperative effects. Acc. Chem. Res. 47, 2545–2557 (2014).
Budzelaar, P. H. M. Mechanisms of branch formation in metal‐catalyzed ethene polymerization. WIREs Comput. Mol. Sci. 2, 221–241 (2012).
Arriola, D. J., Carnahan, E. M., Hustad, P. D., Kuhlman, R. L. & Wenzel, T. T. Catalytic production of olefin block copolymers via chain shuttling polymerization. Science 312, 714–719 (2006).
Resconi, L., Chadwick, J. C. & Cavallo, L. in Comprehensive Organometallic Chemistry III (ed. Crabtree, R. H.) 1005–1166 (Elsevier, Oxford, 2007).
Bochmann, M. The chemistry of catalyst activation: the case of group 4 polymerization catalysts. Organometallics 29, 4711–4740 (2010).
Riddlestone, I. M., Kraft, A., Schaefer, J. & Krossing, I. Taming the cationic beast: novel developments in the synthesis and application of weakly coordinating anions. 57, 13982–14024 (2017).
Alonso-Moreno, C. et al. Ligand mobility and solution structures of the metallocenium ion pairs [Me2C(Cp)(fluorenyl)MCH2SiMe3 +···X−] (M=Zr, Hf; X=MeB(C6F5)3, B(C6F5)4. Organometallics 27, 5474–5487 (2008).
Stahl, N. G., Zuccaccia, C., Jensen, T. R. & Marks, T. J. Metallocene polymerization catalyst ion-pair aggregation by cryoscopy and pulsed field gradient spin-echo NMR diffusion measurements. J. Am. Chem. Soc. 125, 5256–5257 (2003).
Rocchigiani, L., Ciancaleoni, G., Zuccaccia, C. & Macchioni, A. Low-temperature kinetic NMR studies on the insertion of a single olefin molecule into a Zr–C bond: assessing the counterion–solvent interplay. Angew. Chem. Int. Ed. 50, 11752–11755 (2011).
Ciancaleoni, G. et al. Structure–activity relationship in olefin polymerization catalysis: is entropy the key? J. Am. Chem. Soc. 132, 13651–13653 (2010).
Beswick, C. L. & Marks, T. J. Metal-alkyl group effects on the thermodynamic stability and stereochemical mobility of B(C6F5)3-derived Zr and Hf metallocenium ion-pairs. J. Am. Chem. Soc. 122, 10358–10370 (2000).
Margl, P., Deng, L. & Ziegler, T. A unified view of ethylene polymerization by d 0 and d 0 f n transition metals. 3. Termination of the growing polymer chain. J. Am. Chem. Soc. 121, 154–162 (1999).
Dougherty, D. A. The cation–π interaction. Acc. Chem. Res. 46, 885–893 (2013).
Goldbach, V., Roesle, P. & Mecking, S. Catalytic isomerizing ω-functionalization of fatty acids. ACS Catal. 5, 5951–5972 (2015).
Eagan, J. M. et al. Combining polyethylene and polypropylene: enhanced performance with PE/PP multiblock polymers. Science 355, 814 (2017).
Ohtaki, H. et al. Allyl-terminated polypropylene macromonomers: a route to polyolefin elastomers with excellent elastic behavior. Macromolecules 48, 7489–7494 (2015).
Acknowledgements
The authors acknowledge financial support from The Dow Chemical Company. T.L.L. thanks the NSF for partial support under Homogeneous Catalysis grant CHE–1464488. Purchase of NMR instrumentation at IMSERC was supported by the NSF (CHE–1048773). NSF computational resources were provided by the Northwestern University Quest High Performance Computing Cluster (to Y.G.) and CINECA award no. HP10CRFT69 2016 under the ISCRA initiative (to A.M.). The authors thank E. Carnahan, J. Klosin, M. Christianson and A. Young of The Dow Chemical Company for helpful discussions.
Author information
Authors and Affiliations
Contributions
Y.G., T.L.L. and T.J.M. conceived the study. Y.G., T.L.L. and T.J.M. planned the research. Y.G. and Y.W. synthesized and characterized the compounds. Y.G. and J.C. conducted the olefin polymerization experiments. Y.G. and Y.W. conducted the pulse-gradient spin-echo experiments and analysis. D.B.P., Q.J.W. and Y.W.C. designed and conducted the tribological experiments and analysis. A.M. conducted the DFT calculations and analysis. Y.G., T.L.L. and T.J.M. prepared the manuscript. All the authors commented on the manuscript.
Corresponding authors
Ethics declarations
Competing interests
T.J.M., Y.G. and T.L.L. are inventors on US patent application 62/626,879, filed by Northwestern University, which teaches the synthesis of the HBPE products and on US patent application 62/650,462, filed by The Dow Chemical Company, which teaches the synthesis of the soluble borate co-catalysts/activators. J.C., Y.W., D.B.P., A.M., Q.J.W. and Y.W.C. declare no competing interests.
Additional information
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Supplementary Information
Supplementary Methods, Supplementary Notes 1–7, Supplementary Tables 1–7, Supplementary Figures 1–22, Supplementary References
Supplementary Data 1
Cartesian coordinates of optimized structures of key species investigated.
Rights and permissions
About this article
Cite this article
Gao, Y., Chen, J., Wang, Y. et al. Highly branched polyethylene oligomers via group IV-catalysed polymerization in very nonpolar media. Nat Catal 2, 236–242 (2019). https://doi.org/10.1038/s41929-018-0224-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41929-018-0224-0
This article is cited by
-
A general strategy for heterogenizing olefin polymerization catalysts and the synthesis of polyolefins and composites
Nature Communications (2022)
-
Zirconium-Based Catalysts in Organic Synthesis
Topics in Current Chemistry (2022)
-
A simple and versatile nickel platform for the generation of branched high molecular weight polyolefins
Nature Communications (2020)
-
The co-catalyst is the key
Nature Catalysis (2019)