Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Highly branched polyethylene oligomers via group IV-catalysed polymerization in very nonpolar media

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

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

Fig. 1: Polyethylene categories, microstructural branching characteristics and precatalyst activation.
Fig. 2: Trends in CGCZrMe2+B1,n-octyl-catalysed ethylene polymerizations.
Fig. 3: Proposed polymerization mechanism, ion-pairing effects and DFT analysis.
Fig. 4: Tribological evaluations of the CGCZrMe2+B1,n-octyl-catalysed ethylene homopolymerization product HBPE versus commercial PAO4 base oil lubricant.

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. 322) 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

  1. Al-Ali AlMa’adeed, M. & Krupa, I. Polyolefin Compounds and Materials: Fundamentals and Industrial Applications (Springer, New York, NY, 2015).

  2. Stürzel, M., Mihan, S. & Mülhaupt, R. From multisite polymerization catalysis to sustainable materials and all-polyolefin composites. Chem. Rev. 116, 1398–1433 (2016).

    Article  Google Scholar 

  3. Baier, M. C., Zuideveld, M. A. & Mecking, S. Post-metallocenes in the industrial production of polyolefins. Angew. Chem. Int. Ed. 53, 9722–9744 (2014).

    Article  CAS  Google Scholar 

  4. 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).

  5. Chanda, M. Plastics Technology Handbook 5th edn (CRC Press, Boca Raton, FL, 2017).

  6. White, J. L. & Choi, D. D. Polyolefins: Processing, Structure Development, and Properties (Carl Hanser, Munich, 2005).

  7. 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).

    Article  CAS  Google Scholar 

  8. 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).

  9. Falivene, L. et al. Control of chain walking by weak neighboring group interactions in unsymmetrical catalysts. J. Am. Chem. Soc. 140, 1305–1312 (2018).

    Article  CAS  Google Scholar 

  10. Guo, L., Dai, S., Sui, X. & Chen, C. Palladium and nickel catalyzed chain walking olefin polymerization and copolymerization. ACS Catal. 6, 428–441 (2016).

    Article  CAS  Google Scholar 

  11. Wiedemann, T. et al. Monofunctional hyperbranched ethylene oligomers. J. Am. Chem. Soc. 136, 2078–2085 (2014).

    Article  CAS  Google Scholar 

  12. Ittel, S. D., Johnson, L. K. & Brookhart, M. Late-metal catalysts for ethylene homo- and copolymerization. Chem. Rev. 100, 1169–1204 (2000).

    Article  CAS  Google Scholar 

  13. 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).

    Article  CAS  Google Scholar 

  14. 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).

    Article  CAS  Google Scholar 

  15. Arriola, D. J. et al. Hyperbranched ethylene-based oligomers. Patent WO2014209927A1 (2014).

  16. 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).

    Article  CAS  Google Scholar 

  17. 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).

    Article  CAS  Google Scholar 

  18. 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).

    Article  CAS  Google Scholar 

  19. 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).

    Article  CAS  Google Scholar 

  20. 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).

    Article  CAS  Google Scholar 

  21. Macchioni, A. Ion pairing in transition-metal organometallic chemistry. Chem. Rev. 105, 2039–2074 (2005).

    Article  CAS  Google Scholar 

  22. 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).

    Article  CAS  Google Scholar 

  23. Li, H., Stern, C. L. & Marks, T. J. Significant proximity and cocatalyst effects in binuclear catalysis for olefin polymerization. Macromolecules 38, 9015–9027 (2005).

    Article  CAS  Google Scholar 

  24. Rocchigiani, L. et al. Synthesis, characterization, interionic structure, and self-aggregation tendency of zirconaaziridinium salts bearing long alkyl chains. Organometallics. 30, 100–114 (2011).

    Article  CAS  Google Scholar 

  25. Wohlfahrt, C. in Static Dielectric Constants of Pure Liquids and Binary Liquid Mixtures (ed. Madelung, O.) Ch. 2 (Springer-Verlag, Berlin, 1991).

  26. 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).

    Article  CAS  Google Scholar 

  27. 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).

    Article  CAS  Google Scholar 

  28. 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).

    Article  CAS  Google Scholar 

  29. 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).

    Article  CAS  Google Scholar 

  30. 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).

    Article  CAS  Google Scholar 

  31. 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).

    Article  CAS  Google Scholar 

  32. 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).

    Article  CAS  Google Scholar 

  33. Hayduk, W. IUPAC Solubility Data Series: Ethene Vol. 57 (Oxford Univ. Press, Oxford, 1994).

  34. 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).

    Article  CAS  Google Scholar 

  35. 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).

    Article  CAS  Google Scholar 

  36. Budzelaar, P. H. M. Mechanisms of branch formation in metal‐catalyzed ethene polymerization. WIREs Comput. Mol. Sci. 2, 221–241 (2012).

    Article  CAS  Google Scholar 

  37. 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).

    Article  CAS  Google Scholar 

  38. Resconi, L., Chadwick, J. C. & Cavallo, L. in Comprehensive Organometallic Chemistry III (ed. Crabtree, R. H.) 1005–1166 (Elsevier, Oxford, 2007).

  39. Bochmann, M. The chemistry of catalyst activation: the case of group 4 polymerization catalysts. Organometallics 29, 4711–4740 (2010).

    Article  CAS  Google Scholar 

  40. 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).

  41. 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).

    Article  CAS  Google Scholar 

  42. 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).

    Article  CAS  Google Scholar 

  43. 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).

    Article  CAS  Google Scholar 

  44. Ciancaleoni, G. et al. Structure–activity relationship in olefin polymerization catalysis: is entropy the key? J. Am. Chem. Soc. 132, 13651–13653 (2010).

    Article  CAS  Google Scholar 

  45. 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).

    Article  CAS  Google Scholar 

  46. 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).

    Article  CAS  Google Scholar 

  47. Dougherty, D. A. The cation–π interaction. Acc. Chem. Res. 46, 885–893 (2013).

    Article  CAS  Google Scholar 

  48. Goldbach, V., Roesle, P. & Mecking, S. Catalytic isomerizing ω-functionalization of fatty acids. ACS Catal. 5, 5951–5972 (2015).

    Article  CAS  Google Scholar 

  49. Eagan, J. M. et al. Combining polyethylene and polypropylene: enhanced performance with PE/PP multiblock polymers. Science 355, 814 (2017).

    Article  CAS  Google Scholar 

  50. Ohtaki, H. et al. Allyl-terminated polypropylene macromonomers: a route to polyolefin elastomers with excellent elastic behavior. Macromolecules 48, 7489–7494 (2015).

    Article  CAS  Google Scholar 

Download references

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

Authors

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

Correspondence to Tracy L. Lohr or Tobin J. Marks.

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

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

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

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41929-018-0224-0

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing