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. 2023 Sep 29;381(6665):1433-1440.
doi: 10.1126/science.adg6093. Epub 2023 Sep 28.

Diverse functional polyethylenes by catalytic amination

Nicodemo R Ciccia  1   2 , Jake X Shi  1   2 , Subhajit Pal  3 , Mutian Hua  4 , Katerina G Malollari  3 , Carlos Lizandara-Pueyo  5 , Eugen Risto  6 , Martin Ernst  6 , Brett A Helms  4   7 , Phillip B Messersmith  3   4 , John F Hartwig  1   2
Affiliations

Diverse functional polyethylenes by catalytic amination

Nicodemo R Ciccia et al. Science. .

Abstract

Functional polyethylenes possess valuable bulk and surface properties, but the limits of current synthetic methods narrow the range of accessible materials and prevent many envisioned applications. Instead, these materials are often used in composite films that are challenging to recycle. We report a Cu-catalyzed amination of polyethylenes to form mono- and bifunctional materials containing a series of polar groups and substituents. Designed catalysts with hydrophobic moieties enable the amination of linear and branched polyethylenes without chain scission or cross-linking, leading to polyethylenes with otherwise inaccessible combinations of functional groups and architectures. The resulting materials possess tunable bulk and surface properties, including toughness, adhesion to metal, paintability, and water solubility, which could unlock applications for functional polyethylenes and reduce the need for complex composites.

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Conflict of interest statement

Competing interests: A patent application (PCT/US2023/015456) has been filed on the process and composition of resulting materials with N.R.C., C.L.P., E.R., M.E., and J.F.H. as inventors. B.A.H. has a financial interest in Cyklos Materials and Sepion Technologies.

Figures

Fig. 1.
Fig. 1.. Methods to access functional polyethylenes.
(A) Synthesis of functional polyethylenes by copolymerizations. (B) Limitations of current functionalizations of polyethylene. (C) Catalytic C–N bond formation as a platform for the development of new materials.
Fig. 2.
Fig. 2.. Development of the catalytic amination of polyethylenes.
(A) Investigation of the effect of ligands on the yield of amination and on the change in Mn of the polymers. Amide incorporation (mol %) was determined relative to unmodified C2H4 units. Reaction yields were calculated as the percentage of amide that was incorporated. DTBP, di-tert-butyl peroxide. 1,2-DCB, 1,2-dichlorobenzene.(B) Comparison of aminations of polyethylene and n-hexane with L1 or L5 as ligand. Conditions: 1 equiv C2H4 units, 4 mol % benzamide, 0.1 mol % CuI, 0.1 mol % L1 or L5, 8 mol % DTBP, 1,2-DCB, 120°C. (C) Illustration of the range of amide incorporations accessible by this method. (D) Proposed mechanism for the catalytic amination of polyethylenes.
Fig. 3.
Fig. 3.. Scope of polyethylenes and nitrogen-based groups that undergo catalytic amination.
Amide incorporation (mol %) was determined relative to unmodified C2H4 units. DTBP, di-tert-butyl peroxide.1,2-DCB, 1,2-dichlorobenzene. *Unless otherwise specified, starting PE was LDPE, Mn = 2.4 kg mol−1. †Reaction time of 2 hours. ‡Performed on a 3.0-gram scale. §Amide loadings of 2 mol %. ¶Conditions: 1 equiv TBSO groups, 1.5 equiv TBAF, tetrahydrofuran (THF), 75°C. #Conditions: 1 equiv CO2Me groups, excess LiOH, t-amyl alcohol, 90°C. **Conditions: 1 equiv BocNH groups, excess HCl, dichloromethane (DCM), 75°C.
Fig. 4.
Fig. 4.. Range of properties of selected functional polyethylenes.
(A) Bulk properties of functional polyethylenes. (Left) Representative tensile tests of LDPE and N-containing polyethylenes (0.8 to 2.5 mol %). Strain rate = 50 mm min−1.(Middle) Average toughness of 1b with varying percentages of amide incorporation. Error bars represent standard deviation. (Right) Representative tensile tests of waste LDPE (resealable storage bag), waste HDPE (milk jug), 1e (0.3 mol %), and 1f (0.4 mol %). Strain rate = 50 mm min−1. (B) Surface properties of functional polyethylenes. (Left) Lap-shear adhesion tests of 18b (2 mol %) and 5b (2 mol %) as the adhesive interlayers. Error bars represent standard deviation. (Middle) Peel tests of LDPE and 5b. (Right) Water-contact angles of LDPE and 17a-graft-PEG, and image of aqueous solution of 17a-graft-PEG. (C) Rheological measurements. (Left to right) amplitude sweep, frequency sweep, and tan δ plot of LDPE and 1b (2.5 mol %), respectively. Amplitude sweep frequency fixed at 10 rad s−1, frequency sweep fixed at 0.01% strain, temperature 40°C.
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