Precision Oligomeric Building Blocks toward Chemically Recyclable Polyolefin-like Materials

Abstract

The development of chemically recyclable polyolefin-like materials that combine the performance of conventional polyolefins with controlled degradability remains a significant challenge in polymer sustainability. Achieving this goal requires precise control over polymer architecture and the placement of cleavable linkages to enable efficient depolymerization. Precision oligomeric building blocks act as molecular Lego blocks, providing a modular and programmable platform for constructing polyolefin analogues with well-defined structures. Their discrete and uniform nature allows for the strategic incorporation of cleavable sites at predetermined positions, enabling tunable degradation pathways and predictable end-of-life behavior. Compared to traditional polymerization methods, this approach offers enhanced architectural control, sequence definition, and functional site incorporation. This review highlights recent advances in the synthesis and application of these precision oligomeric building blocks toward chemically recyclable polyolefin-like polymers. Emphasis is placed on how their structural precision and modularity enable the construction of high-performance, recyclable polyolefin analogues.

Keywords: building blocks; chemical recycling; cleavable linkages; degradation; polyolefin-like materials; precision oligomers.

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Concept of construction of polyolefin-like materials from precision oligomeric building blocks.

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Representative iterative multistep syntheses to oligomeric building blocks. (a) Chain extension via metal-catalyzed coupling and further reduction. (b) Molecular doubling strategy through Wittig olefination and ensuing functionalization.

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Representative transformations of renewable feedstocks into bifunctional monomers. (a) Thermal rearrangement of ricinoleic acid. (b) Self-metathesis of methyl oleate. (c) Cross-metathesis and functionalization to access ω-amino fatty acid methyl esters and branched diesters. (d) Isomerizing alkoxycarbonylation of unsaturated fatty acids.

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Chain doubling strategy by combination of olefin metathesis and catalytical isomerization reactions to yield long-chain diesters and diols.

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Two biocatalytic pathways for the oxidation of fatty acids, in which β-oxidation pathway can be blocked by deletion of the gene encoding acyl CoA dehydrogenase. Moreover, ω-hydroxy fatty acids can be produced by blocking related genes encoding enzymes for their further oxidation.

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Long-spaced polyamides can bridge the gap between PE with high crystallinity and polyamide with strong hydrogen bonding interactions. (a) ADMET copolymerization affords saturated polyamides with varying amide contents. (b) Peak T _m (blue) and heat of fusion (ΔH) values (red) of saturated polyamides. (c) Schematics for crystal structure of PE as dominated by nonpolar van der Waals interactions and hydrogen bonding interactions between amide groups in polyamides. Reproduced from ref . Copyright 2015 American Chemical Society.

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Synthesis of (a) unsaturated polyester via ADMET polymerization and (b) PE-mimicking polyester PE-30,30 via polycondensation.

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Solid-state structure of the aliphatic polyester PE22,4 according to NMR and SAXS studies. Reproduced with permission from ref . Copyright 2007 American Chemical Society.

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Chemically encoded chain folding and crystal microstructure in PE-like materials. (a) Polyesterification toward polyesters with varying spacer lengths and branches. (b) Representative AFM phase image (tapping mode) of PE-44,5-Prop cooled by steps in the AFM heating stage at 85 °C. Thin, white stripes correspond to the crystalline lamellae. Reproduced from ref . Copyright 2003 Springer Nature.

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Closed-loop recycling of PE-like polyesters and polycarbonates. (a) Aliphatic monomers synthesized from biorefining of plant or microalgae oils could be polymerized into high molecular weight polyesters and polycarbonates. (b) Closed-loop recycling of PC-18 and PE-18,18 via solvolysis and further repolymerization and recycling for PC-18 with an overall polymer-to-polymer recycling rate of ≥96%. Reproduced from ref . Copyright 2021 The Authors, under exclusive license to Springer Nature.

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Catalytic closed-loop recycling of PE-like materials with tunable properties from copolymerization of linear and branched diols. Linear and branched monomers are synthesized from plant or microalgae oils. A catalytic approach for polymerization and chemical recycling of biobased PE-like polyesters with highly tunable mechanical properties is enabled by an earth-abundant Mn complex.

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Biodegradable and compostable HDPE-like materials. (a) Conventional condensation polymerization to PE-m,18. (b) WAXS diffractograms for PE-2,18 and commercial HDPE. (c) Representative stress–strain curves of injection-molded PE-2,18 and commercial HDPE. (d) Hydrolysis of PE-2,18 by HiC, TlL, and AoC at 37 °C and pH 7.2 via quantifying the formation of ethylene glycol (EG). (e) Mineralization curves based on CO₂ evolution measured under industrial composting conditions following the standard ISO 14855-1 for PE-2,18, with cellulose as a reference. Reproduced from ref . Copyright 2022 The Authors, published by Wiley-VCH GmbH.