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Interfacial and Crystalline Gauche OCH 2 –CH 2 O Layers in Biodegradable and Recyclable Polyethylene-like Polyesters Detected by Nuclear Magnetic Resonance

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Polyethylene-like aliphatic polyesters are promising biodegradable polymers; however, their conformational and supramolecular structures are not well understood. Here, we used solid-state nuclear magnetic resonance (NMR) to investigate three synthetically accessible polyesters made from doubly 13 C-labeled ethylene diol units and unlabeled dicarboxylic acids of 12-, 18-, and 48-carbon length (PE-2,12 to PE-2,48). Signals of abundant gauche OCH 2 –CH 2 O conformers observed in all samples are spectrally resolved from the sharp peak of crystalline anti OCH 2 -CH 2 O segments in PE-2,12 and PE-2,18. Layers of disordered and immobilized gauche OCH 2 –CH 2 O units at the crystal–amorphous interfaces are present in all samples. PE-2,12 and PE-2,18 additionally contain mobile amorphous and crystalline gauche OCH 2 -CH 2 O units. The unexpected crystalline gauche conformation deduced from the chemical shift and slow 13 C spin–lattice relaxation was proved by fast decay in centerband-only detection of exchange (CODEX) NMR. The location of these gauche OCH 2 groups deep inside the crystallites was confirmed by 1 H spin diffusion from the amorphous layers. Crystalline gauche moieties, observed in three different samples of PE-2,12, account for about 1/3 of its crystalline OCH 2 groups. Based on quantitative NMR and spin diffusion, specific models of the layered supramolecular structures were developed, with gauche OCH 2 in interfacial layers at the crystal surfaces. While PE-2,18 and PE-2,12 contain two or three anti diol/diester layers within each crystallite, most OCH 2 groups in PE-2,48 are immobilized at the interfaces, and mobile gauche or crystalline anti OCH 2 units are insignificant. Thus, PE-2,48 contains all-polyethylene crystalline lamellae capped by diol/diester interfacial layers, indicating chemical control of the crystallite thickness.

Source: Journal of the American Chemical Society

DOI: 10.1021/jacs.5c10528

Authors: Zhenhuan Sun, Taylor Frederick Nelson, Stefan Mecking, Klaus Schmidt-Rohr

Institutions: Brandeis University, University of Konstanz

Language: English

Topic: biodegradable polymer synthesis and properties

Subfield: Biomaterials

Field: Materials Science

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,500

Funders: National Science Foundation, Alexander von Humboldt-Stiftung, Universität Konstanz, H2020 European Research Council