Inside PEF: Chain Conformation and Dynamics in Crystalline and Amorphous Domains

Abstract

A thorough vibrational spectroscopy and molecular modeling study on poly­(ethylene 2,5-furandicarboxylate) (PEF) explores its conformational preferences, in the amorphous and crystalline regions, while clarifying structure–property correlations. Despite the increasing relevance of PEF as a sustainable polymer, some of its unique characteristics are not yet fully understood and benefit from a deeper comprehension of its microstructure and intermolecular bonding. Results show that in the amorphous domains, where intermolecular interactions are weak, PEF chains favor a helical conformation. Prior to crystallization, polymeric chains undergo internal rotations extending their shape in a zigzag patternan energetically unfavorable geometry which is stabilized by C–H···O bonds among adjacent chain segments. The zigzag conformation is the crystalline motif present in the α and β PEF polymorphs. The energy difference among the amorphous and crystalline chains of PEF is higher than in PET poly­(ethylene terephthalate) and contributes to PEF’s higher crystallization temperature. The 3D arrangement of PEF chains was probed using inelastic neutron scattering (INS) spectroscopy and periodic DFT calculations. Comparing the INS spectra of PEF with that of poly­(ethylene terephthalate) (PET) revealed structure–property correlations. Several low-frequency vibrational modes support the current view that PEF chains are less flexible than those of PET, posing greater resistance to gas penetration and resulting in enhanced barrier properties. The vibrational assignment of PEF’s INS spectrum is a useful guide for future studies on advanced materials based on PEF.

Vibrational Dynamics of Crystalline 4-Phenylbenzaldehyde from INS Spectra and Periodic DFT Calculations

“…70 cm −1 is better ascribed to a collective "external" mode ( Table 2). It should be mentioned that a phenyl torsion frequency of ca 116 cm −1 was recently identified in an ethylene terephthalate polymer (PET) from INS and CASTEP calculations [28].…”

Molecular Insights into Bulk and Porous κ2P,N‐PTA Metal‐Organic Polymers by Simultaneous Raman Spectroscopy and Inelastic Neutron Scattering

“…Inelastic neutron scattering has been successfully used to characterize the structure and the properties of a variety of organic polymers and metal‐organic frameworks …”

AuPd‐Fe3O4 Nanoparticle‐Catalyzed Synthesis of Furan‐2,5‐dimethylcarboxylate from 5‐Hydroxymethylfurfural under Mild Conditions

“…In the past few years, various synthetic reactions have been developed for the synthesis of FDCA that employ heterogeneous catalysts such as Pd, Pt, Au, Ru, bimetallic nanoparticles (NPs), and homogeneous catalysts . Despite significant progress in FDCA production, there have been difficulties in its direct application in industry because of its low solubility in most solvents . Also, product purification is cumbersome and another drawback.…”

“…Although FDCA synthesis proceeds with high yields, quantitative isolation in high purity for polymerization has proven difficult . Owing to the limitations of FDCA, furan‐2,5‐dimethylcarboxylate (FDMC), which is soluble in most common solvents, has generated a lot of interest in the past decade because it has more suitable properties for polymerization . Typically, synthesis of FDMC involves oxidation of the corresponding alcohol to aldehyde in methanol followed by oxidative esterification of the aldehyde to esters in one pot, which obviates the isolation of intermediates.…”