Structural Investigation of Poly(ethylene furanoate) Polymorphs.

Area of Science:

• Materials Science
• Polymer Chemistry
• Crystallography

Background:

• Poly(ethylene furanoate) (PEF) is a bio-based polymer with potential applications as a PET alternative.
• Understanding the crystalline structure of PEF is crucial for optimizing its material properties and processing.
• Polymorphism, the ability of a solid material to exist in multiple crystalline forms, is common in polymers and affects their performance.

Purpose of the Study:

• To determine the precise crystal structures of the α and β phases of poly(ethylene furanoate) (PEF).
• To refine the crystal structure of the α' phase of PEF using existing fiber diffraction data.
• To report the lattice parameters and atomic coordinates for all identified PEF polymorphs.

Main Methods:

• X-ray powder diffraction (XRD) was employed for structure determination.
• Structure resolution in direct space and Rietveld refinement were utilized for detailed structural analysis.
• Analysis of previously reported XRD data for PEF fiber was performed to refine the α' structure.

Main Results:

• Three crystalline polymorphs of PEF were identified and characterized: triclinic α-PEF, monoclinic α'-PEF, and monoclinic β-PEF.
• Specific lattice parameters (a, b, c) and angles (α, β, γ) were determined for each polymorph.
• Final atomic coordinates for all PEF polymorphs were reported, revealing an almost planar configuration of PEF chains in all crystalline forms.

Conclusions:

• The crystal structures of α, α', and β PEF have been definitively determined.
• The reported structural data provide a foundation for understanding PEF's physical and mechanical properties.
• The planar chain conformation is a key feature influencing the packing and properties of PEF crystals.