Regioisomer-Specific Crystallization of Diglycidyl Ether of Bisphenol F Epoxy Resin

Diglycidyl ether of bisphenol F (DGEBF) is a common industrial epoxy resin, desired for its possible replacement of the bisphenol A (BPA) analogue DGEBA because of the potential health hazards of BPA. During curing, crystallization of the DGEBF resin can cause inaccurate resin-to-hardener ratios, resulting in incomplete cross-linking; therefore, understanding the crystallization of DGEBF is important for proper industrial control of the material. This work involved using a combination of single-crystal X-ray diffraction, Raman spectroscopy, and 1H NMR to investigate the crystallization of DGEBF. This report details the observed crystallization and crystal structures of two DGEBF regioisomers: ortho-ortho′-DGEBF and ortho-para′-DGEBF. Notably, para-para′-DGEBF crystallization was not observed, indicating that crystallization of this regioisomer does not occur under ambient conditions. Density functional theory calculations were performed to describe the phonon modes of the ortho-ortho′- and ortho-para′-DGEBF structures, corroborating Raman signatures for the respective isomers. Using a phonon mode analysis, three specific optical vibrational modes were identified at 631.3, 344.1, and 345.6 cm–1 that are unique to the para-monomer. This work offers insights into the crystallization behavior of DGEBF resins under ambient conditions and may inform potential industrial applications of this material.