Beyond Flame Retardancy: Unveiling the Multifaceted Functionality of Phosphonates in Biobased Epoxies

There are environmental safety and economic sustainability issues related to the increasing demand for high-performance epoxy resin polymers. The components of these resins largely depend on the processing of fossil fuels. Recent experiments have introduced flame-retardant biobased epoxy resin monomers, EP1 and EP2, that yield resins with thermo-mechanical properties comparable to their petroleum-based DGEBA counterparts. However, due to the relative difficulty of exploring molecular-scale structural features via experiments alone, comprehensive understanding of the structure/property relationships of biobased epoxy resins is yet to be attained. Here, molecular models of cross-linked resin systems comprising either DGEBA or the biobased EP1 and EP2, cured with 4,4-diaminodiphenylmethane, were subjected to molecular simulations to explore these relationships. Predicted trends of thermo-mechanical properties obtained in simulations are consistent with experiment. Furthermore, the simulations identified the multifunctionality of diethylphosphonate groups originally used to improve flame retardancy in EP1 and EP2. Structural analyses reveal that these pendant groups actively participate in intermolecular hydrogen bonding that may result in superior mechanical integrity while inhibiting backbone mobility to improve the material’s thermal stability. The findings of this work provide a foundation for the development of design strategies that allow thermo-mechanical property fine-tuning for flame-retardant biobased epoxy resins.