The effect of hydrogen bond on the thermal and mechanical properties of furan epoxy resins: Molecular dynamics simulation study

Abstract

The hydrogen bonds (H-bonds) are employed for the thermal and mechanical property enhancement of epoxy networks; however, the formation and evolution of H-bonds, especially in emerging bio-based furan epoxy, cannot be deeply understood at the atomic level in the traditional experimental method. Herein, molecular dynamic (MD) simulation is employed to clearly investigate the H-bonds, free volume and its distribution, mean square displacement, as well as their further influence on thermomechanical behaviors of selected model epoxy resins. The model epoxy resins composed of 2,5-bis [(2-oxiranylmethoxy)-methyl]-furan (BOF), 1,4-bis [(2-oxiranylmethoxy)-methyl]-benzene (pBOB) and 2.5-bis(2-oxiranylmethoxy)-methyl)-cyclopentadiene (BOC), which were cured by 4,4′-diamino diphenyl methane (DDM), respectively. These three epoxy molecules have very similar structure with the only difference in ring blocks of monomers from furan, benzene to cyclopentadiene. Wherein, BOC is artificially designed to further explore the influence of the oxygen atom of furan rings, with ensuring the consistency with the rotation and planarity of BOF. From contrastive simulation results, BOF-DDM has the highest Young's modulus among all these systems due to the least free volume leading by the maximum H-bonds. However, for DDM crosslinking networks, H-bonds seem to have limited influence on Tg of BOF-DDM, and the effect of molecular weight and steric hindrance on Tg is more decisive, which is different from the most relevant reports on furan-based epoxy. Our study gives the significant insight of H-bonds behavior of furan rings, and it is expected to effectively guide the design of epoxy resins.