A Novel Schiff Base Epoxy: Synthesis, Degradability, and Application as a MultiPurpose Modifier for DGEBA/DDM

Abstract

Simultaneously increasing mechanical strength, toughness, thermal stability, and flame retardancy of epoxy thermoset without compromising transparency is appealing but challenging. To address that goal, a Schiff base epoxy VDEP is developed. The neat VDEP-cured product, VDEP_100wt%, not only shows comparable mechanical strength to conventional epoxy thermoset but also can be degraded in 10% H₂SO₄/THF/H₂O solution in 24 h, showing great degradability under mild conditions. More importantly, proper addition of VDEP simultaneously increases the tensile strength, impact strength, T _g, T _d5%, char residue, and UV shielding of cured epoxies while providing self-extinguishing ability. All of those enhancements are achieved without deteriorating transparency. When 15 wt% of VDEP is added, the tensile strength reaches 91.07 MPa, with a 36.7% increase; the impact strength reaches 40.73 kJ m⁻², with a 33.8% increase. The enhancement in mechanical strength is due to the reinforcing effect of intermolecular interaction and compacted network caused by free volume reduction. The higher toughness results from greater mobility of chain segments, reduced crosslinking density and energy dissipative intermolecular interaction. The rigid two benzene-conjugated Schiff base structure and abundant hydrogen bonding contribute to higher T _g. Therefore, this work provides a degradable Schiff base epoxy and high-performance thermoset based on it.