Nitrogen-Free Tetrafunctional Epoxy and Its DDS-Cured High-Performance Matrix for Aerospace Applications

Tetrafunctional epoxy is an indispensable matrix for the aerospace industry, high-temperature adhesives, and encapsulation materials, where high service temperatures (>220 °C) are required. N, N, N ′, N ′-Tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) has long been the dominant candidate in those applications; however, fully cured TGDDM epoxy materials suffer from poor toughness, unwanted side reactions, and inadequate moisture resistance. A novel tetrafunctional epoxy, TFTE, is synthesized to address those issues, which have not been resolved for decades. TFTE can be prepared through a simple three-step procedure using readily available raw materials. Each step shows a high yield (>90%) and involves only mild reaction conditions. When TFTE is mixed with diglycidyl ether of bisphenol A (DGEBA) and cured with 4,4′-diaminodiphenylsulfone (DDS), the cured epoxy shows a T g value of 252 °C, a tensile strength of 80.0 MPa, and, more importantly, a higher toughness (29.8 kJ/m 2 ) and better moisture resistance than the TGDDM/DDS system. In addition, the interfacial strength, thermal stability, and processability of TFTE/DGEBA are comparable to those of TGDDM. These excellent properties and processability make TFTE a potential replacement for TGDDM.