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

Abstract

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/m2) 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.

Tetrafunctional epoxy as an all‐purpose modifier for homopolymerized bisphenol A diglycidyl ether

“…The chemical structures of TFTEs, which was optimized using Smart algorithm with medium quality, 0.001 kcal/mol energy, 9000 times iteration, are shown in Figure . The six noncoplanar benzene rings make those epoxide groups far apart from each other and could minimize unwanted intermolecular cyclization reactions, which is beneficial for achieving higher crosslinking density . Compared to the traditional tetrafunctional epoxy N , N , N ′, N ′‐tetraglycidyl‐4,4′‐diaminodiphenyl methane, the epoxide groups in TFTE could react more completely due to less side reactions .…”

“…The six noncoplanar benzene rings make those epoxide groups far apart from each other and could minimize unwanted intermolecular cyclization reactions, which is beneficial for achieving higher crosslinking density . Compared to the traditional tetrafunctional epoxy N , N , N ′, N ′‐tetraglycidyl‐4,4′‐diaminodiphenyl methane, the epoxide groups in TFTE could react more completely due to less side reactions . In addition, the possible backbiting, which is important in homopolymerization, increases with the increasing spacer length.…”

“…As shown in Scheme , TFTEs of different spacer lengths were synthesized using a three‐step procedure. Details for synthesizing the TFTE with n = 2 (i.e., the spacer is C 4 H 8 ) have been reported previously; details of synthesizing TFTEs with longer spacer lengths ( n = 3, 4, 5) are given in below.…”

“…However, the increases in toughness and tensile strength are accompanied by big reduction in T g . In contrast, further work showed that several epoxide‐terminated hyperbranched polymers, which has flexible alkyl and CCO units and benzene ring structure, could be used as an all‐purpose toughener, which simultaneously improve toughness, tensile strength, elongation at break, and T g . Recently, it is found that 1‐methylimidazole (1MI)‐catalyzed hybrid epoxy system containing 5–10 wt % multifunctional epoxide‐terminated hyperbranched polyether can improve the mechanical and thermal properties of homopolymerized epoxy.…”

Synthesis of tri‐aryl ketone amine isomers and their cure with epoxy resins

“…Demanding design specifications and performance requirements, however, continue to place increased demands upon the matrix resin for next generation composite materials. A lack of toughness or distortional behavior of the matrix in particular, is driving much of the current research into more ductile and impact resistant network polymers . Despite being primarily controlled by crosslink density or the chemical structure of the network, additive approaches to improving toughness are common, including ductile and rigid inclusions, interlayers, and nanoadditives to name a few.…”