Abstract
Toughening of epoxy resins is very important for the application of the resins as advanced specialty materials to aerospace, electronic, or automotive industries. This review has focused on a guiding principle in the toughening of epoxy resins. The method for the toughening is based on two categories : (i) toughening with high-performance epoxy resins or hardners; (ii) toughening with modifiers such as elastomers or thermoplastics. High-performance epoxy resins with rigid biphenyl, dicyclopentadienyl, or naphthalene residues have been developed and successfully used in microelectronic industry. The resins give the cured products with lower crosslinking density and higher toughness, compared to cresol novolac epoxy resins. Epoxy resins containing mesogen units give liquid crystaline thermosetts with high toughness.
Elastomers such as liquid rubbers are good toughening agents for epoxy resins with lowly crosslinked structure, but not for ones with highly crosslinked structure. The use of engineering plastics such as polysulfone, poly (ether sulfone), or poly (ether imide) can result in toughened epoxy resins without significant decreases in modulus, strengths, and thermal properties. The factors that affect the toughening of epoxy resins with engineering plastics have been discussed.
