Amines 2 Brittleness 2 Chain extenders 2 Chain packing 2 Chemical structure 2 Cooperative motion 2 Cross-link densities 2 Crosslink density 2 Crosslinked 2 Crosslinking 2 Cured epoxy 2 Curing 2 Curing agents 2 Epoxy matrices 2 Fracture 2 Fracture property 2 Functional groups 2 Glass transition 2 Glass transition temperature 2 Intermolecular interactions 2 Key factors 2 Mechanical behavior 2 Mechanical properties 2 Microstructure 2 Microstructure-properties relationships 2 Nonstoichiometric 2 Positron annihilation 2 Positron annihilation lifetime spectroscopy 2 Positron annihilation lifetimes 2 Positron annihilation spectroscopy 2