ABSTRACT
The desirable, high glass transition temperatures of epoxy thermosets are largely attributed to their crosslinked state. Unfortunately, high glass transition temperatures are usually obtained at the expense of reduced toughness and damage tolerance caused by the highly crosslinked structure. Although there are many facets to designing a tough, fiber-reinforced composite, the use of a tough resin is axiomatic. The molecular weight between crosslinks can be adjusted in epoxy resins by reaction with diphenolic compounds. The ratio of diphenolic to epoxy determines the degree of advancement. Most epoxy resins are cured via addition reactions with active hydrogen-containing compounds at close to a one-to-one sto-ichiometry, rather than via “catalytic” curing agents. Crosslinkable epoxy thermoplastics resins consist of a mixture of epoxy resins that also contain difunctional extender materials, a multifunctional, dual active curing agent that is capable of linear advancement prior to crosslinking, an additional curing agent, and a latent catalyst to promote the advancement reaction of the epoxy with the diphenol.
