Ductile high-Tg epoxy systems via incorporation of partially reacted substructures
A method is demonstrated for obtaining high glass transition temperature (Tg) plastically deformable crosslinked polymer systems by manipulating the network topology of epoxy systems cured with amines. Long-chain Monoamine-functionalized Partially Reacted Substructures (mPRS) were synthesized by reacting a mixture of tetraglycidyl ether of diaminodiphenylmethane (TGDDM) and polyether monoamine (PEMA) to varying extents. Predetermined amounts of the mPRS having 0%, 60%, and 80% degree of polymerization were added to a mixture of a TGDDM and polyether diamine (PEDA) as well as a mixture of diglycidyl ether of bisphenol-A (DGEBA) and PEDA. Results of quasi-static tensile tests performed on the cured samples reveal pronounced strain hardening and, subsequent, large elongation-to-failure in the modified epoxy systems containing mPRS with elevated degrees of polymerization. Thus materials with distinctly improved elongation-to-failure are obtained for systems with identical overall chemical composition. The striking difference is attributed to plastic microvoid growth aided by the presence of deformable mPRS domains. Fracture surfaces of deformed mPRS modified systems show the characteristic formation of microvoids. In comparison, similar systems based on less deformable diamine functionalized substructures (PRS), on which we reported previously, did not show the same propensity to yield and deform plastically.