INFLUENCE OF CROSS-LINK DENSITY AND CHAIN FLEXIBILITY ON MECHANICAL-PROPERTIES OF MODEL EPOXY NETWORKS

Fully cured epoxy networks having different architectures were prepare d by introducing either a monoamine acting as a chain extender or an a liphatic epoxy monomer. As expected an increase in the amount of the d ifunctional amine leads to a decrease in the crosslink density whereas the introduction of an aliphatic epoxy comonomer leads to more flexib le chains between crosslinks. Values of the Young modulus and the depe ndence of the yield stress as a function of temperature were related t o the occurrence and amplitude of secondary relaxations. The fracture toughness at room temperature was clearly associated with the glass tr ansition temperature as a consequence of plastic deformation, rather t han with chain scission.