Miscibility, morphology and fracture toughness of tetrafunctional epoxy resin/poly (styrene-co-acrylonitrile) blends

Poly(styrene-co-acrylonitrile) (SAN) was found to be miscible with the tetr aglycidylether of 4,4'-diaminodiphenylmethane (TGDDM), as shown by the exis tence of a single glass transition temperature (T-g) over the whole composi tion range. However, SAN was found to be immiscible with the 4,4'-diaminodi phenylmethane (DDM)-cured TGDDM. Dynamic mechanical analysis (DMA) shows th at the DDM-cured TGDDM/SAN blends have two T(g)s. A scanning electron micro scopy (SEM) study revealed that all the DDM-cured TGDDM/SAN blends have a t wo-phase structure. The fracture toughness KIC of the blends increased with SAN content and showed a maximum at 10 wt% SAN content, followed by a dram atic decrease for the cured blends containing 15 wt% SAN or more. The SEM i nvestigation of the KIC fracture surfaces indicated that the toughening eff ect of the SAN-modified epoxy resin was greatly dependent on the morphologi cal structures.