SYNOPSISAromatic polyesters, prepared by the reaction of phthalic or isophthalic acids and a,walkanediols, were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with methyl hexahydrophthalic anhydride. These polyesters were effective as modifiers for toughening of the epoxy resin system. The most suitable composition for modification of the epoxy resins was inclusion of 20 wt % of poly (ethylene phthalate) (MW 7200), which resulted in a 150% increase in the fracture toughness (I&) of the cured resin at no expense of its mechanical properties. The effectiveness of poly (alkylene phthalate) s as modifiers decreased with increasing the chain length of alkylene units. The toughening mechanism was discussed based on the morphological and dynamic mechanical behaviors of the modified epoxy resin system.

SYNOPSISPoly (aryl ether ketone) s were used as modifiers for bisphenol-A diglycidyl ether epoxy resin ( AER 331 ) cured with methyl hexahydrophthalic anhydride. Poly(phthaloy1 diphenyl ether) ( P P D E ) , soluble in the uncured epoxy resin without using solvents, was prepared by the Friedel-Crafts reaction of phthaloyl chloride and diphenyl ether. The mechanical, thermal, and dynamic viscoelastic properties of the modified resins with PPDE were examined and compared to the parent resin (AER 331). The fracture toughness, K~C , for the modified resins increased at no expense to their mechanical and thermal properties on 10 wt % addition of PPDE with molecular weights of more than 17,000. The toughening mechanism is discussed based on the morphological and dynamic viscoelastic behaviors of the modified epoxy resin system.