MODIFICATION OF ACID ANHYDRIDE-CURED EPOXY-RESINS BY N-PHENYLMALEIMIDE-STYRENE COPOLYMERS AND N-PHENYLMALEIMIDE-STYRENE-P-HYDROXYSTYRENE TERPOLYMERS

N-Phenylmaleimide-styrene copolymers (PMS) and reactive N-phenylmaleim ide-styrene-p-hydroxystyrene (HSt) terpolymers (PMSH) containing p-hyd roxyphenyl groups were used to improve the toughness of bisphenol A di glycidyl ether epoxy resin cured with methyl hexahydrophthalic anhydri de. PMS and PMSH were effective modifiers for epoxies. The morphologie s of the modified resins depended on modifier structure and content. T he most effective modification for the cured resins was attained becau se of the co-continuous structure of the modified resins in both PMS a nd PMSH modification systems. When using 15 wt% of PMS (<(M)over bar ( w)> 125 000), the fracture toughness, K-IC, for the modified resin inc reased by 230%, with retention of flexural modulus and glass transitio n temperature, but with a loss of flexural strength, compared with the values for the unmodified epoxy resin. When using PMSH as the reactiv e modifier, the efficiency decreased with increase in HSt content, bec ause of the increasing extent of dispersion of the PMSH-rich continuou s phases. In the modification with 10 wt% PMSH (1.0 mol% HSt unit, <(M )over bar (w)> 294000), the modified resin had balanced physical prope rties.