Preparation of novel soluble poly(ester imide)s containing a trimellitimide moiety and their use as modifiers for aromatic diamine-cured epoxy resin

Poly(ester imide)s, prepared by the reaction of phthalic anhydride, N-(4-ca rboxyphenyl) trimellitimide and 1,2-ethanediol, were used to improve the to ughness of bisphenol-A diglycidyl ether epoxy resin cured with 4,4'-diamino diphenyl sulfone (DDS). The poly(ester imide)s include poly(ethylene phthal ate-co-ethylene N-(1,4-phenylene) trimellitimide dicarboxylate)s (PESIs) ha ving 10, 20 and 30 mol% trimellitimide (TI) units, respectively. PESIs havi ng 10 and 20 mol% TI units were effective as modifiers for toughening the c ured epoxy resin. For example, the inclusion of 20 wt% of PESI (20 mol% TI unit, (M) over bar (W) 19300 gmol(-1)) led to a 55% increase in the fractur e toughness (KIC) of the cured resin (with an increase in flexural strength and modulus) and the modified resin had a particulate morphology. PESI hav ing 30 mol% TI units was not effective because of degradation of the modifi er by DDS. The toughening mechanism is discussed in terms of morphological and dynamic viscoelastic behaviour of the modified epoxy resin system. (C) 2001 Society of Chemical Industry.