Modification of bismaleimide resin by soluble poly(ester imide) containing trimellitimide moieties

Poly(ester imide)s containing trimellitimide moieties have been used to reduce the brittleness of the bismaleimide resin composed of 4,4'-bismaleimidediphenyl methane and o,o'-diallyl bisphenol A. The poly(ester imide)s include poly[ethylene phthalate-co-ethylene N-(1,4-phenylene)-trimellitimide dicarboxylate]s containing 20-40 mol% trimellitimide (TI) unit, and poly[trimethylene phthalate-co-trimethylene N-(1,4-phenylene)trimellitimide dicarboxylate]s (PESIP) containing 20 mol% TI unit. The poly(ester imide)s are effective modifiers for reducing the brittleness of the bismaleimide resin. For example, when using 30 wt% of PESIP (20 mol% TI unit, M-w 13 500 g mol(-1)), the fracture toughness (K-IC) for the modified resin is increased by 80% with retention in flexural properties and a slight loss of the glass transition temperature, compared with the values of the unmodified cured bismaleimide resin. Microstructures of the modified resins have been examined by scanning electron microscopy and dynamic viscoelastic analysis. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviour of the modified bismaleimide resin system. (C) 2004 Society of Chemical Industry.