Toughening of bismaleimide resin by modification with poly(ethylene phthalate) and poly(ethylene phthalate-co-ethylene isophthalate)

Abstract

Aromatic polyesters were prepared and used to improve the brittleness of the bismaleimide resin composed of 4,4′-bismaleimidediphenyl methane and o,o′-diallyl bisphenol A. The aromatic polyesters contain poly(ethylene phthalate) (PEP) and poly(ethylene phthalate-co-ethylene isophthalate) (10 mol % isophthalate unit) (PEPI). PEP and PEPI were effective modifiers for improving the brittleness of the bismaleimide resin. The most suitable composition for the modification of the bismaleimide was inclusion of 20 wt % PEP (MW 18,200), which led to an 80% increase in the fracture toughness with retention of flexural properties and a slight decrease in the glass transition temperature, compared with the mechanical and thermal properties of the unmodified cured bismaleimide resin (Matrimid resin). Microstructures of the modified resins were examined by scanning electron microscopy and dynamic viscoelastic analysis. The thermal stability of the modified resin was slightly lower than that of the unmodified resin by thermogravimetric analysis. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behavior of the modified bismaleimide resin system. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1349–1357, 1997