EFFECT OF MATRIX COMPOSITIONS ON MODIFICATION OF BISMALEIMIDE RESIN BY N-PHENYLMALEIMIDE-STYRENE COPOLYMERS

The effect of matrix compositions on the toughening of bismaleimide re sin by modification with N-phenylmaleimide-styrene copolymers (PMS) we re examined. The bismaleimide resin was composed of 4,4'-bismaleimided iphenyl methane (BMI), o,o'-diallyl bisphenol A (DBA), and triallyl is ocyanurate (TAIC). The matrix structure was controlled by changing the equivalent ratio of the two allyl components (DBA and TAIC). Morpholo gies of the modified resins changed from particulate to cocontinuous a nd to inverted phase structures, depending on the modifier content. Th e most effective mod ification for the cured resins could be attained because of the cocontinuous structure of the modified resins. Inclusio n of TAIC led to a decrease in the extent of dispersion of the coconti nuous phase, and the optimum matrix structure to improve the toughness was obtained on 20 eq % addition of TAIC. For example, when using 20 eq % of TAIC and 5 wt % of PMS (M(w) 303,000), the fracture toughness (K-IC) for the modified resins increased 100% at a moderate loss of fl exural strength and with retention in flexural modulus and the glass t ransition temperature, compared to those of the unmodified cured Matri mid resin. (C) 1996 John Wiley & Sons, Inc.