MODIFICATION OF BISMALEIMIDE RESIN BY POLY(PROPYLENE PHTHALATE), POLY(BUTYLENE PHTHALATE) AND RELATED (CO)POLYESTERS

Aromatic polyesters were prepared and used to decrease the brittleness of the bismaleimide resin composed of 4,4'-bismaleimidediphenyl metha ne (BMI) and o,o'-diallyl bisphenol A (DBA) (Matrimid 5792 resin). The aromatic polyesters included poly(propylene phthalate) (PPP), poly(2, 2-dimethylpropylene phthalate) (PDPP), poly(butylene phthalate) (PBP) and poly(butylene phthalateco-butylene terephthalate) (50 mol% terepht halate unit) (PBPT). The polyesters were effective modifiers for decre asing the brittleness of the bismaleimide resin. For example, inclusio n of 20 wt% PPP (MW 18 700) led to 50% increase in the fracture toughn ess (K-IC) with retention of flexural properties and a slight loss of the glass transition temperature, compared with the mechanical and the rmal properties of the unmodified cured bismaleimide resin. Micro-stru ctures of the modified resins were examined by scanning electron micro scopy and dynamic viscoelastic analysis. The thermal stability of the modified resins was slightly lower than that of the unmodified resin a s determined by thermogravimetric analysis. The toughening mechanism i s discussed in terms of the morphological and dynamic viscoelastic beh aviour of the modified bismaleimide resin system. (C) 1998 SCI.