A bismaleimide monomer, 4,4'-bis(4-maleimidophenoxy)-3,3',5,5'-tetramethyl biphenyl (BMITB), was synthesized in high yield (94%) via a facile four-step reaction from 2,2',6,6'-tetramethyl-4,4'-biphenol. The chemical structure of BMITB was confirmed by FTIR, H-1 NMR, C-13 NMR and elemental analysis. The monomer used to modify the epoxy cresol-formaldehyde novolac resin (ECN)/diaminodiphenyl sulfone (DDS) system. Cured ECN/BMITB/DDS blends with higher BMITB content had two distinct glass transition temperatures that were above 250 degrees C according to differential scanning calorimetry, indicating that an interpenetrated polymer network structure may be formed. The initial thermal decomposition temperature and integral procedure decomposition temperature of the cured ECN/BMITB/DDS blends were >390 and 1080 degrees C, respectively, according to thermogravimetric analyses. No phase separation was observed in dynamic mechanical analysis of cured ECN/BMITB/DDS blends with small amounts of BMITB (5 and 10 wt%). POLYM. ENG. SCI., 49:1525-1532, 2009. (C) 2009 Society of Plastics Engineers