Novel asymmetric bismaleimide (BMI) oligomers with different molecular weights and dianhydrides were designed and synthesized by 3,4 '-oxydianiline (3,4 '-ODA), 2,3,3 ',4 '-oxydiphthalic dianhydride (a-ODPA), and 2,3,3 ',4 '-biphenyltetracarboxylic dianhydride (a-BPDA). The chemical structures of BMI oligomers were confirmed by Fourier transform infrared spectrometry (FTIR) and gel permeation chromatography (GPC). X-ray diffraction (XRD) exhibited broad peaks, suggesting amorphous structures. Heat flow curves of oligomers measured by differential scanning calorimeter (DSC) displayed wide processing window due to low glass transition temperatures (T-g). BMI oligomers exhibited high solubility in common organic solvents. Particularly, the OD-BMI-1 oligomer exhibited excellent solubility of more than 50 wt% in DMAc solvent. T-g value and minimum complex viscosity of OD-BMI-1 oligomer were only 121 degrees C and 8.1 Pa center dot s, respectively. The cured BMI resins possess high thermal and thermal-oxidative stability. The T-g and the temperature of 5% weight loss in nitrogen were above 256 and 449 degrees C, respectively, and the residual weight percentages at 800 degrees C were all >49%. Moreover, films made of BMI resins exhibited excellent mechanical properties flexibility, as confirmed by photograph and DMA results of films. The elongation at break of the prepared films was found to be high (almost >9.6%). POLYM. ENG. SCI., 59:2265-2272, 2019. (c) 2019 Society of Plastics Engineers