Homopolyimides derived from a novel heterocyclic diamine, 2,6-diaminobenzo- [1,2-d:4,5-d]bisthiazole (DABBT), and either pyromellitic dianhydride (PMDA, A-series) or 4,4¡¦-sulfonyldiphthalic dianhydride (SDPA, B-series), as well as copolyimides containing different molar ratios of DABBT and 4,4¡¦-diaminodiphenyl ether (ODA), have been synthesized via soluble polyamic acids (PAA) followed by the thermal imidization. Polymer properties such as viscosity, thermal stability, crystallinity, and solubility were characterized and correlated to their monomer structure. It is found that inherent viscosity of PAA increases with increasing molar ratio of ODA/DABBT; inherent viscosity of A-series ranges from 0.11 - 1.04 dL/g and the B-series from 0.11 - 0.31 dL/g. All the copolyimides can form flexible films; A transition from tough to brittle film is found as more DABBT is added. Results from thermal gravimetric analysis indicate that the degradation temperature at 10% weight loss locates from 561¡V 635 ¢J and char yield at 800 ¢J from 56 ¡V 61% for A series; corresponding data of B-series are 489 ¡V 560 ¢J and 47 ¡V 52%, due primarily to the softer and more flexible solfone unit in SDPA. Also, the degradation temperature remains little changed with varying diamine ratios. X-ray diffractometry suggest all the copolyimides are amorphous and the PMDA/DABBT and SDPA/DABBT homopolyimides are semi-crystalline. The solubility tests indicate that solubility of B-series is better than that of A-series due to the flexible sulfone linkage; the solubility of block copolymers is better than that of random copolymers; in addition, the copolyimides with higher DABBT content have a better solubility.