The mechanical properties and thermal transition behaviors of nylon 6-b-polyimide-b-nylon 6 triblock copolymers have been studied with varying block length and rigidity of the polyimide backbone and compared with those of pure nylon 6, in situ and physical solution blends. From differential scanning calorimetry experiments for liquid nitrogen quenched triblock copolymers, it is found that the crystallization temperature, which appears on successive heating, increases by 10-15 degrees C, indicating relatively slow crystallization kinetics. Dynamic mechanical (DM) experiments show that the triblock copolymers exhibit a storage modulus which is 2 times higher than that of pure nylon 6 in the temperature range of -50 degrees C to 150 degrees C. As the rigidity of the polyimide backbone increases, the storage modulus of the copolymers decreases. In addition, the system with a polyimide block length of 12 000 g mol(-1) shows the highest E’ than any others with the block length shorter or longer than this value. Glass transition behaviors of these materials are also studied via alpha relaxations from DM observations. The relaxation peak temperature of tan delta increases from 60 degrees C of pure nylon 6 to 82 degrees C with 5% incorporation of the polyimide block component in the triblock copolymers. By incorporating a fully aromatic polyimide backbone into the triblock copolymer system, the tan delta peak of the alpha relaxation increases even further to 105 degrees C with the same weight percentage of polyimide block incorporation.