Molecular dynamics and Grand Canonical Monte Carlo simulations have been used to obtain the glass transition temperatures and the water uptake for polyimides synthesized from Naphthalene-1, 4, 5, 8-tetracaboxylic dianhydride (NTDA), 2, 2'-benzidinedisulfonic acid (BDSA), 4, 4'-diaminodiphenylether-2, 2'-disulfonic acid (ODADS), and non-sulfonated diamine monomers. The glass transition temperature Tgs of these polyimide copolymers have been determined from plots of specific volumes versus temperatures above and below Tgs. The simulation results suggest that the ODADS-based polyimide membranes have lower Tgs and better mechanical properties than the BDSA-based polyimides, which can be attributed to high mobility of the backbones of ODADS as supported by the vectorial autocorrelation function (VACF) results of this study. In addition, comparisons of the simulated Tgs for ODADS-based polyimides of various degrees of hydration show that water content in polyimides may enhance their mechanical properties by lowering the Tgs. In the case of water uptake of these polyimide copolymers, the GCMC simulation results indicate better water solubility for more sulfonated polymers.