The effect of nanopores on the glass transition temperature (T-g) of poly (ether imide) was studied with differential scanning calorimetry. Nanoporous poly (ether imide) samples were obtained through the phase separation of immiscible blends of poly(ether imide) and polycaprolactone diol and by the removal of the dispersed minor phase domains with a selective solvent. Microscopy and statistical methods were used to characterize the pore structure and obtain the pore structure parameters. The pore size was found to depend on the processing time and the initial blend composition, mainly because of phase-coarsening kinetics. A decrease in T, was observed in the nanoporous poly(ether imide) in comparison with the bulk samples. The change in Tg was strongly influenced by the pore structure and was explained by the percolation theory. (c) 2006 Wiley Periodicals, Inc.