Polyimides derived from a new dianhydride with p-nitrophenyl pendant groups have been synthesized and their properties compared with those of a reference series, without side groups. The polymers were obtained by combination of the novel monomer with aromatic diamines, in a two-step procedure that involved the synthesis of poly(amic acid) or poly(amic silyl ester) intermediates and the cyclization of them to polyimides by thermal treatment. The introduction of the polar nitro groups caused significant increase of the T(g)s. On the contrary, the thermal stability was reduced because of the breakdown of C-Ar-NO2 linkages around 400 degrees C. A slight decrease in mechanical properties was observed, due to the bulkiness of the side groups, that also produced an important decrease in the strength of the beta relaxation, as determined by dynamic mechanical analysis. The solubility of the current polyimides in organic solvents was as poor as that of the parent unsubstituted polymers.