Two types of NLO active linear polyetherimides (PEI-DANS and PEI-TW PEI-TCN) derived from Mitsunobu reaction of dimide and hydroxy-functionalized DANS or TCN-type chromophores were prepared. The Tg of the resulting polymers ranged between 144-157 degrees C. The poled samples were able to produce PEI-DANS and PEI-TH/PEI-TCN (23.6 % chromophore concentration level) with macroscopic second-order NLO activity, chi((2)), values of 73 pm/V and 56 pm/V, respectively, at 1063 nm. In the latter case, no decay of the second harmonic generation signal was observed up to 125 degrees C. Such excellent thermal stability can be attributed to strong chromophore-chromophore and/or chromophore-polymer backbone interactions.