Graphene oxide produced by Tour's method (GO) and GO functionalized with 4-4' oxydianiline (ODAGO) are incorporated at 0.01 to 0.10 weight percent (wt%) into a polyimide (PI) made from 3,3'-benzophe-nonetetracarboxylic dianhydride (BTDA) and 4-4' oxydianiline (ODA). The performance properties of these two systems GO-PI and ODAGO-PI at extremely low GO concentrations are compared. ODAGO-PI nanocomposite's performance properties are comparable to previous results citing concentrations 10 times higher and displayed significantly greater improvement than unfunctionalized GO-PI films. The 0.01 wt% ODAGO-PI film demonstrated a factor of ten decrease in water vapor permeability. The 0.10 wt% ODAGO-PI film displayed the maximum increase of 82% in Young's modulus. The water vapor permeability results were fit to the Nielsen law. We found that the model yielded unphysically large aspect ratios for the 0.01 wt% ODAGO-PI, 100 times larger than the AFM-measured value. For the GO-PI, we observe less enhancement of the barrier properties. The large aspect ratio indicates tortuosity effects alone cannot explain the enhanced barrier properties. We propose that the improved barrier properties are also due to a stabilizing effect of the flakes on the polymer matrix, where reduced mobility of the PI chain reduces diffusion through the polymer matrix. ATR-FTIR, WAXS, Raman and T-g results support this view. (C) 2016 Elsevier Ltd. All rights reserved.