Side-chain free aromatic polyimides are expected to possess extraordinary mechanical properties and stability because of strong primary and secondary bonding forces. However, their low solubility makes it difficult to characterize, process, and obtain high molecular weight polymers. We have prepared highly stable thin films of side-chain free aromatic polyimides from soluble Diels-Alder (DA) precursors. Heating the films of the precursors above 215 degrees C induced retro-DA reaction, which converted the precursors to the fully aromatic polyimides. The solid-state retro-DA reactions were monitored by attenuated total reflection Fourier transformed infrared (ATR-FTIR) and UV-Vis spectrometry. A critical issue for utilizing precursor chemistry in polymer synthesis is that it may result in porous and/or deformed materials. In this work, profilometry and atomic force microscope (AFM) were applied to study the surface and volume change. Our results showed that smooth and pin-hole free films were obtained after the thermal treatment, while the Volume decreased with a percentage close to the weight loss caused by the retro-DA reaction. (C) 2009 Wiley Periodicals, Inc. J Appl Polyl Sci 112: 2953-2958, 2009