Simultaneous measurement of X-ray diffraction and Raman spectra has been performed for studying the structural changes in the photoinduced solid-state polymerization reaction of diethyl Z,Z-muconate (EMU) single crystal. As the reaction proceeded, the X-ray reflections coming from the polymer species started to appear and shifted the positions toward those of the finally attained polymer product. The Raman bands of the polymer species were also found to shift their frequencies toward those of the final polymer. From these experimental data. combined with the previously reported information on crystal structure and Raman shift data collected for stressed polymer single crystal, it was deduced reasonably that the polymer chains generated in the initial stage of reaction were strongly stressed because of the geometrical constraints coming from the surrounding monomer matrix and that the stress was gradually relaxed as the reaction proceeded. (C) 2003 Elsevier Ltd. All rights reserved.