Poly(ethylene oxide) (PEG) forms with CuCl2 a complex in acetonitrile (AN) solution as well as in solid phase (after evaporation of solvent). During u.v. or visible light irradiation it has been observed that a rapid photo-oxidative degradation of the PEO-CuCl2 complex in AN is caused by free Cl-. and/or Cl-2(.-) radicals (formed from the photolysis of CuCl2). With increasing degradation processes, there is also a pronounced change in the morphology of PEO-CuCl2 complexes. They lose their capability to form spherulites. This results from changes in molecular weight and dispersity that affect crystallization conditions. Both wide angle X-ray spectroscopy and differential scanning calorimetry show that photodegraded PEO molecules are almost amorphous. Low-molecular fractions are formed as a result of chain scission processes. Photodegradation processes in AN solution do not cause crosslinking or formation of a gel fraction.