AbstractExtended chain crystals of polyoxymethylene were irradiated with x‐rays of about 105r./min. An immediate decrease in superheating on melting was noted. After 90 min. of irradiation the melting point level, refractive indices, and density also decreased. After 480 min. the DTA melting peak at a heating rate of 20°C./min. had decreased 25°C., the melting point decreased about 18°C., and the density calculated from refractive indices decreased 0.031 g./cm.−3. These effects are interpreted as indication of chain scission and formation of amorphous d