AbstractTo investigate the morphology of unoriented poly(ethylene terephthalate) (PET) films and the selective character of the aminolysis of PET, 67% crystalline polymer samples were degraded with 40% aqueous methylamine at room temperature. The aminolyzed PET samples were subjected to gel permeation chromatography (GPC), viscometry, electron microscopy, and small‐angle x‐ray diffraction (SAXD). Weight loss and density crystallinity measurements were also made.After 24 hr of aminolysis, the amorphous regions and chain folds were completely removed. The long molecular chains in the semi‐crystalline polymer were reduced to monodisperse rods having a molecular weight of 1,800. The corresponding lamellar thickness was calculated to be 101 Å, consistent with the x‐ray diffraction and electron microscope (EM) measurements. The EM photographs of “stripped” crystals show the lamellar structure previously found for other selectively degraded polymeric materials. The weight of crystalline debris remaining was consistent with the initial crystallinity. After degradation the crystallinity as determined by den