Investigation of Electron‐Irradiation‐Induced Changes in the Molecular Structure of Thermoplastic Polymers by Raman Spectroscopy

ABSTRACT The effects of electron irradiation with an energy of ~2 MeV and fluences ranging from 1 × 10 15 to 2 × 10 16 cm −2 on the molecular structure and phase composition of low‐density polyethylene (LDPE), polyketone, and ethylene–tetrafluoroethylene (ETFE) copolymer were investigated by Raman spectroscopy. For LDPE, irradiation was found to induce the appearance of bands at 1672 and 1720 cm −1 , corresponding to the formation of unsaturated CC bonds and carbonyl CO groups, respectively. The degree of crystallinity of LDPE increased from 42.1% to 45.7% at an electron fluence of 1 × 10 15 cm −2 and decreased with further increases in fluence. The initial increase in crystallinity may be associated with radiation‐induced structural ordering of the polymer chains. In the Raman spectra of ETFE, additional bands at 1688 and 1766 cm −1 were observed at the highest electron fluence (2 × 10 16 cm −2 ), which were attributed to the formation of unsaturated and oxygen‐containing structures. Polyketone exhibited a nonmonotonic evolution of structural parameters with increasing electron fluence. The intensity ratio of the crystalline to amorphous components reached a maximum at an electron fluence of 1 × 10 15 cm −2 , whereas at higher electron fluences, broadening of the bands associated with the crystalline phases was observed, indicating the accumulation of structural disorder. The results demonstrate that the nature of the radiation‐induced changes is governed by the chemical composition of the polymer chain.