Effect of electron beam irradiation on the properties of poly(tetramethylene oxide) and a poly(tetramethylene oxide)-based polyurethane

Polyurethanes (PUs) based on poly(tetramethylene oxide) (PTMO) used in the biomedical sector can be exposed to ionizing radiation in vivo as implants during diagnosis (X-ray) or during radiotherapy treatment (gamma), or ex vivo for sterilization purposes (gamma, electron beam). This ionizing radiation can, at certain levels, cause degradation of the polymer. To understand the effect on those PUs, a high molecular weight PTMO (pTHF) and one PU based on PTMO (pTHF-MDI) were irradiated with electron beam and the changes in their chemical structure and physical properties with the dose were evaluated. Electron beam irradiation produced crosslinking and chain scission without significant predominance of one mechanism over the other in pTHF and predominance of crosslinking for pTHF-MDI. New saturated hydrocarbon species were detected in irradiated pTHF by proton NMR. These species were consistent with a mechanism where radicals were formed at alpha methylenes and chain scission took place at C-C bonds without significant oxidation, in disagreement with the mechanism proposed in literature. Crosslinking decreased significantly the crystallization and melting temperatures of pTHF and pTHF-MDI. Tensile properties of pTHF decreased rapidly with the increase in dose due to chain scission.