Radiation-induced radicals in aliphatic poly(ester urethane)s studied by EPR spectroscopy

Two poly(ester-urethane)s of various weight ratios between hard and soft segments, namely 40:60 (PUR1) and 60:40 (PUR2) respectively, were investigated by EPR spectroscopy upon irradiation in a gamma chamber to a dose of 4 kGy under cryogenic conditions. The mechanisms of radiation induced processes in both phases were proposed. It was found that the relative concentration of paramagnetic species determined in each segment is not proportional to its weight contributions in poly(ester-urethane) and almost all radicals are localized in the dominant component, i.e. in PUR1 soft segments and in PUR2 hard segments. In the ester soft domains following intermediates were confirmed by EPR method: radical anion, α-ester radical and alkyl radical, whereas in the regions of urethane groups the species generated via scission of NC bond and their subsequent products were postulated. Kinetics of radicals decays and transformations were determined on a basis of double integration of EPR spectra and their deconvolution.