Samples of polysiloxaneurethaneurea elastomers were prepared by moisture-curing of the siloxaneurethane prepolymers terminated with NCO groups at 25^oC and 50% R.H. Prepolymers were synthesized from polysiloxanediols of different chain length and diisocyanates using different NCO/OH molar ratio. Sterillisation of samples was made using 28 MeV E-beam or gamma rays to reach 28kGy dose.
In order to investigate free radical formation in sterillisation process, samples were studied using EPR (Electron Spin Resonance) technique 15 min after irradiation had been completed. For samples irradiated at R.T. no free radicals were observed while the clear signals corresponding to paramagnetic fragments of different structures of polymer chain were recorded by EPR for samples exposed to gamma rays at liquid nitrogen temperature. This result indicated that though free radicals were formed in sterillisation process, either recombination or transformation proceeded very quickly at R.T., so no evidence of free radicals was found at that temperature.
FTIR studies did not reveal any distinct differences between samples investigated before and after sterillisation what suggested that mostly recombination leading to crosslinking, not transformation leading to formation of new functional groups was responsible for total decay of free radicals at R.T. Mechanical properties of sterillised and not sterillised samples of the same chemical composition will be compared in order to confirm that assumption.

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