EPR and ab-initio study on the solid state radiolysis of aliphatic and aromatic polyesters

Low temperature matrix EPR spectroscopy was employed to investigate the free radical intermediates in the solid state radiolysis of poly (ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(ethylene naphthalate) (PEN), poly(1,4-cyclohexanedimethylene terephthalate-co-ethylene terephthalate) (PCT-co-ET) and poly(ethylene adipate) (PEA). With PEA the species identified is consistent with the formation of carbon centred radicals stemming from electron capture, C-O scissions and H abstractions, the most abundant species at room temperature being the alpha-ester radical, -CH2-CH center dot-COO-. The radiolysis of PEN is characterized by the predominance of radicals arising from the aromatic section, the preferred reaction being the H atom addition at a position adjacent to the ester unit, leading to the formation of cyclohexadienyl type radicals. In the copolymer, PET and PBT, the role played by the aliphatic and aromatic sections with respect to radical forming processes is of comparable importance. The cyclohexadienyl radicals arising from these latter polymers are reckoned with the prominent H addition at the sites adjacent to the esters groups which are also statistically favoured. The reactivity distribution in the aromatic rings with respect to the formation of cyclohexadienyls was analyzed in greater detail by comparing the experimental results with DFIF B3LYP M.O. calculations. The DFT method has also been employed for assessing the EPR properties of the cyclohexadienyl and ion-radicals from PEN and PET models. (C) 2008 Elsevier Ltd. All rights reserved.