Modifications induced by swift heavy ions on poly(hydroxybutyrate-hydroxyvalerate) (PHB/HV) and poly(epsilon-caprolactone) (PCL). Part 2. Radicals characterization

Modifications induced by different energetic heavy ions (Ar-40(9+), Kr-80(1 5+), Xe-129(24+), Pb-208(53+) and Pb-20(56+)) on poly(epsilon -caprolactone ) (PCL) and poly(hydroxybutyrate-hydroxyvalerate) (PHB/HV) have been invest igated by electron spin resonance (ESR). Indeed, film irradiation by heavy ions leads to, among other phenomena, the formation of radicals in the ion tracks. Thanks to ESR, it is possible to detect these radicals and to ident ify them or at least to characterize them by following the evolution of the radical signal as a function of parameters, like temperature, or the kinet ic of disappearance of the radical species at ambient temperature in vacuum or ambient atmosphere. This study confirmed the generation of radicals by the irradiation of PHB/HV samples with energetic heavy ions reported in the literature. The study on PCL was not pursued after a few preliminary studi es, revealing the presence of an ESR signal in the nonirradiated sample. El ectronic stopping power has a major influence on radical decrease at ambien t temperature. The ion used for the irradiation did not modify very much th e radical signal and the evolution of the radicalar signal intensity with t emperature. Different reasoning and experiments revealed that the glass tra nsition temperature is a key temperature above which irreversible recombina tions of the most stable radicals take place. A simulation study indicated that the most stable radical produced was probably a tertiary radical forme d by the stabilization of the secondary radical resulting from the abstract ion of a highly mobile hydrogen adjacent to the carbonyl. (C) 2000 Elsevier Science B.V. All rights reserved.