Effects of ionizing radiation on the aging of polyester based polyurethanebinder

The effects of radiation on the aging of estane were investigated using bot h electron beam and gamma irradiation at various dose rates in the presence and absence of oxygen. It was found using GPC technique that, in the prese nce and absence of oxygen, estane primarily undergoes rapid cross-linking, by means of a carbon-centered secondary alkyl radical. It was also conclude d that estane partially undergoes scission reactions as a result of breakag e in the backbone of the main chain at C-O, N-C, and C-C bonds. The C-cente red free radical which is produced via C-C scission (primary alkyl radical) is rapidly converted to a long-lived allylic species, which, in the presen ce of oxygen, undergoes a fast reaction to produce a peroxyl radical; this radical decays with a 1.7 h half-life by pseudo first-order kinetics to neg ligible levels in 13 h. FTIR measurements show an increase in carbonyl, ami ne and carboxylic groups as a result of reaction of H atoms with R-C-O-., ( NH)-N-.-R, and R-COO.. The FTIR results also demonstrated the production of the unsaturation resulting from hydrogen atom transfer during intrachain c onversion of the primary alkyl radical to the allyl species, prompt trans-v inylene production in tetramathylene units, and hydrogen atom abstraction b y alkyl radicals from alkyl radicals on neighboring chains. (C) 2001 Publis hed by Elsevier Science Ltd.