Photodegradation and Oxidation of Other Poly alkylene terephthalate s

2 Photodegradation and Oxidation of Other Poly(alkylene terephthalate)s 

Several studies have been conducted over the last twenty years on the effect of UV irradiation on poly(butylene terephthalate) (PBT) [26, 43-56]. In general, the reaction schemes of photolysis and photooxidation are virtually identical to those of PET, except that there is some controversy about if the Norrish II scission, via a six-membered ring intermediate, is significant in PBT. 

Despite its increasing commercial importance, studies on the UV degradation of poly(trimethylene terephthalate) (PTT) are lacking. It is currently assumed that the mechanisms of photolysis and photo-oxidation of PTT will be broadly similar to those previously discussed for PET. 

Studies have been carried out on the UV degradation of poly(ethylene-co-l,4-cyclohexanedimethylene terephthalate) [35,38,56]. The PET sections of the chain will undergo the various initiation, abstraction and oxidation processes already considered, but a tertiary hydrogen on the cyclohexane ring of the poly(l,4-cyclohexanedimethylene terephthalate) units means that formation of tertiary alkyl radicals and subsequent autoxidation at this site will predominate over formation of secondary alkyl radicals on methylene units or elsewhere 

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