An electron spin resonance study on γ-irradiated poly(l-lactic acid) and poly(d,l-lactic acid)

ESR studies of photosensitized degradation of poly(L-lactic acid) via photoionization of dopant

“…Babanalbandi et al observed the two types of main‐chain scission radicals 5 and 6, which, respectively, exhibit five‐line peaks and a singlet peak in ESR spectra, after γ‐irradiation of PLA (see Radical 6). 10 In our case, we could not observe such a singlet signal attributed to acyl Radical 6 in the ESR spectrum after irradiation. This is because the ester group of PLA is not directly excited by UV light (λ c = 356 nm), and only the anionic radical species is present in PLA after irradiation.…”

“…Poly( L ‐lactic acid) (PLA) is considered one of the most favorable polyesters from this viewpoint because of the high ester linkage concentration in its backbone. Babanalbandi et al studied γ‐irradiation effects on PLA and poly( D , L ‐lactic acid)10 as well as PLA‐related copolymers11 from the viewpoint of their use as biodegradable implant materials using electron spin resonance (ESR) and gel permeation chromatography (GPC) measurements. It is generally said that, in the case of γ‐irradiation of polymer materials, various cationic and anionic species are simultaneously produced in the polymer matrix after irradiation, and several reaction processes proceed because of the high energy of γ rays.…”

Thermal stability of poly(lactic acid) before and after γ-radiolysis

“…Previous studies on the radiolysis of PLA 9,10 have demonstrated that it undergoes chain scission on g-radiolysis, with the loss of ester links and the evolution of CO and CO 2 . In addition, a range of new saturated and unsaturated chain-ends have been identi®ed following radiolysis, but it is apparent that these new chain-ends are incapable of premature initiation of any thermal degradation reaction.…”

Electron-beam treatment of poly(lactic acid) to control degradation profiles

“…E-beam irradiation causes backbone main chain scission due to the high energy of the radiation breaking the attractive forces between the atoms. Active species such as alkyl free radicals and peroxyl free radicals are formed during irradiation as a result of hydrogen abstraction or chain scission at the ester groups of the polymer macromolecule [26]. The propagation of these radicals, in particular the peroxyl free radicals, greatly enhances chain scission whereas their recombination can lead to chain branching [27,28].…”