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Poly radical-based degradation

Molecular oxygen, O2, readily reacts with free radicals, and since free radicals play a dominant role in the radiolysis of polymers, O2 can significantly affect radiation-induced chemical alterations. For instance, it enhances the radiation-induced degradation of most polymers. Linear polymers, including polyethylene, polypropylene, polystyrene and poly(vinyl chloride), that crosshnk in the absence of oxygen undergo predominantly main-chain scission in its presence. As a typical example, a free-radical-based reaction mechanism proposed for the oxidative degradation of polyethylene is shown in Scheme 5.16. [Pg.277]

Ahn et al. deduced the concentration profile of heat-induced radicals in a poly-imide resin. In vitro degradation of poly(ortho esters) containing 30 mol% lactic acid has been studied by ID and 2D spectral-spatial ESRI, based on pH-sensitive nitroxide spin probes. Efforts to understand the failure of ultrahigh molecular weight polyethyleue (UHMWPE) in orthopedic components has been studied by spectral-spatial ESRI in Y-irradiated UHMWPE. ... [Pg.95]

FIpBc I61I4 Protective effect against degradation by y>radiation provided by styrene units in random copolymers of styrene and methyl methacrylate, shown by tim radical yidds G(R ) derived from the ESR spectra, (a) Experimental values for y irradiation at 77 K (b) experimental values for r>in ation at 300 K. The lines correspond to the G(R ) values for the copolymers calculated from the G(R ) values for poly(mediyl methacrylate) and polystyreiK based on the additivity of electron densities... [Pg.272]

Coltelli. M.B.. Bronco. S.. and Chinea, C. (2010) The effect of free radical reactions on structure and properties of poly(lactic acid) (PLA) based blends. Polym. Degrad. Stabil, 95. 332-341. [Pg.387]

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See also in sourсe #XX -- [ Pg.188 ]



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Base radical

Degraded poly

Poly radical

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