Radiation damage in polyethylene as studied by electron spin resonance

Abstract

The electron spin resonance method was employed to study the nature, concentration and kinetics of the disappearance under varying conditions of radicals produced in polyethylene by fast electron irradiation at 77°K. The predominant radical species at 77°K is the alkyl radical —CH 2 —ĊH—CH 2 —. On being warmed to room temperature it disappears rapidly, revealing a more stable un­identified radical. The kinetics of the decay at room temperature of both radicals was observed. Their stabilities were found to vary in polyethylene samples of differing physical and chemical properties. G values for these radicals are given. Comparison was made with spectra obtained under similar conditions with two pure paraffins and a pure olefin to evaluate the effect of crystallinity branching, molecular weight and unsaturation. In the olefin there is evidence for a build-up of allyl radicals due to the encounter of an alkyl radical with main chain unsaturation. This supports the view that alkyl radicals are mobile, and cross-linking occurs when two such radicals meet.

Vitamin E-stabilized UHMWPE for Total Joint Implants: A Review

“…Due to radiolytic bond scission, free radicals are produced in irradiated UHMWPE [15,18,20,30,38], which react with oxygen and trigger the oxidation cascade [2, 16, 17, 20, 22, 25-27, 54, 69] ( Fig. 2A, Reactions 1-4).…”

The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

“…In irradiated UHMWPE, the prevalent free radicals are the carbon free radicals resulting from the breakage of the C-H bonds (14) and these radicals are found in three forms: the alkyl, allyl and polyenyl free radicals (15)(16)(17), the latter being formed especially at higher radiation doses ((18) , Fig 1). Most of these free radicals recombine in the amorphous portion of the polymer (19), where the chains are highly mobile.…”

Chemical Orthogonality in Surface-Patterned Poly(ethylene glycol) Microgels

“…We refer to the radiation-induced functionality at high doses in all three PEG systems as amine reactivity rather than, for example, acid functionality, because we do not know exactly what specific groups are produced by the e-beam radiation. While there have been several groups who have researched various aspects of hydrogel formation during the electron or γ irradiation of PEG-based systems, − particularly in the cases involved hydrated PEG, a detailed understanding of the mechanistic aspects of the radiation chemistry is much less established. ,, Substantially more is known about the electron radiation chemistry of polyethylene. ,− Notably, the irradiation of polyethylene in the presence of oxygen (e.g., air), or in vacuum followed by air exposure, can produce aldehydes, ketones, as well as carboxylic acid groups. − In contrast to polyethylene, the PEG main chain contains an ether oxygen, which can contribute to similar reactions. Such amine-reactive radiation products are even more likely to form when PEG is irradiated in air .…”

“…Electron radiation cross-links the PEG to form microscopic gels (microgels) and covalently grafts these to the underlying substrate. Similar to the cross-linking process in irradiated polyethylene, , cross-linking in PEG has been attributed to the knock-on release of hydrogen that then leads to cross-linking by a free-radical process. ,− The degree of cross-linking and, hence, the microgel swelling properties can be controlled by the incident electron dose and by the molecular weight of the precursor polymer. , Higher doses produce more cross-links and, thus, less swelling, which in the extreme of very high electron doses destroys the antifouling properties characteristic of PEG.…”