Thermal oxidation and its analysis at low levels in polyethylene

Jelinski, Lynn W.; Dumais, Joseph J.; Luongo, J. P.; Cholli, Ashok L.

doi:10.1021/ma00139a002

Cited by 38 publications

(14 citation statements)

References 6 publications

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“…If peroxyl termination rather than transfer is expected to occur then this will lead to alcohol formation and/or aldehydes (see Scheme 2). Indeed, the presence of alcohol decomposition products has been confirmed by MS, 61 IR, 56-57 17 O NMR 60 and 13 C NMR studies 54,58,62 in PE and PP. For example, secondary and tertiary alcohols were found in PP after thermal aging at 50, 80…”

Section: Studies Of Polymer Degradation Productsmentioning

confidence: 80%

The Fate of the Peroxyl Radical in Autoxidation: How Does Polymer Degradation Really Occur?

2018

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Bolland and Gee's basic autoxidation scheme (BAS) for lipids and rubbers has long been accepted as a general scheme for the autoxidation of all polymers. This scheme describes a chain process of initiation, propagation, and termination to describe the degradation of polymers in the presence of O. Central to this scheme is the conjecture that propagation of damage to the next polymer chain occurs via hydrogen atom transfer with a peroxyl radical. However, this reaction is strongly thermodynamically disfavored for all but unsaturated polymers, where the product allylic radical is resonance-stabilized. Paradoxically, there is no denying that the autocatalytic degradation and oxidation of saturated polymers still occurs. Critical analysis of the literature, described herein, has begun to unravel this mystery. One possibility is that the BAS still holds for saturated polymers but only at unsaturated defect sites, where H transfer is thermodynamically favorable. Another is that peroxyl termination rather than H transfer is dominant. If this were the case, tertiary peroxyl radicals (formed at quaternary centers or quaternary branching defects) may terminate to form alkoxy radicals, which can much more readily undergo chain transfer. This process would lead to the creation of hydroxy groups on the degraded polymer. On the other hand, primary and secondary peroxyl radicals would terminate to form nonradical products and halt further degradation. As a result, under this scenario the degree of branching and substitution would have a major effect on polymer stability. Herein we survey studies of polymer degradation products and of the effect of polymer structure on stability and show that indeed peroxyl termination is competitive with peroxyl transfer and possibly dominant under some conditions. It is also feasible that oxygen may not be the only reactive atmospheric species involved in catalyzing polymer degradation. Herein we outline plausible mechanisms involving ozone, hydroperoxyl radical, and hydroxyl radical that have all been suggested in the literature and can account for the experimentally observed formation of hydroperoxides without invoking peroxyl transfer. We also show that oxygen itself has even been reported to slow the degradation of poly(methyl methacrylate)s, which might be expected if peroxyl radicals are unreactive toward hydrogen transfer. Discrepancies between the rate of oxidation and the rate of degradation have been observed for polyolefins and also support the counterintuitive notion that oxygen stabilizes these polymers against degradation. We show that together these studies support alternative mechanisms for polymer degradation. A thorough assessment of kinetic studies reported in the literature indicates that they are limited by their propensity to use models based on the BAS, disregarding the chemical differences intrinsic to each class of polymer. Thus, we propose that further work must be done to fully grasp the complex mechanism of polymer degradation under ambient conditions. Nonetheless, ...

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Section: Studies Of Polymer Degradation Productsmentioning

confidence: 80%

The Fate of the Peroxyl Radical in Autoxidation: How Does Polymer Degradation Really Occur?

2018

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“…[12][13][14][15][16][17][18][19][20] Methods include chemical titration (such as of iodide, ferrous ion, SF 4 /HF mixtures, and sulfur dioxide) [12][13][14][15][16] and spectroscopic techniques (FTIR and NMR). [17][18][19][20] Due to the low penetration by chemical agents (such as iodide and ferrous ion) into polymers, the formation of H 2 SO 4 by SO 2 treatment, 14,16 the overlap of the hydroperoxide with alcohol absorption in FTIR spectra (a broad absorption at ϳ 3400 cm Ϫ1 ), 21,22 and the low sensitivity to hydroperoxide in NMR (the polymer must be highly oxidized), 19,20 determination of the concentration of hydroperoxide in polyethylene is difficult. Lacoste et al [21][22][23] recently developed an infrared method to quantitatively determine the concentration of hydroperoxide and alcohol in polyethylene independently, using prior exposure to nitric oxide (NO) to produce derivatives with an improved IR resolution and sensitivity.…”

Section: Introductionmentioning

confidence: 99%

Hydroperoxide formation in irradiated polyethylene

Shen

McKellop

et al. 1999

J. Polym. Sci. A Polym. Chem.

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Spectroscopic analysis for hydroperoxide in irradiated ultrahigh molecular weight polyethylene, on the basis of the formation of a nitrate derivative after exposure to dilute nitric oxide, is examined. Hydroperoxide is found to be an important intermediate in the oxidation of polyethylene and is believed to result from hydrogen abstraction reactions by peroxy radicals in a polyethylene matrix. During γ irradiation in air, the rates of bimolecular combination of peroxy radicals on the surface to form ketones or hydrogen abstraction to form hydroperoxides are similar. However, as a result of bimolecular combination, the concentration of peroxy radicals decreases. After irradiation and storage in ambient air, isolated peroxy radicals below the polymer surface induce a slow chain reaction leading to a long‐term increase in hydroperoxides and carbonyls. Differences in hydroperoxide and oxygen content for samples irradiated in air or vacuum are primarily confined to or near the surface. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3309–3316, 1999

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“…The signal at 186 ppm is, in accordance with low molecular weight thiophenes, assigned to ketone or aldehyde formation in the a-carbon position of the alkyl side chain. 24 The signals at 25 and 42 ppm, Figure 4, are further evidence that a ketone in the 3-position is formed after thermooxidation.25 These signals are associated with the neighboring carbon atoms on the side chain. Moreover, no signs of carboxylic acids or alcohols can be seen with carbon-13 NMR.…”

Section: Resultsmentioning

confidence: 96%