Polyolefins, oxidation

Identification of Products from Polyolefin Oxidation by Derivatization Reactions... 

A few relatively recent published examples of the use of NMR spectroscopy for studying polymer degradation/oxidation processes will now be discussed briefly. At the early stages of degradation, the technique can be used to provide chemical identification and quantification of oxidised species for polyolefins, oxidation sites can be identified by the chemical shifts of -CH2- groups a and ji to carbons bonded to oxygen [85]. Spin-spin relaxation times may be determined by a pulse sequence known as the Hahn spin-echo pulse sequence. 

K. Jacobsson, P. Eriksson, T. Reitberger, B. Stenberg, Chemiluminescence as a tool for polyolefin oxidation studies, In A.C. Albertsson (Ed.), Long Term Properties of Polyolefins, Advances in Polymer Science, Springer, 2004, Vol. 169, p. 151. 

Poly(methylstyrene peroxide) radical polymerization, 707 stmcmre, 709 Polyolefins oxidized, 673 unsamrated, 740 Polyoxides... 

Porter NA, Roe AN, McPhail AT (1980) Serial cydizationof peroxy free radicals models for polyolefin oxidation. J Am Chem Soc 102 7574-7576... 

Fundamental understanding of the chemistry of polyolefin oxidation and the mechanisms of their stabilisation has been pivotal in achieving the current body of knowledge and the development of the vast structural diversity of stabiliser molecules that are available today. This chapter aims to project, with mechanistic perspectives, a technological overview of recent progress made in the stabilisation of polyolefins that are suitable for human-contact applications. 

Another type is made from polyolefins oxidized with peracetic acid. These have more epoxide groups, within the molecule as well as in terminal positions, and can be cured with anhydrides, but require high temperatures. Many modifications of both types are made commercially. Halogenated bisphenols can be used to add flame-retardant properties. See epoxy novolak. 

The use of a profluorescent nitroxide, in this case the phenanthrene analog TMDBIO, offers the prospect of not only quantifying the alkyl radical scavenging efficiency in the earliest stages of polyolefin oxidation (in the retardation period) as demonstrated here, but also integration over time of the total alkyl radical population formed on oxidation. Future prospects include imaging of the zones of degradation by fluorescence microscopy. 

Over 80% of the oxygen consumed can be accounted for by the known products observed However, the scheme is not complete since there are products that have not been considered. One of these products is y-lactone, also reported by Adams (11) in polyolefin oxidation. 

Polyolefins.—Polyolefin oxidation continues to be a subject of considerable controversy. Wiles and co-workers have written a comprehensive review of polyolefin photo-oxidation mechanisms with particular emphasis on the role of... 

Ultraviolet and fluorescent microscopy has been applied to a variety of polymer systems to investigate changes of morphology and composition on the scale of 0.25 ym upwards. Studies are briefly described on the behaviour of stabilisers in polypropylene, diffusion of additives in polymers, spherulite morphology, polyolefin oxidation, inhomogeneities in epoxy resins and polymer blends. 

Polyolefins are difficult to hydrolysis. It also inert towards enzymatic or physical degradation. Oxidative degradation is the main type of degradation observed in polyolefin. Oxidative degradation is the main type of degradation observed in polyolefin [30]. 

Carlsson D.J., R. Brousseau, C. Zhang, and D.M. Wiles. 1987a. Polyolefin oxidation Quantification of alcohol and hydrojreroxide products by nitric oxide reactions. Polym Degr Stab 17 303-323. 

It has been recognized for many years that polyolefins are susceptible to oxidative degradation, and a great deal of research has been done to determine why and how, and what to do about it. The reader is encouraged to consult monographs and review articles (8-13) in order to acquire some of the details and complexities of polyolefin oxidation (see also Degradation Stabilization). In essence, oxidative degradation can be summarized as follows. 

Eriksson, P., Jacobson, K., Reitberger, T., Stenberg, B. Chemiluminescence as a Tool for Polyolefin Oxidation Studies, in A.C. Albertsson (Ed), Long-term Properties of Polyolefins Series, vol. 169, Springer, 2004. 

---