Free radical degradation

Additionally, organotin mercaptides can act as antioxidants, as they can sequester free-radical degradation mechanisms (48). The one drawback of mercaptide-based tin stabilizers is the discoloration of the sulfur after exposure to uv-radiation. Special precautions or formulations need to be developed for outdoor apphcations. 

From the studies described above, it was concluded that the presence of unreacted photoinitiator in a cured polymer initiates a free radical degradation of the polymer upon irradiation with UV light. It was further concluded that the rate of degradation is dependent on the structure of the initiator and the initiator concentration. 

The discussion of the essential features in the experimental and theoretical approaches to the free radical degradation of polymers is thus completed. We introduce the next section with a summary table which is subdivided according to the two extremes of degradation unzipping and random scission. The first part of Table III describes the influence of basic structure and the second deals with secondary factors for a given structure. When a polymer is processed at elevated temperatures, volatilization and deterioration of physical properties during short time intervals are a matter of concern hence initial rates are important. 

Free radical degradation of PO CORE ICRR, Graftable monomer may McCullough Bradford, 1996... 

Auto-oxidation — an autocatalytic free-radical degradation in the presence of O. It affects polymers during aging, thus it is controlled by diffusion of in the solid state. 

Zhong, S.P., Doherty, P.J., and Williams, D.E, 1994. A preliminary study on the free radical degradation of glycolic acid/lactic acid copolymer. Lastics, Rubber and Composites Processing and Application, 21 89. 

Simha, R., The kinetics of free radical degradation. Transactions of the Faraday Society, 54, pp. 1345-1354 (1958). 

These ionic pathways typically occur at temperatures (150-300°C) that are below those of typical free-radical degradation reactions. However, if polymers belonging to the above classes are subjected to higher temperatures, radical reactions are likely to prevail. Furthermore, polymers containing less polar functional groups, like ethers and azomethynes, tend to undergo radical cleavage even when they decompose at relatively low temperatures. ... 

A typical Py-FI mass spectrum for a hydrocarbon polymer (isotactic polypropylene) is shown in Figure 6.9 TTie spectrum shows the initial pyrolyzates that are formed as the polymer is held at 400°C in the direct probe. Volatile pyrolyzates are observed at every carbon number up to -1400 Da (Cioo). It is interesting that the principal oligomer series at low mass is simply multiples of the propylene monomer xmit (MW = 42n, series A). The principal series at higher mass values, however, is an a, -diene series (MW = 42n -l-12, series E). The pyrolysis mechanism may be explained by a free radical degradation pathway. ... 

Oxidative free-radical degradation by hydroperoxides can be catalyzed by certain transition metal ions, especially those of copper, cobalt, and manganese. To reduce the rate of free radical formation, two classes of additives are used (1) organic phosphines, amines, and sulfides which catalyze the decomposition of the hydroperoxides to noiuadical products, and (2) metal-ion chelators (e.g., Ph-CH=NNH-CO-CO-NHN=CH-Ph). Tertiary phosphines are thus oxidized to phosphine oxides, tertiary amines to amine oxides, and sulfides to sulfoxides, e.g.,... 

Free radical degradation of PO by addition of peroxides CORI, ICRR, CRNI Graftable monomer may also be added McCullough and Bradford 1996... 

J Curry, S Jackson, B Stoehrer, A van der Veen. Free radical degradation of polypropylene. Chem Eng Progr 84(ll) 43-46, 1988. 

E. Machova, S. Bystricky, Antioxidant capacities of mannans and glucans are related to their susceptibility of free radical degradation, Int. J. Biol. Macromol, 61,308-311,2013. 

J. D. Funkhouser, and N.N. Aronson, Chitinase family GH18 evolutionary insights from the genomic history of a diverse protein family, BMC Evolutionary Biology, 1 (1), 96,2007. S.-C. Hsu, T.-M. Don, and W.-Y. Chiu, Free radical degradation of chitosan with potassium persulfate. Polymer Degradation and Stability, 75 (1), 73-83,2002. 

Hrabarova E, Katarina Valachova, Ivo Juranek, LadislavSoltes. Free-Radical Degradation of High-Molar-Mass Hyaluronan Induced by Ascorbate plus Cupric Ions Evaluation of Antioxidative Effect of Cysteine- Derived Compounds, CHEMISTRY BIODIVERSITY - Vol. 9 (2012). 

---