Charge-transfer complexes polymer-oxygen

It is conceivable that excited oxygen and/or ozone molecules and charge-transfer complexes of oxygen molecules with polymers may be involved in the initiation step of photodegradation of polymers. 

Based on the accumulated experimental evidence we can summarize by saying that HALS protect polymers by a combined mechanism where the principal activities are free radical scavenging, hydroperoxide deactivation, and formation of charge transfer complexes with oxygen. The stabilization action of HALS can be adversely affected by some other substances, like organic thioether costabilizers, halogen flame retardants, or an acidic environment. Several N-substituted HALS derivatives have... 

Free radicals might be also obtained by photolysis (C) of the charge-transfer complexes between oxygen and various sites along the polymer chains. 

After irradiation, a silver-colored thin polymer layer totally covers the liquid phase. During the irradiation process, the color of the liquid phase has changed from yellow to a deep red one. The red color is due to a charge transfer complex between iodine and the thiophene ring dissolved in the liquid. The polymerization process takes place only at the surface of the irradiated sample. However, it was observed that when the UV-irradiation by excimer laser is over, the polymerization process continues, but only at the surface of the irradiated sample a postpolymerization without incident UV-photons takes place. It was also observed that the presence of oxygen during... 

Lu et al. have reported that the fluorescence intensities of Eu3+ and Tb3+ are markedly enhanced when they are bound on to a poly(acrylamide-acrylic acid copolymer). Dhake et al. have observed interesting differential effects of pressure on the fluorescence of a polymer and the corresponding monomer. Sterically hindered piperidines have for long been of interest as efficient photostabilisers of polymers. Gugumus has now reported that these stabilisers form charge-transfer complexes with molecular oxygen, thereby preventing the formation of such complexes with the polymer. 

The recent observation of the formation of charge transfer complexes between a number of polymers and oxygen explains the bathochromic shift of their absorption [622, 623]. Such complexes absorb the radiation in the range up to 3400 A and may be excited by it. The absorbed energy may cause the dissociation of bonds in the polymer. This problem is not... 

According to Gugumus [34] the activity of nickel chelates is partly ascribed to their ability to quench excited polymer oxygen charge transfer complexes. 

Abdou, M.S.A., Orfino, F.P., Son, Y. and Holdcroft, S., Interaction of oxygen with conjugated polymers Charge transfer complex formation with poly(3-aIkylthio-phenes), J. Am. Chem. Soc., 119, 4518 524, 1997. 

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