Polymer stabilization light stabilizers

I. Feugt, Stabilization of Synthetic Polymers Against Light and Heat Effect, Chemistry Publishers, Leningrad, p. 26-29 (1972). 

The early recognition of the role of stable nitroxyl free radicals, e.g., 2,2,6,6-tetramethyl-4-oxopiperidine, and their hindered amine precursors, in polymer stabilization soon led to the development of the hindered amine light stabilizer (HALS) class of photoantioxidants. The first HALS, Tinuvin 770, AO-33, (commercialized in 1974) proved to offer much higher UV-stabil-ity to polymers than any conventional UV-stabilizer available at the time such as UV-absorbers, nickel compounds and benzoates. Table 3). 

Nitroxyl radicals are formed as intermediates in reactions of polymer stabilization by steri-cally hindered amines as light stabilizers (HALS) [30,34,39,59]. The very important peculiarity of nitroxyl radicals as antioxidants of polymer degradation is their ability to participate in cyclic mechanisms of chain termination. This mechanism involves alternation of reactions involving alkyl and peroxyl radicals with regeneration of nitroxyl radical [60 64],... 

Polymer-stabilized bimetallic nanoparticles containing both a light transition metal element and a precious metal element can also be prepared by a modified alcohol reduction method. For example, Cu/Pd bimetallic nanoparticles were successfully prepared with various Cu Pd ratios by refluxing a glycol solution of the hydroxides of Cu and Pd in the presence of PVP or by thermal decomposition of metal acetates. 

Cobalt complexes find various applications as additives for polymers. Thus cobalt phthalocyanine acts as a smoke retardant for styrene polymers, and the same effect in poly(vinyl chloride) is achieved with Co(acac)2, Co(acac)3, C02O3 and C0CO3. Co(acac)2 in presence of triphenyl phosphite or tri(4-methyl-6-f-butylphenyl) phosphite has been found to aa as an antioxidant for polyenes. Both cobalt acetate and cobalt naphthenate stabilize polyesters against degradation, and the cobalt complex of the benzoic acid derivative (12) (see Section 66.4) acts as an antioxidant for butadiene polymers. Stabilization of poly(vinyl chloride)-polybutadiene rubber blends against UV light is provided by cobalt dicyclohexyldithiophosphinate (19). Here again, the precise structure does not appear to be known. 

In the work [305] it is shown that the load limits possible set of means of polymer stabilization and a number of light stabilizers, used for stabilization of non-loaded polymer samples, appeared to be low-effective for light stabilization of stressed samples. In connection with this light stabilizing effect of hexaazocyclanes has been studied not only under conditions of photoageing, but also of photomechanical destruction of PETP. 

R. Foigt, Stabilization of synthetic polymers against light and heat action, Leningrad (1972), publishing house Chemistry (in Russian). 

Hindered Amine Light Stabilizers (HALS) are a new class of highly efficient stabilizers protecting polyolefins and other polymers against light-induced deterioration. They were initially developed into commercial products in our laboratories. In this review we describe the details of how they were synthesized, evaluated and developed. 

Outdoor weathering is undoubtedly the most valuable test of practical polymer stability because of the extreme complexity of the natural conditions. Indeed, though photodegradation is initiated by light, ambient temperature, humidity, rainfall and atmospheric contaminants all have an influence on the course of the degradation, and the interrelationship of these factors is not yet fully understood. Several chemical reactions, the relative importance of which are dependent on the weathering conditions, usually contribute to the failure of the sample. 

H.J. Heller and H.R. Blattmann, Some aspects of stabilization of polymers against light, Pure Appl. Chem. 1973, 36, 141-161. 

E.N. Step, J. Turro, M.E. Gande, andP.P. Klemchuck, Mechanism of polymer stabilization by hindered-amine light stabilizers (HALS). Model investigations of the interaction of peroxy radicals with HALS amines and amino ethers, Macromolecules 1994, 27, 2529-2539. 

Although each of the above mechanisms may contribute to polymer stabilization, a comprehensive perspective on the mechanism of the light stabilizing effectiveness o the hindered amine is not yet available. 

Good-rite Antioxidants. [BFGoodiich/ Spec. Polymers] Antioxidant light stabilizer for plastics. 

---