Poly photochemical stability

Ultraviolet Stability of PMMA—PVdF Poly blends. The potential ultraviolet resistance of this polyblend was of considerable interest. Let us first consider what is known of the photochemical stability of the components. 

The mechanisms of the thermal and photochemical degradation of poly(vinyl chloride) (PVC) continue to be active areas of research in polymer chemistry mainly because its high chemical resistance, comparatively low cost and wide variety of application m e PVC one of the most widely used thermoplastic materials. The wide variety of forms which the material can take includes pastes, lattices, solutions, films, boards and moulded and extruded pieces and depends to a very large extent on the good electrical and mechanical properties of the polymer. In spite of these advantages the even wider application of the material has been restricted by its low thermal and photochemical stability. Thermal instability is a problem since processing of the polymer is carried out at about 200 C and the photochemical instability places a limit on the extent of the outdoor applications which can be developed. 

Yousif E, Abdalla M, Ahmed A, Salimon J, Salih N. Photochemical stability and photosta-bilizing efficiency of poly(methyl methacrylate) based on 2-thioacetic acid-5-phenyl-1,3, 4-oxadiazole complexes. Arab J Chem 2011. 

The introduction of triazine-type high performance HALS was the next leap in HALS technology. Triazine backbones made excellent carriers for piperidinyl groups, affording superior thermal and photochemical stability as well as low volatility. Two of the most commonly used HALS of this class are 1,6-hexanediamine, A(,A( -bis(2,2,6,6-tetramethyl)-4-(piperidmyl)-, polymers with 2,4-dichloro-6-(4-morpholinyl)-l,3,5-triazine (CYASORB UV-3346 light stabilizer) and poly-[[6-[(l,l,3,3-tetramethylbutyl)amino]-l,3,5-triazine-2,4-diyl][2-(2,6,6-tetramethyl-4-piperidinyl)imino]-l,6-hexane-diyl [2,2,6,6-... 

Sionkowska A, Wisniewski M, Skopinska J. Photochemical stability of coUagen/poly (vinyl alcohol) blends. Polym Degrad Stab. 2004 83 117-25. 

Sionkowska A. Photochemical stability of collagen/poly(ethylene oxide) blends. J Photochem Photohiol A. 2006 177 61-7. 

Sionkowska et al. [46] farther studied the photochemical stability of poly(vinyl pyrrolidone) in the presence of 1, 3 and 5 % collagen irradiated at X, = 254 nm in air for 24 h and characterized the samples by by UV-Vis and FTIR spectroscopy and thermal analysis (TGA, DTG). It was observed that PVP was thermally and photo-chemically less stable in the presence of collagen. Collagen led to ciosslinking of PVP and increased its polarity during irradiation, indicating surface photo-oxidation. 

Sionkowska, A., Kozlowska, J., Planecka, A, Skopinska-Wisniewska, J. Photochemical stability of poly(vinyl pyrrolidone) in the presence of collagen. Polym. Degrad. Stab. 93, 2127-2132 (2008)... 

Since poly(phosphazenes) have potential use in outdoor environments, an investigation of their photochemical stability is imperative. The UV absorption spectra of PMPP in air-saturated methylene chloride before and after irradiation with 300 nm Rayonet lamps are shown in Figure 7. The absorption band around 240 - 260 nm, due to the perturbed phenyl groups on the phosphazene backbone, decreases as the irradiation is carried out, whereas the band around 270 nm increases. The decrease in 240 - 260 nm absorption indicates loss of phenyl groups attached to the -P=N- backbone of the polymer, while the new absorption band appearing around 270 nm is due to the photoproducts. 

The photodegradation of synthetic polymers can be prohibited (or at least reduced) upon addition of UV-stabilizers. These compounds transform the absorbed light energy into thermal energy thus preventing all sorts of photochemically initiated reactions. Films of poly-(m-phenylene-isophthalamide) were used which contained appropriate amounts of UV-stabilizers of the 2-(2 -hydroxy-5 -methylphenyl)benzotriazole type or their 21-methoxy derivatives. The following results were obtained ... 

Polyaniline (137) is one of the most promising conductive polymers and the conductivity could be reversibly controlled by oxidation or protonic doping mechanisms228,229. In addition, polyaniline displays good environmental and thermal stability, and its undoped form is solution processable from both organic and aqueous acid solutions. The polymerization of aniline is usually carried out by a chemical or electrochemical oxidation reaction230,231. However, photochemical methods toward the preparation of poly aniline have recently been reported232-240. 

Chemiluminescence processes in thermal and photochemically oxidised poly (ethylene - co - 1,4- cyclohexanedimethylene terephthalate). N. S. Norman, S. Allen, G. Guillaume Rivalle, M. Mchele Edge, T. Teresa Corrales, F. Fernando Catalina/ZPoZjroer degradation and stability (2002), 75, 2, 237 - 246. 

Poly(ethylene-co-1,4-cyclohexane dimethylene terephthalate) The thermal and photochemical oxidation processes of a polyester based on poly(ethylene-co-l,4-cyclohexanedimethylene terephthalate) (PECT) with approximately 30% of 1,4-cyclohexanedimethanol have been studied by means of chemiluminescence [88], Also, the stabilization activity of some commercial antioxidants has been evaluated, and it has been related to hydroperoxide levels in the polymer. 

---