A Kinetic Evidence for the Nitroxyl Radicals Recycling Mechanism in the Photostabilizing Process of HALS

The photoinduced bulk polymerization of a reactive-hindered amine light stabilizers (r-HALS), 4-acryloyl-2, 2, 6,6-tetramethylpiperidinyl (ATMP), was performed at 80 C by using a DPC technique. An unique periodic exponential attenuation-type oscillating curve was found when the polymerization was carried out in air, but this phenomenon was not found in nitrogen. It is supposed that this unique kinetic performance may be attributed to nitroxyl radicals that are produced in situ from the oxidation of ATMP. ATMP polymer with narrow polydispersity (d = 1.03) can be obtained by photoinduced solution polymerization of ATMP. The signal detected in ESR may be assigned to the nitroxyl radicals in the matrix of ATMP polymer. Since this kind of recycling of nitroxyl radicals is well documented for the photostabilizing mechanism of HALS, the present results may serve as a kinetic evidence for this mechanism.

Research on Effect of Four Natural Ultraviolet Light Absorbers on Photostabilization of Azadirachtin-A

This study examined the photostabilization of Azadirachtin-A （Aza-A） when exposed to ultraviolet light in the presence of some natural absorbers. Aza-A extract solutions with and without natural UV light absorbers in methanol were applied onto the surface of glass slides. At particular intervals, the remaining concentration of Aza-A was analyzed by HPLC. Using first-order kinetic equation, the dissipation half-life values （DT^0） for the degradation of Aza-A under ultraviolet radiation were obtained. It indicated that the addition of ferulic acid, gallic acid, and rutin provided moderate degree of photostabilization of Aza-A and that addition of aloin provided the best photostabilization of Aza-A, among these UV absorbers studied. Photostabilization of Aza-A by different UV light absorbers appears to be due to the competitive energy absorption of UV photons by the absorbers molecules. The dissipation half-life values of Aza-A after irradiation under ultraviolet light suggested that the addition of aloin （in 1 ： 1 mol ratio） can provide better photostabilization of azadirachtin molecule.

Increasing of photostability of HNS explosive in the presence of UV photostabilizers

The photostabilies of hexanitrostillbene(HNS)were studied at 1%wt.of photostabilizers.The photostabilizers of Chiguard BP-12(UV-531),ADK STAB LA-326(UV-326),ADK STAB LA-32(UV-P),Irganox 1010 and Everstab LS944 were used in this study.A photoreactor including a 30 W monochromatic UV lamp was used for investigation of photodegradations of solid HNS.The changes in surface area of HNS peak in HPLC chromatogram at time intervals of 2,4,6 and 8 h were used for calculation of kinetic rate constants of photodegradation process.The compound of UV-P photostabilizer was found to have the greatest effect on enhancing photostability for HNS among the investigated photostabilizers.The kinetic rate constants were obtained 6.2×10^(-2) and 4.1×10^(-2)h^(-1),respectively,for photodegradation process of HNS in absence and in presence of UV-P.

AN EXAMINATION OF THE INFLUENCE OF STABILIZERS ON THE PHOTOCHEMICAL STABILITY OF DISPERSE DYES

There is a powerful market-need for superfast disperse dyes in special use, e.g. for automotivefabrics. The photochemical fading reactions of dyes are often very complicated, and no singlphotodegradation pathway can be involved for all kinds of dyes. To enhance the photostability of the commonly used disperse dyes, a series of tests on the ef-fect of variable stabilizers on the photodegradation rate of nine representative disperse dyes werecarried out both in ethyl acetate solution and on cellulose acetate film. A moderate light sourceemitting above 300 nm was adopted in this study to simulate the photofading under practical appli-cations. The results show that, in solution, 2,2,6,6-tetramethyl-piperidine is the most effectivegeneral stabilizer for all the tested dyes, but on cellulose film, nickel diethyl-dithiocarbamateshows the greatest general protecting effect, and a synergistic effect is observed for special combina-tions of stabilizers.

POLYETHYLENE CROSSLINKED WITH ULTRAVIOLET LIGHT

It was first proposed by Oster in 1956 that polyethylene could be crosslinked with ultraviolet fight in the presence of some photosensitizers. But the photocrossfinking method was not used in industry for a long period because the penetration of the light is limited. The recent work done by Rnby et al. is outstanding in the improvement on this method, and it is competitive to the high-energy irradiation method and the thermalchemistry method. Therefore, the photocrosslinking has a promising prospect in application now. This note is a brief introduction to the results about the theoretical analysis and