Thermally stimulated chemiluminescence in photo-oxidized poly(ethylene 2,6-naphthalene dicarboxylate)

Poly(ethylene 2,6-naphthalene dicarboxylate) exhibits thermally stimulated chemiluminescence after exposure to ultraviolet radiation and oxygen. The chemiluminescence spectrum is essentially the same as the fluorescence spectrum of the polymer with a maximum intensity at 430 nm. Upon heating, the decay of the luminescence follows a first-order law with an activation energy of 26.3 ± 0.3 kcal/mole. A comparison of the ultraviolet absorption spectra of the polymer before and after exposure to ultraviolet light and oxygen indicates that the naphthalene ring is oxidized. Heating the polymer above 80°C causes decomposition of the initial photo-oxide to produce luminescence.     

Photodegradation of polyvinylacetophenone. I. Long-wave photolysis

Polyvinylacetophenone (PVAP) films were exposed to long-wave (λ ≥ 300 nm) ultraviolet radiation in the absence of oxygen. The gaseous products, determined quantitatively by mass spectrometry, were methane, ethane, carbon monoxide, and acetaldehyde. These indicated that the polymer was undergoing photodecomposition via a Norrish type I reaction. The polymer also undergoes crosslinking reactions, becoming insoluble after 100 hr irradiation, and the ultraviolet and phosphorescence spectra indicate loss of carbonyl chromophores. The mechanism of photolysis is discussed, and the implications of the effects of photodegradation on the efficiency of the polymer as a sunlight energy transfer agent are examined.     

ESR study of radiation damage in TPX polymer (poly-4-methylpentene-1)

Electron spin resonance spectroscopy has been used to study the effects of 15 MeV electrons, x-rays, and ultraviolet radiation on poly-4-methylpentene-1 (TPX) both at 77°K and at room temperature. At least seven identifiably different paramagnetic species are observable in unstabilized oxygen-free TPX after irradiation, and additional species exist in the stabilized grades. The species which predominates under most conditions is interpreted as being due to the loss of hydrogen from a main-chain tertiary carbon atom; interpretations of most of the other species are also given. Oxygen is found to diffuse rapidly into the polymer and to react with the free radicals to form peroxy species. In the absence of oxygen the radiation damage is expected to lead ultimately to crosslinking or double-bond formation, or with oxygen to degradation. The general nature of the free radicals produced by electron or x-ray irradiation is the same, but there are significant differences for ultraviolet irradiation. The observed spectra for irradiated TPX and their interpretations are in good agreement with the spectra and later interpretations for irradiated polypropylene, but are in less satisfactory agreement with the published papers on polybutene-1 and poly-3-methylbutene-1.     

Effects of gamma irradiation on poly(ethylene isophthalate)

Radiation methods are largely used for polymerisation and polymer modification, since irradiation induces transformations in the structure of materials which can be exploited to improve their performance. On the other hand, combined action of ionising radiation and oxygen may lead to degradation of the polymer, with worsening of properties such as mechanical strength or electrical insulation resistance. Therefore, the change of the chemical and physical properties of polymers under irradiation is a dynamic topic of research. In this work there are discussed data on the physical features of a polyester, poly(ethylene isophthalate) (PEI), subjected to gamma irradiation up to 1 MGy. PEI is a semicrystalline polymer with a structure similar to polyethylene terephthalate. Viscosity and differential scanning calorimetry measurements were carried out which allowed the monitoring of changes in the structure in terms of variations in the molecular weight, as well as of the percentage crystallinity depending on the dose. Furthermore, positron annihilation lifetime spectroscopy supplied information on the free volume present in the amorphous phase of the irradiated polymer.     

Inactivation of Food-borne Spoilage and Pathogenic Micro-organisms on the Surface of a Photoactive Polymer

The photodynamic action of a novel photoactive polymer comprising covalently bound anthraquinone (AQ) moieties was evaluated after developing a methodology to reliably immobilize viable micro-organisms onto polymer film surfaces. The survival of Escherichia coli, Bacillus cereus (vegetative cells and spores), Fusarium oxysporum and Saccharomyces cerevisiae microbes inoculated on the surface of inert polymeric substrates was assessed to determine the effect of inoculum composition, drying rate and exposure to ultraviolet (UV-A) radiation. Their survival was highly dependent on microbial genus, with E. coli consistently displaying markedly shorter survival times than the other microbes, and B. cereus spores being the most resistant. Inoculation of the microbes onto the surface of the photoactive polymer films, followed by exposure to UV-A radiation, dramatically accelerated the inactivation of all microbial types studied compared with their survival on the surface of inert polymer substrates. Simultaneous exposure to both oxygen and UV-A radiation is required to affect cell survival, which is consistent with this effect most likely originating from the photoinduced production of singlet oxygen by the photoactive polymer. These results provide further compelling evidence that singlet oxygen produced exogenously by this photoactive polymeric substrate can successfully inactivate a broad spectrum of microbes on the substrate’s surface.     

Sandwich structure containing liquid crystal polymer grafted on polymer support

Graft post-polymerization of mesogenic monomers onto fluorine-containing polymer support was initiated by the simultaneous action of vacuum ultraviolet radiation and atomic oxygen. The resultant two-layer structure possesses the combined physical–mechanical properties of the polymer-supporting film and the optical characteristics of the anisotropic liquid crystal layer.     

Study of ultraviolet light and ozone surface modification of polypropylene

Chemical reactions of the surface of a polypropylene (PP) film in the presence of various combinations of ultraviolet light and ozone gas (UVO) conditions were studied. Exposure of the polymer surface was carried out in a laboratory-scale UVO reactor in which the following parameters could be varied: ozone concentration, wavelength of ultraviolet (UV) radiation, pulsed operation of the UV lamps, the treatment distance between the PP film and the lamps, and water vapor concentration. Advancing and receding contact angle measurements were used to monitor surface energy changes imparted by the treatment. Two spectroscopic techniques, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR), were used to monitor changes in the polymer surface chemistry. Oxidation of the PP surface is proposed to occur through two alternate mechanisms: (1) insertion of an O (¹D) atom to form ether linkages, or (2) hydrogen abstraction by O (³P), followed either by crosslinking or by reaction with oxygen species to form carbonyl and/or carboxyl functional groups. It was found that reaction 1 dominates initially, but that its rate is reduced by the formation of products from reaction 2. It appears that the ether functional groups produced by reaction 1 are responsible primarily for increased surface energy. Carbonyl, carboxyl, and hydroxyl groups formed in reaction 2 appear to have little additional effect on surface energy; it is proposed that these groups are involved strongly in intramolecular hydrogen bonding, thereby decreasing their availability to contribute to increased surface energy. High-energy UV radiation was found to play only a minor role in the surface modification of PP. Of the narrow range of ozone concentrations studied, no clear relationship was found to exist between ozone concentration and rate of modification of the surface; thus, the concentration of ozone must not affect the relative concentrations of products from the competing reactions. Increased surface oxidation and decreased contact angles were observed when the lamp-to-sample distance was minimized. The presence of water vapor during UVO treatment was found to lead to greater oxygen uptake after short-term treatments but did not result in increased surface energy. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2489–2501, 1999     

Kinetics of polymeric radical oxidation with molecular oxygen in poly(methyl methacrylate) films

In poly(methyl methacrylate) films, the kinetics of the oxidation of polymeric radicals and azobenzenenitrenes with molecular oxygen dissolved in the polymer is studied. The free radicals are produced at 77 K by irradiating the polymer with UV light, fast electrons, or γ rays. The concentration of oxygen is varied from 4.5 × 10¹⁸ to 3.1 × 10¹⁹ cm^?3; the temperature of the reaction, from 90 to 130 K. The reaction is carried out in excess oxygen. The kinetics of radical oxidation is shown to be independent of the type of radiation that stimulates the formation of radicals and coincides with the kinetics of the oxidation of azobenzenenitrenes, which are uniformly dissolved in the polymer. It is concluded that the structure of the polymer in the vicinity of the radicals is virtually the same as the structure of the polymer bulk. The activation energy of the oxygen diffusion coefficient calculated according to the radical oxidation kinetics amounts to ～30 kJ/mol.     

Comparison of photo- and radiation-induced radical formation in polyethylene by ESR spectroscopy

The behaviors of free radicals produced in polyethylene irradiated with ultraviolet light and electron beams were compared in connection with primary processes of radical formation and trapping regions of free radicals. In the case of irradiation with ultraviolet light, an ESR spectrum observed at ?196°C immediately after irradiation is an eight-line spectrum due to alkyl radicals of the type ? CH₂? ?H? CH₃, while in the case of ionizing radiation, a six-line spectrum due to ? CH₂? ?H? CH₂? was observed. The former radicals are produced by the Norrish type I reaction of the carbonyl groups contained in the polymer, followed by radical rearrangement; and the latter are formed by dissociation of hydrogen atom from the excited state of the polymer or ion-molecular reactions. From the sensitivity to oxygen molecules, it was deduced that free radicals are trapped in amorphous regions after ultraviolet irradiation, but mainly in crystalline regions after irradiation with electron beams. Saturation studies of ESR spectra seem to support this conclusion.     

真空紫外辐照对加成型硅橡胶光学性能的影响

考察了加成型硅橡胶在真空环境中经1000ESH紫外辐照后的性能变化。结果表明,辐照后材料均出现发黄的现象,光学透过率大幅度 下降,同时加入硅酸钾包覆后制备的热控涂层反射率下降。经原位测试与离位测试,发现加成型硅橡胶在两种不同条件下测得的结果差异较小,而在有机硅橡胶中加入ZnO后原位与离位测试结果则差异明显,表现出明显的漂白作用。     

PHOTOCHIMIE DES ACIDES AMINES AROMATIQUES EN SOLUTION - I. dl-PHENYLALANINE, dl-TYROSINE ET l-DOPA

Abstract— The action of ultraviolet radiation on dl -phenyldanine, dl -tyrosine and l -dopa has been studied in dilute aqueous solutions (10^-2M–5 × 10^-3M). Irradiation was performed in nitrogen or in air, at a wavelength of 254nm. The photoproducts of low molecular weight (amino acids, carboxylic acids, amines) were isolated either by chromatography on an ion exchange column or by thin-layer chromatography and identified mainly by ultraviolet absorption and staining with ninhydrin. The isolation of photopolymers was carried out by chromatography on a Biogel column; identification of these photoproducts was mainly achieved by ultraviolet and infrared spectroscopy. With phenylalanine, which is the most photosensitive amino acid, the principal reaction results in splitting of the side chain, giving alanine, glycine, and four other amine compounds whose structure has not been determined. In air, additional minor products resulting from photooxydation are obtained: ortho, meta and paratyrosine. Traces of phenylethylamine were isolated after irradiation in an inert atmosphere. The polymers produced under air and nitrogen are similar. They probably result from rearrangement of aromatic radicals formed by splitting of the side chain. Tyrosine and dopa, irradiated in air, yield mainly melanin; before polymerization, tyrosine is first converted into dopa. In a inert atmosphere, these aromatic aminoacids also polymerize, giving monophenolic and biphenolic compounds with structure close to that of melanin. The biphenolic polymer (thus obtained from dopa) shows the properties of a leuco derivative of melanin. The monophenolic polymer can be converted into melanin by the combined action of oxygen and ultraviolet radiation. Other reactions give only minor products: parahydroxy-phenyllactic acid and 3,4-dihydroxyphenyllactic acid by deamination-hydroxylation of tyrosine and dopa (in air): meta and paratyrosine by dehydroxylation of dopa, either in air or in nitrogen.     

Effects of ultraviolet radiation on aqueous polyelectrolyte solutions

The effects of ultraviolet radiation on dilute aqueous solutions of poly(acrylic acid) and of other polyelectrolytes were studied by viscosity measurements in connection with the effects of ionizing radiation. It was found that ultraviolet light of wavelength below about 2300 Å brought about degradation of polymer chains mainly by indirect action via water, while light of wavelength above 2300 Å caused degradation by direct action in some polymers. It was deduced from the experiments that the protective effect of NaCl could be largely attributed to a decrease in the indirect action. It was also found that a low concentration of methanol was effective in preventing degradation by direct action, although methanol promoted degradation when present in high concentration. Since the promotive effect was not observed when light of wavelength below 3700 Å was eliminated by a filter, this effect was attributed to active products of the irradiation of methanol.     

Increased level of oxidative stress in genomically unstable cell clones

Recently, we reported that ultraviolet radiation induces delayed mutations in mammalian cells. At the same level of cell death the oxidative component of sunlight (ultraviolet A radiation) was as potent in inducing this kind of genomic instability as ultraviolet B radiation. Ultraviolet B radiation predominantly harms cells by direct damage to DNA and thus is much more mutagenic than ultraviolet A radiation. From that study, clones with a significantly increased mutation rate in the hypoxanthine phosphoribosyl transferase gene were obtained. These genomically unstable clones were also found to have a higher variance in the number of chromosomes than the unirradiated control cells, indicating chromosomal instability. The mechanisms for induction and maintenance of radiation induced genomic instability are not known, but some studies suggest that reactive oxygen species might be involved. In the present study, we have measured the level of potentially mutagenic peroxides in the genomically unstable clones. The levels of intracellular peroxides and lipid peroxides were measured using the probes dihydrorhodamine 123 and diphenyl-1-pyrenyl-phosphine, respectively. The unstable clones had elevated levels of oxidants, supporting the hypothesis that intermediate reactive oxygen species might have a role in the maintenance of genomic instability induced by ultraviolet radiation.     

Photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution. The role of some dyes in the degradation

The influence of some dyes on the photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution has been studied. It has been found that, among the dyes used, only riboflavin sensitizes and accelerates the degradation of the polymer. It is proposed that under ultraviolet irradiation riboflavin undergoes photoreduction to lumichrome, which sensitizes the photodegradation of the polymer. It is also possible that the mechanism of photodegradation involves the participation of singlet oxygen.     

Polymers derived from fluoroketones. III. Monomer synthesis,polymerization, and wetting properties of poly(allyl ether) and poly(vinyl ether)

The synthesis and polymerization of a series of perhaloalkyl allyl and vinyl ethers derived from perhaloketones is described. Data on the critical surface tension of wetting (γ_c) for high molecular weight polymers of heptafluoroisopropyl vinyl ether and low molecular weight poly(heptafluoroisopropyl allyl ether) is also presented. Preparation of the allyl ethers is a one-step, high-yield displacement reaction between the potassium fluoride–perhaloacetone adduct and an allyl halide, such as allyl bromide. The vinyl ethersare prepared by a two-step process which involves displacement of halide from a 1,2-dihaloethane with a KF–perhaloacetone adduct and dehydrohalogenation of the 1-halo-2-perhaloalkoxyethane to a vinyl ether. Low molecular weight polymers were obtained with heptafluoroisopropyl allyl ether by using a high concentration of a free-radical initiator. The low molecular weight poly(heptafluoroisopropyl allyl ether) had a γ_c of 21 dyne/cm. No polymer was obtained with tributylborane–oxygen or with VCl₃–AIR₃, with gamma radiation, or by exposure to ultraviolet light. High molecular weight polymers were obtained from heptafluoroisopropyl vinyl either by using either lauryl peroxide or ultraviolet light but not by exposure to BF₃–etherate. The γ_c for poly(heptafluoroisopropyl vinyl ether) ranged from 14.2 to 14.6 dyne/cm., and the significance of this value is discussed in relation to the γ_c for poly(heptafluoroisopropyl acrylate).     

Synergetic effect of the action of atomic oxygen and vacuum ultraviolet radiation on polymers in the Earth’S ionosphere

A procedure for the bench-test simulation of the physicochemical interactions of polymers with flows of atomic oxygen and vacuum ultraviolet radiation in the ionosphere of the Earth has been developed. The threshold values of the ratios of the vacuum ultraviolet flux density to the flux of atomic oxygen, which characterize the synergistic effect on the ablation of polymers (the polyimides Kapton-H and PM-1E, polyethylene, and Teflon 100A) have been obtained.     

Photodecomposition of polymethylsiloxane

Infrared spectroscopy studies were undertaken to determine the effects of ultraviolet light radiation on a methylsiloxane resin. The results indicate that SiCH₂Si linkages were formed as a result of irradiation at wavelengths above 281 mμ from a xenon are lamp; on the other hand, Si? OH and SiCH₂CH₂Si linkages were formed instead when the resin was exposed to the lower wavelengths emitted from a mercury vapor lamp. The different effects on the resin induced by the two ultraviolet light sources are attributed to the fact that only the energies from the mercury vapor lamp radiation are sufficient to cause the excitation of oxygen molecules in the air surrounding the irradiated polymer. The excited oxygen molecules prevented the formation of SiCH₂Si structures by interacting with active %tbond;Si units that were formed as a result of Si? C bond rupture to produce Si? OH; SiCH₂CH₂Si linkages were formed as the result of a secondary reaction.     

辐射交联聚乙烯的正电子湮灭研究

Positron annihilation lifetime spectroscope(PALS) was applied to investigate the micro-structural changes of polyethylene(PE) which was irradiated by γ-ray or ultraviolet radiation, the spectra were decomposed into three lifetime components using PATFIT package. Then it was found that the shifts of the degree of cross linking and crystallinity were detected effectively in samples. Moreover, a small quantity of oxygen, which involved in the cross linking process, was measured sensitively by PALS. The regularity of positron lifetime intensity vs radiation intensity in γ irradiated sample was opposite to that in ultraviolet irradiated one, which is due to the preparation methods of samples and the change of polar functional group in initiator. Furthermore, contrastive patterns were studied by positron doppler broaden(DB) method and the results were agreed well with PALS data mentioned above.     

Role of additives in wood–polymer composites. Relationship to analogous radiation grafting and curing processes

Wood polymer composites (WPC) were prepared by impregnating an Australian softwood, Pinus radiata with methyl methacrylate which subsequently underwent in situ polymerisation utilising either γ radiation or the catalyst–accelerator method. Novel additives including thermal initiator, crosslinking agents, an inclusion compound and oxygen scavenger were incorporated to improve the polymer loading and properties of the resulting WPC. Polymer loadings of WPC obtained utilising the accelerator–catalyst method corresponded well with those obtained using γ radiation with 20 kGy radiation dose. The mechanistic significance of the current work in analogous radiation grafting and curing processes is discussed.     

Effect of electron beam irradiation on physico-chemical properties of pullulan

Many widely used polymers undergo main chain scission or crosslinking when exposed to radiation. Effects of electron beam irradiation at different doses up to 500?kGy on the biodegradable pullulan polymer films have been investigated by ultraviolet?Cvisible (UV?CVIS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) techniques. UV?CVisible study shows increase of optical absorbance with increase of doses, attributing to the formation some groups or radicals. FTIR and TGA results reveal the processes of both crosslinking and degradation of polymer taking place depending upon the dose of e-beam radiation. The surface morphology of the film is found to be altered by the e-beam radiation as indicated by SEM micrographs.