聚烯烃的光化学与辐射化学改性

本文介绍了光化学及幅射化学交联的机理及其对聚合物结构与性能的影响,举例说明了它们在聚烯烃薄膜与电缆改性上的应用。     

Polymer-Bound Chiroptical Molecular Switches; Photochemical Modification of the Chirality of Thin Films

Photobistable chiral polymers were obtained by covalent attachment of inherently dissymmetric 2-hydroxy-9-(7′methyl-1′,2′,3′,4′-tetrahydrophenanthrene-4′-ylidene)-9H-thioxanthene to methacrylate copolymers with appropriate spacers. Upon irradiation at 300 nm the optical activity of thin films of these polymers could be altered.     

Photochemical studies of rancidity

1. Experiments with oils irradiated by means of color filters selected so that successive portions of the visible spectrum are absorbed show that blue light is more conducive to the formation of peroxides and the development of rancidity than the red end of the spectrum for the same time of irradiation. 2. The results of these experiments seem to indicate that the formation of peroxides and the development of rancidity are accelerated in proportion to the amount of blue light transmitted by the filter. 3. The development of rancidity does not necessarily parallel the formation of peroxides. This is shown by the fact that an oil protected by green and not organoleptically rancid may have a peroxide value as high as, or higher than, an oil which has not been so protected and which is rancid. 4. Experiments show that, with respect to the formation of peroxides and the development of rancidity, lard, and animal fat, responds to selective light in the same way as do corn and cotton-seed oils. 5. Containers or wrappers designed for enclosing oil-bearing foods should exclude both ends of the visible spectrum, more especially the blue, in order to prevent or delay the development of rancidity. 6. The color which affects the development of rancidity the least is green delimited by 4,900 to 5,800 Ångström units.     

Photochemical dechlorination of PCBs

An effective process scheme for photochemical PCBs dechlorination reaction in alkaline isopropylalcohol has been studied. Based on the experimental obs     

Photochemical degradation of thermoplastics

The general mechanism of polymer photodegradation is outlined, and various aspects are then discussed with reference to polyolefins, particularly polyethylene. It is shown that various impurities accelerate degradation and that carbonyl groups play a complex role in the process. Polyolefins can be stabilised against photodegradation by incorporation of suitable u.v. stabilisers or pigments, and the principles involved, including the synergism between u.v. stabilisers and antioxidants, are discussed.     

Photochemical Etching of Silicon

Silicon that was immersed in hydrofluoric acid can be etched photochemically by laser, and it was found to produce long and regular columnar structure, if the laser power density is greater than 10 mW/mm². Another criterion is that the laser wavelength should be at the blue end of visible spectrum. Fine wires with diameter 300–200 nm were also observed at the top of these columns. The dimension of these fine wires is near to quantum confinement dimension, thus can be taken as supporting evidence for quantum confinement. The photoluminescence spectra full width half maximum was narrower than that from porous silicon fabricated from conventional anodisation method. The narrower full width was attributed to the uniformity of the porous silicon structure. A physical model is proposed to explain the observed strong directional etching. The model showed that once the etch sites have randomly initiated, the etching rate becomes directional under the influence of laser. The intensity of laser controls the etching direction such that silicon columns are formed if the intensity of the laser is strong enough.     

Photochemical preparation of polymer-clay composites

Polymer–clay composites of poly([2-(methacryloxy)ethyl]trimethylammonium chloride) and various clayey minerals have been prepared by visible light-induced free radical polymerization. The starting monomer–clay formulation contained: (i) the initiating dye, Rose bengal derivative, (2′[6-(3-trimethylaminopropoxy)-2,4-diiodo-3-oxo-3H-xanthen-9-yl]-benzyloxy-propyltrimethyl-ammonium dibromide, DBEE); (ii) the electron donor, 2-(dimethyl-amino)ethyl methacrylate; and (iii) the crosslinking monomer, poly(ethylene glycol) dimethacrylate. The method allows to prepare 1–2 mm thick foils that can be formed under both artificial lights and the sunlight exposition. The foil is flexible and insoluble in water. The clay is not rinsed out from the composite even after hundreds of hours of water treatment. The obtained composites do not exhibit good mechanical properties.     

二苯氯甲烷的光化学合成

以无水氯化锌为催化剂,苯与氯化苄为原料,经Friedel Crafts反应制得二苯甲烷,收率为72 6%;在可见光照射下,二苯甲烷与氯气发生自由基取代反应生成二苯氯甲烷。通过系列实验得出了二苯氯甲烷光化学合成的优化工艺条件:n(二苯甲烷)∶n(氯气)=1∶1 02,光源采用碘钨灯,反应温度90～100℃,通氯时间12h,以二苯甲烷计二苯氯甲烷收率82 2%,产品质量分数≥98%,通过红外和质谱对其结构进行了确证。     

几个有合成价值的光化学反应

光化学反应是以洁净、节能、节约为目标的化学合成方法 ,它为有机合成化学提供了新途径、新方法和新技术 ,是合成化学中最活跃、最有生命力的研究领域之一 ,深入研究光化学反应必将为现代有机合成的发展注入新的活力 .本论文重点研究了具有应用价值的烯烃光敏氧化、脱肟成酮光敏氧化及汉斯酯 1 ,4 二氢吡啶衍生物芳香化等光化学反应 ,取得了一系列重要的研究结果 .1　烯烃的光敏氧化反应烯烃的光敏氧化反应是具有重要应用前景的光化学反应之一 .敏化剂的优劣直接影响反应的产率和选择性 .我们利用Nafion膜特殊的结构特点 ,制备了以Nafion膜…     

Process Modeling of Laser Photochemical Reactor

Abstract

The applicability of conventional process engineering terms like value function, separative work unit, etc. to the laser isotope separation process has been established through appropriate formulation of the problem. The value function developed in this paper has been shown to be useful in arriving at guidelines for optimal design and operation of an isotope separation plant. A direct and simple model has been developed for a single-phase single-component laser photoreactor stage. This model, incorporating the key features and constraints of the laser isotope separation process, can provide an analysis and design basis to the process engineer.     

Thermal and Photochemical Decomposition of Dihydrooxadiazinones

3,6-Dihydro-1,3,4-oxadiazin-2-ones may be prepared from either α-ketols or from α-diketones and carbethoxyhydrazine. These substances undergo thermal or photolytic (253.7 nm) decomposition to give N₂, CO₂ and olefins. Oxadiazinones derived from medium ring α-ketols give bicyclic hydrocarbons in addition to olefins. These are shown to be formed by decomposition of the intermediate vinyldiazene to vinyl radicals, followed by transannular hydrogen abstraction and alkyl radical addition to the olefin. A series of 5,6-dihydro-1,3,4-oxadiazin-2-ones have also been prepared and their thermal and photolytic behavior studied.     

Photochemical switching of hydrogel film properties

A copolymer of N-isopropyl acrylamide and acrylic acid was modified in a polymer analogous reaction by an acridizinium chromophore capable of reversible photochemical dimerization. The acridizinium chromophore allows a faster and more complete photocrosslinking and a better photoreversibility as compared to stilbene and stilbazolium chromophores. Due to its hydrophilic nature the chromophore only moderately affected cloud points T_c of the copolymer and lower critical solution temperatures (LCST) of photocrosslinked films of the copolymer, even at high chromophore content (3.5% w/w). Such films can be swollen in water to form hydrogels. LCST and T_c depend on the content and on the counterion of the chromophore, on the solvent from which films are prepared, and on the degree of crosslinking. The latter dependence allows the exploitation for isothermal switching of film properties by exposure to light.     

Photochemical Regulation of Restriction Endonuclease Activity

Removal by the light : The photochemical regulation of restriction endonucleases, which are important enzymes in molecular biology, has been investigated. Photolabile protecting groups have been installed on DNA substrates and have been demonstrated to inhibit restriction endonuclease activity until removed by UV light irradiation. Interestingly, these groups do not appear to dramatically affect initial binding of the enzyme to the DNA substrate, but rather prevent recognition of the specific cleavage site.

     

Photochemical Degradation of Recycled High-Impact Polystyrene

Photooxidative aging of high-impact polystyrene sheets at 25°C was followed for different intervals of 25, 40, 50, 75, and 80 h. Five different types of samples were used, viz. virgin, and recycled once, twice, three, and four times. The optical properties of exposed samples exhibited changes as a result of discoloration. The transmittance and reflection deceases whereas absorbance increases with increasing recycling of high-impact polystyrene.     

Photochemical Tendering Activity of Sulphur Dyes

The photochemical tendering activity of a series of sulphur dyes on cotton cloth has been assessed in terms of (I) the changes in the physical and chemical properties of the fibre and (2) the extent of fading of the dyes and the formation of hydrogen peroxide during exposure.     

Photochemical Decomposition of Some Triazine Reactive Dyes

The photochemical degradation of some selected monoand di– chlorotriazine dyes – C. I. Reactive Orange 13, C. I. Reactive Orange 4, C. I. Reactive Yellow 2, C. I. Reactive Blue 4, C. I. Reactive Blue 5 – and starting compounds used for various applications to cotton are examined. The simple, exponential relationship between relative number of decomposed molecules and absorbed energy is verified. It is found that the structure of the base (chromophore)influences the tendency of a dye to exhibit photodegradation. The bases improve in fastness to light in the following order: base of CI. Reactive Orange 4 and Orange 13 > base of CI. Reactive Yellow 2 > base of C. I. Reactive Blue 4 and Blue 5. By linking the base to the reactive part of the molecule, an increase in resistance to photochemical degradation is brought about, in dependent of the number of reactive chlorine atoms. A covalent bond between the dye and the fibre may, in some cases (C. I. Reactive Yellow 2), cause a decrease in photodegradation.