光氧化反应的研究 Ⅵ.敏化光氧化反应合成胆甾烯烃衍生物

本文应用敏化剂荧光黄素(LF)和9,10-二氰蒽(DCA)研究了三种胆甾烯烃(1—3)在几种溶剂中的敏化光氧化。该反应提供了一种合成5或7-位取代胆甾烯烃衍生物方便和实用的方法。实验发现,LF敏化胆固醇1于苯中的光氧化导致3β-羟基-5烯-7-酮(1c,40％)的生成。敏化剂与溶剂对于此光化学合成反应的影响也进行了讨论。     

蒈烯芳氰敏化光氧化反应的研究：Ⅱ.光敏氧化产物的分布及其…

本文报道蒈烯在不同溶剂中光敏氧化反应产物的组成和分布及其与溶剂及敏化剂性质的关系。研究结果指出在以孟加拉玖瑰红为敏化剂时，主要生成典型的“ｅｎｅ”型产物，而以９，１０一二基蒽敏化蒈烯的光氧化反应除生成“ｅｎｅ”型产物外还生成相当量的非“ｅｎｅ”型产物。实验证明蒈烯芳氰敏化光氧化反应过程，首先发生电子转移，而后产生自由基中间体和单重态氧并生成相应产物。     

光氧化反应的工业应用前景

光化学是一门新兴的学科,它的工业应用研究,总的来说还处在初期。近20年来,染料敏化光氧化反应方面的研究,有了很大的进展。当前一个重要问题是如何把光氧化反应推向工业生产,从工业应用的角度来看,光引发的自氧化反应与染料敏化光氧化反应,是二类截然不同的,但是都具有工业应用前景的光氧化反应,本文将就这些反应在化工生     

蒈烯芳氰敏化光氧化反应的研究——Ⅱ.光敏氧化产物的分布及其反应机理

本文报道蒈烯在不同溶剂中光敏氧化反应产物的组成和分布及其与溶剂及敏化剂性质的关系。研究结果指出在以孟加拉玖瑰红(RB)为敏化剂时,主要生成典型的“ene”型产物,而以9,10一二腈基蒽敏化蒈烯的光氧化反应除生成“ene”型产物外还生成相当量的非“ene”型产物。实验证明蒈烯芳氰敏化光氧化反应过程,首先发生电子转移,而后产生自由基中间体和单重态氧并生成相应产物。     

抗氧剂BHA对松香及其衍生产品的光氧化反应影响

利用聚乙烯膜微量反应器,在30℃恒温箱中,254 nm紫外光照射下,进行添加了抗氧剂BHA的松香及其衍生品(枞酸和松香季戊四醇酯)的固态光氧化反应。采用紫外分光光度法跟踪监测了它们的光氧化进程;探究了抗氧剂BHA对松香及其衍生产品光氧化反应的影响。结果表明,抗氧剂BHA的添加能有效减缓松香及其产品的光氧化速率,抗氧剂BHA对产品的抗氧化效果顺序从大到小为：松香>枞酸>松香季戊四醇酯。松香添加抗氧剂BHA的用量选择应在5%以内;松香季戊四醇酯中添加抗氧剂BHA的用量选择应在5%～7%之间;枞酸中添加抗氧剂BHA的用量选择应在7%以内。     

超高分子量聚乙烯的热和光氧化

据《Polym．Ddgrad．Stab．》1997，58，41－54报道，意大利学者采用FTIR和其派生的技术研究了超高分子量聚乙烯（UHMWPE）的热和光氧化。氧化过程的引发物质是机械氧化降解所产生的过氧化物，也涉及非游离基协同机理和形成酯基和酸基。第二氧化过程发生。具有诱导期并与关于线性低密度聚乙烯（LLDPE）的文献中所叙述的相类似。热和光氧化过程之间主要的差异是光氧化形成较大量的酸。机理方面在热氧化的情况下主要的是8一断裂，而光氧化主要是NorrishI和NorrishII反应。超高分子量聚乙烯的热和光氧化…     

9,l0-二氰基蒽光敏化香豆素加成反应的研究

光化学中的电子转移反应近年来引起了人们广泛的重视。9,10-二氰基蒽(DCA)作为贫电子敏化剂敏化的各类烯烃的光氧化反应,光重排反应,光加成反应等均有报道。我们在研究DCA光敏化香豆素反应时发现,香豆素与DCA能够发生电子转移的给体—受体加成反应,联苯(BP)可以充当二次电子转移体加速反应。     

电子转移光氧化反应在有机合成中的应用

电子转移光氧化反应与光敏化的单重态氧反应是光氧化反应的两个最重要的组成部分。电子转移光氧化是随着光诱导电子转移反应研究的广泛开展而得以迅速发展的。近年来,与光诱导电子转移反应有密切关联的过渡金属配合物的可见光催化反应也已成为研究热点。一些过渡金属配合物催化的电子转移光氧化反应也已出现。本文根据电子转移光氧化反应的不同机理,对这些反应进行分类,介绍了不同类型的电子转移敏化剂(包括氰基芳烃类光敏剂、鎓盐类阳离子光敏剂、过渡金属配合物类光敏剂以及有机染料类光敏剂)引发的电子转移光氧化反应,并讨论了各类电子转移光氧化反应中底物的各种活性中间体、反应中氧的活性形式、可能的反应途径以及在有机合成中的应用。     

阻燃PP的光氧化

据《Ｐｏｌｙｍ．ｄｅｇｒ．ａｎｄ Ｓｔａｂ》，１９９９，６４：４１１～４１７报道，法国学者发表了关于阻燃配方的聚丙烯（ＰＰ）光氧化的研究报告。他们研究了使用芳香结构的阻燃剂（十溴二苯醚）时对ＰＰ光氧化的影响情况。辐照后的样品经红外光谱分析后，表明ＰＰ的光氧化机理不受阻燃剂的影响，但氧化速率却显现出惊人的增高。此外还研究了阻燃ＰＰ稳定化后的光化学行为。发现使用氧化还原机理的抗氧剂（ＨＡＳ）稳定的ＰＰ样品所得到的稳定性很差。阻燃PP的光氧化@朱福海$广州合成材料研究院     

α-蒎烯的光氧化反应研究

α-蒎烯和氧能在基态条件下形成CCT复合物,在与CCT复合物吸收相应波长的光辐照下,有利于促进蒎烯的光氧化反应。在氧化反应中,存在着明显的溶剂极性的影响,极性愈大,反应的速度愈快。这一切都说明电荷转移在反应中起着重要的作用。此外,正由于存在着基态的CCT复合物,因此α-蒎烯的氧化反应也能在暗的条件下进行。根据蒎烯光氧化和暗氧化反应产物的分析,可以肯定蒎烯在本工作实验条件下的氧化反应是通过自由基机理而进行的。     

Photo-oxidation and photoprotection of the surface resin of a glass fiber–epoxy composite

The rapid photo-oxidation of the surface epoxy resin of a commercial seven-ply laminate (Scotchply 1009-26) is due principally to the epoxy novolac resin component. The photo-oxidation rate of this resin is eight times that of the other component, a bisphenol A epoxy resin. This rate depends on the conditions of cure, and photo-initiation occurs in part through aromatic carbonyl groups formed by oxidation of the methylene linkages of the novolac at the cure temperature (160–180°C). Inhibition of this thermal oxidation by vacuum cure or a chain-terminating antioxidant increases the photostability. Photoprotection of thin resin sections by the UV stabilizer 2-hydroxy-4-isooctoxybenzophenone and an epoxidized analog is assessed.     

光氧稳定剂对塑木复合材料性能的影响

以紫外光稳定剂531和抗氧剂2246为光氧稳定剂,研究了塑木复合材料受光氧影响时的弯曲性能、色泽变化、氧化诱导期和外观变化.研究表明,经紫外光照射后,光氧稳定剂对材料的弯曲性能影响不大,但添加有光氧稳定剂的材料的表面色泽变化小,发白不明显.在紫外光稳定剂531和抗氧剂2246的添加量分别为0.3%时,材料经300h紫外...     

聚苯乙烯光氧老化行为及其模型研究

研究了自然曝晒试验后的聚苯乙烯(PS)样品结构和性能的变化,同时对其拉伸强度保持率的变化进行回归拟合,并建立了光氧老化模型。结果表明:太阳辐照是影响PS光氧老化的主要因素,水分对其起促进作用;PS老化过程中有羰基基团生成;老化模型可以反映光、热、水综合作用的强弱。     

Photo-oxidation mechanisms of poly(2,6-dimethyl-1,4-phenylene oxide).

A re-examination of the photo-oxidation mechanism of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at both long and short irradiation wavelengths under accelerated conditions is reported. The formation rate of poly-2,6-dimethylphenoxy (PDMP) radicals, have been observed by esr spectroscopy, while benzylic-type radicals have been detected by spin trapping experiments using nitrosodurene under UV irradiation conditions. The changes of FTIR spectra obtained under accelerated photo-oxidative conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical cations and superoxide anions by a photo-induced electron-transfer reaction is suggested under our conditions. In addition, some results on the of photo-oxidation PPO/PS blends as a function of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend containing atactic polystyrene. This effect has been ascribed to the absence of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO with bromine gave a bromomethylated PPO with different amounts of CH₂ Br groups, which has been used for further substitution reactions with alkoxy sodium salts of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMPP). The accelerated photo-oxidation of a modified copolymer PPO-PMPP containing a 60% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a commercially available hindered amine light stabilizers (HALS) and a modified copolymer PPO-PMPP are also reported under the same photo-oxidative conditions.     

Photo-oxidation and photoreduction of bis(dithiobenzil)nickels

Photo-oxidation and photoreduction of bis(dithiobenzil)nickels have been investigated. The quantum yields for photo-oxidation of anionic bis(dithiobenzil)nickels by u.v. irradiation (313 nm) were in the range 0.07–0.14 in dichloromethane, and this photo-oxidation on poly(methylmethacrylate) was also observed. Some of the neutral bis(dithiobenzil)nickels in acetonitrile/benzene mixture were photoreduced in the presence of methylene blue as a sensitiser by irradiation in visible light (>390 nm), and a significant substituent effect was observed.     

Photo-oxidation of phenoxy resin

A study has been made of the photolysis and photo-oxidation of phenoxy resin. Photolysis results in the evolution of hydrogen, methane, ethane, propene, propane, toluene, and the oxides of carbon. Also observed are increased yellowing, a rapid rise in gel content, and a decrease in intrinsic viscosity and elongation. Photo-oxidation causes similar changes, but produces oxidized chain fragments, more gel, and less yellowing as well as broad absorptions in the hydroxyl and carbonyl regions of the infrared spectrum. A free-radical mechanism is proposed in which both chain scission and crosslinking occur.     

Photo-oxidation of polystyrene film: 1. Photo-oxidation of polystyrene films with light absorbed by polymer

The photo-oxidation of polystyrene films irradiated with light absorbed by the polymer has been studied. The overall quantum yield of hydroperoxide as well as the relationship between the concentration of acetophenone-type carbonyl products and α,β-enone and diketone products were found. The spatial distribution of the different types of carbonyl products was investigated.     

Role of TiO2 and carbon nanotubes on polyethylene,and effect of accelerated weathering on photo oxidation and mechanical properties

In this work, LLDPE‐based composite films were prepared by melt mixing followed by compression molding to investigate the role of titanium oxide nanoparticles (TONPs) and/or multiwalled carbon nanotubes (CNTs) on the accelerated weathering samples (maximum of 39 days). Accelerating weathering caused the emerging of oxidation peaks in the FT‐IR spectra for LLDPE and LLDPE/TONPs. These peaks were not pronounced in the LLDPE/CNTs samples. The same prevention of oxidation peaks were noticed for the hybrid additives samples. Tensile properties decreased by exposing the composite samples to accelerating weathering. TONPs increased the tensile strength of the samples by 11.5% but deterioration of this property is the same as the pristine sample after accelerated weathering for 39 days. Addition of CNTs had negligible effect on the tensile strength but it kept the same approximate value of the original before the accelerated weathering (e.g., 23.2 MPa for 1 wt% of CNTs). CNTs also protected the samples even with the presence of TONPs because of the absorbance and antioxidants effects. The addition of CNTs into LLDPE network have not only retarded decomposition of LLDPE but also decreased catalytic activity of TONPs to activate degradation due to accelerated weathering. J. VINYL ADDIT. TECHNOL., 25:19–25, 2019. © 2018 Society of Plastics Engineers     

Photo-oxidation of polystyrene film: 2. Photo-oxidation of polystyrene film with light absorbed by the polystyrene-oxygen complex

Photo-oxidation of polystyrene films prepared from carefully purified polymer, irradiated with light absorbed only by a polystyrene-oxygen complex has been studied. It was found that photo-oxidation of polystyrene under such conditions results in carbonyl compound and hydroperoxide formation. Photo-oxidation of polystyrene with light of a frequency abosrbed by the polystyrene-oxygen complex occurs throughout the whole volume of sample.     

山梨醇醚存在下聚乙烯的光氧化降解特性研究

通过特性粘度、凝胶含量、羧基含量及红外光谱测试,分析了山梨醇醚含量为0%、0.1%、0.3%、0.5%、l%、5%、8%的7种聚乙烯膜样品在人工加速老化实验下的光氧降解特性研究,并通过扫描电镜对山梨醇醚含量为1%的聚乙烯膜表面形貌进行了分析.结果表明,光照过程中,山梨醇醚在7种膜中引发自由基反应,致使聚乙烯分子交联、断...