Photo-oxidation of polystyrene in dichloromethane solutions

Photo-oxidation of polystyrene in dichloromethane solution irradiated with light absorbed by the polymer was investigated. The quantum yields of the formation of acetophenone-type carbonyl compounds as well as α, β-enone and dicarbonyl products were calculated based on the analysis of u.v. absorption spectra of irradiated solutions. The relationship between the concentration of these products was found.     

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.     

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.     

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。     

基于红外光谱法的PE-HD光氧老化行为及氧化物生成规律

采用衰减全反射傅里叶红外光谱技术分析了滚塑包装箱专用高密度聚乙烯（PE-HD）材料老化过程中羰基指数、羟基指数、支化程度、断链程度、不饱和度所对应特征谱带吸光度的变化趋势,进一步确定其老化行为,并通过对氧化产物特征谱带洛伦兹分峰,探究了不同类型氧化产物的生成规律。结果表明,整个老化周期内,材料不饱和双键吸光度呈现上升趋势,支化和断链程度呈现较大幅度的增长,且老化初期断链占主导地位,老化后期支化作用更显著;氧化产物生成规律表现出氧化产物以酮羰基为主,且羧酸羰基、酯羰基和醛羰基、γ内酯羰基在前期增长较快,后期增速放缓达到一个稳定值。     

Photooxidation of polystyrene: Irradiation at 254 and 365 nm

Studies have been made of the near surface photooxidation of atactic polystyrene films prepared in the absence of air. The samples were photooxidized on exposure to air at two frequencies, 254 and 365 nm, using a calibrated mercury irradiation source with filters. Most studies were made at 40°C and as a function of irradition time with the reactions characterized by changes in molecular weight and composition. The former was evaluated by gel permeation chromatography and the latter by transmission Fourier transform infrared spectroscopy and by multiple-internal-reflectance infrared spectra using different angles and different crystals to evaluate compositions as a function of film depth. Species identified in photooxidation include the generation of hydroperoxides and the appearance of carbonyl bands with the latter identified by the spectral shift asociated with the exposure of the photooxidized polystyrene surface to ammonia. These results suggest that principal products of near-surface oxidation of polystyrene are carboxylic acids.     

The phosphorescence spectrum and photodegradation of polystyrene films

Low-temperature polarized phosphorescence spectroscopy of polystyrene polymerized under different conditions is used to detect emission from phenyl alkyl ketone endgroups in addition to triplet excimer emission from phenyl groups. The carbonyl group concentration can only be lowered by vigorous chemical reduction; and from the phosphorescence excitation spectrum, these carbonyl groups are considered responsible for the initiation of polystyrene photodegradation by solar radiation.     

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...     

Photo-oxidation stabilization of polystyrene by aromatic ultraviolet light absorbers forming charge transfer complexes

Summary The aim of this work was to investigate the influence of UV light absorbing additives on the rate of ultra violet light initiated degradation of polystyrene (PS) in solutions. Anthracene (ANT), chloranil (CA) nitrobenzene (TNB) which can form cnarge transfer complexes between each other were used. It was found for illuminated PS-solutions by light of =254 nm that independently of the screening efficiency of these compounds, tne formed CT complexes ANT-CA and ANT-TNB cause a decrease of tne rate constant of degradation and of the value of the number average of chain scission S. This effect is due to the energy transfer from the excited polymer chain segments to the low energy triplets of these CT-complexes thus hindering the rection of polymer chain segments with oxygen leading to slowing down of photodegradation.     

Thermolysis of polystyrene

Styrene was recovered from polystyrene (molecular weight of 138,000) by thermolysis in a nitrogen atmosphere at temperatures between 368 and 407°C. The results were independent of the initial weight of polystyrene, which was varied between 30 and 480 g. Up to 90% of the polystyrene was converted to liquid products. The liquid products had a styrene concentration as high as 90% and the styrene yield increased with temperature. Above 390°C, the residue left in the reactor (less than 30% of initial polystyrene charge) consisted mainly of styrene monomer, dimer, and trimer (MW of 190). The kinetics support a first-order reaction with regard to the rate of production of volatiles. The activation energy was estimated to be 166.5 kJ/mol. © 1995 John Wiley & Sons, Inc.     

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.     

Characterization and dual functionalization of polystyrene with propionic anhydride and cyanate derivatives

First, Friedel–Crafts reactions were used for the acylation process. For this, polystyrene (PS) was reacted with propionic anhydride in the presence of Lewis acid catalyst. The amount of acyl group linked PS as a result of acylation has been identified as volumetric. Second, the bromination and lithiation reactions of acylated PS containing carbonyl groups were realized. Also, the lithiated PS containing acyl groups has been modified a second time with various isocyanates and isothiocyanate derivatives in the presence of n?BuLi catalyst. Some important reaction parameters were assigned in order to optimize the process. The structure all of the products were characterized by Fourier transform infrared, ¹H NMR (Proton Nuclear Magnetic Resonance), and thermogravimetric methods. In addition, reaction yields were determined according to the result of elemental analysis. Dual functionalization yields were realized between 62.2% and 69.9%. For kinetic analysis, the TG/DTG (Thermal Gravimetric Analysis/Differantial Thermal Analysis) data obtained at three different heating rates were processed by Kissinger–Akahira–Sunose method. The results demonstrated that the acylation reaction, bromination and lithiation reactions, and dual functionalization reactions with cyanate derivatives can be carried out to obtain a significantly functionalized polymer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1351‐1362, 2013     

Vacuum UV photo-oxidation of polystyrene

Polystyrene (PS) was treated with vacuum UV (VUV) (λ = 104.8 and 106.7 nm) photo-oxidation and X-ray photoelectron spectroscopy detected a controlled increase in the atomic percentage of oxygen up to a saturation level of ca. 20 at% O. Initially, C–O and carbonyl groups are observed due to the formation of alcohols, ethers, esters, and ketones. Water contact angle measurements showed ca. 25% increase in hydrophilicity of the surface with oxidation. Atomic Force Microscopy observed little changes in surface roughness with treatment time. The super water absorbent polymer poly(acrylic acid) was thinly grafted to the modified PS surface.     

Acid-catalyzed cracking of polystyrene

The effects of catalyst acidity and the restricted reaction volume afforded by HZSM-5 on the volatile cracking products derived from poly(styrene) are investigated. Three catalysts: silica/alumina, HZSM-5, and sulfated zirconia, were employed as cracking catalysts. Styrene, which is the principal radical depolymerization product from poly(styrene), is a minor catalytic cracking product. The most abundant volatile product generated by catalytic cracking is benzene. Alkyl benzenes and indanes are also detected in significant yields. Various thermal analysis techniques are employed to obtain volatilization activation energies for polymer-catalyst samples and to elucidate probable reaction pathways. Detected products are explained by reaction mechanisms that begin with protonation of poly(styrene) aromatic rings. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1287–1298, 1997     

Cathodic crossed hydrocoupling XIII. Synthetic aspect of the cathodic crossed hydrocoupling reaction of aliphatic carbonyl compounds with electrophiles in aqueous sulfuric acid

For the purpose of organic electrosynthesis, the cathodic crossed hydrocoupling of aliphatic carbonyl compounds with some electrophiles was investigated. When mixtures of carbonyl compounds (such as ketone and aldehyde) and electrophiles (such as activated olefin, pyridine, and cyanamino compound) were electrolysed with various kinds of cathodes in aqueous sulfuric acid, these compounds were coupled reductively to give many useful products in the field of synthetic organic chemistry. In most of the couples of carbonyl compounds and electrophiles, the reduction potentials of the formers were more positive than those of the latters under the electrolysis condition. The yield, current efficiency, and selectivity of products depended on electrolytic conditions, especially cathode material.     

Intermolecular interactions in blends of functionalised propylene polymers with poly(vinylchloride) or polystyrene

Atactic and isotactic polypropylene (APP and IPP), and ethylene-propylene copolymers (EP). functionalised by reacting the molten polymer with diethylmaleate (DEM) in the presence of dicumylperoxide (DCP). have been blended with poly(vinylchloride) (PVC) and polystyrene (PS). These mixtures have been investigated by means of infrared spectroscopy at different compositions in the region of carbonyl absorption. The features of this last band in the mixture suggest the occurrence of intermolecular interactions involving mainly the carbonyl groups of the functionalised polymer and the methine hydrogens of PVC.     

Functionalization at the double-bond region of jojoba oil. 9. solid-state nuclear magnetic resonance characterization of substituted jojoba wax chemically bonded to a polystyrene matrix

Solid extractants for metal ions have been prepared by chemical bonding of jojoba wax to a polystyrene backbone, followed by phosphonation or sulfur-chlorination of the jojoba moiety. In this study, the intermediates and final solid products of the reactions were characterized by solid-state ¹³C and ³¹P nuclear magnetic resonance spectroscopy. The spectra showed the expected chemical shifts of the atoms involved in the chemical reactions, as well as other parts of the reacting molecules. Thus, the carbonyl carbon of the jojoba chain appears at 175 ppm, the methyl carbons at 15 ppm, the polystyrene backbone at 40–42 ppm (aliphatic carbons) and 128, 137, 143–147 (aromatic carbons). Carbons adjacent to N, S, and P appear at 45–55, 60, and 48 ppm, respectively.     

Photooxidation of benzil groups in the presence of hindered amine stabilizers in the polystyrene film

The photoperoxidation at λ > 400 nm of benzil (BZ) groups with the air oxygen to benzoyl peroxide (BP) groups in the polystyrene matrices was investigated in the presence of hindered amine stabilizer (HAS). HAS was used as a free molecule or was bound in combined molecule with BZ. HAS was in the form of parent amine as 2,2,6,6‐tetramethyl‐4‐hydroxypiperidine (TMP) and in the form of stable nitroxyl radical 1‐oxo‐2,2,6,6‐tetramethyl‐4‐hydroxypiperidine (NO). Both HAS forms effected the photooxidation of BZ structures. The main product of the photooxidation in the presence of parent amine TMP as well as in its absence is benzoyl peroxide (BP). The rate of BZ consumption increases in the presence of TMP. Irradiation of BZ in the presence of sufficient concentration of freely added NO results only in the formation of benzoic acid esters and benzoic acid, which are the main decomposition products of BP. The benzoic acid esters/benzoic acid ratio increases with the increasing concentration of NO. Bounding of BZ and TMP into one molecule (BZNH) results in slower dicarbonyl depletion, as compared with the case when mixture of BZ and TMP was used. Very slow depletion of BZ carbonyl absorption was observed in the case of bounded BZ and NO in one molecule (BZNO), in comparison with the mixture of free NO and BZ. In the case of BZNO, an effective intramolecular quenching of BZ excited triplet states with NO structures proceeds. Steady stay and dynamic emission (phosphorescence) measurements also show an effective quenching of BZ excited states by unbounded or bounded NO. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4420–4428, 2006     

Formation of C-C Bonds via Ruthenium Catalyzed Transfer Hydrogenation: Carbonyl Addition from the Alcohol or Aldehyde Oxidation Level

Under the conditions of ruthenium catalyzed transfer hydrogenation employing isopropanol as terminal reductant, π-unsaturated compounds (1,3-dienes, allenes, 1,3-enynes and alkynes) reductively couple to aldehydes to furnish products of carbonyl addition. In the absence of isopropanol, π-unsaturated compounds couple directly from the alcohol oxidation level to form identical products of carbonyl addition. Such "alcohol-unsaturate C-C couplings" enable carbonyl allylation, propargylation and vinylation from the alcohol oxidation level in the absence of stoichiometric organometallic reagents or metallic reductants. Thus, direct catalytic C-H functionalization of alcohols at the carbinol carbon is achieved.     

Photo‐oxidation of polystyrene/clay nanocomposites under accelerated UV exposure: Effect on the structure and molecular weight

The present work investigates the effects of photo‐oxidation under accelerated UV conditions on the structure, the molecular weight and the morphology of polystyrene (PS)/organophilic montmorillonite (OMMT) at various clay contents: 2.5, 5, and 7 wt %. Fourier transform infrared spectroscopy, viscosimetry and scanning electron microscopy were used to evaluate the extent of degradation of nanocomposite samples in comparison with neat PS, up to 216 h of exposure. The study has shown that the formation rates of both carbonyl and hydroperoxide groups increase with exposure time, being much higher for PS/OMMT nanocomposites. Moreover, it is also observed that all samples exhibit a large increase in the scission index, however less pronounced for neat PS. These results clearly indicate the formation of low molecular weight products that could arise from chain scission. Further, the photo‐oxidation rate seems to be more affected by the presence of clay, which acts as a catalyst, rather than by the variation of clay contents. Finally, the degraded materials exhibit eroded surface. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009