聚酰胺热氧化降解机理

通过详细分析测定反应产物 ,研究了聚酰胺 (PA6)的热氧化降解机理 .用化学方法测定了PA6热氧化过程中几种主要基团含量的变化 ,对PA6热氧化的气相挥发产物进行收集和分析鉴定 ,还对经过氧化的PA6样品进行水解并用GC MS法对水解产物进行了分析鉴定 .在这些实验结果的基础上 ,提出了较完整的聚酰胺热氧化降解机理 .该机理包含了自由基在与酰胺基的羰基相连的亚甲基上的夺氢反应及一系列自由基加成环化和诱导断链的反应 ,能很好地解释反应产物的分析结果 .     

Investigation of thermal degradation characteristics of polyamide-6 containing melamine or melamine cyanurate via direct pyrolysis mass spectrometry

In this work the changes in thermal degradation characteristics of polyamide 6 (PA6) in the presence of melamine (Me) or melamine cyanurate (MC) were investigated systematically via direct pyrolysis mass spectrometry. Though thermal stability of PA6 was not affected by the presence of flame retardants, the changes in the products and in their distributions were detected. The reaction of carbonyl groups of PA6 with amine groups of melamine was the main cause for the changes in the product distribution. In the presence of melamine cyanurate, new products due to the reaction of cyanic acid generated by the decomposition of cyanurate, with the amine groups of PA6 were detected. Significant increases in the evolution temperatures of melamine and melamine cyanurate in the presence of PA6 were attributed to intermolecular interactions, most probably by H-bonding, with PA6.     

Inhibition and dispersion of Pseudomonas aeruginosa biofilms with reverse amide 2-aminoimidazole oroidin analogues

The marine alkaloid oroidin along with a small library of reverse amide (RA) 2-aminoimidazoles were synthesized and assayed for anti-biofilm activity against PAO1 and PA14, two strains of the medically relevant gamma-proteobacterium Pseudomonas aeruginosa. Analogues that contained a long, linear alkyl chain were more potent inhibitors than the natural product at preventing the formation of PAO1 and PA14 biofilms. The most active compound in the series was also shown to disperse established PAO1 and PA14 biofilms at low micromolar concentrations.     

Structural screening by multiple reaction monitoring as a new approach for tandem mass spectrometry: presented for the determination of pyrrolizidine alkaloids in plants

In tandem mass spectrometry the multiple reaction monitoring (MRM) mode is normally used for targeted analysis but this mode also has the potential to screen for structural similarities of analytes. On the basis of the fact that in general similar molecular structures result in similar fragments or losses of neutrals, this approach was used for pyrrolizidine alkaloid (PA) screening but could also be easily adapted to screen for other compound classes. PA are plant toxins of which several hundred individual compounds have been identified. Our MRM screening approach uses the structural relation and similar core structure of all PA which results in a common and thus predictable mass spectrometric fragmentation behaviour. On this basis a method was developed which screens for PA structures by MRM transitions and allows the detection of each individual PA down to a low microgram per kilogram concentration range. The approach was applied to investigate plants from the families of Asteraceae (several species of Senecio and Eupatorium), Boraginaceae (Echium, Cynoglossum, Borago and Anchusa officinalis as well as Heliotropium europaeum) and Fabaceae (Crotalaria incana) for a complete qualitative and quantitative PA characterisation. All analytes that were detected as possible PA by MRM screening were further investigated by recording product ion spectra. Analytes which exhibited a typical PA fragmentation pattern were either confirmed as PA or otherwise deleted as false positive signals (false positive rate was below 10 %). Sum formulas of confirmed PA were determined by additional measurements applying high resolution mass spectrometry. In that way 121 unknown PA were identified and for the first time complete PA profiles of different PA plants were delivered.     

An example of quality control of fine chemical intermediates: related impurity analysis of industrial phthalic anhydride by reversed-phase high-performance liquid chromatography

A reliable reversed-phase high-performance liquid chromatographic method has been developed for analysis of related impurities in industrial phthalic anhydride (PA). Maleic acid (hydrolysis product of maleic anhydride), phthalimide, and benzoic acid were separated from phthalic acid (Pa, hydrolysis product of PA) on a C₁₈ column by gradient elution with acetonitrile and 0.1% (v/v) aqueous perchloric acid solution. This method is simple, sensitive, and accurate, and has been successfully applied to quality control of PA for industrial use.     

The analysis of 1-propanol and 2-propanol in humid air samples using selected ion flow tube mass spectrometry

Following the observation that propanol is present in the breath samples of cystic fibrosis (CF) patients infected by Pseudomonas aeruginosa (PA), a study of the reactions of H(3)O(+), NO(+) and O(2) (+.) with 1-propanol and 2-propanol has been conducted using selected ion flow tube mass spectrometry (SIFT-MS). In this study the number and the distribution of the product ions from NO(+) reactions with the two propanol isomers under humid air conditions were able to differentiate between the two isomers. The reaction mechanisms and the structures of the product ions for these reactions, especially those with H(3)O(+) and NO(+), have been proposed. As an example, 2-propanol was shown to be present in a breath sample from one CF patient infected with PA, and also in a PA isolate from another CF patient grown on Pseudomonas-selective media. The results of this study allow an analytical procedure to be advanced for the analysis of the two propanol isomers, which can also be utilised in other applications.     

Mechanistic variations in the oxidation of Piloty's acid by metal complexes

The reactions of N-hydroxybenzenesulfonamide (Piloty's acid, PA) with a variety of metal oxidants are reported. Either nitric oxide or nitrite is the final reaction product, along with benzenesulfinate and the reduced metal compound. The nitrogen product depends on the oxidation potential of the metal oxidant and its ability to further oxidize NO to nitrite. The observation and preliminary interpretation of unusual kinetic behavior of Piloty's acid as a reductant is also described. Analogues of PA were also prepared and found to show similar reactivity.     

超支化聚磷酸酯阻燃剂对尼龙6的成炭促进作用

以三氯氧磷和双酚A为原料制备了具有超支化结构的聚磷酸酯阻燃剂(HPPEA),通过红外(FTIR),核磁(1H-NMR,31P-NMR)及热重分析表征了产物的结构和热稳定性.将HPPEA与三聚氰胺聚磷酸盐(MPP)进行复配,通过熔融共混法制备阻燃尼龙6,通过氧指数法和垂直燃烧法测试了其阻燃性能,采用热重分析(TGA)研究...     

Polyamide‐6,6‐based blocky copolyamides obtained by solid‐state modification

Copolyamides based on polyamide‐6,6 (PA‐6,6) were prepared by solid‐state modification (SSM). Para‐ and meta‐xylylenediamine were successfully incorporated into the aliphatic PA‐6,6 backbone at 200 and 230 °C under an inert gas flow. In the initial stage of the SSM below the melting temperature of PA‐6,6, a decrease of the molecular weight was observed due to chain scission, followed by a built up of the molecular weight and incorporation of the comonomer by postcondensation during the next stage. When the solid‐state copolymerization was continued for a sufficiently long time, the starting PA‐6,6 molecular weight was regained. The incorporation of the comonomer into the PA‐6,6 main chain was confirmed by size exclusion chromatography (SEC) with ultraviolet detection, which showed the presence of aromatic moieties in the final high‐molecular weight SSM product. The occurrence of the transamidation reaction was also proven by ¹H nuclear magnetic resonance (NMR) spectroscopy. As the transamidation was limited to the amorphous phase, this SSM resulted in a nonrandom overall structure of the PA copolymer as shown by the degree of randomness determined using ¹³C NMR spectroscopy. The thermal properties of the SSM products were compared with melt‐synthesized copolyamides of similar chemical composition. The higher melting and higher crystallization temperatures of the solid state‐modified copolyamides confirmed their nonrandom, block‐like chemical microstructure, whereas the melt‐synthesized copolyamides were random. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5118–5129     

四甲基氢氧化铵降解苯酐固化双酚A型环氧树脂的研究

将四甲基氢氧化铵(TMAH)降解聚酯的方法移植用于降解苯酐(PA)固化双酚A型环氧树脂(DGEBA),降解生成的邻苯二甲酸二甲酯(DMP)可被气相色谱―质谱(GC-MS)快速检测到,同时通过内标法考察了TMAH用量对降解率的影响,结果表明TMAH降解苯酐固化环氧树脂效率较高,甲酯化率在95%以上。此项研究为剖析毫克级酸酐固化环氧树脂中的固化剂提供了一种快速且有效的方法。