Exchange reactions occurring through active chain ends: Melt mixing of nylon 6 and polycarbonate

The chemical reactions occurring in the melt mixing of nylon6/polycarbonate (Ny6/PC) at 240°C were investigated. The reaction of equimolar Ny6/PC blends can be reconciled within the overall scheme of an exchange reaction occurring with the attack of active amino terminals on the inner carbonate groups. We have performed the synthesis of low molecular weight amino-terminated nylon 6 and the effect of the active amino terminal groups on the exchange kinetics was investigated. The exchange reaction yields sizeable amounts of copolymer, in fact after 75 min of melt mixing the (initially equimolar) blend contains 30 mol of unreacted PC and 70 mol of Ny6/PC copolymer (all the Ny6 was therefore incorporated in the copolymer). Trifluoroacetylation of nylon 6 was used to produce CHCl₃-soluble Ny6/PC copolymers, that could be analyzed by NMR. The NMR analysis yielded, beside the copolymer composition, evidence of the presence of urethane units interconnecting the Ny6 and PC blocks. The amount of urethane units increased with the reaction time, indicating a reduction of the block size as a function of the extent of exchange. Our study established the structure of the products formed, provided the materials balance of the process, and investigated some salient kinetic aspects. A thermal degradation study was also performed by thermogravimetry and direct pyrolysis mass spectrometry, to identify the products formed in the thermal treatment of the blends and to investigate the possible role of the inner amide groups in the intermolecular exchange reactions occurring between Ny6 and PC. Our results prove that these reactions occur above 300°C, and that only the cleavage of carbonate groups, by means of Ny6 amino end groups, is actually occurring at 240°C. © 1994 John Wiley & Sons, Inc.     

Prediction of paper permanence by accelerated aging II. Comparison of the predictions with natural aging results

Accelerated aging tests are credible and useful to predict paper permanence only if such tests can be shown to correlate with natural aging. In the first part of this study, a kinetic model was developed based on the accelerated aging results. In this report, we have shown that this kinetic model can indeed predict the natural aging results of lignin-free sheets with a statistical confidence. This is the first quantitative comparison of accelerated aging with natural aging.     

Fe3+-TiO2/SiO2光催化降解罗丹明B的研究

以硅胶为载体,采用溶胶-凝胶法制备了不同掺杂量的Fe3+-TiO2/SiO2光催化剂,并采用SEM,Raman和DRS等手段对其进行了分析和表征.以氙灯为光源,通过对可溶性染料罗丹明B的降解反应,考察了Fe3+-TiO2/SiO2催化剂的光催化活性,探讨了光催化反应中溶液pH值和起始浓度对催化反应的影响.     

Thermal degradation of poly(methyl-n-hexylsilylene)

Thermal degradation of poly(methyl-n-hexylsilane) in the solid state in absence of oxygen reveals formation of a cyclic pentamer between 150 and 250°C. Polymer is gradually degraded to an intermediate molecular weight distribution. The weight average of this new distribution is not only temperature-dependent, but is also a function of viscosity of the polymer and nature of chain ends. As no insolubles or Si? H groups are formed, the degradation mechanism is most likely a back-biting mechanism induced by active chain ends such as silyl anions or Si? Cl rather than a homolytic cleavage of the main chain. A concurrent intramolecular rearrangement reaction is also proposed. Moreover, this study proposes an explanation to the trimodal molecular weight distribution obtained by the Wurtz coupling of dichlorosilanes with molten sodium in refluxing toluene. © 1995 John Wiley & Sons, Inc.     

HPLC determination of urinary 2,4- and 2,6-toluendiamines as potential degradation products of polyurethane breast implants

Summary A reversed-phase HPLC method has been developed for the urinary determination of mutagenic 2,4- and 2,6-toluendiamines. These amines are degradation products of polyurethane, a material used to cover textured silicone breast implants. FMOC-Cl was used as fluorescent derivatising agent in order to obtain a limit of detection of 15 ng/ml in urine. Pre-treatment of urine samples was by liquid/liquid extraction and urine specimens of patients after surgury were analysed.     

光降解性聚乙烯薄膜降解过程的表征

用全反射傅里叶红外光谱、Ｘ射线光电子能谱和示差扫描量热仪研究了含光敏剂的低密度聚乙烯薄膜在光降解过程中降解速率的变化规律，结果表明，光降解性聚乙烯薄膜在降解过程初期，降解速率很小，光敏剂显示抗氧化剂性能；降解２４ｈ后，降解速率迅速增加，直至薄膜破坏，光敏剂显示光引发剂性能。作为对比，同时研究了光敏剂和其它两种添加剂对聚乙薄膜光解速率的协同效应和两种添加剂体系显示的性能。     

Catalytic oxygenative degradation of 4-chlorocatechol by a nonheme iron(III) complex—Mechanism and prevention of catechol ester formation

We examined the oxygenative degradation of 4-chlorocatechol and 4-tert-butylcatechol catalyzed by iron(III)-tris(pyridin-2-yl)amine complex from the standpoint of repressing the formation of 4-chlorocatechol esters of the oxygenated products that causes the incomplete degradation of 4-chlorocatechol. Analysis of the products revealed that 4-chlorocatechol esters are formed by the reaction of muconic anhydride, which is the monooxygenated product, with catechols. It was found that the use of MeOH as the solvent instead of MeCN completely suppressed the catechol ester formation through the methanolysis of muconic anhydride, which greatly improves the degradation efficiency of 4-chlorocatechol.     

Influence of media nutrients on synthesis of lignin peroxidase from Aspergillus sp

The effect of carbon and nitrogen sources, lignocellulosic substrates, and metal ions on lignin peroxidase (LiP) activity of Aspergillus sp., which was isolated from a mangrove area, was studied. Glucose (1%) was found to be the best carbon source. Among the various lignocellulosic substrates used, coir pith at 3% concentration increased LiP activity twofold on the second day of incubation. Peptone and KNO₃ completely inhibited the enzyme synthesis while (NH₄)₂SO₄ at 12.5 mM produced maximum activity. Since seawater contained all the requisite metal ions, any added ions had a negative effect on activity. Cu²⁺ had the most inhibiting effect while K⁺ the least. When all the optimized conditions were provided, in nitrogen- and carbon-sufficient medium, a maximum LiP activity of 345 U/mL was obtained on the second day of incubation.     

Study on permeation behavior and chemical degradation of PA66 in acid solution

In many polymers under corrosive liquids, degradation followed after permeation of environmental solution for a long period. The permeation rate of environmental solution, in many cases, is very low in corrosion-resistant polymeric materials. Therefore, the observation of the permeation of environmental solution and degradation of polymeric materials are very difficult in practical application. A simulation of permeation of solution is required in order to understand the permeation behavior of environmental solution and polymer degradation. A detailed analysis of the permeation behavior of solution accompanied by chemical reaction is important to study for improving the lifetime of polymers. Polyamide 66 (PA66) and sulfuric acid solution were used to investigate the quantitative study of permeation of environmental solution and its relation to degradation of polymeric materials. Correlation between diffusion process and degradation of PA66 related to the decrease of weight average molecular weight was defined. The diffusion rate of sulfuric acid solution was found to increase by decreasing weight average molecular weight of PA66 due to the established chain scission by hydrolysis reaction. The permeation of sulfuric acid solution that affected the decomposition reaction was modeled and quantitative evaluation of permeation of sulfuric acid was established.     

Thermal degradation of the polymer obtained by oxidation of C60 fullerene by oleum

Degradation of (C₆₀) _n polymer and the C₁₂₀ and C₁₂₀O dimers at different temperatures was studied by IR and ESR spectroscopy. The formation of C₆₀ was revealed. The polymer stability was found to be higher than the stability of the dimers. Peculiar features of the IR spectra of three-dimensional hyper-crosslinked polymers obtained by liquid-phase polymerization of C₆₀ are discussed.