Spin Probe Study of IPN-like Systems based on Polyethylene and Polymethacrylates

A system similar to an interpenetrating polymer network (IPN), based on polyethylene/poly(methylmethacrylate-co-dodecyl methacrylate), was studied by the spin probe method with a nitroxide spin probe, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). The influence of changes in the composition of the copolymer (methyl methacrylate-co-dodecyl methacrylate) on the molecular mobility and composition of the IPNs is characterized by changes of the empirical spectral parameters T_50G and τ_R. The molecular mobility was shown to diminish with rising content of methyl methacrylate in the copolymer. © of SCI.     

2-甲基烯丙醇催化氧化为2-甲基烯丙醛的研究

对2-甲基烯丙醇选择性催化氧化为2-甲基烯丙醛的体系进行了研究。实验表明,TEMPO、CuI、1,10-菲罗啉组成了一个稳定的络合体系,不但反应活化能降低,而且催化体系更加稳定,从而使反应速度和产率显著提高,为该体系的进一步研究提供了一定的理论参考。     

Regulating the pore structure of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) oxidized cellulose membranes: impact of drying method and organic solvent processing

Cellulose‐based membrane is a satisfactory candidate for the separator of lithium‐ion batteries due to its renewability, abundant pore structure and outstanding thermal–chemical stability. In this study, 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) oxidized cellulose fiber (TOCF) membranes with different oxidation degrees were prepared. Membranes with high oxidation degree are faced with a pore closure issue, resulting in low porosity. In order to improve the pore structure, the TOCF membranes were dried differently through air drying, vacuum drying and freeze drying. Furthermore, air‐dried membranes were processed by three organic solvents – n‐butyl alcohol, carbon tetrachloride and n‐heptane. The physical properties, pore structure characteristics, mechanical properties and the electrochemical performance of the membranes were measured and characterized. From the results, freeze drying is found to provide the highest porosity and mean pore diameter. Unfortunately, Young’s modulus of the freeze‐dried membranes is the smallest as well. However, membranes processed by n‐butyl alcohol have weak tensile properties. Compared to non‐processed membranes, membranes processed by organic solvents present better pore structure and significantly better electrochemical performance. With all properties considered, TOCF membranes processed by carbon tetrachloride or n‐heptane are qualified for serving as battery separators as they possess improved pore structure, enhanced Young’s modulus, considerable tensile strength and improved electrochemical properties. © 2020 Society of Chemical Industry     

Application of a nitroxide radical as overcharge protection in rechargeable lithium batteries

Redox shuttle electrolyte additives have been suggested as a possible mean of internal overcharge protection of secondary lithium-ion batteries. TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) is one of these redox shuttles for overcharge protection of 3 V class Li-ion cells. The electrochemical reversibility and the diffusion coefficient of this molecule has been evaluated by mean of cyclic voltammetry. The redox shuttle voltage was found to be 3.5 V versus Li/Li⁺ and D = cm² s⁻¹. The electrochemical stability of TEMPO in different overcharging conditions has been evaluated by long-term cycling using Li/Li₄Ti₅O₁₂ cells. Results show that the TEMPO redox system does not act as an ideal shuttle. When dissolved in the electrolyte at 0.5 M, this additive is able to level off the cell potential at 3.5 V for a long period at low overcharging current (C/200 to C/50). Nevertheless, it appears that the cell capacity fades drastically at the first cycles and with time. This phenomenon is probably related to the stability of the oxidized and reduced form of the TEMPO molecule.     

Biodegradable polymers and their layered silicate nanocomposites: In greening the 21st century materials world

This review aims at highlighting on recent developments in preparation, characterization, properties, crystallization behaviors, melt rheology, processing, and future applications possibilities of biodegradable polymers and their layered silicate nanocomposites. These materials are attracting considerable interest in materials science research. Montmorillonite and hectorite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. In their pristine form they are hydrophilic in nature, and this property makes them very difficult to disperse into biodegradable polymer matrices. The most common strategy to overcome this difficulty is to replace the interlayer clay cations with quarternized ammonium or phosphonium cations, preferably with long alkyl chains.

A wide range of biodegradable polymer matrices is described in this review with a special emphasis on polylactide because of more eco-friendliness from its origin as contrast to the fully petroleum-based biodegradable polymers and control of carbon dioxide balance after their composting.

Preparative techniques include (i) intercalation of polymers or prepolymers from solution, (ii) in situ intercalative polymerization method, and (iii) melt intercalation method.

This new family of composite materials frequently exhibits remarkable improvements of mechanical and material properties when compared with virgin polymers or conventional micro- and macro-composites. Improvements can include a high storage modulus both in solid and molten states, increased tensile and flexural properties, a decrease in gas permeability and flammability, increased heat distortion temperature and thermal stability, increase in the biodegradation rate, and so forth.     

Rhodium‐Catalyzed Oxidative Homocoupling of Boronic Acids

Oxidative homocoupling of aryl‐ and alkenylboronic acids was achieved with Wilkinson’s catalyst. Commercially available 2,2,6,6‐tetramethylpiperidine‐N‐oxyl radical (TEMPO) was used as a stoichiometric oxidant.     

机械浆长纤维的TEMPO选择性催化氧化

采用TEMPO/NaBr/NaC10体系将机械浆长纤维精基单元中的伯羟基选择性氧化成羧基来提高纸浆纤维羧基的含量.研究了TEMPO、NaBr和NaC10的用量以及浆浓对纸浆纤维氧化的影响,同时研究了羧基含量对机械浆长纤维性能的影响.结果表明,在氧化过程中,随着TEMPO和NaBr用量的增加,反应速度提高,而氧化后的纸浆纤维羧基含量没有增加,随着NaC10用量的增加,纸浆纤维的羧基含量上升.随着纸浆纤维浓度的增加.羧基含量先上升后下降,浆浓在1.3%时,羧基含量达到最高值.随着纸浆纤维羧基含景的增多,浆料抄片的抗张指数和耐破指数上升,撕裂指数下降,氧化的纸浆纤维对细小纤维的留着率下降;浆料的保水值上升而游离度下降;浆纤维的卷曲和扭曲系数降低.研究还发现,低羧基含量的纤维能够吸附部分有机溶解物以及其他物质,使得白水中的有机溶解物和总有机碳的含量下降,这种吸附性能随着羧基含量的增加而下降.     

TEMPO氧化细菌纤维素基纳米复合凝胶的结构及光催化性能研究

通过微波辅助溶剂热原位合成反应,制备了纳米硫化镉（CdS）颗粒负载量更高且光催化吸附降解性能更优的氧化细菌纤维素@纳米硫化镉（TOBC@CdS）复合凝胶材料。结果表明,在羧基的络合作用下,立方晶型纳米CdS团簇以类细胞感受器的形貌吸附在TOBC纤维非结晶区域,形成了较为稳定的有机无机杂化结构。可见光照射180 min后,TOBC@CdS纳米复合凝胶可有效光催化降解87.27%的亚甲基蓝（MB）;实验重复5次后,其光催化降解性能没有明显衰减。     

Laccase/2,2,6,6‐Tetramethylpiperidinoxyl Radical (TEMPO): An Efficient Catalytic System for Selective Oxidations of Primary Hydroxy and Amino Groups in Aqueous and Biphasic Media

Copper salts/2,2,6,6‐tetramethylpiperidinoxyl radical (TEMPO) catalytic systems enable efficient aerobic oxidations of primary alcohols but they generally show a reduced reactivity in aqueous medium. Herein, we report an oxidative catalytic system composed of Trametes versicolor laccase and TEMPO, which is able to work in buffer solutions at room temperature using ambient air. Although this catalytic system displays great efficiency in aqueous systems, the addition of methyl tert‐butyl ether allows the reduction of TEMPO loading, also enhancing the solubility of hydrophobic compounds. This practical methodology promotes the chemoselective aerobic oxidation of hydroxy or amino groups, leading to interesting organic derivatives such as aldehydes, lactones, hemiaminals or lactams.

     

New radical salts based on TEMPO-substituted 2,4,6-triphenylpyridinium and transition metal complexes

Series of radical salts derived from a 2,4,6-triphenylpyridinium (TPP) carrying TEMPO-substituent and transition metal complexes were prepared by the anion exchange of the TPP–TEMPO tetrafluoroborate with [n-Bu₄N][Ni(dmit)₂], [n-Bu₄N]₂[Pd(dmit)₂], [n-Bu₄N]₂[Pt(dmit)₂], [n-Bu₄N][Ni(mnt)₂], or [n-Bu₄N]₂[Ni(mnt)₂] to give crystals with different structural features. While weak antiferromagnetic interactions of the Curie–Weiss behavior of S = 1/2 spin are predominantly observed in the salts of Pd(dmit)₂, Pt(dmit)₂ and Ni(mnt)₂, the magnetic behavior of 1:1 Ni(dmit)₂ salt can be explained by the additional contribution from the spins on Ni(dmit)₂ anions (χ − χ_TEMPO), obeying the 2D Heisenberg model. A couple of the oxidized salts, [TPP][Ni(dmit)₂] as well as [TPP]₂[Pd(dmit)₂], exhibit semi-conducting properties with relatively high room temperature conductivities.