TEMPO氧化纤维素纳米纤丝对多壁碳纳米管分散性的影响

以竹粉为原料,采用2,2,6,6-四甲基哌啶-1-氧自由基（TEMPO）氧化法通过改变NaClO的添加量制备出不同羧基含量及形态的纤维素纳米纤丝（CNFs）,并将制备的CNFs作为分散剂对多壁碳纳米管（MWCNTs）进行分散处理,得到不同分散浓度的CNFs/MWCNTs悬浮液,采用Beer-Lambert定律对MWCNTs的分散量进行测定,并采用原子力显微镜（AFM）、激光粒度分析仪（LPSA）等手段评价了不同羧基含量及形态的CNFs对MWCNTs的分散效果。结果表明:随着NaClO添加量的增加,CNFs的横截面直径逐渐变小,羧基含量逐渐增加,同时,CNFs对MWCNTs的分散量逐渐增大;当CNFs的羧基含量从0.635 mmol/g增加到1.646 mmol/g时,对MWCNTs的分散量从19%增加到39%;不同CNFs/MWCNTs悬浮液中的粒度分布系数（PDI）值均小于0.3,且不同悬浮液的Zeta电位绝对值均高于30 mV,表明不同羧基含量的CNFs均能对MWCNTs有较好的分散效果;同时,随着羧基含量的增加,CNFs对MWCNTs的分散效果越好,CNFs/MWCNTs复合薄膜的抗拉应力逐渐增大,而且电阻率逐渐降低,当CNFs羧基含量为1.646 mmol/L时,CNFs/MWCNTs复合薄膜抗拉应力达到了91 MPa,薄膜电阻率低至0.1460 Ωcm。      

TEMPO体系对粘胶纤维的氧化过程研究

2,2,6,6-四甲基哌啶氧化物自由基(TEMPO)-NaClO-NaBr是一种新的选择性氧化体系,文章研究了该体系对粘胶纤维的氧化过程。CP/MAS13C-NMR反映该体系对粘胶纤维是C6位选择性氧化,并能完全氧化成纤维素糖醛酸;用CP/MAS13C-NMR、耗碱量法和酸碱中和法研究了反应过程中羧基含量的变化;粘度法对聚合度的研究显示,粘胶纤维的降聚现象在反应一开始就非常显著。     

Copolymerization and addition of styrene and N‐phenylmaleimide in the presence of nitroxide

The copolymerization and addition reaction of styrene (S) with N‐phenylmaleimide (PMI), either neat or in xylene, have been found to proceed at 125°C in the presence of 2,2,6,6‐tetramethylpiperidin‐1‐yloxy (TEMPO) radicals. TEMPO‐terminated alternating S‐PMI copolymers and comonomer adducts were obtained. The amounts of the low molecular weight compounds increased with the increasing content of PMI in the initial mixture. The reaction suggests formation of monofunctional unimolecular initiators. In the autopolymerization of neat comonomers, a mediating role of TEMPO was observed. The synthesized copolymers containing TEMPO end groups were used as macroinitiators to initiate polymerization of styrene. The molecular weight distributions of resulting poly(styrene‐alt‐N‐phenylmaleimide)‐block‐polystyrene copolymers indicated the presence of both low molecular weight termination products and some copolymer precursor. The copolymers and comonomer adducts were characterized using the nitrogen analysis, size‐exclusion chromatography (SEC), and NMR spectroscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1093–1099, 2000     

木素对TEMPO氧化竹浆制备纳米纤维素的影响

以卡伯值不同的2种未漂硫酸盐竹浆(卡伯值为25.5和11.7的竹浆分别标记为SHK和SLK)为原料,通过TEMPO/NaBr/NaClO体系氧化及高压均质处理,制备了TEMPO氧化纳米纤维素(TOCN),并利用抽滤法制备TOCN膜。系统地研究了2种竹浆的TEMPO氧化过程、TEMPO氧化浆性能、TOCN性能及TOCN膜的力学性能等,探讨了木素对竹浆TEMPO氧化过程和TOCN制备的影响。结果表明,SHK的TEMPO氧化速率高于SLK,但SLK-TEMPO氧化浆的羧基含量达到1.01 mmol/g,高于SHK-TEMPO氧化浆的羧基含量(0.89 mmol/g)。2种TOCN形态结构差异不大,均呈纤丝状结构,直径约为5～8 nm,长径比>100,且均保持纤维素I的晶型结构;SLK-TOCN的结晶度和悬浮液的透光度均略高于SHK-TOCN。2种TOCN膜均具有优良的光学性能和力学性能,SLK-TOCN膜的杨氏模量、拉伸强度及裂断伸长率分别为2.6 GPa、92 MPa和10.9%,均高于SHK-TOCN膜的2.4 GPa、90 MPa和8.7%。     

Hydroxylamine as a Source for Nitric Oxide in Metal‐Free 2,2,6,6‐ Tetramethylpiperidine N‐Oxyl Radical (TEMPO) Catalyzed Aerobic Oxidation of Alcohols

The communication reports on the metal‐free 2,2,6,6‐tetramethylpiperidine N‐oxyl radical (TEMPO) catalyzed aerobic oxidation of various alcohols to aldehydes and ketones. A novel catalyst system that uses 1–4 mol% of TEMPO in combination with 4–6 mol% of aqueous hydroxylamine is introduced. No other additives are necessary and corrosive by‐products are not formed during oxidation. Nitric oxide which is important for the catalytic cycle is generated in situ by reaction of the hydroxylamine with TEMPO. A catalytic cycle for the overall oxidation process is suggested.     

激光诱导萘醌激发三重态猝灭反应的TR-ESR研究

利用时间分辨电子自旋共振（TR-ESR）方法,研究了稳定自由基TEMPO和生物抗氧化剂维生素C（VC）对萘醌（NQ）激发三重态 的猝灭机理和猝灭动力学。光解NQ/EG体系, 从EG上抽氢生成萘醌中性自由基 和乙二醇碳自由基。当体系中加入稳定自由基TEMPO时,TEMPO对3NQ* 有明显的猝灭作用,猝灭速率常数为1.14*106Lmol-1s-1。对于NQ/VC/EG-H2O溶液,3NQ*不仅可以从EG上夺氢,还从VC上夺氢,VC对3NQ*也有明显的猝灭作用,猝灭速率常数为1.11*107Lmol-1s-1。TEMPO和VC对3NQ*的猝灭反应都受扩散控制。     

TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展

2,2,6,6-四甲基哌啶氧自由基(TEMPO)共氧化剂体系被广泛应用于选择性氧化纤维素的C6位伯醇羟基。在氧化过程中,纤维素的聚合度大幅度降低,因此被应用于制备纳米纤维素。随着TEMPO/NaClO/NaBr氧化技术的发展成熟,TEMPO/NaClO/NaClO2和4-乙酰胺基-TEMPO/NaClO/NaClO2体系都得到了广泛关注。随着研究的深入,TEMPO及其衍生物氧化体系已经成为一种高效且全pH范围适用的选择性氧化体系。TEMPO/NaClO/NaBr氧化体系在pH范围9～11活性最高,TEMPO/NaClO/NaClO2体系能够应用于pH中性的条件下,4-乙酰胺基-TEMPO/NaClO/NaClO2体系一般的pH使用范围为3.5～6.8。传统的TEMPO氧化过程需要持续手动控制pH恒定,操作繁琐,可控性差,应用缓冲溶液可控制TEMPO氧化过程中pH在一定范围内恒定,从而实现了TEMPO氧化体系的智能控制。文章综述了TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展。     

Selective Oxidation of Alcohols to Carbonyl Compounds Mediated by Fluorous‐Tagged TEMPO Radicals

Oxidation of primary, benzylic and secondary alcohols into their corresponding aldehydes and ketones with safe, inexpensive oxidants was achieved in good yields under mild conditions in the presence of catalytic amounts of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radicals bearing perfluoroalkyl substituents. These “fluorous‐tagged” TEMPOs were readily isolated from the reaction products by liquid‐liquid or solid‐phase extraction, considerably simplifying the purification step. Their recyclability was strongly influenced by the nature of the oxidizing system. The best results were obtained using either [bis(acetoxy)iodo]benzene (BAIB) or aqueous NaOCl as the primary oxidants. Fluorous TEMPO 10 could be reused up to six times in the BAIB oxidation of 1‐octanol with only minor loss of catalytic activity.     

Interpolymer radical coupling: A toolbox complementary to controlled radical polymerization

The current review focuses on the relevance and practical benefit of interpolymer radical coupling methods. The latter are developing rapidly and constitute a perfectly complementary macromolecular engineering toolbox to the controlled radical polymerization techniques (CRP). Indeed, all structures formed by CRP are likely to be prone to radical coupling reactions, which multiply the available synthetic possibilities. Basically, the coupling systems can be divided in two main categories. The first one, including the atom transfer radical coupling (ATRC), silane radical atom abstraction (SRAA) and cobalt-mediated radical coupling (CMRC), relies on the recombination of macroradicals produced from a dormant species. The second one, including atom transfer nitroxide radical coupling (ATNRC), single electron transfer nitroxide radical coupling (SETNRC), enhanced spin capturing polymerization (ESCP) and nitrone/nitroso mediated radical coupling (NMRC), makes use of a radical scavenger in order to promote the conjugation of the polymer chains. More than a compilation of macromolecular engineering achievements, the present review additionally aims to emphasize the particularities, synthetic potential and present limitations of each system.