负载型TEMPO催化剂研究进展

在均相催化体系中,小分子TEMPO是醇选择性氧化为相应醛和酮最重要的有机催化剂之一,但因价格昂贵且回收工艺复杂等因素限制了均相TEMPO催化剂的大规模应用。负载型TEMPO催化剂因在两相体系中易与产物分离实现回收再利用而备受关注。TEMPO催化剂的固载化处理有效实现TEMPO的回收再利用,经多次重复使用仍保持较高的催化活性,且催化剂载体的特性赋予其比均相催化更高的催化活性。根据载体不同,分别介绍固体颗粒负载型TEMPO催化剂(包括无机颗粒和有机非溶性聚合物颗粒)和可溶性聚合物负载型TEMPO催化剂应用于醇氧化的研究进展,并评价两类负载型TEMPO催化剂的优缺点,对负载型TEMPO催化剂的发展前景进行展望。     

Effect of Co and V complexes on polymerization of methyl methacrylate initiated by AlEt2Br‐TEMPO catalyst

2,2,6,6‐Tetramethyl piperidinoxy (TEMPO) activated with diethyl aluminum bromide was employed as an initiator system for methyl methacrylate polymerization. Effect of addition of Co(acac)₃ and VO(acac)₂ complexes to the initiators system on methyl methacrylate polymerization were studied in benzene solvent. Various reaction parameters such as Al/TEMPO, monomer concentration, reaction temperature and time applied to the polymerization were investigated. The polymer yields, molecular weight and molecular weight distributions can be controlled with the addition of Co(acac)₃ to the initiator system. PMMA's of molecular weight distributions, as low as 1.10 was obtained under relatively mild conditions, in the temperature range 40–60°C in benzene solvent. However, Co and V complexes did not influence the micro structure of the PMMA's formed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

How meaningful is the assessment of antioxidant activities in microheterogeneous media?

Ignoring environmental factors in microheterogeneous solutions of antioxidants may lead to significant distortions and inconsistencies in the assessment of their activities. The importance of the hydrophobicity of the antioxidants and of the assaying radicals in such media is illustrated by comparing the reactivities of three phenols of different hydrophobicity, 3,5-di-t-butyl-4-hydroxytoluene (BHT), 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox) and Quercetin compared to radicals TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and 4-amino-TEMPO in micellar solutions of variable acidity of reduced Triton-X 100. The relative reactivities of these radicals, measured by EPR spectroscopy, indicated that the hydrophobicity of the involved species is a factor that should always be considered in the evaluation of antioxidants, with the risk of arriving at wrong conclusions regarding their activities.     

Incorporation of a stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in an electrochromic device

A stable organic radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), was studied. We employed TEMPO as a cathodic radical provider in propylene carbonate (PC) and poly(3,4-propylenedioxythiophene) derivatives (PProDOT-Et₂) as an anodic electrochromic (EC) thin film, which was obtained through electropolymerization. On assembling them together in a device, the electrochemical and optical performances of this hybrid electrochromic device (ECD) showed reversible cycling stability and high absorbance attenuation in the visible range. By selecting proper electrolytes (LiClO₄/PC) and controlling the deposited charge of the PProDOT-Et₂ thin film, it was possible to obtain a transmittance change (ΔT) of up to 59% at 590 nm with no noticeable degradation after operating between 0 and 0.9 V for 1000 cycles. Furthermore, an electrochemical quartz crystal microbalance (EQCM) was used to investigate ion migrations in the PProDOT-Et₂ thin film, which influenced its long-term stability.     

Facile synthetic route toward poly(vinyl benzyl amine) and its versatile intermediates

Poly(vinyl benzyl amine) (PVBAm) has been synthesized by modifying poly(vinyl benzyl chloride) (PVBC) via an unique synthetic route. According to the literature, most polyamines are synthesized from PVBC through the Gabriel reaction. In this investigation, we adopt Staudinger synthesis to avoid drastic decomposition which occurs in the Gabriel reaction during synthesis. Three types of polyamine polymers - homopolymer, block copolymer and random copolymer, were synthesized without incurring any crosslinking reaction. The amine-containing polymers can further undergo ring-opening addition reaction with N-phenyl-3,3-dimethyl-azetidine-2,4-dione. Notably, the intermediates, phosphine imine and azide functionalities can be easily converted into various functionalities such as carbodiimide, imine, amine, triazo, aziridine, etc. by adding suitable reagents.     

Effect of oat β‐glucan and its oxidised derivative on the quality characteristics of sponge cake

The objective of this study was to investigate the characteristics of sponge cakes containing native oat β‐glucan (BG‐B) and its oxidised derivative with TEMPO (2, 2, 6, 6‐tetramethyl‐1‐piperidine oxoammonium ion) (Oxi‐B). BG‐B and Oxi‐B were substituted at 1% (w/w) into a formulation, and then the effects of BG‐B and Oxi‐B addition on the pasting properties of wheat flour and the physicochemical and textural properties of sponge cakes were determined. The pasting parameters of wheat flour were increased by BG‐B, whereas they were decreased in wheat flour with added Oxi‐B. The cake containing Oxi‐B had a lower volume, and a higher symmetry and uniformity than the BG‐B cake. The Oxi‐B cake exhibited smaller L* and b* values and a higher a* value than the control in crumb and crust colour. According to texture profile analysis, the BG‐B cake had increased hardness, chewiness and gumminess, whereas the Oxi‐B cake had decreased hardness.     

Hierarchical Assembly of Nanocellulose‐Based Filaments by Interfacial Complexation

In the present study, interfacial complexation spinning of oppositely charged cellulose‐materials is applied to fabricate hierarchical and continuous nanocellulose based filaments under aqueous conditions by using cationic cellulose nanocrystals with different anionic celluloses including soluble sodium carboxymethyl cellulose and insoluble 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy radical‐oxidized cellulose nanofibers and dicarboxylated cellulose nanocrystals (DC‐CNC). The morphologies of the wet and dry nanocellulose based filaments are further investigated by optical and electron microscopy. All fabricated continuous nanocellulose based filaments display a hierarchical structure similar to the natural cellulose fibers in plant cells. As far as it is known, this is not only the first report about the fabrication of nanocellulose based filaments by interfacial complexation of cationic CNCs with anionic celluloses but also the first demonstration of fabricating continuous fibers directly from oppositely charged nanoparticles by interfacial nanoparticle complexation (INC). This INC approach may provide a new route to design continuous filaments from many other oppositely charged nanoparticles with tailored characteristics.     

基于分子修饰C-COS的高吸湿保湿机理

采用漆酶/2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)体系氧化壳寡糖制备了一种高吸湿保湿性羧基化壳寡糖(C-COS)。利用低场核磁共振(LF-NMR)、FTIR和13CNMR考察了其分子间氢键的变化并进一步推测出吸湿保湿机理。结果表明:在C-COS的吸湿过程中,聚合物分子与水之间存在着分子间氢键作用力。C-COS分子上极性较强的羧酸根产生了新的氢键效应,结合升温红外中3363、1643 cm~(–1)处吸收峰强度的减小和同样波数下吸收峰频率的蓝移以及溶胀红外中1643cm~(–1)处吸收峰强度的增加,确定了C-COS分子中羧酸根与水之间所形成的水合氢键(H—O—H···O—C==O)。另外,C-COS的保湿机理在于聚合物溶解在水体系中能够形成一种巨大的聚合物-水网状结构,促使水分子以氢键的形式被牢牢地锁住在这种网状结构中。     

Cellulose nanofibers produced from various agricultural residues and their reinforcement effects in polymer nanocomposites

Cellulose nanofibers (CNFs) have gained widespread attention due to their extraordinary potential as superior reinforcement to improve physical and mechanical properties of polymer matrix nanocomposites. Biomass residues from local North Dakota represent a potential source for these high value structural constituents. Two types of soybean hull, wheat straw, and softwood flour were subjected to chemical pretreatments followed by mechanical fibrillation to produce CNFs. Atomic force microscopy and scanning electron microscopy results show that nanofibers with uniform diameters in the nanometer range can be easily synthesized. The nanofibers reinforcement potential was then explored via integration of the fibers into a poly(ethylene oxide) polymer matrix. Significant reinforcement effect of the nanofibers was observed from the nanocomposites: tensile modulus and yield strength of the nanocomposites were increased up to 154% and 103%, respectively. The CNFs extracted from the two types of soybean hull and wood flour showed stronger reinforcement (in terms of both modulus and yield strength) than that of the traditional wood pulp based CNFs. The nanofibers extracted from wheat straw showed higher strength but lower modulus compared with those of the traditional CNFs. More work is however needed to improve production reliability/repeatability of the agricultural residue based nanofibers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46304.