双水相萃取体系的研究

有机溶剂;分相机理;双水相萃取体系的研究     

温控液/液两相催化进展*

本文以作者在温控水/有机两相及温控非水液/液两相催化领域的研究工作为主线,对这一领域的研究进展作一评述,重点是环绕经典水/有机两相催化体系存在“应用范围受底物水溶性限制”的根本问题展开。特别是对“温控相转移催化”作了较为详细的介绍,同时,按体系介质不同,对氟两相体系、PEG两相体系、离子液体两相体系等非水液/液两相体系以及温控相分离催化分别作了阐述。     

液/液两相催化高碳烯烃氢甲酰化反应

结合作者近年来的研究工作 ,对液/ 液两相催化高碳烯烃氢甲酰化的研究进展作一综述 ,针对经典的水/有机两相体系不能用于高碳烯烃氢甲酰化的问题 ,全面介绍了适用于高碳烯烃水/有机两相氢甲酰化的温控相转移催化等 6种改进方法。同时 ,对 90年代以来发展迅速的氟两相、离子液体两相、超临界流体等非水液/液两相体系中的高碳烯烃氢甲酰化作了系统阐述 ,对它们的应用前景进行了评较。     

温控离子液体/有机两相体系中纳米Rh催化烯烃氢甲酰化反应

将具有"高温混溶、室温分相"功能的离子液体[CH3(OCH2CH2)16N+Et3][CH3SO3–](ILPEG750)与甲苯-正庚烷组成的两相体系用于纳米Rh催化的烯烃氢甲酰化反应中,在优化的反应条件下,1-辛烯转化率和醛收率分别为99%和91%.催化剂经简单分相即可与产物分离,且可连续使用8次,其活性基本保持不变.     

温控聚乙二醇两相体系中纳米钯催化肉桂醛选择性加氢反应

将具有“高温混溶、室温分相”功能的聚乙二醇4000(PEG₄₀₀₀)与甲苯-正庚烷组成的两相体系用于纳米钯催化的肉桂醛选择性加氢反应中.在优化的反应条件下,肉桂醛转化率和氢化肉桂醛选择性分别为99%和98%.钯纳米催化剂经简单分相即可与产物分离,且循环使用8次,其活性和选择性基本保持不变.     

三元醇丙烯酰胺键合色谱固定相的制备及评价

利用巯基与乙烯基的"点击化学"反应合成了一种新型含多羟基的硅烷偶联剂,再将其与硅胶反应制得含多羟基的亲水固定相。经过元素分析表征证明多羟基官能团已成功键合到硅胶表面。采用一系列不同性质的标准物质考察了亲水色谱模式下固定相的溶质保留机理。由于固定相结构中既具有极性多羟基官能团,也有短的疏水碳链,因此固定相兼具疏水性与亲水性。将此固定相成功应用于亲水与反相色谱两种模式,并对比了两种模式下流速对柱效的影响。最后将固定相应用于烷基苯、水溶性维生素以及核苷的分离中,取得了较好的分离效果,证明了固定相良好的应用前景。     

添加剂对PVDF相转化过程及膜孔结构的影响

研究了PVP、PEG及LiCl 3种成孔添加剂下PVDF DMAc H2 O 添加剂体系的成膜机理 .无论那种添加剂的铸膜液相转换成膜过程中都存在凝胶分相和液液分相两种相变方式 ,在 30～ 6 0℃时凝胶分相在较低的非溶剂浓度下先于液液分相发生 ,LiCl作为添加剂较PEG、PVP对铸膜液有较强的致凝胶作用 ,成膜过程中凝胶分相段时间依PVP、PEG、LiCl的顺序延长 ,导致液液分相初始分相点处聚合物浓度增大 ,阻止了大孔结构的充分发展 .制得的膜依PVP、PEG、LiCl的顺序有效孔隙率和通量降低 ,结晶度升高 .以LiCl为添加剂制得的膜几乎不改变PVDF膜的疏水性 ,而以PVP或PEG为添加剂的膜隔水压差降低约 2 0kPa .     

两相催化——均相催化多相化新进展*

评述了水溶性膦配体和两相催化研究领域的进展, 探讨了固载水相催化、温控相转移催化和氟两相体系等新型两相催化体系。两相催化在烯烃的氢甲酰化反应、不饱和化合物的加氢反应以及其它有机反应中获得了广泛的应用。     

超临界二氧化碳/聚乙二醇两相体系的性质及其在催化反应中的应用

非均相催化过程中常常出现产物的转化率低、选择性差的问题, 而均相催化过程往往具有优异的催化性能, 但是却受制于催化剂、产物难于分离而达到循环使用的缺点. 近年来两相催化体系的发展为这些问题的解决提供了一条新途径. 超临界二氧化碳/聚乙二醇参与的两相体系是使用超临界二氧化碳作流动相, 聚乙二醇作为另一溶剂之一, 用于固定和稳定催化剂, 进行有机催化反应. 其显著特点是: 可在反应的同时实现分离的操作, 可实现均相催化过程的连续化. 综述了超临界二氧化碳/聚乙二醇体系的相行为及其性质, 并介绍了其在催化合成反应中的应用.     

两相催化体系中长链烯烃氢甲酰化反应研究进展

水溶性有机金属络合物为催化剂的两相催化体系,由于反应条件缓和,产物和催化剂分离简便等特点,已成为发展环境友好的绿色化学的重要方向。本文介绍了近年来两相催化体系中长链烯烃氢甲酰化反应和催化剂研究进展。     

热致相分离聚丙烯微孔膜

对聚丙烯－稀释剂体系热致相分离过程制备聚丙烯微孔膜的意义、原理、过程及研究现状进行了评述。     

Evidence of mechanisms occurring in thermally induced phase separation of polymeric systems

Thermally induced phase separation is a fabrication technique for porous polymeric structures. By means of easy‐to‐tune processing parameters, such as system composition and demixing temperature, a vast latitude of average pore dimensions, pore size distributions, and morphologies can be obtained. The relation between demixing temperature and morphology was demonstrated via cloud point curve measurement and foams fabrication with controlled thermal protocols, for the model system poly‐l ‐lactide–dioxane–water. The morphologies obtained at a temperature lower than cloud point showed a closed‐pore architecture, suggesting a “nucleation‐and‐growth” separation mechanism, which produced larger pores at higher holding times. Conversely, the porous structures attained when holding the sample above the cloud point exhibited open pores with dimensions independent of time, denoting a phase separation occurring during sample freezing. Finally, the influence of the cooling rate on final morphology was investigated, showing a clear correlation with microstructure and pore size. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 979–983     

Synthesis of a new amino acid/sulfur dioxide copolymer and its use in aqueous two‐phase polymer systems

The amine salt N,N‐diallyl‐N‐5‐carbomethoxypentylammonium chloride was copolymerized with sulfur dioxide in dimethyl sulfoxide with ammonium persulfate or 2,2′‐azobisisobutyronitrile and afforded a cationic polyelectrolyte (CPE) with a five‐membered cyclic structure on the polymeric backbone. The CPE, upon acidic hydrolysis of the pendent ester groups, gave a corresponding cationic acid salt (CAS) having the equivalent of chloride salt of 6‐N,N‐diallylammoniohexanoic acid as the monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and a polybetaine (PB), having the monomeric unit equivalent of sodium 6‐N,N‐diallylaminohexanoate and 6‐N,N‐diallylammoniohexanoate, by treatment with 2 and 1 equiv of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. The basicity constant of the amine functionality in APE was apparent and as such followed the modified Henderson–Hasselbalch equation; the protonation of the APE became more and more difficult as the degree of protonation of the whole macromolecule increased. The compositions and phase diagrams of the aqueous two‐phase systems of APE and poly(ethylene glycol) were studied. The PB was found to be insoluble in water, and this paves the way for the potential use of APE in aqueous two‐phase polymer systems for protein purification and its removal and recycling by conversion into PB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2464–2477, 2002     

Effect of shear flow on the phase‐separation behavior in a blend of polystyrene and polyvinyl methyl ether

The phase behavior and phase‐separation dynamics of polystyrene/polyvinyl methyl ether (PS/PVME) blend with a critical composition of 70 vol % PVME were examined with a light scattering technique under a shear‐rate range of 0.1–40 s^?1. If the shear rates were less than 8 s^?1 and the starting temperatures of the measurement were 343 and 383 K, respectively, two cloud points were observed, whereas after the shear rate was higher than 8 s^?1, only one cloud point existed, 20 K higher than that of the static state of the blend. Investigation of the phase‐separation dynamics at 443 K suggested that in the vorticity direction the phase‐separation behavior at the early stage and the later stage can be explained by Cahn–Hilliard linearized theory and the exponent growth law, respectively. Phase separation occurs after a shearing time, which was called a delay time τ_d. The delayed time τ_d, the apparent diffusion coefficient, and the exponent term of the blend show strong dependence on shear rates. A theoretical prediction of the phase behavior of PS/PVME under a shear flow field by introducing an elastic energy term into Flory's equation‐of‐state theory was made, and the prediction was consistent with the experimental results. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 661–669, 2003     

Competition between Liquid-liquid De-mixing,Crystallization, and Glass Transition in Solutions of PLA of Different Stereochemistry and DEET

Liquid-liquid(L-L)de-mixing and vitrification of solutions of either crystallizable poly(L-lactic acid)(PLLA)or non-crystallizable poly(D/L-lactic acid)(PDLLA)with 50 m%N,N-diethyl-3-methylbenzamide(DEET)were analyzed by calorimetry and cloud-point measurements,which allows drawing conclusions about the effect of polymer stereochemistry on the phase behavior.Regardless of the PLA stereochemistry,vitrification of the solutions on fast cooling,hindering crystallization of PLLA,occurred below-20℃ and suppressed prior L-L de-mixing.The experimental results prove that crystallization in samples containing crystallizable PLLA,observed at around 55℃ on slow cooling,is not preceded by L-L de-mixing.     

Morphology Evolution during the Phase Separation of Polyetherimide/Epoxy Blends

The results of time‐resolved light scattering for the phase separation of epoxy/polyetherimide/anhydride blends show that the evolution of scattering vector q_m follows a Maxwell‐type relaxation equation. The relaxation time may be suggested as the time taken for the diffusion of the epoxy‐anhydride n‐mers from the PEI‐rich phase by their relaxation movement, and the apparent activation energy of the relaxation movement is obtained.

Values of q_m versus time at different temperatures.     

Study of the purifying affects of thermal annealing for polymer‐wall liquid crystal cells

The thermal annealing process was proposed to purify the pixel regions of a liquid crystal (LC) cell with polymer walls. This technique, based on thermal‐induced phase separation, successfully evicts the residual monomers from the LC volume and significantly improves electro‐optical properties of the polymer‐wall LC devices. The influence of the annealing process on the purity of LC‐rich domain and the electro‐optic properties of a LC cell was explored with a series of experiments. According to the experimental results, the annealing technique is extremely prospective for constructing flexible polymer‐wall LC display applications.     

Spinodal decomposition in N‐isopropylacrylamide gel

Spinodal decomposition in a chemically crosslinked N‐isopropylacrylamide (NIPA) polymer gel was investigated using turbidity and ultrasonic techniques. The turbidity of the quenched NIPA gel was measured over five orders of magnitude of timescales. With an increase of time, the gel transfers from a transparent and swollen gel to a cloudy and inhomogeneous gel, and eventually to a transparent and collapsed gel. The first transformation is a rapid process that only involves local arrangement of the polymer network and solvent into dilute and dense domains. The second transformation is a very slow process that involves global arrangement of the polymer network and solvent. The characteristic time for disappearance of the turbidity is proportional to the linear size squared at a constant temperature above T_c and increases exponentially as a function of the quenching depth of T ? T_c. By probing the movement of domains, a possible time‐dependent gel structure in the spinodal decomposition region is presented. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2168–2174, 2001     

Scattering properties,stability analysis,and phase separation of polyelectrolyte mixtures

The conditions of stability for weakly charged polyelectrolyte mixtures are analyzed from a scattering theory developed previously. In the thermodynamic limit of zero wave vector q = 0, it is found that electrostatic interaction induces a compatibility enhancement which is discussed for various cases of charge distributions. The condition of microphase separation transition at the wave vector for which the scattering is a maximum is also discussed. © 1993 John Wiley & Sons, Inc.     

Theory of a helicoidal cholesteric phase induced by an external field

We present a mean field theory to describe a helicoidal cholesteric phase for mixtures of a chiral nematic liquid crystal (LC) and a polymer chain as well as for pure chiral nematic LC molecules in the presence of a longitudinal external field parallel to the pitch axis of a cholesteric (Ch) phase. The free energy of the helicoidal Ch phase (Ch_H) is derived as a function of a usual orientational order parameter and an order parameter of the Ch_H phase. On increasing the strength of the external field, we find that the Ch phase changes to the nematic (N) phase through the Ch_H phase. Depending on the temperature and the strength of the external field, we find the second-order N–Ch_H and Ch_H–Ch phase transitions and the first-order paranematic (pN)–N, pN–Ch_H and pN–Ch phase transitions. We also predict phase diagrams in mixtures of a flexible polymer and a Ch LC molecule under the external field.