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Bengt Wesslén Eva Andreasson Krister Holmberg 《Journal of the American Oil Chemists' Society》1989,66(8):1107-1112
Ethoxylation of nonyl phenol has been carried out at 130°C and at an absolute pressure of two bars. Alkali metal hydroxides
were used as catalysts, either neat or in conjunction with added co-catalysts such as 18-crown-6 and tetramethyl ethylene
diamine (TMEDA). The overall reaction rates were found to increase fivefold on the addition of the co-catalysts. The use of
TMEDA as the sole catalyst gave equally high reaction rates. This fact can be explained by the high basicity of TMEDA and
by the formation of a highly reactive ion pair similar to those found in phase transfer catalysis. The differences in the
kinetics of the reactions were analysed by computer simulation, using a five parameter model. According to this model, the
crown ether-catalyzed ethoxylation of nonyl phenol was found to proceedvia protonated ethylene oxide, while pure alkali catalysis proceeded mainlyvia uncomplexed ethylene oxide. Small differences in the oligomer distributions were noted. 相似文献
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Fernanda M. B. Coutinho Tereza C. J. Rocha Ivana L. Mello Denise S. S. Nunes Bluma G. Soares Marcos A. S. Costa 《应用聚合物科学杂志》2005,98(6):2539-2543
High‐cis polybutadiene produced by catalyst systems based on a rare earth is an elastomer used to produce green tires. This type of tire presents lower rolling resistance, which allows higher fuel economy, and thus fewer chemical compounds are discharged into the atmosphere. In this work, the influence of electron donors [tetrahydrofuran (THF) and tetramethylethylenediamine (TMEDA)] present in the polymerization solvent on the microstructure and molecular weight characteristics of the polybutadiene produced by neodymium catalysts was studied. The catalyst synthesis was carried out in glass bottles for 1 h at a temperature between 5 and 10°C. The catalyst components were diisobutylaluminum hydride, neodymium versatate, and tert‐butyl chloride. The polymerization reaction was carried out for 2 h. The reaction temperature was kept at 70± 3°C. The addition of TMEDA or THF above a determined concentration reduced the catalytic activity, molecular weight, and concentration of cis‐1,4 units (<96%), whereas the polydispersity increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2539–2543, 2005 相似文献
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To expand the application of electrospun fibers or electrosprayed beads, micro-nano hierarchical structures of polystyrene (PS) have been constructed through the adjustment of solvent, polymer concentration, environment humidity, electrospinning temperature, etc. Primary structures, such as fibers, beads and bead-on-string structure, as well as secondary structures, such as nanopores, nanopapilla and net-work structure, have been constructed. Solvent plays an important role in the construction of both primary structures and secondary structures. By using N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and mixed solvent of DMF/THF, the micro-nano hierarchical structures can be controlled. Humidity is a key factor to the construction of secondary structures. The obtained fibers or beads have smooth surface at low humidity. While at high humidity, secondary structures tend to appear. For the PS/DMF system, vapor-induced phase separation may be the most pertinent mechanism to explain the formation of secondary structures. While for the PS/THF system, breath figure theory can explain the formation of uniform nanopores properly. 相似文献
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The living nature of cationic polytetrahydrofuran (THF), photoinduced in the presence of diphenyliodonium hexafluorophosphate (initiator), was investigated. In the bulk polymerization of THF, the linear relationship between percent conversion and the number-average molecular weight of the resulting polymer strongly suggests the living nature of this polymer and this was confirmed by the monomer addition technique, that is, cationic poly(THF) is capable of initiating a newly added monomer. The loss of the living nature of the cationic poly(THF) in a polar solvent, dichloromethane, is explained in terms of the stabilization of the five-membered cyclic oxonium ion, a propagating species of cationic polymerization of THF, by ion-pair formation with a less nucleophilic counterion, hexafluorophosphate. Based on the living nature of cationic poly(THF), a diblock copolymer, composed of THF and N-2-(hydroxyethyl)ethyleneÍimine (HEEI) was synthesized by subsequent monomer addition method; however, it was found that the HEEI block of the compolymer has a nonlinear structure. The factors affecting the structure of the HEEI block are also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 611–618, 1998 相似文献
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Styrene/isoprene/butadiene integrated rubber prepared by anionic bulk polymerization in a twin‐screw extruder
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Styrene/isoprene/butadiene integrated rubber (SIBR) was synthesized using anionic bulk polymerization in a corotating intermeshing twin‐screw extruder. In order to study the relationship between microstructure and physical properties, three SIBRs were synthesized using different initiator complexes: n‐BuLi (N‐butyl lithium), n‐BuLi/THF (tetrahydrofuran), and n‐BuLi/TMEDA (tetramethylethylenediamine). The microstructure of the rubber products was analyzed by gel permeation chromatography and H nuclear magnetic resonance. SIBR prepared with pure n‐BuLi exhibited a multiblock microstructure. With the addition of THF or TMEDA, the vinyl content of the alkadiene increased; and the microstructure of SIBRs was randomized, indicated by the presence of a high weight content of styrene microblocks. Transmission electron microscopy demonstrated similar morphology in both the SIBRs and SSBR2003 (an industrial product). Dynamic mechanical analysis of the vulcanized SIBRs showed that the randomized SIBRs were quite suitable for the preparation of high‐performance tires. Tensile and tear test results of SIBRs were equivalent to those of SSBR2003. The low manufacturing cost of reactive extrusion technology will allow the large‐scale industrialization of SIBRs. POLYM. ENG. SCI., 55:1163–1169, 2015. © 2014 Society of Plastics Engineers 相似文献
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Shuaishuai Liang Jiang Li Xiaomin Li Jia Man Janine K. Nunes Haosheng Chen 《Journal of the American Ceramic Society》2018,101(9):3787-3796
In this study, the diffusion‐induced external gelation is combined with a microfluidic technique to prepare monodisperse ZrO2 ceramic microspheres. The gelation of sol droplets is traced by fluorescence visualization of the local pH, and it illustrates the effect of the external concentration of triggering agent (tetramethylethylenediamine, TMEDA) on the formation of the gel network, which results in 3 kinds of deformation of the gel particles. The deformation mechanism mainly lies in the imbalanced Laplace pressure exerted on the gel network during the competition between the gelation and the drying processes. By regulating the concentration of TMEDA, the monodisperse ZrO2 ceramic microspheres with high sphericity can be readily fabricated. 相似文献
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Linear styrene-butadiene block copolymers of polyA-block-polyB-block-polyA type (SBS) were synthesized in the presence of varying amounts of THF functioning as the polar structure modifier. The efficiency of this modifier was studied by analyzing the microstructure of synthesized polymers using 13C-NMR, and the effect of THF on polymerization kinetics was determined by progressive buildup of the molecular weight measured by GPC. Polymerization at 4000 ppm THF concentration resulted in the highest styrene polymerization rate while a 1 wt % concentration gave the highest butadiene polymerization rate. The vinyl content increased from 20 to 64% with an increase in the amount of THF from 200 ppm to 1 wt % while the content of trans-1,4 and cis-1,4 units decreased. For SBS polymer synthesized via a sequential process, the use of THF as the structure modifier enhanced the crossover efficiency that would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymer made via a coupling process, the coupling efficiency decreased when the amount of THF exceeded a certain limit. The temperature dependence of the coupling efficiency was also investigated. © 1996 John Wiley & Sons, Inc. 相似文献
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Gas hydrates have recently emerged as a better alternative for the production, storage, and transportation of natural gases. However, factors like slow formation rate and limited storage capacity obstruct the pos-sible industrial application of this technique. Different types of promoters and synergists have been developed that can improve the kinetics and storage capacity of gas hydrates. This review focuses on dif-ferent kinetic promoters and synergists that can be utilized to enhance the storage capacity of hydrates. The main characteristics, structure and the possible limitations of the use of these promoters are likewise portrayed in detail. The relationship between structure and storage capacity of hydrates have also been discussed in the review. Current status of production of gas from hydrates, their restrictions, and future difficulties have additionally been addressed in the ensuing areas of the review. 相似文献
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Virgilio A. González Roberto C. Cabriales Ivanna Moggio Eduardo Arias 《Polymer Bulletin》2007,58(4):627-634
Summary In this paper, we report the crossed aldol condensation between the acetone and the 2,5-bis(octyloxy)-terephthalaldehyde (OTP)
to obtain new photoluminescent oligomers as potential candidates for the construction of organic luminescent diodes (OLED’s).
The reaction is carried out in ethanol as solvent, but when THF is added to the reaction medium as co-solvent, a higher molecular
weight can be obtained. The analysis of the structure of the product obtained when THF is added was elucidated by 1H NMR, infrared, ultraviolet-visible (UV-Vis) and fluorescence spectroscopy and the results indicate that the number of repetitive
units corresponds with that of a tetramer with an excellent solubility in common organic solvents and intense fluorescence
in the green region. Moreover it can be processed by self-assembly in homogeneous thin films with controlled thickness. These
results are promising in view of the possible application of this oligomer in electroluminescent diodes. 相似文献
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This paper describes a convenient one-pot terpolymerization of CO2, cyclohexene oxide (CHO) and maleic anhydride (MAH) to afford a poly (ester-carbonate) with a low content of ether units (2.9-4.3 mol%) using a highly active Zn-Co(III) double metal cyanide complex (DMCC) catalyst. Terpolymerization was carried out in tetrahydrofuran (THF) at 75-90 °C and 1.0-4.0 MPa and no cyclic carbonate was observed in NMR spectra. The number-average molecular weight (Mn) of the terpolymer was up to 14.1 kg/mol with a narrow molecular weight distribution of 1.4-1.7. The apparent efficiency of the catalyst was up to 12.7 kg polymer/g Zn, representing the highest catalytic activity for terpolymerization of CO2, epoxides and cyclic anhydrides to date. THF dramatically inhibited polyether formation in this terpolymerization owing to its nucleophilicity towards the Zn2+ center of Zn-Co (III) DMCC. This presents the first example of solvent-assisted selectivity for inhibiting ether units in CO2 polymerization catalyzed by a heterogeneous system. Kinetic analyses of MAH/CHO/CO2 terpolymerization (MAH/CHO 0.2) suggested that polyester production was slightly faster than polycarbonate production in the early stage. A mechanism for this terpolymerization catalyzed by Zn-Co (III) DMCC catalyst was proposed. Moreover, addition of small amounts of MAH (MAH/CHO molar ratio ≤0.2) during CO2/CHO copolymerization can improve the thermal properties of the resultant terpolymers. 相似文献
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Tobias Abt Miguel Sánchez‐Soto Silvia Illescas Jon Aurrekoetxea Mariasun Sarrionandia 《Polymer International》2011,60(4):549-556
A new method of toughening polymerized cyclic butylene terephthalate (pCBT) with tetrahydrofuran (THF) is proposed. The pCBT was prepared by in situ ring‐opening polymerization of a commercial cyclic butylene terephthalate, a cyclic form of poly(butylene terephthalate), in the presence of THF. In comparison to conventionally polymerized pCBT, the resultant material was found to be ductile, showing a strain at break of well above 100% in tensile tests. Other matrix properties, such as tensile modulus, tensile strength and glass transition temperature, were not significantly altered by the addition of THF. It was found that the presence of THF enhanced the polymerization reaction, resulting in an increased molecular weight and a narrowed molecular weight distribution. Moreover, remaining oligomers after polymerization were extracted by the THF and a toughened oligomer‐free pCBT was obtained. The influence of time and temperature on the long‐time toughening action of THF was studied. The results showed that samples became brittle after 3 months when subjected to a temperature of 80 °C, resulting in a reduction of the toughening action. Copyright © 2010 Society of Chemical Industry 相似文献
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The ROP of cyclic ethers, carbonates and esters in the presence of commercially available methylaluminoxane/trimethylaluminum system has been studied. MALDI-ToF end groups analysis indicates that in a majority of systems considered, the polymerization process is initiated by insertion of a monomer into the Al-O-Al bond, generating alkoxide species, which are active sites in coordination polymerization. The polymerization of six-membered carbonates proceeds selectively, forming linear polydiols with high yields at moderate temperatures. The polymerization of oxiranes and lactones is, however, accompanied by back-biting reactions leading to cyclic oligomers. The interaction of oxirane with aluminoxane electrophilic sites causes also the formation of cationic species, which initiate the polymerization of THF. The cationic species formed in those systems were trapped by triphenylphosphine and identified by 31P NMR spectra. 相似文献
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Oku Jun-ichi Hasegawa Takashi Kubota Yoshiharu Takaki Mikio Asami Ryuzo 《Polymer Bulletin》1992,28(5):505-509
Summary The anionic polymerization of dimethylphenylvinylsilane with sec-butyllithium/N,N,N,N-tetramethylethylenediamine (TMEDA) was investigated. The polymerization proceeded up to 100% yield and afforded the polymer having isomerized-structure units. The polymerization was accompanied by chain transfer reaction to the monomer and the polymerization rate in the presence of TMEDA was much lower than in the absence of TMEDA. 相似文献
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A four‐armed star‐shaped poly(tetrahydrofuran) (THF) having a pentaerythritol unit at the center of the molecule was synthesized from photoinduced cationic copolymerization of THF and pentaeryithritol tetrakis(3,4‐epoxybutanoate) (PETE) in the presence of diphenyliodonium hexafluorophosphate. It was found that the molecular weight of the resulting polymer increases with increasing percent conversion and the rate of cationic polymerization of THF is remarkably increased by the addition of PETE when the concentration of PETE is kept much lower than that of THF. A similar enhancement effect was also observed in the photoinduced cationic polymerization of THF in the presence of epichlorohydrin (ECH). The enhancement effect of ECH and PETE was ascribed to the increased concentration of the cationic propagating species due to a rapid protonation process. The living nature was explained in terms of the stabilization of the cationic growing chain end by ion pair formation. Accordingly, the arm length of the polymer was determined by the molar ratio of THF and PETE. However, the polymer of well‐defined structure was only obtainable in the early stage of the reaction because chain transfer to the polymer process plays an important role when the concentration of the polymer becomes high. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2637–2644, 1999 相似文献
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Monodispersed poly(styrene–maleic anhydride) alternating copolymer (SMA) is synthesized through radical polymerization, and characterized by GPC, DSC, FT-IR and 1H NMR spectra. The mole fraction, χ, of styrene in the copolymer is 0.51, determined from integrated 1H NMR spectrum, this value is consistent with the alternating structure. FT-IR spectra show that maleic anhydride moieties on the backbone chains hydrolyze in a THF solution containing water, and HCl can accelerate the hydrolysis process. Atomic force microscopy reveals that well-arrayed and uniform-sized holes formed in thin SMA films on single crystal silicon wafer substrates spin-cast from the THF solutions containing HCl. HCl can also influence hydrogen bonding between the carboxylic acid groups in the THF solution, which is crucial for the formation of holes in the thin films. The volatilization process in the spin-casting is divided into two stages, THF and water volatilization. The formation of holes is interpreted as the trace of water droplets emulsified by the hydrolyzed SMA in the second stage, i.e. water volatilization. Results also indicate that there are both mobile and bound water populations in the solution, and that the bound water is responsible for the hole or valley pattern of these thin films. 相似文献
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Hidefumi Nakatsuji Jun‐ichi Morita Tomonori Misaki Yoo Tanabe 《Advanced Synthesis \u0026amp; Catalysis》2006,348(15):2057-2062
An efficient method for esterification between acid chlorides and alcohols in water as solvent has been developed by combining the catalytic amines, N‐methylimidazole and N,N,N′,N′‐tetramethylethylenediamine (TMEDA). The present Schotten–Baumann‐type reaction was performed by maintaining the pH at around 11.5 using a pH controller to prevent the decomposition of acid chlorides and/or esters and to facilitate the condensation. The choice of catalysts (0.1 equiv.) was crucial: the combined use of N‐methylimidazole and TMEDA exhibited a dramatic synergistic effect. The catalytic amines have two different roles: (i) N‐methylimidazole forms highly reactive ammonium intermediates with acid chlorides and (ii) TMEDA acts as an effective HCl binder. The production of these intermediates was rationally supported by a careful 1H NMR monitoring study. Related amide formation was also achieved between acid chlorides and primary or secondary amines, including less nucleophilic or water‐soluble amines such as 2‐(or 4‐)chloroaniline, the Weinreb N‐methoxyamine, and 2,2‐dimethoxyethanamine. 相似文献