共查询到20条相似文献,搜索用时 15 毫秒
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Wen-Jun Wang Edward Kolodka Shiping Zhu Archie E. Hamielec 《Journal of polymer science. Part A, Polymer chemistry》1999,37(15):2949-2957
The solution copolymerization of ethylene (1) with octene-1 (2) in Isopar E using constrained geometry catalyst system, [C5Me4(SiMe2NtBu)]TiMe2 (CGC-Ti)/tris(pentafluorophenyl)boron (TPFPB)/modified methylaluminoxane (MMAO), has been carried out in a high-temperature, high-pressure continuous stirred-tank reactor (CSTR) at 140°C, 500 psig and with a mean residence time of 4 min. A series of copolymer samples with octene-1 content up to 0.337 mole fraction were synthesized and characterized. The estimated reactivity ratios were r1 = 7.90 and r2 = 0.099. The CGC-Ti showed a higher ability to incorporate high α-olefins than other metallocene catalysts investigated in the literature due to its open structure. The presence of octene-1 lowered the catalyst activity, particularly at octene-1 levels higher than 0.45 mole fraction. Octene-1 was also found to reduce the molecular weight of polymer and broaden the molecular weight distributions. The triad distributions were measured by 13C-NMR. A minor penultimate effect was observed. The penultimate octene-1 unit appeared to slow down monomer insertion rates. A comparison of the propagation rate of octene-1 with the incorporation rate of macromonomer in the homopolymerization of ethylene suggests that the addition of macromonomer is effectively instantaneous after it is generated with diffusion to or from the active center reaction volume playing a minor role. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2949–2957, 1999 相似文献
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A green method for the controlled synthesis of aliphatic polymers is presented. The ring-opening polymerizations of cyclic monomers including several lactones, such as caprolactone (CL) or pentadecalactone (PDL), and cyclic anhydride monomers, such as succinic anhydride (SUC) and tetrahydrofuran (THF), catalyzed by a series of metal triflates (trifluoromethanesulfonate) were studied. Aluminum triflate was found to be an advantageous candidate to catalyze the ring-opening polymerization of cyclic monomers. The details of the ring-opening polymerization of CL catalyzed by aluminum triflate were studied. The maximum number average molecular weight (Mn), polydispersity (Mw/Mn) and yield of the obtained poly(-caprolactone) (PCL) at 60 °C for 6 hours were 18,400, 1.94 and 89 wt%, respectively. Those of poly(pentadecalactone) (PPDL) at 100 °C for 6 hours were 12,400, 2.24 and 49 wt%, respectively. The Mn, Mw/Mn and yield of the obtained poly(butylene succinate) (PBS) from SUC and THF at 100 °C for 48 hours were 4,900, 2.03 and 84 wt%, respectively. Furthermore, the mechanism of the polymerization was discussed based on the relationship between the conversion of CL and time. The molecular weight buildup of PCL was linear with a conversion in 50 min before the conversion reached 100 % and with Mw/Mn stabilized at about 1.5. The Mw/Mn of PCL then gradually increased. From these data, a living polymerization with a small transesterification was suggested from the PCL polymerization by aluminum triflate. 相似文献
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Nicky Chan Michael F. Cunningham Robin A. Hutchinson 《Macromolecular rapid communications》2011,32(7):604-609
The use of copper tubing as both the reactor and as a catalyst source is demonstrated for continuous controlled radical polymerization of methyl acrylate at ambient temperature and at low solvent content of 30%. The high surface area provided by the copper walls mediates the reaction via the single electron transfer–living radical polymerization (SET‐LRP) mechanism. The polymerizations proceeded quickly, reaching 67% conversion at a residence time of 16 min. Ligand concentration could also be reduced without a sharp drop in polymerization rate, demonstrating the potential for decreased raw material and post‐process purification costs. Chain extension experiments conducted using synthesized polymer showed high livingness. The combination of living polymer produced at high polymerization rates at ambient temperature and low volatile organic solvent content demonstrate the potential of a copper reactor for scale up of SET‐LRP.
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The ring-opening polymerization of adipic anhydride and the ring-opening copolymerization of adipic anhydride with ε-caprolactone catalyzed by single component rare earth trisphenolate have been reported. The structure of the copolymer poly(CL-b-AA) has been characterized by SEC, ^1H NMR and DSC. 相似文献
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Poly(ε-caprolactone) (PCL) with weight-average molar mass over 10000 g/mol was synthesized by microwave-assisted ring-opening polymerization of ε-caprolactonc (ε-CL) with malcic acid (MA) as initiator (2.45 GHz, 360 W, 85 min). Ibuprofen-PCL controlled release system was prepared directly by the ROP of ε-CL in its mixture with ibuprofen. The release of ibuprofen from the system was sustained and steady. 相似文献
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Zhiquan Shen Xianhai Chen Youqing Shen Yifeng Zhang 《Journal of polymer science. Part A, Polymer chemistry》1994,32(4):597-603
Ring-opening polymerization of ε-caprolactone has been carried out by using rare earth coordination catalysts for the first time. The rare earth compounds, RE(acac)3.3H2O, Nd(P204)3, Nd(P507)3, Nd(naph)3, Nd(BA)3.2H2O, etc. (where RE = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Lu, Y; acac = acetylacetone; BA = benzoylacetone), combined with trialkyl aluminum, greatly increased the degree of conversion and the molecular weight of poly(ε-caprolactone) (PCL). The influence of reaction conditions on the polymerization of ε-caprolactone catalyzed by the Nd (acac)3.3H2O-AlEt3 system has been examined in detail. The kinetics indicates that the polymerization rate has the first-order in monomer and a half-order in catalyst. The overall activation energy of the ring-opening polymerization amounts to 59.4 kJ/mol. By IR and UV-Vis spectra, 1H- and 13C-NMR data, it is assumed that the ring-opening polymerization of ε-caprolactone catalyzed by the Nd(acac)3.3H2O-AlEt3 system proceeds via complexation of monomer to catalyst, acyl-oxygen cleavage insertion propagation mechanism. © 1994 John Wiley & Sons, Inc. 相似文献
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Experimental and computational studies of ring‐opening polymerization of ethylene brassylate macrolactone and copolymerization with ε‐caprolactone and TBD‐guanidine organic catalyst 下载免费PDF全文
Ana Pascual Haritz Sardón Fernando Ruipérez Raquel Gracia Pallavi Sudam Antonio Veloso David Mecerreyes 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):552-561
The ring‐opening polymerization (ROP) of ethylene brassylate, catalyzed by the cyclic guanidine 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) is reported. Several experimental parameters were evaluated for bulk ROP process and polyesters, resulting in molecular weights between 3 and 15 kg mol?1. End‐group analysis by 1H nuclear magnetic resonnance (NMR) and matrix assisted laser desorption ionization time of flight computational studies supports the dual behavior of TBD, which can act as both a catalyst and initiator of the polymerization process. Under optimum conditions, semicrystalline poly(ethylene brassylate‐co‐ε‐caprolactone) random copolymers were synthesized. Depending on the comonomer content, our results showed a range of melting temperatures between 39 and 69 °C. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 552–561 相似文献
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联用反应动力学、电荷衡算和物料衡算建立阴极冷却固定床草酸电合成乙醛酸反应器模型方程.针对反应器连续化操作过程,用正交配置法数值求解该模型方程.结果表明,在连续化操作的反应初期,反应液中的乙醛酸能够较快地达到预定浓度,但继续增加反应器的长度,反应的效果不明显.该模型还模拟了分段温控和部分回流对反应的影响.结果表明,分段温控和部分回流均可较好地提高乙醛酸在阴极液中的浓度.计算结果与试验操作基本相符.该结果对阴极冷却固定床草酸电合成乙醛酸的连续化操作工艺和反应器的优化具有重要的参考意义. 相似文献
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Tiziana Fuoco 《高分子科学杂志,C辑:聚合物评论》2020,60(1):86-113
AbstractThiol chemistry is an efficient tool to manipulate the microstructure of aliphatic polyesters and open the way to different applications. Synthetic strategies that aim to synthesize thiol-functionalized aliphatic polyesters are reviewed herein. The introduction of thiol-editable groups on aliphatic polyesters can occur both at chain ends and along the chains, enabling diverse modifications of the polymeric chains and imparting new properties and functions. The use of thiol chemistry for postpolymerization modification of this class of polymers and the (co)polymerizations of monomers bearing thiol groups has also been described herein. 相似文献
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Hui Li Rama M. Shakaroun Sophie M. Guillaume Jean-François Carpentier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(1):128-138
Poly(hydroxy acid)s are a family of biocompatible and (bio)degradable polyesters with various outcomes in different domains of application. To date, poly(hydroxy acid)s are best prepared by ring-opening polymerization (ROP) of the corresponding cyclic esters. Using racemic chiral monomers featuring side-chain groups enables to access, providing a stereoselective catalyst/initiator system is implemented, stereoregular functional polymers, thereby improving their physico–chemical properties, and ultimately, widening their range of uses. Here, we highlight a few important advances in metal-mediated stereoselective ROP of cyclic esters towards the synthesis of (functional) stereoregular poly(hydroxy acid)s that have recently been disclosed, emphasizing on (functional) β- and γ-lactones, diolide and O-carboxyanhydride (OCA) monomers and yttrium-based catalysis. Fine-tuning of the substituents flanked on the catalyst ligand enables reaching poly(hydroxy acid)s with syndiotactic and also isotactic microstructures. The stereocontrol mechanisms at work and their probable origin, relying on steric but also electronic factors imparted in particular by the ligand substituents, are discussed. Taking advantage of such stereoselective ROPs, original copoly(hydroxy acid)s with gradient or alternated patterns then become accessible from the use of mixtures of chemically different, oppositely configured enantiopure monomers. 相似文献
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Peter C. Zhu Zhihong Wu Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》1997,35(3):485-491
The stable cyclic ketene acetal, 2-methylene-1,3-dioxepane, 7, has been polymerized cationically in pentane, CH2Cl2 and THF at 25°C to form a polymer which is composed of both ring-opened (40–50%) and ring-retained (50–60%) structures. Initiation was catalyzed by using H2SO4-supported on activated carbon black. This unique outcome differs significantly from the cationic polymerization of several other five- and six-membered ring cyclic ketene acetals which gave 100% 1,2-vinylpolymerization under these conditions. As the polymerization temperature increased in cationic polymerization of 7 the ring-opened content increased and the molecular weight of the polymers decreased in such solvents as cyclohexane, 1,2-dichloroethane, dimethoxyethane, and bis-(2-methoxyethyl) ether. The mechanism of this polymerization is discussed. This research also illustrated the ability to initiate the cationic polymerization of cyclic ketene acetals by acidified carbon black while avoiding subsequent polymer decomposition. © 1997 John Wiley & Sons, Inc. 相似文献
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Polyethylene with Reverse Co‐monomer Incorporation: From an Industrial Serendipitous Discovery to Fundamental Understanding 下载免费PDF全文
Dimitrije Cicmil Dr. Jurjen Meeuwissen Dr. Aurélien Vantomme Dr. Jian Wang Ilse K. van Ravenhorst Dr. Hendrik E. van der Bij Dr. Ara Muñoz‐Murillo Prof. Dr. Bert M. Weckhuysen 《Angewandte Chemie (International ed. in English)》2015,54(44):13073-13079
A triethylaluminium(TEAl)‐modified Phillips ethylene polymerisation Cr/Ti/SiO2 catalyst has been developed with two distinct active regions positioned respectively in the inner core and outer shell of the catalyst particle. DRIFTS, EPR, UV‐Vis‐NIR DRS, STXM, SEM‐EDX and GPC‐IR studies revealed that the catalyst produces simultaneously two different polymers, i.e., low molecular weight linear‐chain polyethylene in the Ti‐abundant catalyst particle shell and high molecular weight short‐chain branched polyethylene in the Ti‐scarce catalyst particle core. Co‐monomers for the short‐chain branched polymer were generated in situ within the TEAl‐impregnated confined space of the Ti‐scarce catalyst particle core in close proximity to the active sites that produced the high molecular weight polymer. These results demonstrate that the catalyst particle architecture directly affects polymer composition, offering the perspective of making high‐performance polyethylene from a single reactor system using this modified Phillips catalyst. 相似文献
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Dr. Wensi Tang Dr. Lunan Zhang Dr. Tianyu Qiu Prof. Huaqiao Tan Prof. Yonghui Wang Dr. Wei Liu Prof. Yangguang Li 《Angewandte Chemie (International ed. in English)》2023,62(30):e202305843
The development of a new electrolytic water hydrogen production coupling system is the key to realize efficient and low-cost hydrogen production and promote its practical application. Herein, a green and efficient electrocatalytic biomass to formic acid (FA) coupled hydrogen production system has been developed. In such a system, carbohydrates such as glucose are oxidized to FA using polyoxometalates (POMs) as the redox anolyte, while H2 is evolved continuously at the cathode. Among them, the yield of glucose to FA is as high as 62.5 %, and FA is the only liquid product. Furthermore, the system requires only 1.22 V to drive a current density of 50 mA cm−2, and the Faraday efficiency of hydrogen production is close to 100 %. Its electrical consumption is only 2.9 kWh Nm−3 (H2), which is only 69 % of that of traditional electrolytic water. This work opens up a promising direction for low-cost hydrogen production coupled with efficient biomass conversion. 相似文献
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Catalytic Chemistry of Supported Heteropolyacids and Their Applications as Solid Acids to Industrial Processes 总被引:1,自引:0,他引:1
Yuichi Kamiya Toshio Okuhara Makoto Misono Atsuyuki Miyaji Katsuyuki Tsuji Tetsuo Nakajo 《Catalysis Surveys from Asia》2008,12(2):101-113
This article reviews recent research and development of supported heteropolyacid (HPA) catalysts; focusing on the acidic and
catalytic properties. First the basic knowledge of solid HPAs is provided briefly to facilitate understanding of heterogeneous
catalysis of HPAs. Secondly, the structure as well as the physical and chemical properties of supported HPA catalysts is described.
Especially the layer structure of HPA dispersed on the surface of SiO2 and the changes in the surface acidity with the loading level of HPA are discussed. For this purpose, temperature programmed
desorption of benzonitrile devised by Okuhara and Kamiya’s group is useful. This method is capable to assess the surface acidity
of the supported HPA, which controls the catalytic activity for the reactions proceeding by surface-type catalysis. Then,
two new industrial processes developed by Showa Denko K. K. are described; (i) production of ethyl acetate from ethylene and
acetic acid and (ii) oxidation of ethylene to acetic acid. Supported HPA catalysts are utilized for both processes, which
were recently much improved by finely controlling the catalysts and reaction conditions. 相似文献
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反应控制相转移催化剂催化环己烯氧化制己二酸 总被引:5,自引:0,他引:5
The goal of modern organic synthesis is to develop efficient catalytic methods to produce desired compounds in a cost-effective and environmentally benign manner. Hydrogen peroxide is a highly attractive oxidant because it is a cheap, mild and environmentally friendly reagent with a high content of active oxygen, and water is the only by-product. 相似文献