ChemCatChem
·
2017
·Vol. 9
·期 17
·3364-3373
·
IF 4.803
Qiaoqiao Sun,Ruihua Cheng,Zhen Liu,Xuelian He,Ning Zhao,Boping Liu
Graphical The fluorine effect : Fluorinated Phillips catalysts (Cr/F-SiO 2 ) exhibit an enhanced reactivity towards ethylene polymerization and copolymerization. DFT calculations show that the difference of the Gibbs free energy barriers between chain transfer and chain propagation increased after the introduction of the fluoride onto the silica surface, which is in accordance with the increased molecular weight of the polyethylene formed using the Cr/F-SiO 2 catalyst. In this work, a fluoride-modified Phillips catalyst was investigated by using combined experimental and computational methods. The addition of fluoride to the Phillips Cr/SiO 2 catalyst can increase the activity of the catalyst calcined at a low temperature and the molecular weight of the polyethylene product. DFT calculations were performed to show that the difference of the Gibbs free energy barriers between chain transfer and chain propagation increased after the introduction of the fluoride onto the silica surface, which is in accordance with the increased molecular weight of the polyethylene produced by the fluoride-modified Phillips Cr/F-SiO 2 catalyst. The computational results also reflect the increase of the activity of the ethylene/1-hexene copolymerization after the introduction of fluoride, although the modification has little effect on the regioselectivity of the produced ethylene/1-hexene copolymer. Moreover, copolymers produced by the fluoride-modified Phillips catalyst with more short-chain branches (SCBs) in the high-molecular-weight fraction and a significant enhancement of the environmental stress crack resistance can be explained from the results of the DFT calculations.
研究领域:
化学工程
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材料科学
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计算化学
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DOI
高影响因子
DALTON TRANSACTIONS
·
2015
·Vol. 45
·期 4
·1496-1503
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IF 4.197
Xiaohui Hu,Shengyu Dai,Changle Chen
The synthesis, characterization and ethylene polymerization properties of a series of salicylaldimine Ni(II) complexes with a dibenzhydryl moiety are described. These Ni complexes are designed to bear systematically varied electron donating and withdrawing substituents. These complexes are among the most active salicylaldimine Ni(II) catalysts in ethylene polymerization. Moreover, these complexes demonstrate good thermal stability, maintaining high activity at 80 °C. The polyethylene generated possesses a high molecular weight, moderate branching density and high melting temperature. Surprisingly, the electronic perturbations only exert moderate influence on the ethylene polymerization process despite the covalently close proximity of the electron donating or withdrawing substituents to the metal center. Comparing with the traditional iso-propyl substituted nickel analogue, these new complexes show up to an order of magnitude higher activity, generating polyethylene with much higher molecular weight, similar or slightly lower branching density and much higher melting temperature.
研究领域:
材料化学
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催化化学
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DOI
PubMed
高影响因子
ACS Omega
·
2021
·
IF 3.512
Tianyu Lan,Na Zhang,Liduo Chen,Cuiqin Li,Jun Wang
The 1.0G dendrimer polyamidoamine (PAMAM), 3,5-dichlorosalicylaldehyde, and TiCl4·2THF were used as synthetic materials, and the dendritic salicylaldehyde imide ligand with substituent hindrance and its titanium catalyst were synthesized by the condensation reaction of Schiff base. The structure of the synthesized products was characterized by infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy, ultraviolet spectroscopy, electrospray mass spectrometry, and inductively coupled plasma-mass spectrometry. Activated methylaluminoxane (MAO) was used as a catalyst precursor for ethylene polymerization in the process of ethylene catalytic. The effects of ethylene polymerization were studied in terms of the Al/Ti molar ratio, reaction time, reaction temperature, polymerization pressure, and ligand structure of the catalyst. The results show good catalytic performance (70.48 kg PE/mol Ti·h) for ethylene polymerization because of the existence of ortho substituent hindrance on the salicylaldehyde skeleton. Furthermore, high-temperature gel permeation chromatography (GPC)-IR, differential scanning calorimetry (DSC), and torque rheometer were used to characterize the microstructure, thermal properties, and viscoelastic state of the polyethylene samples obtained. The results showed that the product was ultrahigh-molecular-weight polyethylene.
研究领域:
化学
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材料科学
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DOI
PubMed
高影响因子
ANALYTICA CHIMICA ACTA
·
2021
·
IF 6.558
Qiu Zhuang,Cheng Zhang,Haiyan Zhuang,Hanyu Deng,Xiangpeng Lin,Yan Li,Hao Chen,Aming Xie,Wei Dong
The antibiotic tetracycline (Tc) is a major contaminant in food and water, with adverse effects on both ecosystems and human health. The development of novel sensors for tetracycline detection is of great importance. In this work, we develop a novel heteroatom-free conjugated tetraphenylethylene polymer (TPE-CMP) fluorescence sensor for the detection of tetracycline. In the presence of Tc, the emission fluorescence of TPE-CMP was quenched by the photoinduced electron transfer mechanism to achieve high sensitivity. The polymers can detect tetracycline at a concentration of 0–100 μg/mL with a good linear correlation (0.99), and the limit of detection (LOD) is 1.23 μg/mL. Furthermore, TPE-CMP has excellent selectivity in detecting Tc in the presence of various anti-interference analytes, including ions and antibiotics. In addition, the practical feasibilities of TPE-CMP for Tc sensing were further investigated in milk, urine and wastewater samples with satisfactory recoveries (from 94.96% to 112.53% for milk, from 96.41% to 99.31% for urine and from 98.54% to 100.52% for wastewater). We have designed and synthesized TPE-CMP based on heteroatom-free for the specific fluorescence detection of tetracycline, expanding the range of fluorescence detection sensors and offering great promise for practical applications.
研究领域:
分析化学
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环境科学
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食品科学
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DOI
高影响因子
ACS Applied Materials & Interfaces
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2014
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IF 5.9
Jian Hu,Dongliang Wan,Wenguang Zhu,Langhuan Huang,Shaozao Tan,Xiang Cai,Xiuju Zhang
A novel cross-linked quaternized composite anion-exchange membrane based on poly(epichlorohydrin) (PECH) was prepared by a facile route. First, PECH was cross-linked with 2-methylimidazole and combined with a poly(tetrafluoroethylene) (PTFE) membrane to form cross-linked PECH/PTFE (CPECH/PTFE). Then, CPECH/PTFE was quaternized by 1-methylimidazole to obtain cross-linked quaternized PECH/PTFE (CQPECH/PTFE). 1H NMR and Fourier transform infrared spectroscopic data indicated that CQPECH was successfully synthesized, and the CQPECH/PTFE membrane had a dense and homogeneous structure demonstrated by the field-emission scanning electron microscopy. The results showed that the use of 2-methylimidazole as the cross-link agent could avoid the solubility of the composite membrane in water and dimethyl sulfoxide. With an increase of 2-methylimidazole, the solubility of the PECH ionomer was decreased. M-3, one of the CQPECH/PTFE membranes, showed good thermal properties (stable below 250 °C under an N2 atmosphere), excellent mechanical strength (a tensile strength of 67.3 MPa), moderate water uptake of 45.3%, and very low swelling degree of 9.01% at 30 °C. Besides, M-3 showed a hydroxide conductivity of up to 27 mS/cm and good long-term stability in a 1 M KOH solution at 60 °C for 15 days. In addition, a single H2/O2 fuel-cell test using M-3 at 50 °C indicated a peak power density of 23 mW/cm2. These results suggested that the CQPECH/PTFE membrane had a good perspective for application in an alkaline fuel cell.
研究领域:
材料科学
·
能源工程
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DOI
PubMed
高影响因子
JOURNAL OF ORGANOMETALLIC CHEMISTRY
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2019
·
IF 2.066
Yi Zhou,Rui Zhang,He Ren,Xuelian He,Bao Liu,Ning Zhao,Boping Liu
A series of novel V/Ti bimetallic polyethylene catalysts were developed successfully through the introduction of vanadium species into the (SiO 2 /MgR 2 /MgCl 2 )·TiCl x Ziegler-Natta Catalyst. The organometallic heterogeneous catalysts combined advantages of reducibility of magnesium alkyl on the activation of secondary metal active sites (vanadium active sites), which successfully enhanced average molecular weight in homopolymer products and produced dominantly bimodal molecular weight distribution in copolymer products. Catalyst preparation conditions including calcination temperature and magnesium dosage were investigated to explicit the effect on the relative performance of different metal active centers. Moreover, the factors including hydrogen and ethylene/1-hexene copolymerization were systematically studied. The bimetallic catalysts exhibit 63.9% enhancement on activity, 37.3% better hydrogen response than the original (SiO 2 /MgR 2 /MgCl 2 )·TiCl x organic magnesium Ziegler-Natta catalyst. Moreover, a simplified schematic model was proposed to elaborate on the reason why the bimetallic catalysts showed much higher activity than the original one, and each active species performance well. Vanadium active sites react quickly in the initial reaction time on the external surface of the support, which helps titanium active sites crack the catalyst particles together in the fragmentation and activation stage; then the released internal surface active sites, which were accessible to the monomer in the slurry phase, speed up the polymerization reaction during the latter reaction process.
研究领域:
材料科学
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化学工程
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DOI
高影响因子
JOURNAL OF COLLOID AND INTERFACE SCIENCE
·
2013
·
IF 3.172
Ying Yang,Zhi Liu,Dayong Wu,Man Wu,Ye Tian,Zhongwei Niu,Yong Huang
We investigated the effect of amphiphilic Laponite nano-discs, which were edge-modified by hydrophobic chains, on the properties of Pickering emulsions and Pickering emulsions polymerization. Comparing to unmodified Laponites, these amphiphilic nano-discs can greatly reduce the surface tension, resulting in very stable Pickering emulsions. These particles uniquely combine the Pickering effect with amphiphilic properties similar to the surfactant . Taking advantage of these amphiphilic Pickering emulsifiers , miniemulsion polymerization of styrene was performed. Homogeneous polystyrene nanoparticles with size around 150 nm could thus be prepared.
研究领域:
材料科学
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化学工程
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产品关联
DOI
PubMed
高影响因子
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
·
2016
·
IF 2.567
Bing Xue,Lei Hui,Huaqin Yang,Yulai Zhao,Linxi Hou,Wei Li
A macroporous SiO2 (Macro-SiO2), which has uniformed macropores, an open-framework structure, and thin walls, was synthesized to support Ziegler–Natta catalysts. The immobilization behaviors of the Ziegler–Natta catalysts inside the Macro-SiO2 were investigated. Notable agglomerations of δ-MgCl2/titanium complex were observed because of the unconstrained environment of the Macro-SiO2. A highly superficial Ti content and a heterogeneously chemical structure of Ti active sites were thus achieved inside the Macro-SiO2. The ethylene polymerization results revealed that the Macro-SiO2/MgCl2/TiCl4 exhibited much higher catalytic activity (i.e., 12.1 × 106 g PE·(mol Ti·h)−1 or 17.8 × kg PE·(g cat·h)−1) than that of the traditional 955-SiO2 supported catalyst (i.e., 2.0 × 106 g PE·(mol Ti·h)−1 or 2.7 × kg PE·(g cat·h)−1). Finally, the fragmentation behavior of Macro-SiO2/MgCl2/TiCl4 was investigated during the polymerization. This unconstrained environment of Macro-SiO2 afforded fewer resistances to the diffusion of reactants and also the polymer growth.
研究领域:
材料科学
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化学工程
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高分子科学
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DOI
高影响因子
JOURNAL OF APPLIED POLYMER SCIENCE
·
2019
·Vol. 137
·期 17
·48620
·
IF 2.188
Jianfeng Liu,Lu Shao,Xiu Feng,Sheng Xu,Puke Mi
In this article, four constrained geometry complexes 4a [(η 5 -C 5 H 4 )CH 2 (α-C 4 H 3 N)]Ti(NMe 2 ) 2 , 7a [(η 5 -C 9 H 6 )CH 2 (α-C 4 H 3 N)]Ti(NMe 2 ) 2 , 4b [(η 5 -C 5 H 4 )CH 2 (α-C 4 H 3 N)]Zr(NEt 2 ) 2 , 7b [(η 5 -C 9 H 6 )CH 2 (α-C 4 H 3 N)]Zr(NEt 2 ) 2 with pyrrole-bridged fragment were synthesized and characterized by 1 H NMR, 13 C NMR, MASS, and EA. When combined with MAO, complex 4b given the highest activity, the activity of copolymerizing ethylene and 1-hexene reached 2.48 × 10 6 g polymer/mol·M·h. The effects of temperature, pressure, and ratio of Al/Metal on the polymerization reaction and properties of polymers had been investigated. The polymers with these complexes were characterized by 13 C NMR and DSC, and the results shown that polymer with 4a had the highest α-olefin incorporation, the incorporation of 1-hexene reached up to 9.81 mol%, and the 1-octene was 8.84 mol%. Actually, there was no [HH] or [OO] sequence in the copolymer, according to the formula of reactivity ratio, rE • rH = 0, all these results suggested that the copolymerization mode is alternating copolymerization. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137 , 48620.
研究领域:
高分子化学
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催化化学
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DOI
高影响因子
PROCESS SAFETY AND ENVIRONMENTAL PROTECTION
·
2023
·
IF 7.8
Andong Yu,Juan Zhou,Min Hua,Xuhai Pan,Juncheng Jiang,Sanming Wang
The process of styrene polymerization is a typical hazardous chemical process. Due to its high reaction temperature and high product viscosity , it is very prone to thermal runaway accidents. In order to reduce the occurrence of such accidents, this work investigates the thermal hazard of the polymerization process by reaction calorimetry experiments and deduces the thermal runaway criterion for the styrene polymerization reaction by combining the results of gas chromatography experiments. The phase space of the system was reconstructed by the delayed coordinate method to obtain the reconstructed divergence criterion ( re-div ). The results showed that the exothermic heat and adiabatic temperature rise of the polymerization reaction showed a logarithmic increase with the increase of the initial reaction temperature. Compared with the div calculated by numerical method and analytical method, the analytical method div is more accurate and effective. The analytical divergence criterion ( div ) curve is strictly decreasing in the post-polymerization case, which indicates that it can be used as an off-line criterion to determine the safety of the reaction process by the initial reaction condition parameters. After the experimental verification, it can be confirmed that the re-div can predict whether the reaction is out of control in advance and accurately.
研究领域:
化学工程
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安全科学
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产品关联
DOI
高影响因子
ORGANOMETALLICS
·
2020
·
IF 3.804
Shaofeng Liu,Yanhong Xing,Quande Zheng,Yutong Jia,Zhibo Li
Dinuclear titanium complexes syn-Ti2 and anti-Ti2 bearing anthracene-bridged bisphenoxyimine ligands (syn-L and anti-L) have been prepared and characterized by NMR and elemental analyses. The molecular structure of syn-Ti2 was defined by X-ray diffraction, revealing a separation of 7.183 Å between the two Ti centers. The mononuclear complex [(2,6-iPr2-C6H3N═CH-C6H2-3,5-tBu-2-O)TiCl3(THF)] (Ti1) was also prepared for control experiments. In the presence of MAO as a cocatalyst, syn-Ti2 and anti-Ti2 were active toward ethylene homopolymerization but had distinct catalytic properties. The complex syn-Ti2 with a shorter metal–metal separation exhibited higher activity and produced polymers with higher molecular weights, in comparison to anti-Ti2, having a longer metal–metal separation, and the mononuclear catalyst control Ti1 under identical conditions. More importantly, the complex syn-Ti2 exhibited excellent thermal stability and thus the a greater activity can be obtained at 100 °C, which is a preferred temperature for industrial operations. For ethylene/1-hexene copolymerization, the activity, Mw, and incorporation of 1-hexene by syn-Ti2 were 2.3×, 3.2×, and 6.0× those of anti-Ti2 under identical conditions.
研究领域:
有机化学
·
高分子化学
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DOI
高影响因子
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY
·
2024
·Vol. 149
·期 10
·4491-4503
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IF 3
Chen Yongjia,Zhao Yilin,Hua Min,Pan Xuhai,Jiang Huichun,Jiang Juncheng
We investigated the inhibition of thermal runaway of styrene polymerization by DNPB. DNBP is an inhibitor in styrene polymerization reaction. Polymerization is one of eighteen hazardous processes. Styrene polymerization reaction is characterized by high heat production and fast reaction rate. Firstly, differential scanning calorimetry (DSC) and adiabatic calorimetry (ARC) were chosen to study the effect of different mass of DNBP on thermal behavior in non-isothermal and adiabatic environments. Secondly, exploring the inhibitory effect of DNBP at different runaway temperatures using an oil bath reactor. The results showed that when DNBP was at 0.80%, effective inhibition was obtained at different runaway temperatures. Finally, GC/MS and Gauss16 were used to infer the mechanism of inhibition in terms of macroscopic products and microscopic instabilities. The results showed that the products of the oil bath reactor experiments were related to the mass of DNBP, and when DNBP was 0.80%, the products increased and the main reaction was inhibited. Finally, it was deduced that the nitro group undergoes a possible path of direct addition reaction with the styrene radical before bond breaking.
研究领域:
化学工程
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材料科学
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安全工程
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产品关联
DOI
高影响因子
危险品化学品经营许可证（带存储）