检索结果-南通市图书馆

Deactivation Effect Caused by Catalyst-Cocatalyst Pre-contact in Propylene Polymerization with MgCl2-supported Ziegler-Natta Catalyst

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2019年第10期37卷 1023-1030,I0005页

作者： Zhen Zhang Bai-Yu Jiang Biao Zhang zhi-Sheng Fu zhi-qiang fan Ministry of Education Key Laboratory of Macromolecular Synthesis and Functionalization Department of Polymer Science and Engineering Zhejiang University

Propylene slurry polymerization with a MgCl2-supported Ziegler-Natta catalyst containing internal electron donor was conducted after different durations of pre-contact of the catalyst with triethylaluminum cocatalyst. The number of active centers([C*]/[Ti])was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and measuring sulfur content in the polymer. The pre-contact treatment caused selective deactivation of a part of active centers with low stereoselectivity and much lower activity in the initial stage of polymerization as compared with the polymerization run without the pre-contact stage. The active center concentration and polymerization activity decreased with prolonging of the pre-contact stage. The proportion of stereoselective active centers was increased by prolonging the pre-contact stage, so the isotacticity of produced polypropylene was enhanced. Release of active centers through catalyst particle fragmentation was significantly retarded, and the polymerization rate curve changed from decay type to induction type by the precontact treatment. In the induction period both non-stereoselective and stereoselective active centers were released and activated, resulting in gradual reduction of the polymer’s isotacticity in the first 5-10 min of polymerization. Selective deactivation of non-stereoselective active centers also took place in propylene polymerization using the catalyst without pre-contacting with the cocatalyst. In this case, the polymerization rate decayed with time after a short induction period of 2-5 min. Over reduction of the active center precursors with low stereoselectivity by triethylaluminum was considered as the reason for their deactivation during the pre-contact or the polymerization processes.

关键词： Propylene Polymerization Supported Ziegler-Natta catalyst Cocatalyst Pre-contact

Improvement in hydrogen storage performance of MgH_(2) by vanadium doped with ZIF-8 derived a single-atom catalyst V-N-C

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2024年第6期43卷 2623-2635页

作者： Fei-fan Hong Wei-Tao Shi Ruo-Lin Zhao Yi fan Zi-Qi Liu Si-zhi Ding Hai-Zhen Liu Wen-Zheng Zhou Jin Guo zhi-qiang Lan Guangxi Novel Battery Materials Research Center of Engineering Technology and Center on Nanoenergy Research Guangxi Colleges and Universities Key Laboratory of Blue Energy and Systems IntegrationCarbon Peak and Neutrality Science and Technology Development InstituteSchool of Physical Science and TechnologyGuangxi UniversityNanning 530004China Nanning Engineering Technology Research Center for Power Transmission System of New Energy Vehicle Transportation CollegeNanning UniversityNanning 530200China

Herein,the successful preparation of a singleatom catalyst V-N-C using vanadium-doped zeolitic imidazolate framework(ZIF)-8 as a precursor is *** experimental results showed that the V-N-C had a good promoting effect on the hydrogen storage performance of MgH_(2),and the optimal addition amount of V-N-C was 10wt%.The hydrogenation and dehydrogenation apparent activation energies of 10 wt%V-N-C-catalyzed MgH_(2)were reduced by 44.9 and 53.5 kJ·mol^(-1),respectively,compared to those of additive-free MgH_(2).The 10 wt%V-N-C-catalyzed MgH_(2)could reabsorb 5.92 wt%of hydrogen in 50 min at 150℃,with a capacity retention rate of 99.1%after 30 cycles of hydrogen absorption and *** analysis showed that V-N-C was partially transformed into VN and metallic V when it was milled with MgH_(2);the in-situ-formed VN and metallic V played an important role in improving the hydrogen storage performance of MgH_(2).This approach provides a potential solution for obtaining high-performance Mg-based hydrogen storage materials through synergistic interactions between V,N and C.

关键词： MgH_(2) Hydrogen storage materials Catalyst Hydrogen storage perormance

STYRENE POLYMERIZATION MEDIATED BY CYCLIC TRITHIOCARBONATE AS RAFT AGENT

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2006年第6期24卷 593-597页

作者： Qi Wang Yi-xian Li Jian Hong zhi-qiang fan Department of Polymer Science ＆ Engineering Zhejiang University Hangzhou 310027 China

The novel cyclic trithiocarbonate was synthesized by dialkylation of trithiocarbonate anion with 2,2＇- bis（bromomethyl）biphenyl in a two-phase system using an onium salt as a phase-transfer agent. Styrene polymerization was carried out in the presence of cyclic trithiocarbonate （CTTC）. CTTC undergoes ring opening-polymerization and the incorporated trithiocarbonate moiety derived from CTTC performs as the reversible addition-fragmentation chain transfer （RAFT） agent. Through this mechanism, multiblock polys-tyrenes containing various narrow polydispersity blocks can be prepared.

关键词： Cyclic trithiocarbonate Multiblock polymer RAFT polymerization Styrene.

A comprehensive review on microchannel heat sinks for electronics cooling

在线全文

学校读者我要写书评

暂无评论

International Journal of Extreme Manufacturing 2024年第2期6卷 133-162页

作者： zhi-qiang Yu Mo-Tong Li Bing-Yang Cao Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering MechanicsTsinghua UniversityBeijing 100084People’s Republic of China

The heat generation of electronic devices is increasing dramatically,which causes a serious bottleneck in the thermal management of electronics,and overheating will result in performance deterioration and even device *** the development of micro-machining technologies,the microchannel heat sink(MCHS)has become one of the best ways to remove the considerable amount of heat generated by high-power *** has the advantages of large specific surface area,small size,coolant saving and high heat transfer *** paper comprehensively takes an overview of the research progress in MCHSs and generalizes the hotspots and bottlenecks of this *** heat transfer mechanisms and performances of different channel structures,coolants,channel materials and some other influencing factors are ***,this paper classifies the heat transfer enhancement technology and reviews the related studies on both the single-phase and phase-change flow and heat *** comprehensive review is expected to provide a theoretical reference and technical guidance for further research and application of MCHSs in the future.

关键词： microchannel heat sink thermal management of electronics microscale heat transfer heat transfer enhancement

Morphology and Thermoresponsive Behavior of Hybrid Micelles of Polystyrene-b-Poly((N-isopropyl acrylamide)-co-(4-vinylbenzyl chloride)) with Prussian Blue

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2015年第7期33卷 1038-1047页

作者： Xi-xian Ke 徐君庭 Bin-yang Du zhi-qiang fan MOE Key Laboratory of Macromolecular Synthesis and Functionalization Department of Polymer Science & EngineeringZhejiang University

The hybrid micelles of polystyrene-b-poly（（N-isopropyl acrylamide）-co-（4-vinylbenzyl chloride）） block copolymer（PS-b-P（NIPAM-co-VBC）） with Prussian blue（PB） in the corona were prepared by reaction of pentacyano（4-（dimethylamino）-pyridine）ferrate（Fe-DMAP）-attached PS-b-P（NIPAM-co-VBC） with Fe Cl3. The formation of the PB framework inside the micelles was verified by UV-Vis, FTIR and TGA. The morphology of the hybrid micelles was studied by TEM and compared with that of the neat and Fe-DMAP-attached PS-b-P（NIPAM-co-VBC）. It is found that attachment of Fe-DMAP may change the short rod-like micelles of the neat PS-b-P（NIPAM-co-VBC） into spherical ones and lead to a smaller micelle size. The morphology of the hybrid micelles may be altered or remain unchanged after formation of the PB framework, depending on the chain structure of PS-b-P（NIPAM-co-VBC） and starting concentration. The thermoresponsive behavior of different micelles was studied using DLS. It is observed that attachment of Fe-DMAP can improve the hydrophilicity of the P（NIPAM-co-VBC） block, leading to weaker hysteresis of the micelle size during the heating and cooling cycle. However, the crosslinked PB framework in the micellar corona may result in a more evident hysteresis phenomenon and blur the two-stepwise change of the micellar size with temperature.

关键词： Block copolymer Thermosensitivity Prussian blue Micelle Hybrid

Comparative Studies on Properties of Polymers with Bulky Side Groups Synthesized by Cyclopolymerization of α,ω-Dienes and α,ω-Diynes

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2019年第2期37卷 149-156页

作者： Shao-Fei Song Xiao-Yu Liu Hao Zhang zhi-Sheng Fu Jun-Ting Xu zhi-qiang fan Ministry of Education Key Laboratory of Macromolecular Synthesis and Functionalization Department of Polymer Science and Engineering Zhejiang University

Four polymers containing five-membered rings in the main chain, with or without conjugation structure along the backbone and with or without conjugated pendent groups, were designed and synthesized by metathesis cyclopolymerization of functionalized α,ω-diynes, and cyclopolymerization of functionalized α,ω-dienes catalyzed by the α-diimine palladium-based catalyst, respectively. High to moderate monomer conversions were achieved. Chain structure, molecular weight, and molecular weight distribution(MWD) of the cyclopolymerization products were characterized by ~1 H-, ^(13) C-NMR, FTIR, and GPC. The polymers showed regular main chain structures,moderately high molecular weight, and narrow MWD. Thermal properties and chain stacking behaviors of the polymers were investigated by differential scanning calorimetry(DSC) and X-ray diffraction(XRD) as well as atomic force microscopy(AFM). The polymer with conjugation system in both the backbone and the pendent groups exhibited UV-Vis absorption at a much longer wavelength than those with the conjugation only in the backbone or only in the side groups. The polymers with conjugated backbone need more space for chain stacking, and the conjugated backbone causes enhanced size of polymer particles assembled from solution. The results showed that primary microstructures of the polymer exerted significant influences on the physical properties.

关键词： Cyclopolymerization α,ω-Diene α,ω-Diyne Conjugation system Properties

Precise Asymptotics in Limit Theorems for a Supercritical Branching Process with Immigration in a Random Environment

在线全文

学校读者我要写书评

暂无评论

数学学报（英文版） 2024年第8期40卷 1850-1874页

作者： Chun Mao HUANG Rui ZHANG zhi qiang GAO Department of Mathematics Harbin Institute of Technology(Weihai)Weihai 264209P.R.China School of Mathematical Sciences Beijing Normal UniversityBeijing 100875P.R.China

Let(Zn)be a supercritical branching process with immigration in an independent and identically distributed random *** necessary moment conditions,we show the exact convergence rate in the central limit theorem on log Zn and establish the corresponding local limit theorem by using the moments of the natural submartingale and the convergence rates of its *** similar approach and with the help of a change of measure,we also present the so-called integro-local theorem and integral large deviation theorem to characterize the precise asymptotics of the upper large deviations.

关键词： 60F05 60F10 60J80 60K37 Branching process with immigration central limit theorem large deviation random environment

A convenient,highly-efficient method for preparation of hydroxyl-terminated isotactic poly(propylene) and functional di-block copolymer

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Chemical Letters 2014年第4期25卷 596-600页

作者： Ya-Nan Ye Pei-Yuan Li Yong-Gang Shangguan zhi-Sheng Fu qiang Zheng zhi-qiang fan MOE Key Laboratory of Macromolecular Synthesis and Functionalization.Department of Polymer Science and Engineering Zhejiang University

Both terminated functional isotactic polypropylene （iPP） and block copolymers containing iPP segment are desirable for commercial applications. This paper provides a convenient, highly-efficient method to prepare hydroxyl-terminated isotactic polypropylene （iPP-t-OH） and functional di-block copolymer containing the iPP segment through a combination of coordination polymerization and coupling reaction. The coordination polymerization was catalyzed by TiCI4/MgCI2/AIEt3 catalyst system using ZnEt2 as chain transfer agent. Further, the Zn-terminated iPP was oxidized and subsequently hydrolyzed to provide iPP-t-OH. Soxhlet extraction and 13C NMR were used to calculate the isotacticity of iPP-t-OH. The degree of polymerization and the number of hydroxyl groups at the chain end of iPP-t-OH were measured by GPC and 1H NMR. Despite the high molecular weight and heterogeneous reaction, iPP-t-OH is effectively linked with PEG-t-NCO to produce di-block copolymers. DSC analysis of the di-block copolymer shows an obvious decrease in Tm and To, which indicated that PEG was successfully linked to the terminal end of iPP.

关键词： Hydroxyl-terminated isotacticpoly(propylene) Di-block copolymer Functionality Coupling reaction

Radical involved reactive wetting and retarding mechanism of alumina refractory ceramic by molten slags under weak static magnetic field

在线全文

学校读者我要写书评

暂无评论

Journal of Iron and Steel Research(International) 2024年第6期31卷 1355-1366页

作者： Sheng-hao Li Ao Huang fan-bo Zeng Hui Peng Hao-ran Wei Xue-chun Huang Sheng-qiang Song Hua-zhi Gu The State Key Laboratory of Refractories and Metallurgy Wuhan University of Science and TechnologyWuhan 430081HubeiChina

High alumina slag will cause severe corrosion at the interface of alumina refractory,and the wetting behavior of slag is a key factor influencing the corrosion resistance of refractory *** static magnetic field is a promising solution for improvement in the slag resistance of *** wetting of alumina refractory ceramics with different basicities of high alumina slags under a weak static magnetic field was analyzed,given that a weak static magnetic field can affect the corrosion behavior of refractory *** slag S_(3) as an example,when there was an external static magnetic field of 1.0 mT at 1600 ℃,the thickness of calcium aluminate reaction layer at the interface decreased by 36.7%,the denting depth of interface decreased by 35.6%,and the apparent wetting angle increased by 20%.The living radicals and their formation path in oxide melts were verified by first-principles calculation combined with electron paramagnetic resonance spectroscopy *** influence of the flux density of a weak static magnetic field on the wetting behavior of slags was also *** contact angle of the slags increased owing to the inhibitory effect of magnetic field on the radicalinvolved reaction at the interface of the slag and the alumina refractory *** relationships between the magnetic flux density,diffusion coefficient,slag microstructure(hyperfine coupling constant),and contact angle were *** provides a theoretical basis for the field control of radical involved reactive wetting between inorganic oxide slags and solid oxide ceramics.

关键词： Alumina refractory ceramic Molten slag Weak magnetic field effect Reactive wetting Free radical