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61.
Enrique Saldívar‐Guerra Jos Bonilla Gregorio Zacahua Martha Albores‐Velasco 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):6962-6979
Mechanisms and simulations of the induction period and the initial polymerization stages in the nitroxide‐mediated autopolymerization of styrene are discussed. At 120–125 °C and moderate 2,2,4,4‐tetramethyl‐1‐piperidinyloxy (TEMPO) concentrations (0.02–0.08 M), the main source of radicals is the hydrogen abstraction of the Mayo dimer by TEMPO [with the kinetic constant of hydrogen abstraction (kh)]. At higher TEMPO concentrations ([N?] > 0.1 M), this reaction is still dominant, but radical generation by the direct attack against styrene by TEMPO, with kinetic constant of addition kad, also becomes relevant. From previous experimental data and simulations, initial estimates of kh ≈ 1 and kad ≈ 6 × 10?7 L mol?1 s?1 are obtained at 125 °C. From the induction period to the polymerization regime, there is an abrupt change in the dominant mechanism generating radicals because of the sudden decrease in the nitroxide radicals. Under induction‐period conditions, the simulations confirm the validity of the quasi‐steady‐state assumption (QSSA) for the Mayo dimer in this regime; however, after the induction period, the QSSA for the dimer is not valid, and this brings into question the scientific basis of the well‐known expression kth[M]3 (where [M] is the monomer concentration and kth is the kinetic constant of autoinitiation) for the autoinitiation rate in styrene polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6962‐6979, 2006 相似文献
62.
Alberto Giaconia Giuseppe Filardo Onofrio Scialdone Alessandro Galia 《Journal of polymer science. Part A, Polymer chemistry》2006,44(13):4122-4135
A laboratory‐scale continuous reaction system using a stirred tank reactor was assembled in our laboratory to study the dispersion polymerization of vinyl monomers in supercritical carbon dioxide (scCO2). The apparatus was equipped with a suitable downstream separation section to collect solid particles entrained in the effluent stream from the reactor, whose monomer concentration could be measured online with a gas chromatograph. The dispersion polymerization of methyl methacrylate in scCO2 was selected as a model process to be investigated in the apparatus. The experiments were performed at 65 °C and 25 MPa with 2,2′‐azobisisobutyronitrile as the initiator and a reactive polysiloxane macromonomer as a surfactant to investigate the effect of the mean residence time of the reaction mixture on the monomer conversion, polymerization rate, polymer molecular weight, and particle size distribution. The results were compared with those obtained in batch polymerizations carried out under similar operative conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4122–4135, 2006 相似文献
63.
Jorge F. J. Coelho Ana M. F. P. Silva Anatoliy V. Popov Virgil Percec Mariana V. Abreu Pedro M. O. F. Gonalves M. H. Gil 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):3001-3008
The synthesis of a block copolymer poly(vinyl chloride)‐b‐poly(n‐butyl acrylate)‐b‐poly(vinyl chloride) is reported. This new material was synthesized by single‐electron‐transfer/degenerative‐chain‐transfer‐mediated living radical polymerization (SET‐DTLRP) in two steps. First, a bifunctional macroinitiator of α,ω‐di(iodo)poly (butyl acrylate) [α,ω‐di(iodo)PBA] was synthesized by SET‐DTLRP in water at 25 °C. The macroinitiator was further reinitiated by SET‐DTLRP, leading to the formation of the desired product. This ABA block copolymer was synthesized with high initiator efficiency. The kinetics of the copolymerization reaction was studied for two PBA macroinitiators with number–average molecular weight of 10 k and 20 k. The relationship between the conversion and the number–average molecular weight was found to be linear. The dynamic mechanical thermal analysis suggests just one phase, indicating that copolymer behaves as a single material with no phase separation. This methodology provides the access to several block copolymers and other complex architectures that result from combinations of thermoplastics (PVC) and elastomers (PBA). From industrial standpoint, this process is attractive, because of easy experimental setup and the environmental friendly reaction medium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3001–3008, 2006 相似文献
64.
Xiaoqing Liu Chuncheng Li Dong Zhang Yaonan Xiao 《Journal of Polymer Science.Polymer Physics》2006,44(6):900-913
This article investigated the melting behaviors, crystallization kinetics, and spherulitic morphologies of poly(butylene succinate) (PBS) and its copolyester (PBSR) modified with rosin maleopimaric acid anhydride, using wide‐angle X‐ray diffraction, differential scanning calorimeter (DSC), and polarized optical microscope. Subsequent DSC scans of isothermally crystallized PBS and PBSR exhibited two melting endotherms, respectively, which was due to the melt‐recrystallization process occurring during the DSC scans. The equilibrium melting point of PBSR (125.9 °C) was lower than that of PBS (139 °C). The commonly used Avrami equation was used to describe the isothermal crystallization kinetics. For nonisothermal crystallization studies, the model combining Avrami equation and Ozawa equation was employed. The result showed a consistent trend in the crystallization process. The crystallization rate was decreased, the perfection of crystals was decreased, the recrystallization was reduced, and the spherulitic morphologies were changed when the huge hydrogenated phenanthrene ring was added into the chain of PBS. The activation energy (ΔE) for the isothermal crystallization process determined by Arrhenius method was 255.9 kJ/mol for PBS and 345.7 kJ/mol for PBSR. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 900–913, 2006 相似文献
65.
Degradation of 4-chlorophenol in aqueous solution by γ-radiation and ozone oxidation 总被引:5,自引:2,他引:3
HU Jun WANG Jianlong & CHEN Rong . Laboratory of Environmental Technology Institute of Nuclear Energy Technology Tsinghua University Beijing China . State Key Joint Laboratory of Environmental Simulation Pollution Control Tsinghua University Beijing China Correspondence should be addressed to Wang Jianlong 《中国科学B辑(英文版)》2006,(2)
The application of radiation technology in the en-vironmental protection was listed as one of the mostimportant research fields by the International AtomicEnergy Agency (IAEA) for the peaceful use of nuclearenergy. It has great research value and potential appli-cation. Because of their broad-spectrum antimicrobialproperties, Cholophenols (CPs) have been used aspreservative agents for wood, paints, vegetable fibersand leather and as disinfectants. In addition, they havebeen widely employed… 相似文献
66.
The composting of organic solid waste, the mixture of fruit and vegetable leftovers enriched with night soil, was investigated
in a closed thermally insulated reactor. It was found that 80.9 % of the original substrate biodegraded after 14 days. A mathematical
model of the column reactor was proposed where the biodegradation rate of the organic solid waste was described using simple
n-thorder kinetics. A good prediction of process performance was obtained using the proposed kinetics and experimentally obtained
reaction heat.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
67.
The kinetics of muonic atoms of hydrogen isotopes in an axially symmetric trap is studied. The problem of the determination of the initial kinetic energy distribution of µp and µd atoms from time-of-flight spectra is discussed. The effects of the scattering of muonic atoms from gas and of the stopping distribution are evaluated. When the collision length is much larger than the target radius, the moments of the kinetic energy distribution are shown to be determined by the time-of-flight spectrum in a model-independent way. 相似文献
68.
兖州高硫煤的加氢热解脱硫及脱硫动力学 总被引:5,自引:1,他引:5
在加压热天平上,考察了氢气和氮扬气氛下高硫煤的热解脱硫。利用气相色谱在线分析研究了硫化氢氢气的逸出规律。结果表明,加氢热解比氮气下的热解有着更显著的脱友作用,脱硫率可达90%以上。而且加氢热解下65%的脱除硫转化为气相硫化氢,而氮气下热解是有80%的硫转化为液相。 相似文献
69.
取向聚对苯二甲酸乙二酯纤维的非等温结晶动力学张志英,赵家森(天津纺织工学院材料科学系天津300160)关键词取向高聚物,聚对苯二甲酸乙二酯,非等温结晶,结晶动力学研究高聚物结晶动力学常用的等温方法有光透射法、密度法、显微镜法、X-射线衍射法、差示扫描... 相似文献
70.
Xu Wen-Yang Guo Chang-Jie Do Tao 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(4):325-331
A member of the novel family of crystalline microporous aluminophosphates, AlPO4-12, was synthesized by hydrothermal crystallization using different aluminum-containing compounds. Three new crystalline phases were obtained by varying the composition of the reaction mixture. The effect of the synthesis conditions on the hudrothermal process and the kinetics of crystallization are discussed. The apparent activation energies obtained for AlPO4-12 are 20.9 and 14.6 kcal/mol for nucleation and crystallization, respectively. The adsorption isotherms of one AlPO4-12 product were measured. 相似文献