共查询到20条相似文献,搜索用时 15 毫秒
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Fei Wen Wangqing Zhang Peiwen Zheng Xu Zhang Xinlin Yang Yao Wang Xiaowei Jiang Guanwei Wei Linqi Shi 《Journal of polymer science. Part A, Polymer chemistry》2008,46(4):1192-1202
A method of one‐stage soap‐free emulsion polymerization to synthesize narrowly dispersed core‐shell microspheres is proposed. Following this method, core‐shell microspheres of poly(styrene‐co‐4‐vinylpyridine), poly(styrene‐co‐methyl acrylic acid), and poly[styrene‐co‐2‐(acetoacetoxy)ethyl methacrylate‐co‐methyl acrylic acid] are synthesized by one‐stage soap‐free emulsion polymerization of a mixture of one or two hydrophobic monomers and a suitable hydrophilic monomer in water. The effect of the molar ratio of the hydrophobic monomer to the hydrophilic one on the size, the core thickness, and the shell thickness of the core‐shell microspheres is discussed. The molar ratio of the hydrophobic and hydrophilic monomers and the hydrophilicity of the resultant oligomers of the hydrophilic monomer are optimized to synthesize narrowly dispersed core‐shell microspheres. A possible mechanism of one‐stage soap‐free emulsion polymerization to synthesize core‐shell microspheres is suggested and coagglutination of the oligomers of the hydrophilic monomers on the hydrophobic core is considered to be the key to form core‐shell microspheres. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1192–1202, 2008 相似文献
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《Magnetic resonance in chemistry : MRC》2018,56(4):251-256
Measurement of the spin–spin NMR relaxation time (or its inverse, the rate) of water molecules in aqueous nanoparticle dispersions has become a popular approach to probe of the nature and structure of the particle surface and any adsorbed species. Here, we report on the characterisation of aqueous dispersions of hollow amorphous nanoparticles that have two liquid accessible surfaces (inner cavity surface and outer shell surface) plus the solid (silica) and core‐shell (titania–silica) nanoparticle precursors from which the hollow particles have been prepared. In all cases, the observed water relaxation rates scale linearly with particle surface area, with the effect being more pronounced with increasing levels of titania present at the particle surface. Two distinct behaviours were observed for the hollow nanoparticles at very low volume fractions, which appear to merge with increasing surface area (particle concentration). Herewith, we further show the versatility of solvent NMR spectroscopy as a probe of surface character. 相似文献
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Hollow poly(divinylbenzene-co-methacrylic acid) (P(DVB-co-MAA)) microspheres were prepared by the selective dissolution of the non-crosslinked poly(methacrylic acid) (PMAA) mid-layer in ethanol from the corresponding silica/PMAA/P(DVB-co-MAA) tri-layer hybrid microspheres, which were afforded by a three-stage reaction. Silica/PMAA core-shell hybrid microspheres were prepared by the second-stage distillation polymerization of methacrylic acid (MAA) via the capture of the oligomers and monomers with the aid of the vinyl groups on the surface of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified silica core, which was prepared by the Stöber hydrolysis as the first stage reaction. The tri-layer hybrid microspheres were synthesized by the third-stage distillation precipitation copolymerization of functional MAA monomer and divinylbenzene (DVB) crosslinker in presence of silica/PMAA particles as seeds, in which the efficient hydrogen-bonding interaction between the carboxylic acid groups played as a driving force for the construction of monodisperse hybrid microspheres with tri-layer structure. The morphology and the structure of silica core, silica/PMAA core-shell particles, the tri-layer hybrid microspheres and the corresponding hollow polymer microspheres with movable silica cores were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). 相似文献
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Electrorheological (ER) fluids are usually suspensions of solid polarizable particles in nonpolar carrier liquids. Such systems are particularly sensitive to the presence of electric fields, which transform them reversibly into solid‐like bodies. Fast (within milliseconds) and fully reversible reaction of ER fluids to electric field is a subject of great interest because of many possible applications in tunable vibration dampers, clutches, valves, or brakes. A novel type of ER fluids with composite microspheres composed of polymer electrolyte shell with defined shell thickness and inorganic hollow cores has been synthesized and tested in the presence of an electric field. It has been found that suspensions with composite grains possessed more stable ER response with temperature and lower power consumption in comparison to their polymer‐based counterparts. ER effect of the prepared fluids was measured and related to the applied electric field and solid phase properties. It has been also shown that suspensions of composite materials exhibited improved long‐term sedimentation stability in comparison to polymer‐based suspensions due to the formation of weak microstructure which suppressed the sedimentation of solid phase in off‐field state. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Crosslinked x-P(St-MAA) seed latex was first prepared via soap-free emulsion copolymerization of styrene (St) and methyl methacrylic acid (MAA) with divinyl benzene as crosslinker and ammonium persulfate as initiator, and x-P(St-MAA)/x-P(St-NaSS) core/shell latex particles were then synthesized through a novel seeded emulsion copolymerization of St and sodium styrene sulphonate (NaSS) in the presence of water-soluble crosslinker N,N′-methylene bisacrylamide (BAA) using oil-soluble 2,2-azobis isobutyronitrile as initiator. TEM observation indicated that narrow dispersed core/shell latex particles were obtained, and element analysis showed that NaSS unit content in the whole particle and in the shell reached 22.8 wt% and 51.2 wt%, respectively. 相似文献
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In the presence of Fe3O4 nano-particles, a new type of super-paramagnetic Fe3O4/Au microspheres with core/shell structures was prepared by reduction of Au3+ with hydroxylamine. The formation mechanism of the core/shell microspheres was studied in some detail. It was shown that the formation of the complex microspheres can be divided into two periods, that is, surface reaction-controlled process and diffusion-controlled process. The relative time lasted by either process depends upon the amount of Fe3O4 added and the initial concentration of Au3+. XPS analysis revealed that along with increasing in coating amount, the strength of the characteristic peaks of Au increased, and the Auger peaks of Fe weakened and even disappeared. Size distribution analysis showed that the core/shell microspheres are of an average diameter of 180 nm, a little bit larger than those before coating. 相似文献
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Production of soft core/hard shell composite polymer particles by the stepwise heterocoagulation method with heat treatment 总被引:1,自引:0,他引:1
Soft core/hard shell composite polymer particle was prepared by the stepwise heterocoagulation, which was proposed by authors
in 1990, of many cationic hard small polymer particles (SPs) onto an anionic soft large polymer particle (LP). The powder
was obtained by freeze-drying at 0 °C which was higher than glass transition temperature of LP (−7 °C) and lower than that of SP (90 °C).
Received: 9 December 1997 Accepted: 12 May 1998 相似文献
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Florent Jasinski Victoria L. Teo Rhiannon P. Kuchel Monique Mballa Mballa Stuart C. Thickett Richard H. G. Brinkhuis William Weaver Per B. Zetterlund 《Journal of polymer science. Part A, Polymer chemistry》2017,55(15):2513-2526
The synthesis of composite latex particles possessing core–shell and gradient morphologies, respectively, using seeded starve‐fed semibatch emulsion polymerization of styrene (St) and methyl methacrylate (MMA) is presented. The focus is on the effect of the monomer feed order on the particle morphology development. The particle morphology is assessed using a novel approach which entails comparing the experimental surface composition as a function of polymerization time (particle growth) obtained by X‐ray photoelectron spectroscopy with the predicted surface composition using a mass balance mathematical model. Both types of composite latexes (core–shell and gradient) feature changes with polymerization time in the oxygen/carbon surface composition which enables one to track the morphology development. Differential scanning calorimetry is also implemented to analyze the extent of phase separation. The monomer feed order is shown to play a crucial role—under the present conditions, gradient and core–shell particles are obtained if the feed order is St/MMA (St fed first), but not if the feed order is reversed. These findings illustrate that thermodynamic factors are important, given that thermodynamically it is more favorable for MMA‐rich chains to occupy the oil–water interface to reduce the interfacial tension. Systems where St is the second stage monomer lead to mixed structures rather than the targeted core–shell or gradient morphology with St‐rich chains at the particle surface. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2513–2526 相似文献
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Pengcheng Du Peng Liu Bin Mu Yunjiao Wang 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):4981-4988
Facile strategy was developed for the fabrication of the monodisperse superparamagnetic pH‐sensitive single‐layer chitosan (CS) hollow microspheres with controllable structure. The carboxyl group‐functionalized polystyrene microspheres prepared by soap‐free emulsion polymerization were used as the templates. After the Fe3O4 nanoparticles were in situ formed onto the surface of the templates, the single‐layer CS was self‐assembled and cross‐linked with glutaraldehyde subsequently. Then, the magnetic single‐layer CS hollow microspheres were obtained after the templates were removed. It was found that the feeding ratio of the monomer acrylic acid in the soap‐free emulsion polymerization had played an important role on the particle size and surface carboxyl group content of the templates, which determined the particle size and shell thickness of the magnetic single‐layer CS hollow microspheres in the proposed strategy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
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Micron-sized monodispersed polymethyl methacrylate (PMMA)/polystyrene (PS) (PMMA/PS=2/1, wt ratio) composite particles consisting
of PMMA-core and PS-shell were successfully produced by seeded dispersion polymerization of styrene in a methanol/water medium
in the presence of about 2 μm-sized monodispersed PMMA particles. From the view point of thermodynamic equilibrium, such a
morphology is difficult to form by usual seeded polymerization in a polar medium such as water. It is concluded that seeded
dispersion polymerization in which almost all monomers and initiators exist in the medium has an advantage to produce core/shell
polymer particles in which polymer layers accumulate in their order of the production regardless of the hydrophobicity of
polymers, because of high viscosity in polymerizing particles.
Received: 9 December 1996 Accepted: 26 February 1997 相似文献
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Michael F. Cunningham Hadi K. Mahabadi Heather M. Wright 《Journal of polymer science. Part A, Polymer chemistry》2000,38(2):345-351
Polymer particles with controlled morphologies and having diameters from about 1–20 μ can be prepared using a new suspension polymerization‐based procedure. In contrast to existing procedures using emulsion polymerization, this process allows efficient preparation of supermicron particles that can be easily isolated as a dry powder. Control of the particle morphology is obtained by manipulating the monomer conversion at the beginning of the second stage of the reaction (when the second monomer is added). Two systems are studied. The first system uses styrene added to a partially polymerized MMA host particle, whereas the second system uses styrene added to a partially polymerized 45 wt % styrene to 55 wt % butyl methacrylate host particle. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 345–351, 2000 相似文献
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Jie Cai Jia Guo Minglei Ji Wuli Yang Changchun Wang Shoukuan Fu 《Colloid and polymer science》2007,285(14):1607-1615
Fe3O4/SiO2/poly (N-isopropylacrylamide-co-N,N-dimethylaminoethyl methacrylate) [P(NIPAM-co-DMA)] multiresponsive composite microspheres with core–shell structure were synthesized by template precipitation polymerization.
First, the magnetite nanoparticles were coated with silica and then modified with 3-(trimethoxysilyl)-propyl methacrylate
(MPS). Subsequently, the Fe3O4/SiO2 particles grafted with MPS were used to seed the precipitation copolymerization of NIPAM and DMA. The composite microspheres
with core–shell structure were superparamagnetic, pH-sensitive, and thermoresponsive. The swelling ratio (D25 °C,
pH = 3/D50 °C,
pH = 9)3 coupling of pH and temperature increased up to 21.2, which was much higher than that without comonomer DMA. 相似文献
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Haiyang Zhang Lei Ding Yu Chen Wantai Yang Jianping Deng 《Journal of polymer science. Part A, Polymer chemistry》2012,50(21):4415-4422
This article reports on optically active core/shell nanoparticles constituted by chiral helical polymers and prepared by a novel approach: using self‐assembled polymer micelles as reactive nanoreactors. Such core/shell nanoparticles were composed of optically active helical‐substituted polyacetylene as the core and thermosensitive poly(N‐isopropylacrylamide) as the shell. The synthetic procedure is divided into three major steps: (1) synthesis of amphiphilic diblock copolymer bearing polymerizable C[tbond]C bonds via atom transfer radical polymerization, followed by (2) self‐assembly of the diblock copolymer to form polymer micelles; and (3) catalytic emulsion polymerization of substituted acetylene monomer conducted using the polymer micelles as reactive nanoreactors leading to the core/shell nanoparticles. The core/shell nanoparticles simultaneously exhibited remarkable optical activity and thermosensitivity. The facile, versatile synthesis methodology opens new approach toward preparing novel multifunctional core/shell nanoparticles.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
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Chia‐Fen Lee Mei‐Ling Hsu Chun‐Hsun Chu Tsung‐Yuan Wu 《Journal of polymer science. Part A, Polymer chemistry》2014,52(23):3441-3451
In this work, the poly(methyl methacrylate‐co‐methacrylic acid)/poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive composite semi‐hollow latex particles was synthesized by three processes. The first process was to synthesize the poly(methyl methacrylate‐co‐methacrylic acid) (poly (MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. The second process was to polymerize methacrylic acid (MAA), N‐isopropylacrylamide (NIPAAm), and crosslinking agent, N,N′‐methylenebisacrylamide, in the presence of poly(MMA‐MAA) latex particles to form the linear poly(methyl methacrylate‐co‐methacrylic acid)/crosslinking poly(methacrylic acid‐co‐N‐isopropylacrylamide) (poly(MMA‐MAA)/poly(MAA‐NIPAAm)) core–shell latex particles with solid structure. In the third process, part of the linear poly(MMA‐MAA) core of core–shell latex particles was dissolved by ammonia to form the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles. The morphologies of the semi‐hollow latex particles show that there is a hollow zone between the linear poly(MMA‐MAA) core and the crosslinked poly(MAA‐NIPAAm) shell. The crosslinking agent and shell composition significantly influenced the lower critical solution temperature of poly(MMA‐MAA)/poly(MAA‐NIPAAm) semi‐hollow latex particles. Besides, the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles were used as carriers to load with the model drug, caffeine. The processes of caffeine loaded into the semi‐hollow latex particles appeared four situations, which was different from that of solid latex particles. In addition, the phenomenon of caffeine released from the semi‐hollow latex particles was obviously different from that of solid latex particles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3441–3451 相似文献
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Chia‐Fen Lee Yu‐Cheng Wang Wen‐Yen Chiu 《Journal of polymer science. Part A, Polymer chemistry》2013,51(13):2880-2891
In this study, the poly(N‐isopropylacrylamide‐methylacrylate acid)/Fe3O4/poly(N‐isopropylacrylamide‐methylacrylate acid) (poly(NIPAAm‐MAA)/Fe3O4/poly(NIPAAm‐MAA)) two‐shell magnetic composite hollow latex particles were synthesized by four steps. The poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles were synthesized first. Then, the second step was to polymerize NIPAAm, MAA, and crosslinking agent in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly(NIPAAm‐MAA) core–shell latex particles. Then, the core–shell latex particles were heated in the presence of NH4OH to dissolve the linear poly(MMA‐MAA) core to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, the Fe3O4 nanoparticles were generated in the presence of poly(NIPAAm‐MAA) hollow polymer latex particles and formed the poly(NIPAAm‐MAA)/Fe3O4 magnetic composite hollow latex particles. The fourth step was to synthesize poly(NIPAAm‐MAA) in the presence of poly(NIPAAm‐MAA)/Fe3O4 latex particles to form the poly(NIPAAm‐MAA)/Fe3O4/poly(NIPAAm‐MAA) two‐shell magnetic composite hollow latex particles. The effect of various variables such as reactant concentration, monomer ratio, and pH value on the morphology and volume‐phase transition temperature of two‐shell magnetic composite hollow latex particles was studied. Moreover, the latex particles were used as carriers to load with caffeine, and the caffeine‐loading characteristics and caffeine release rate of latex particles were also studied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2880–2891 相似文献
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Analysis of stepwise heterocoagulation for the preparation of soft core/hard shell composite polymer particles 总被引:1,自引:0,他引:1
The stepwise heterocoagulation of small cationic hard particles (SPs) onto a large anionic soft particle (LP) for the preparation
of soft core/hard shell composite polymer particles was examined using dynamic light scattering and spectrophotometry. The
effects of the pH value, the emulsifier content which was pre-added to the LP emulsion, and the heat treatment time on the
covering of a LP by SPs, and the stability of the heterocoagulated emulsion were clarified.
Received: 12 May 1998 Accepted: 31 July 1998 相似文献
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Xi Mao Mian Wang Shaohong Jin Jingyi Rao Renhua Deng Jintao Zhu 《Journal of polymer science. Part A, Polymer chemistry》2022,60(11):1653-1669
Polymer particles are key materials in various biomedical applications, including drug delivery, cellular immunity, cell capture, biochip, etc. Droplets produced by microfluidics have been widely applied as templates for the fabrication of polymer particles with controllable sizes and narrow size distributions. Compared to smooth polymer particles, those with surface microstructures (e.g., tentacles, bubbles, wrinkles and pits) are more attractive due to their increased surface area and biomimetic structural characteristics. In this review, we summarized representative methods for the preparation of monodispersed polymer particles with various surface microstructures based on droplet microfluidics, as well as their typical bioapplications in drug delivery, cellular immunity and cell capture. Finally, the current challenges and further development in this research area are discussed. 相似文献