Preparation of composite particles with magnetic silica core and fluorescent polymer shell

Dual functions of magnetic and fluorescent properties were created in composite particles that incorporated magnetite (Fe₃O₄) nanoparticles in particle cores of silica and fluorescent pyrene in particle shells of polystyrene. The Fe₃O₄ nanoparticles were prepared with a conventional homogeneous precipitation method and surface modified with a coupling agent of carboxyethylsilanetriol. The silica particles incorporating Fe₃O₄ nanoparticles were synthesized with a modified Stöber method in which the Fe₃O₄ nanoparticles were added to a system of tetraethylorthosilicate (TEOS)/ammonia/water/ethanol. Then, the magnetite/silica composite particles were coated with the pyrene/polystyrene shell in a soap-free emulsion polymerization, which was conducted in the presence of pyrene in a mixed solvent of water/ethanol. The composite particles prepared in the mixed solvent had both magnetic and fluorescent properties. The fluorescent spectrum of the particles with Fe₃O₄ was very similar to that without Fe₃O₄, indicating that the magnetic component within the core particles scarcely interfered with the fluorescent emission from the polymer shell.     

Atom transfer radical polymerization synthesis and magnetic characterization of MnFe2O4/polystyrene core/shell nanoparticles

An atom transfer radical polymerization route is developed for the coating of MnFe2O4 nanoparticles with polystyrene yielding the core-shell nanoparticles with size <15 nm. Magnetic studies show a decrease in coercivity after the formation of polystyrene shell, which is considered due to the reduction of magnetic surface anisotropy upon polymer coating. The MnFe2O4 nanoparticles as the magnetic core were separately prepared by a reverse micelle microemulsion method. Polymerization initiators are chemically attached onto the surface of nanoparticles. The modified nanoparticles are then used as macro-initiators in the subsequent polymerization reaction. This approach provides great flexibility in the selection of magnetic core. Consequently, magnetic tunability is able to be introduced into these core/shell nanoparticulate systems to achieve the desired superparamagnetic response.     

Functional colloidal particles stabilized by layered silicate with hydrophilic face and hydrophobic polymer brushes

In this study, we describe a new strategy for producing narrowly dispersed functional colloidal particles stabilized by a nanocomposite with hydrophilic clay faces and hydrophobic polystyrene (PS) brushes on the edges. This method involves preparation of polymer brushes on the edges of clay layers and Pickering suspension polymerization of styrene in the presence of the nanocomposites. PS brushes on the edges of clay layers were prepared by atom transfer radical polymerization. X‐ray diffraction and thermogravimetric analysis results indicated that PS chains were grafted to the edges of clay platelets. Transmission electron microscope results showed that different morphologies of clay‐PS particles could be obtained in different solvents. In water, clay‐PS particles aggregated together, in which PS chains collapsed forming nanosized hydrophobic domains and hydrophilic clay faces stayed in aqueous phase. In toluene, clay‐PS particles formed face‐to‐face structure. Narrowly dispersed PS colloidal particles stabilized by clay‐PS were prepared by suspension polymerization. Because of the negatively charged clay particles on the surface, the zeta potential of the PS colloidal particles was negative. Positively charged poly(2‐vinyl pyridine) (P2VP) chains were adsorbed to the surface of PS colloidal particles in aqueous solution at a low pH value, and gold nanoparticles were prepared in P2VP brushes. Such colloidal particles may find important applications in a variety of fields including waterborne adhesives, paints, catalysis of chemical reactions, and protein separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1535–1543, 2009     

Preparation and application of cross-linked core-shell PBA/PS and PBA/PMMA nanoparticles

This paper reports the preparation of cross-linked core-shell poly(butyl acrylate)/polystyrene (PBA/PS) and poly(butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) nanoparticles via seeded emulsion polymerization and their application in nylon-based composites. A highly cross-linked structure was formed in both the cores and the shells by using a cross-linking agent, which could prevent the migration of hydrophobic PS shells to the inside of particles. There were covalent bonds on the interfaces between the cores and the shells of both particles. The average particle sizes were 40–50 nm, and the size distributions were narrow. The kinetics of polymerization was investigated. Well-defined core-shell structure and narrow particle size distribution could be achieved under starved conditions of monomer feeding. Furthermore, PBA/PMMA particles were used to fill nylon 6, good dispersion was obtained because of the strong interfacial interaction between the nanoparticles and the nylon 6 matrix and the good deformation ability of nanoparticles, and the toughness and rigidity of the composites were improved evidently. __________ Translated from Acta Polymerica Sinica, 2005, (6) (in Chinese)     

Synthesis of diblock copolymers with cellulose derivatives 4. Self-assembled nanoparticles of amphiphilic cellulose derivatives carrying a single pyrene group at the reducing-end

Self-assembled cellulose-pyrene nanoparticles were prepared from amphiphilic cellulose derivatives carrying a single pyrene group at the reducing-end, N-(1-pyrenebutyloyl)-β-cellulosylamine (CELL13Py and CELL30Py, the number average degrees of polymerization (DP_n) of 13 and 30, respectively) and N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-β-cellulosylamine (CELL13C15Py and CELL30C15Py, DP_n of 13 and 30, respectively). Transmission electron microscopy (TEM) observation revealed that CELL13C15Py and CELL30C15Py formed self-assembled nanoparticles with the average diameters of 108.8 and 40.0 nm, respectively. The average radius of CELL30C15Py nanoparticles (20.0 nm) agreed well with the molecular length of its cellulose chain (19.2 nm). CELL30C15Py nanoparticles were expected to have monolayered structure, consisting of cellulose shell with radial orientation and hydrophobic core of 15-(1-pyrenebutyloylamino)-pentadecanoyl groups. The fluorescent spectrum of CELL30C15Py nanoparticles showed an excimer emission due to dimerized pyrene groups, indicating that the pyrene groups at the reducing-end of cellulose are associating in the particles. The balance of hydrophilic and hydrophobic parts of the cellulose derivatives controlled their self-assembled nanostructures. X-ray diffraction measurements revealed that radially oriented cellulose chains of CELL30C15Py nanoparticles were mostly amorphous, and at the same time exhibited weak reflection pattern of cellulose II, which is believed to have anti-parallel orientation.     

交联核壳结构PBA/PS和PBA/PMMA纳米微球的制备与应用

考察了聚丙烯酸丁酯/聚苯乙烯(PBA/PS)以及聚丙烯酸丁酯/聚甲基丙烯酸甲酯(PBA/PMMA)交联核壳结构纳米高分子微球的制备方法,并对其在尼龙复合材料中的应用进行了初步研究.结果表明,通过交联剂的引入使粒子核层和壳层内部均形成了高度交联的结构,可以限制亲水性较小的聚苯乙烯(PS)壳层向粒子内部迁移的趋势;制备出的微球平均粒径为40~50 nm,粒径分布很窄.采用饥饿态加料方式加入第二单体不仅可以使微球具有较高的产率和凝胶率,而且可以使其具有更理想的核壳结构和更窄的粒径分布.此外,将合成出的PBA/PMMA核壳粒子对尼龙6基体进行复合的结果表明,由于该微球表面与尼龙6基体之间具有较强的界面相互作用且微球具有较大的形变能力,可以在基体中形成良好的分散,在保持材料强度的同时有效地提高了其刚性和韧性.     

pH‐responsive polymer core–shell nanospheres for drug delivery

Stimuli‐responsive polymer nanoparticles are playing an increasingly more important role in drug delivery applications. However, limited knowledge has been accumulated about processes which use stimuli‐responsive polymer nanospheres (matrix nanoparticles whose entire mass is solid) to carry and deliver hydrophobic therapeutics in aqueous solution. In this research, pyrene was selected as a model hydrophobic drug and a pyrene‐loaded core‐shell structured nanosphere named poly(DEAEMA)‐poly(PEGMA) was designed as a drug carrier where DEAEMA and PEGMA represent 2‐(diethylamino)ethyl methacrylate and poly(ethylene glycol) methacrylate, respectively. The pyrene‐loaded core‐shell nanospheres were prepared via an in situ two‐step semibatch emulsion polymerization method. The particle size of the core‐shell nanosphere can be well controlled through adjusting the level of surfactant used in the polymerization where an average particle diameter of below 100 nm was readily achieved. The surfactant was removed via a dialysis operation after polymerization. Egg lecithin vesicles (liposome) were prepared to mimic the membrane of a cell and to receive the released pyrene from the nanosphere carriers. The in vitro release profiles of pyrene toward different pH liposome vesicles were recorded as a function of time at 37 °C. It was found that release of pyrene from the core‐shell polymer matrix can be triggered by a change in the environmental pH. In particular the pyrene‐loaded nanospheres are capable of responding to a narrow window of pH change from pH = 5, 6, to 7 and can achieve a significant pyrene release of above 80% within 90 h. The rate of release increased with a decrease in pH. A first‐order kinetic model was proposed to describe the rate of release with respect to the concentration of pyrene in the polymer matrix. The first‐order rate constant of release k was thus determined as 0.049 h^?1 for pH = 5; 0.043 h^?1 for pH = 6; and 0.035 h^?1 for pH = 7 at 37 °C. The release of pyrene was considered to follow a diffusion‐controlled mechanism. The synthesis and encapsulation process developed herein provides a new approach to prepare smart nanoparticles for efficient delivery of hydrophobic drugs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4440–4450     

Synthesis of highly monodisperse particles composed of a magnetic core and fluorescent shell

Highly monodisperse particles composed of a magnetic silica core and fluorescent polymer shell were synthesized with a combined technique of heterocoagulation and soap-free emulsion polymerization. Prior to heterocoagulation, monodisperse, submicrometer-sized silica particles were prepared with the Stober method, and magnetic nanoparticles were prepared with a modified Massart method in which a cationic silane coupling agent of N-trimethoxysilylpropyl- N, N, N-trimethylammonium chloride was added just after coprecipitation of Fe (2+) and Fe (3+). The silica particles with negative surface potential were heterocoagulated with the magnetic nanoparticles with positive surface potential. The magnetic silica particles obtained with the heterocoagulation were treated with sodium silicate to modify their surfaces with silica. In the formation of a fluorescent polymer shell onto the silica-coated magnetic silica cores, an amphoteric initiator of 2,2'-azobis[ N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was used to control the colloidal stability of the magnetic cores during the polymer coating. The polymerization of St in the presence of a hydrophobic fluorophore of pyrene could coat the cores with fluorescent polymer shells, resulting in monodisperse particles with a magnetic silica core and fluorescent polymer shell. Measurements of zeta potential for the composite particles in different pH values indicated that the composite particles had an amphoteric property originating from VA-057 initiator.     

Titania-coated polystyrene hybrid microballs prepared with miniemulsion polymerization

Hybrid microballs with polystyrene cores coated by titania nanoparticles were prepared in miniemulsion polymerization. Acrylic acid was used as a comonomer to promote locating titania nanoparticles on the polymer's surface. The addition of a hydrophobic agent effectively prevents monomer diffusing into the aqueous phase. The morphology of hybrid particles was examined with the transmission electron microscope, and its change pattern with reactive conditions was observed. The infrared spectra of hybrid nanoparticles showed that there existed a certain interaction between titania nanoparticles and polymers. The crystallization morphology of hybrid particles before and after calcination was characterized with X-ray diffraction.     

Magnetic polymer particles: Synthesis and properties

A possibility of preparation of monodisperse magnetic polymer particles containing carboxylic groups by the methid of emulsion (co)polymerization in the presence of a magnetic liquidis considered. Angulation of the magnetite nanoparticles by polymeric spheres of styrene-acroleine copolymer followed by incapsulation to the polystyrene coat is studied. Monodisperse particles with inclusion of the magnetite nanoparticles 30 nm to 1 μm size containing up to 5.6 μmol g^?1 surface carboxylic groups are obtained, their electrosurface and magnetic properties are studied.     

Fabrication of hierarchical microparticles by depositing the in situ synthesized surface nanoparticles on microspheres during the seed emulsion polymerization

A general strategy for the synthesis of polymeric hierarchical microparticles containing surface nanoparticles through modified seed emulsion polymerization is proposed. This modified seed emulsion polymerization has a character that suitable amount of monomer miniemulsion is added during the polymerization. The in situ synthesized surface nanoparticles which are resulted from the monomer miniemulsion as well as the shell-forming polymer coagulate on the seed particles and therefore hierarchical microparticles are fabricated. Various polymeric hierarchical microparticles containing 20-36 nm poly(styrene-co-acrylamide), poly(styrene-co-acrylic acid), and polystyrene surface nanoparticles are synthesized following the proposed method. The advantages in the present synthesis including both the well controls in the size, the composition, and the number of the surface nanoparticles and the convenience are demonstrated. The proposed strategy is anticipated to be a general method to fabricate hierarchical microparticles and is believed to have promising application in particle surface modification.     

Formation of nanostructured materials via coalescence of amphiphilic hollow particles

A new, simplified route to amphiphilic core-shell nanotubes, microfibers, and microrods has been developed that does not involve the traditional utilization of well-defined block copolymers. Thus, amphiphilic graft copolymers (PEI-g-PMMA) are prepared by an aqueous free radical polymerization that self-assemble in situ to form uniform core-shell nanoparticles. The hydrophobic homopolymer (PMMA) that is also formed is incorporated in the cores. Slight cross-linking of the shells followed by extraction of the homopolymer results in hollow nanoparticles that coalesce to form nanotubes. When the shells are not cross-linked, the hollow particles coalesce to form microrods and microfibers. The sizes and shapes of the micromaterials can be controlled by varying the experimental conditions.     

苯乙烯和N-乙烯基吡咯烷酮共聚物/Ag复合微球的制备及性能研究

首先用无皂乳液聚合法制备了单分散聚苯乙烯(PSt)乳液,以此为种子乳液,使用N,N-亚甲基双丙烯酰胺(MBA)为交联剂,过硫酸钾(KPS)为引发剂,进行苯乙烯和N-乙烯基吡咯烷酮(NVP)共聚合制备了以PSt为核、St和NVP共聚物为壳的具有核-壳结构的聚合物微球(P(St-NVP)).以此微球为模板通过化学沉积法得到了粒径分布均匀、单分散的P(St-NVP)/Ag复合微球.傅里叶红外光谱、X-射线衍射、扫描电镜、透射电镜、激光粒度仪和紫外-可见光谱对复合微球的结构、形貌、物相及催化性能进行了表征.结果表明,P(St-NVP)/Ag复合微球具有规则的球形结构,粒径在400～700 nm之间,随交联剂浓度或种子乳液浓度的增加,复合微球粒径减小.粒径在十几个纳米左右的银粒子均匀分布在微球表面和内部.载银复合微球在NaBH4还原4-硝基苯酚为4-氨基苯酚的模型反应中表现出较高的催化活性.     

基于D,L-丙交酯开环聚合制备具有自分散能力的毛发状聚合物微球

通过无皂乳液聚合法制备了单分散苯乙烯与甲基丙烯酸羟乙酯共聚的交联微球[poly(St-co-HEMA)], 利用其活性羟基, 引发D,L-丙交酯单体的开环聚合, 制备出一种新型的疏水性毛发状微球, 并用扫描电子显微镜、红外光谱及热失重分析等技术表征微球结构. 结果表明, 采用此方法不但能够成功地制备出一系列具有不同壳层厚度的疏水性毛发状聚合物微球, 而且随着D,L-丙交酯单体用量的增加, 微球在有机溶剂中的分散能力显著提高. 实验结果证明, 该方法是一种在聚合物微球表面生成高效、可控接枝疏水性大分子链的新方法.     

Amphiphilic polysaccharides: useful tools for the preparation of nanoparticles with controlled surface characteristics

Polymeric surfactants obtained by hydrophobic modification of dextran are used as stabilizers for oil-in-water emulsions. The kinetics of interfacial tension decrease is studied as a function of polymer structural characteristics (degree of hydrophobic substitution) and at various polymer concentrations. Several hydrocarbon oils, either aliphatic (octane, decane, dodecane, and hexadecane) or aromatic (styrene), are tested. Kinetics exhibits the same general trends no matter which oil or polymer is considered. The emulsifying properties of the polymeric surfactants are illustrated by the preparation of oil-in-water emulsions. The droplet size at the preparation is correlated to the amount of oil and to the polymer concentration in the aqueous phase. For low polymer/oil ratios, it is shown that the droplet size is limited by the initial amount of polymer. On the contrary, for high polymer/oil ratios, the droplet size seems to level down, indicating that other parameters become predominant. Emulsion aging occurs by Ostwald ripening, and it is demonstrated that the theoretical equation of Lifshitz, Slyozov, and Wagner (LSW) correctly describes the experimental results. The nature of the oil has important effects on emulsion aging, as described by the LSW equation. The aging of emulsions containing oil mixtures is quantitatively described on the basis of the results with pure oils. The influence of polymer chemical structure can be conveniently correlated to interfacial tension results through the LSW equation. On the contrary, the influence of oil volume fraction seems to be overestimated by the usual correction factor, k(phi). The effect of temperature on emulsion aging is finally examined. Miniemulsions stabilized with dextran derivatives are used for the radical polymerization of styrene. Following this procedure, polysaccharide-covered polystyrene nanoparticles are prepared and characterized (size and surface coverage). The size of the particles is directly correlated to that of the initial droplets for styrene volume fractions around 10%. On the contrary, for initial styrene volume fractions around 20%, particles exhibit a larger size than the initial droplets, indicating that coalescence processes take place during polymerization. The amount of dextran at the surface of the particles is determined and compared to the adsorbed amounts resulting from emulsion preparation.     

Impact of initiators in preparing magnetic polymer particles by miniemulsion polymerization

Sub-micron sized polystyrene particles containing magnetite more than 30 wt.% were prepared by miniemulsion polymerization with commercially available ferricolloid. The effects of some water-soluble initiators and/or oil-soluble initiators on the particles characteristics, such as the size, morphology, magnetic properties and colloidal stability, were studied. The size of monomer droplets/polymer particles increased from 60 to 300 nm during polymerization, keeping magnetic in core when potassium persulfate (KPS) or ammonium persulfate (APS) was used as the sole initiator. These particles were easily separated from the medium within short time scale in external magnetic field, while such characteristics were controlled by the amount of persulfate used for the polymerization. In contrast, when 2,2′-azobis isobutyronitrile (AIBN) was used as the initiator, the size of droplets/particles was retained to be 90 nm at the most and magnetite nanoparticles located at the surface of polystyrene particles, which were so colloidally stable that they were not separated in external magnetic field. The above-mentioned effect of initiators on particle size in persulfate system was likely originated from the decrease of pH value and the increase of ionic strength, which induced the fusion of droplets/particles containing magnetite. Mixed-initiators system resulted in intermediate characteristics, compared with each initiator system. The location of magnetite in the particle seems to depend on where initiation/polymerization occurred in each initiator system.     

表面功能化聚苯乙烯纳米微球的制备及自组装

用乳液聚合的方法合成了表面富含羧基的聚苯乙烯纳米微球，采用热分析、红外、透射电镜和X射线粉末衍射仪等对其进行了结构和性能表征;并用自组装的方法将其在玻璃表面组装成膜.考察了制备条件，通过对自组装薄膜原子力显微镜形貌图的分析，确立了最佳组装方案.     

超声无皂乳液聚合制备BA/St/AM三元共聚物乳胶粒及其聚合机理研究

将超声技术引入到无皂乳液聚合方法中,在不加入任何引发剂和乳化剂的情况下,制备了丙烯酸丁酯(BA)/苯乙烯(St)/丙烯酰胺(AM)三元共聚纳米乳胶粒.研究了不同超声时间对单体转化率、乳胶粒粒径以及乳液粘度的影响.同时还探讨了超声无皂乳液聚合机理,认为AM在聚合过程中起到了引发和稳定的作用.TEM照片表明,乳胶粒直径大约在80nm左右,FTIR及DSC分析表明产物为三元共聚物,而不是共混物.     

具有疏水核/亲水壳的双亲胶体粒子的制备

制备了具有疏水性聚苯乙烯核/亲水性聚丙烯酰胺壳的双亲粒子.疏水核通过超浓乳液聚合制备,亲水壳层通过过氧化羟基异丙苯和硫酸亚铁的界面引发制备.控制条件可得到网孔(半包覆)、褶皱(全包覆)两种形态的壳层.壳层孔的存在使得核层聚合物能够与外界接触.粒子的双亲性通过吸水吸油率进行表征.     

基于聚合物核壳纳米粒子的Hg~(2+)比率型荧光检测传感器

采用一步聚合的方法,制备了以疏水的聚甲基丙烯酸甲酯(PMMA)为核、亲水性的聚电解质支化聚乙烯亚胺(PEI)为壳的纳米粒子分散液.将供体荧光团4-胺基-7-硝基-N-辛基苯并[1,2,5]噁二唑(NBD)以包埋的方式在聚合过程中直接引入PMMA核内部,而受体荧光团罗丹明衍生物SRHB通过吸附作用进入PEI-PMMA核壳界面,构成了含有两种不同荧光分子且可对Hg2+进行荧光比率检测的传感器.考察了含荧光分子的聚合物粒子光谱学性质,证明两种荧光分子均被引入了聚合物粒子体系.在汞离子的荧光检测试验中,加入Hg2+后,体系中的NBD荧光强度下降,而罗丹明的特征发射峰在579 nm处出现,并随着Hg2+浓度的增加,受体/供体的荧光强度比值呈现增长趋势.研究还发现,聚合物粒子基荧光探针对于Hg2+具有较好的选择性,且最佳使用范围是体系pH值在5～8之间,其检测Hg2+的最低浓度可达到1μmol/L.