Uniform nonspherical latex particles as model interpenetrating polymer networks

Polystyrene/polystyrene latex interpenetrating polymer networks (IPNs) were prepared by seeded emulsion polymerization of styrene–divinylbenzene mixtures in crosslinked monodisperse polystyrene particles. The resulting latexes comprised uniform nonspherical particles, e.g., ellipsodal and egg-like singlets, symmetry and asymmetric doublets, and ice cream cone-like and popcorn-like multiplets. The nonspherical particles, which were formed by separation of the second-stage monomer from the crosslinked seed network during swelling and polymerization, are excellent models for studying phase separation in IPN's. The degree of phase separation increased with increasing degree of crosslinking of the seed particles, monomer/polymer swelling ratio, polymerization temperature, and seed particle size, and with decreasing divinylbenzene concentration in the swelling monomer. The results were consistent with a thermodynamic analysis based on the elastic-retractile force of the polymer network, the monomer/polymer mixing force, and interfacial tension force.     

Phase separation in polystyrene latex interpenetrating polymer networks

Polystyrene/polystyrene latex interpenetrating polymer networks (IPNs) were prepared by seeded emulsion polymerzation of styrene–divinylbenzene mixtures in crosslinked monodisperse polystyrene seed latexes. The resulting latexes comprised uniform nonspherical particles, which were formed by separation of the second-stage monomer from the crosslinked seed network during swelling and polymerization. The kinetics of phase separation were investigated by examining the changes in particle morphology using optical microscopy, which revealed that the phase separation was induced by the relaxation of the polymer chains before polymerization began and was enhanced by increased conversion. The thermodynamics of phase separation were investigated by analysis of the free-energy changes during swelling and polymerization, and the phase separation was described by a nucleation-and-growth mechanism. The results of this study have been applied to the design and synthesis of a series of uniform nonspherical particles of different morphology.     

聚苯乙烯包覆Y_2O_3:Eu~(3 )颗粒及表征

采用柠檬酸表面修饰 Y2 O3:Eu3 颗粒 ,苯乙烯乳液聚合的方法 ,制备出核 -壳型的 Y2 O3:Eu3 /聚苯乙烯颗粒 .在 FTIR谱图上 ,羰基伸缩振动峰向低波数位移 ;在 XPS谱图上 ,Y3d5 / 2 的电子结合能向高能方向移动 ,表明柠檬酸和颗粒表面发生键合作用 .说明此过程符合吸附层媒介作用机理 :柠檬酸使颗粒表面变成两亲性 ,从而使苯乙烯可吸附在颗粒表面形成包覆无机核的乳液结构 .EDS谱图表明聚苯乙烯均匀地包覆在颗粒表面     

Surface-modified hemispherical polystyrene/polybutyl methacrylate composite particles

Micrometer-sized polystyrene/poly(n-butyl methacrylate) composite particles of hemisphere morphology and narrow size distribution were prepared by a process of single-step swelling of uniform polystyrene template microspheres with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide in the presence, or absence, of the co-swelling agent toluene. Butyl methacrylate was then polymerized at 73 degrees C within the template microspheres. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, XPS, advancing contact angle, light microscope, SEM, and cross-sectional TEM. Selective surface functionalization of the poly(n-butyl methacrylate) phase of the composite particles was performed by carrying out a similar swelling and polymerization process in the presence of a water-soluble vinylic monomer such as acrylamide.     

表面亲水性粒度单分散交联PMMA树脂的合成及表征

用种子溶胀聚合方法 ,合成出了粒度单分散的交联聚甲基丙烯酸甲酯微球 .将微球通过水解 ,使其转化为表面带羧基的树脂 .分别用多糖化合物Dextran和DEAE Dextran对水解树脂表面进行包覆涂层 ,然后用n 丁二醇双环氧丙醚分别进行交联 ,制备出两种表面带高交联多糖覆盖层的树脂 .以两种改性树脂为填料 ,以人血清蛋白为试样 ,用HPLC方法对树脂的亲水性能进行了表征 .研究表明 ,两种改性树脂均有很好的亲水性 ,蛋白质的回收率分别在 97%和 99%以上 ,并有良好的机械强度和化学稳定性     

Synthesis and characterization of micrometer‐sized particles of narrow size distribution with chloromethyl functionality on the basis of single‐step swelling of uniform polystyrene template microspheres

Polystyrene template microspheres of 1.4 ± 0.1 μm were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. These template particles were then swelled at room temperature in a single step with emulsion that was prepared in sodium dodecyl sulfate aqueous solution from a swelling solvent (dibutyl phthalate) containing the initiator (benzoyl peroxide) and monomer(s) (chlormethylstyrene, divinylbenzene, or ethylene dimethacrylate). Composite uniform particles composed of the template polystyrene and noncrosslinked or crosslinked polychloromethylstyrene were prepared by polymerizing the monomer(s) within the swelled particles at 73 °C. Crosslinked uniform polychloromethylstyrene particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. The influence of various reaction parameters, such as dibuthyl phthalate concentration, chloromethylstyrene concentration, crosslinker type and concentration, and so forth on the molecular weight, size, size distribution, shape, morphology, surface area, and decomposition temperature of the particles was investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1342–1352, 2002     

Synthesis of nonspherical colloidal particles with anisotropic properties

We describe a promising and flexible technique for fabricating uniform nonspherical particles with anisotropic phase and surface properties. Our approach is based on the seeded polymerization technique in which monomer-swollen particles are polymerized. The polymerization causes a phase separation to occur, giving rise to two-phase nonspherical particles. We show that the elastic contraction of the swollen polymer particles induced by elevated polymerization temperatures plays an important role in the phase separation. Moreover, chemical anisotropy of nonspherical particles can be obtained by using immiscible polymer pairs and by employing surface treatments. Furthermore, we are able to produce amphiphilic dumbbell particles consisting of two different bulbs: hydrophilic poly (ethylene imine)-coated polystyrene and hydrophobic polystyrene. Controlled geometries of these amphiphilic nonspherical particles will allow a wide range of potential applications, such as engineered colloid surfactants.     

Synthesis and characterization of magnetic and non-magnetic core-shell polyepoxide micrometer-sized particles of narrow size distribution

Core polystyrene microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Uniform polyglycidyl methacrylate/polystyrene core-shell micrometer-sized particles were prepared by emulsion polymerization at 73 degrees C of glycidyl methacrylate in the presence of the core polystyrene microspheres. Core-shell particles with different properties (size, surface morphology and composition) have been prepared by changing various parameters belonging to the above seeded emulsion polymerization process, e.g., volumes of the monomer glycidyl methacrylate and the crosslinker monomer ethylene glycol dimethacrylate. Magnetic Fe(3)O(4)/polyglycidyl methacrylate/polystyrene micrometer-sized particles were prepared by coating the former core-shell particles with magnetite nanoparticles via a nucleation and growth mechanism. Characterization of the various particles has been accomplished by routine methods such as light microscopy, SEM, FTIR, BET and magnetic measurements.     

Styrene emulsion polymerization: Kinetics and particle size distributions in highly swollen latex systems

The results are reported of studies on the kinetics and the time evolution of the particle size distribution in seeded styrene emulsion polymerization systems wherein the seed latex particles were highly swollen with monomer as a result of prior swelling by dodecane. Conditions were such that no new latex particles were formed nor was a significant number of monomer droplets present (“Interval III”). The data were fitted to obtain values for the rate coefficients for entry and exit (desorption) of free radicals. It was found that, during the early part of the polymerization (when the polymer:monomer ratio in the latex particles is considerably less then in an equivalent emulsion polymerization system without dodecane), the entry rate coefficient was much smaller than that measured in systems without dodecane. This effect is consistent with an entry mechanism wherein entering free radicals must displace surfactant molecules from the latex particles.     

Preparation of micrometer-sized polymer particles with control of initiator dissociation during soap-free emulsion polymerization

A previously proposed method of soap-free emulsion polymerization employing an amphoteric initiator, 2,2'-azobis [N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate (VA-057), was extended to synthesize micrometer-sized polystyrene particles with low polydispersity in an acidic region of pH from 3.3 to 4.6. A buffer system of CH3COOH/CH3COONa was used for the adjustment of pH, which was aimed at effective promotion of particle coagulation in early stage of the polymerization. In these experiments, CH3COOH concentration was varied from 20 to 360 mM at a CH3COONa concentration of 10 mM. Polymer particles with an average size of 1.8 microm and low polydispersity were obtained at the CH3COOH concentration of 40 mM for the concentrations of 1.1 M styrene monomer and 10 mM initiator. To more precisely control dispersion stability of particles, experiments in which pH was stepwisely changed during the polymerization were also carried out. This polymerization method could enhance the average size of particles to 2.2 microm while retaining the monodispersity of particles. Furthermore, combination of pH stepwise change and monomer addition during the polymerization could produce particles with an average size of 3.0 microm and low polydispersity.     

Preparation of colored latex with polyurea shell by miniemulsion polymerization

Colored latexes with polyurea shell were prepared by applying interfacial polycondensation reaction to the miniemulsion polymerization process. These colored latexes were composed of polystyrene core and polyurea shell, and their particle size was adjusted to <100 nm. Diisocyanate was used as a hydrophobic monomer, and the equivalent mole of diamine was used as a hydrophilic monomer for interfacial polymerization. It was important to control the rate of interfacial polycondensation reaction in order to prepare small particles. Dye preservation property of colored latex loaded with oil-soluble dye was investigated. Polyurea shell formed at the surface of latex particles could restrain the migration of dyes from the latex particles and improve the dye preservation property. The ability to prevent dye migration depended on the composition of the polyurea shell.     

Microparticle sampling by electrowetting-actuated droplet sweeping

This paper describes a new microparticle sampler where particles can be efficiently swept from a solid surface and sampled into a liquid medium using moving droplets actuated by the electrowetting principle. We successfully demonstrate that super hydrophilic (2 microm and 7.9 microm diameter glass beads of about 14 degrees contact angle), intermediate hydrophilic (7.5 microm diameter polystyrene beads of about 70 degrees contact angle), and super hydrophobic (7.9 microm diameter Teflon-coated glass beads and 3 microm size PTFE particles of over 110 degrees contact angles) particles on a solid surface are picked up by electrowetting-actuated moving droplets. For the glass beads as well as the polystyrene beads, the sampling efficiencies are over 93%, in particular over 98% for the 7.9 microm glass beads. For the PTFE particles, however, the sampling efficiency is measured at around 70%, relatively lower than that of the glass and polystyrene beads. This is due mainly to the non-uniformity in particle size and the particle hydrophobicity. In this case, the collected particles staying (adsorbing) on the air-to-water interface hinder the droplet from advancing. This particle sampler requires an extremely small amount of liquid volume (about 500 nanoliters) and will thus be highly compatible and easily integrated with lab-on-a-chip systems for follow-up biological/chemical analyses.     

Surface modification of monodisperse hydroxyl functionalized polymeric microspheres using ceric ammonium nitrate

The surface modification of monodisperse hydroxyl functionalized polymeric microspheres was carried out by utilizing a redox initiation system. Styrene, divinylbenzene and hydroxyethyl methacrylate were used as the second monomer in the seeded polymerization. An excessive amount of the second monomer emulsion was swollen into the polystyrene (PS) seed particles completely by controlling the medium solvency and swelling temperature. The hydroxyl functional groups were radicalized by the ceric ammonium nitrate in nitric acid solution, and the methyl methacrylate was reacted uniformly on the surface of microspheres. From the SEM, and FE-TEM measurements, highly monodisperse microspheres having a smooth surface, and polymethylmethacrylate (PMMA) coating layer were observed, respectively. The surface characteristics of the PS seed particles, hydroxyl functionalized and surface-modified polymeric microspheres were confirmed by utilizing FT-IR, XPS and thermal analysis.     

表面富集季胺盐的交联聚苯乙烯微球合成与表征及其溶胀行为研究

在聚合物微球表面引入不同的基团 (如亲水性的羟基或羧基 ) ,可以改善聚合物微球的稳定性甚至生物相容性[1～ 4] ;利用表面基团可以把无机半导体微粒和功能有机分子以及生物分子引入聚合物微球[5～ 8] ,赋予聚合物微球特殊的性能 ,使其广泛应用于涂料、光电功能材料和生物医用材料等领域[9～ 15] .其中 ,表面带有阳离子的聚合物微球在絮凝剂、胶粘剂、水性涂料等方面已经得到广泛研究[16～ 2 0 ] .通常阳离子聚合物微球可以根据不同的需要利用常规乳液聚合、核壳乳液聚合等方法来合成 .亲水性和疏水性单体进行的无皂乳液聚合[2 1] ,因其能在…     

Evidence for and against concentration gradients in polymerizing latex particles

A single-charge emulsion polymerization involving a monomer which is a good solvent for its polymer is considered. It is shown to be unlikely that within the polymerizing latex particles there are concentration gradients large enough measurably to affect the kinetics of the reaction. The average displacement of monomers due to Brownian motion within the latex particles and in the absence of concentration gradients is calculated. This diffusive mean free path, corresponding to an interval involving less than 1% change in conversion, is shown to be much longer than the radius of the latex particle. Consequently, loci where monomer concentration is perturbed by conversion to polymer are immediately swamped by unreacted monomer. Also, direct experimental evidence exists showing that the monomer concentration in latex particles is about the same when nonpolymerizing latex particles are saturated or during polymerization in the presence of monomer excess. The thermodynamics of saturation swelling preclude the possibility of the existence of large concentration gradients. The arguments that have been advocated in the literature for core–skin separation within polymerizing latex particles were based on conversion data which were thought to be linear with time, while a reexamination indicates that they were not. The observed core–skin separation obtained when butadiene or tritiated styrene were copolymerized with styrene in the presence of a polystyrene homopolymer seed latex has questionable relevance to single-charge homopolymerization. There are reasons to doubt that the distribution of co-monomers within latex particles can be frozen by their conversion to polymers in a two-stage emulsion polymerization.     

Synthesis of quantum dot-tagged submicrometer polystyrene particles by miniemulsion polymerization

Submicrometer fluorescent polystyrene (PS) particles have been synthesized via miniemulsion polymerization using CdSe/ZnS core-shell quantum dots (QDs). The influence of QD concentration, QD coating (either trioctylphosphine oxide (TOPO)-coated or vinyl-functionalized), and surfactant concentration on the polymerization kinetics and the photoluminescence properties of the prepared particles has been analyzed. Polymerization kinetics were not altered by the presence of QDs, whatever their surface coating. Latexes exhibited particle sizes ranging from 100 to 350 nm, depending on surfactant concentration, and a narrow particle size distribution was obtained in all cases. The fluorescence signal of the particles increased with the number of incorporated TOPO-coated QDs. The slight red shift of the emission maximum was correlated with phase separation between PS and QDs, which occurred during the polymerization, locating the QDs in the vicinity of the particle/water interface. QD-tagged particles displayed higher fluorescence intensity with TOPO-coated QDs compared to those with the vinyl moiety. The obtained fluorescent particles open up new opportunities for a variety of applications in biotechnology.     

Particle nucleation and monomer partitioning in styrene O/W microemulsion polymerization

Particle nucleation in the polymerization of styrene microemulsions was found to take place throughout the polymerization as indicated by measurements of the particle number as a function of conversion. A mechanism based on the nucleation in the microemulsion droplets was proposed to explain the experimental findings although homogeneous nucleation and coagulation during polymerization were not completely ruled out. A thermodynamic model was developed to simulate the partitioning of monomer in the different phases during polymerization. The model predicts that the oil cores of the microemulsion droplets were depleted early in the polymerization (4% conversion). Due to the high monomer/polymer swelling ratio of the polymer particles, most of the monomer resides in the polymer particles during polymerization. The termination of chain growth inside the polymer particles was attributed to the chain transfer reaction to monomer. The low n? (less than 0.5) of the microemulsion system was attributed to the fast exit of monomeric radicals.     

Synthesis and characterization of micrometer‐sized homo and composite polyacrylonitrile particles of narrow size distribution on the basis of single‐step swelling of uniform polystyrene template microspheres

Polyacrylonitrile/polystyrene micrometer‐sized composite particles of narrow size distribution were prepared by a single‐step swelling of uniform polystyrene template microspheres with emulsion droplets of methylene chloride containing the monomer acrylonitrile and the initiator benzoyl peroxide. Methylene chloride was then evaporated carefully, followed by polymerization of acrylonitrile at 70 °C within the shrunken template particles. Polymerization of acrylonitrile also occurred at the particles' surface due to the interaction of surface polyacrylonitrile oligoradicals with acrylonitrile dissolved in the aqueous phase. Uniform polyacrylonitrile particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, TGA‐DSC, XRD, XPS, advancing contact angle, light microscope, SEM and cross‐sectional TEM. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4847–4861, 2004     

Nucleation of gold nanoparticles on latex particle surfaces

Gold particles were nucleated on functionalized (i.e., sulfonate or imidazole groups) latex particle surfaces. Gold ions were associated with the functional groups present on the surface of the latex particles by metal‐ligand formation and were then reduced to nucleate gold particles on the particle surface. The use of imidazole groups favored the metal‐ligand formation more effectively compared with sulfonic acid groups, so gold nucleation was investigated on the surface of imidazole‐functionalized model latex particles. The desorption of gold atoms or their surface migration first occurred during the reduction process and then gold nanoparticles were nucleated. The utilization of strong reductants, such as NaBH₄ and dimethylamine borane (DMAB) under mildly acidic conditions (i.e., pH 4) led to the deprotonation of imidazole‐rich polymer chains present on the surface of the model latex particles followed by deswelling of hydrophilic polymer surface layers. As a result, well‐dispersed gold nanoparticles were embedded in the hydrophilic polymer surface. On the other hand, the use of weak reductants led to the formation of localized gold aggregates on the surface of the latex particles. The removal of residual styrene monomer is very important because gold ions can be coordinated with the vinyl groups present in styrene monomer and would then be reduced by nucleophilic water addition. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 912–925, 2008     

Grafting of amino functional monomer onto initiator-modified polystyrene particles

Polystyrene nanoparticles with grafted chains of an amino functionalized polymer were prepared by a two-step polymerization process. In the first step, the polystyrene seed particles were synthesized by the conventional batch emulsion polymerization using terpolymer HAS (hydroperoxide monomer, acrylic acid, and styrene) as a surface-active initiator. The surface of the obtained particles contains carboxyl groups, which are responsible for the latex stability, and residual undecomposed hydroperoxide groups. Therefore, in the second step, an amino functional monomer was grafted onto the hydroperoxide modified polystyrene particles by a "grafting from" approach. X-ray photoelectron spectroscopy, NMR, and scanning electron microscopy were used to examine the surface of the amino functionalized particles. The amount of incorporated amino groups onto the particles was determined by fluorescenometric titration. In general, the number of amino groups on the particle surface increased with the increase of the functional monomer content in the reaction mixture. The incorporation of the functional monomer was also confirmed by electrophoretic measurements. Final particles possess amphoteric character due to the presence of amino and carboxyl groups on the surface. Adsorption of human immunoglobulins G onto the amino functionalized particles was studied as a function of pH and ionic strength. The covalent binding of human IgG was performed using the glutaraldehyde preactivation method. The immunoreactivity of the latex-IgG complex was examined by the latex agglutination test.