Polystyrene microspheres with narrow particle size distribution

Crosslinked polystyrene microspheres of a diameter of the order of more than 2 μm and a narrow particle diameter distribution were synthesized by emulsifier-free emulsion polymerization. The dependence of various parameters such as an electrolyte (NaCl), an initiator (K₂S₂O₈), the phase volume ratio, the reaction temperature and time on the diameter and the particle size distribution has been discussed.     

In-situ encapsulation of quantum dots into polymer microspheres

We have incorporated fluorescent quantum dots (QDs) into polystyrene microspheres using functionalized oligomeric phosphine (OP) ligands. We find that a uniform distribution of quantum dots is loaded inside each polymer bead. Some local close-packing of quantum dots in the beads is attributed to the self-polymerization of the functionalized ligands. The presence of quantum dots disturbs the nucleation and growth processes during the formation of polymer microspheres and results in a wider size distribution of the quantum dot-embedded polystyrene beads than for the control without dots. The change in quantum efficiency of the quantum dots before (approximately 20%) and after (12%) loading into the beads substantiates the protection of oligomeric phosphine ligands yet indicates that the properties of these quantum dots are still affected during processing.     

交联聚苯乙烯单分散微球的制备

微米级粒度均匀的聚合物微球作为功能高分子材料在分析化学、生物化学、标准计量以及某些高新技术领域中应用广泛。制备聚合物微球的传统方法有乳液和悬浮聚合法。乳液聚合只能制备粒径为0．1-0．7μm的颗粒，采用无皂或低皂乳液聚合法制成的单分散聚合物微球粒径接近1μm，但难于达到1μm以上，且后处理比较麻烦；悬浮聚合制备的聚合物微球粒径则一般在100-1000μm之间，且是多分散性的。而分散聚合获得的微球呈单分散性，是制备粒径为1-10μm的单分散聚合物微球的有效方法。     

Stabilization and encapsulation of human immunoglobulin G into biodegradable microspheres

The instability of protein during preparation, storage, and release has become a major concern in recent years in the encapsulation of proteins into biodegradable polymers for controlled release systems. The present investigation was performed to study the mechanism of degradation of human immunoglobulin G (IgG) in double emulsion and solid-in-oil-in-water (S/O/W) encapsulation processes. The stabilizing effects of various excipients during the period of protein atomization using spray freeze-drying and subsequent encapsulation into polylactide-co-glycolide (PLGA) microspheres were explored. The size-exclusion high-performance liquid chromatography (SEC-HPLC) results showed that ultrasonication did not change the primary structure of IgG significantly. However, enzyme-linked immunosorbent assay (ELISA) revealed that the subsequent double-emulsion solvent evaporation process denatured nearly 80% of the total amount of IgG. This was possibly due to the adsorption, unfolding, and aggregation of IgG at the water/organic solvent interface. Both mannitol and trehalose could stabilize IgG during spray freeze-drying, with over 90% retention of its molecular integrity and immunoactivity, which were verified using SEC-HPLC and ELISA. Solid protein microparticles were further entrapped into monolithic-type microspheres of PLGA using the S/O/W method. FTIR results suggested that the incomplete release that is often observed in the formulation of controlled protein release systems may be due to the degradation or aggregation of protein in the solid polymer matrix.     

Photoinitiated dispersion polymerization of methyl methacrylate: A quick approach to prepare polymer microspheres with narrow size distribution

Photoinitiated dispersion polymerization of methyl methacrylate was carried out in a mixture of ethanol and water as dispersion medium in the presence of poly(N‐vinylpyrrolidone) (PVP) as the steric stabilizer and Darocur 1173 as photoinitiator. 93.7% of conversion was achieved within 30 min of UV irradiation at room temperature, and microspheres with 0.94 μm number–average diameter and 1.04 polydispersity index (PDI) were obtained. X‐ray photoelectron spectroscope (XPS) analysis revealed that only parts of surface of the microspheres were covered by PVP. The particle size decreased from 2.34 to 0.98 μm as the concentration of PVP stabilizer increased from 2 to 15%. Extra stabilizer (higher than 15%) has no effect on the particle size and distribution. Increasing medium polarity or decreasing monomer and photoinitiator concentration resulted in a decrease in the particle size. Solvency of reaction medium toward stabilizer, which affects the adsorption of stabilizer on the particle surface, was shown to be crucial for controlling particle size and uniformity because of the high reaction rate in photoinitiated dispersion polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1329–1338, 2008     

Preparation of polystyrene particles with narrow particle size distribution by γ-ray initiated miniemulsion polymerization stabilized by polymeric surfactant

Co-60 γ-ray initiated miniemulsion polymerization of styrene stabilized by an alkali soluble polymeric surfactant (ASPS) was studied in this work. The affecting factors, including absorbed dose, dose rate, surfactant concentration, and hexadecane (HD) concentration, were systematically studied. The particle size and particle size distribution (PSD) of final latexes was determined by transmission electron microscope (TEM). The results indicated that polystyrene (PS) particles with narrow PSD could be easily prepared by this method, and the particle size could be controlled from 50 nm to 250 nm by adjusting the concentration of HD and ASPS. HD concentration, surfactant concentration, dose rate and total absorbed dose strongly affected the particle size and PSD of PS latexes.     

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 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     

Equilibrium encapsulation of polystyrene latex particles

We have performed a series of seeded styrene emulsion polymerizations in which the second stage of growth was initiated only after the second-stage monomer charge had achieved equilibrium saturation with the seed particles. The final particles were observed in the electron microscope by using two means of distinguishing between the first- and second-generation polymer: (a) butadiene tagging and osmium tetroxide staining coupled with ultramicrotomy and (b) tritiated-styrene tagging coupled with autoradiographic detection. We find that the first- and second-generation polymer chains are not uniformly mixed throughout the final latex product; rather, the second-generation polymer overcoats the seed polymer in a core–shell fashion. In order to explain these results, we present the viewpoint that monomer actually concentrates at the periphery of the swollen particle to form a monomer-encapsulated structure, rather than swelling the particle uniformly as has always been envisioned. We believe the encapsulation phenomena to be governed by the microscopic thermodynamic environment of the latex particles which has, in turn, a profound effect upon the conformational behavior of the long-chain polymer molecules as they interact with the particle–water interface.     

Synthesis and characterization of spherical and hemispherical polyepoxide micrometer‐sized particles of narrow size distribution by a single‐step swelling of uniform polystyrene template microspheres with glycidyl methacrylate

Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. Spherical and hemispherical polystyrene/poly(glycidyl methacrylate) microspheres of narrow size distribution were prepared by a single‐step swelling of the polystyrene template microspheres with the swelling solvent monomer glycidyl methacylate, followed by polymerization of the monomer within the swollen template microspheres at 73 °C. Uniform polystyrene/poly(glycidyl methacylate‐ethylene glycol dimethacrylate) polyepoxide composite microspheres were synthesized similarly, substituting glycidyl methacylate for glycidyl methacylate and ethylene glycol dimethacrylate. Uniform crosslinked poly(glycidyl methacylate‐ethylene glycol dimethacrylate) polyepoxide microspheres have been prepared by dissolution of the PS template polymer of the former composite microspheres. Particles with different properties, for example size, size distribution, shape, surface morphology, surface area, and so forth, were prepared by changing various parameters belonging to the swelling and/or polymerization steps, for example, volume of the swelling monomer/s and/or the swelling solvent dibutyl phthalate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4612–4622, 2007     

PVA-g-PS复合微球的制备与粒径控制研究

由链转移自由基聚合与端基置换反应法,合成了苯乙稀基单封端的聚醋酸乙烯酯(PVAc)大分子单体,使其与苯乙烯在乙醇/水的混合介质中进行自由基分散共聚,得到了表面以PVAc为接枝链的聚苯乙烯(PVAc-g-PSt)微球。将所得微球在碱性条件下醇解,形成了以亲水性聚乙烯醇(PVA)为壳、聚苯乙烯为核的复合微球(PVAc-g-PSt)。用核磁共振对聚合物的结构进行表征,定出了PVAc末端双键的含量;并用激光光散射、扫描电子显微镜对微球的粒径与形态进行了表征。研究结果表明,在共聚反应体系中大分子单体的分子量与浓度、苯乙烯浓度、引发剂浓度及溶剂的组成对微球的形态和粒径大小有明显影响。     

The synthesis of polymer suspension with narrow particle size distribution for immunochemical investigations

 Heterophase polymerization of styrene in the presence of di-p-tolyl-o-carbalkoxyphenylcarbinol (DTC) soluble in monomer and insoluble in water, as stabilizer, was investigated. The factors affecting polymer particle diameter, their size distribution and stability were investigated. It was suggested that polymer particles are formed from monomer droplets. The polystyrene suspension with narrow particle size distribution synthesized in the presence of DTC, was used for immunochemical research. Received: 10 March 1998 Accepted: 8 June 1998     

Preparation of protein microcapsules with narrow size distribution by sonochemical method

Protein microcapsules with narrow size distribution have been prepared by sonochemical method which is a simple, fast, environmental friendly and cost-effective method. The prepared microcapsules are composed of a water-insoluble core and an outer protein shell. The hydrophobic drugs could be encapsulated into protein microcapsules directly via sonochemical method by dissolving drugs in the nontoxic and edible vegetable oil before ultrasonication, which is a potential solution for drug resistance by hiding cytotoxic drugs in the carrier and allows for the delivery of high doses in relatively small volume. The size and size distribution of protein microcapsules are very important for their practical application. In this paper, the factors affecting the size and size distribution of protein microcapsules are investigated in detail. Moreover, confocal laser scanning microscopy and transmission electron microscopy confirmed that the protein microcapsules with narrow size distribution were obtained.     

Colloidal dispersions of molybdenum disulfide with a narrow particle size distribution

Colloidal dispersions of MoS₂ in DMF were obtained, and a procedure for the preparation of the fraction of particles with the size distribution 1.5 times narrower than that in the original dispersion was developed. It was shown that for the gradual centrifugation of dispersions with an increase in the acceleration from 126g to 2016g the average thickness of nanosheets decreased from 35 to 8 nm and the average lateral sizes decreased from 250 nm to a constant value of 160 nm. A linear dependence of the absorbance of the dispersions on the concentration of MoS₂ was established.     

Developing a hybrid emulsion polymerization system to synthesize Fe3O4/polystyrene latexes with narrow size distribution and high magnetite content

A hybrid emulsion polymerization was formulated for synthesizing Fe₃O₄/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe₃O_4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe₃O₄/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007     

One-pot, high-yield synthesis of size-controlled gold particles with narrow size distribution

Here, we first report a facile one-step one-phase synthetic route to achieve size-controlled gold micro/nanoparticles with narrow size distribution by using o-diaminobenzene as a reducing agent in the presence of poly(N-vinyl-2-pyrrolidone) via a simple wet-chemical approach. All experimental data including that from scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques indicates that the gold micro/nanoparticles with a narrow size distribution were produced in high yield (approximately 100%).     

Synthesis of polypyrrole nanoparticles by oil-in-water microemulsion polymerization with narrow size distribution

Conductive spherical polypyrrole nanoparticles were obtained by polymerization in oil-in-water (o/w) microemulsions using sodium dodecyl sulfate (SDS) as anionic surfactant, ethanol as co-surfactant, and potassium persulfate (KPS, 0.017 wt.%) as oxidizing agent. The average particle diameter (Dp) of the nanoparticles was between 38 and 45 nm with narrow particle size distributions (D _w/D _n < 1.2). Dp increases with the ethanol concentration due to the intercalation between the polar heads of SDS, promoting instability of the nanoparticles and some coagulation. In this work, low surfactant concentration was used, and the molar ratio of the oxidizing agent to monomer was 8.5 × 10⁻³, a value much lower compared with others reported in the literature. Increasing the ethanol concentration in the recipes enhanced the conductive properties of the polymers due to the high π-conjugation length obtained.     

A technique for production of nanocrystalline cellulose with a narrow size distribution

Nanocrystalline cellulose (NCC) was prepared by sulfuric acid hydrolysis of microcrystalline cellulose. A differential centrifugation technique was studied to obtain NCC whiskers with a narrow size distribution. It was shown that the volume of NCC in different fractions had an inverse relationship with relative centrifugal force (RCF). The length of NCC whiskers was also fractionized by differential RCF. The aspect ratio of NCC in different fractions had a relatively narrow range. This technique provides an easy way of producing NCC whiskers with a narrow size distribution.     

Recognition-induced transformation of microspheres into vesicles: morphology and size control

Polystyrene functionalized with diamidopyridine (DAP) recognition units self-assembles in nonpolar media to form thermally reversible micrometer-scale spherical aggregates. The size and the thermal stability of these microspheres can be controlled by the molecular weight of the polymer. The addition of thymine-functionalized polymer to these self-assembled microspheres converted them into vesicular aggregates with a controlled size. The morphology change was reversible: the addition of DAP-functionalized polymer converted the vesicles back to microspheres.