PMMA colloid particles armored by clay layers with PDMAEMA polymer brushes

Poly[2‐(dimethylamino) ethyl methacrylate] (PDMAEMA) brushes on the surfaces of clay layers were prepared by in situ free‐radical polymerization. Poly (methyl methacrylate) (PMMA) colloid particles stabilized and initiated by clay layers with PDMAEMA polymer brushes were prepared by Pickering emulsion polymerization. Transmission electron microscopy was used to characterize the structure and morphology of the colloid particles. The X‐ray diffraction (XRD) results indicated that the intercalated structures of the clay layers were almost destroyed in Pickering emulsion polymerization, and clay layers with exfoliated structures were created. The surface of the colloid particles was analyzed by using X‐ray photoelectron spectroscopy (XPS). The XPS results provide direct evidence that the clay layers with PDMAEMA chains cover the PMMA colloid particles. © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 2632–2639, 2008     

Synthesis of PS and PDMAEMA mixed polymer brushes on the surface of layered silicate and their application in pickering suspension polymerization

An ammonium free radical initiator was ion exchanged onto the surface of clay layers. Polystyrene (PS) and poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) mixed polymer brushes on the surface of clay layers were prepared by in situ free radical polymerization. PS colloid particles armored by clay layers with mixed polymer brushes were prepared by Pickering suspension polymerization. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the structure and morphology of the colloid particles. Clay layers on the surface of PS colloid particles can be observed. Because of the cationic nature of the PDMAEMA brushes the colloid particles have positive zeta potentials at low pH values. X‐ray photoelectron spectroscopy (XPS) was used to analyze the surface of the colloid particles. N_1s binding energy of PDMAEMA chains on the surface of clay layers was detected by XPS. The two peaks of the N_1s binding energy indicate two different nitrogen environments on the surface of clay layers. The peak with a lower binding energy is characteristic of neutral nitrogen on PDMAEMA chains, and the peak with a higher binding energy is attributed to protonated nitrogen on PDMAEMA chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5759–5769, 2007     

High spin/low spin phase transitions of a spin-crossover complex in the emulsion polymerization of trifluoroethylmethacrylate (TFEMA) using PVA as a protective colloid

We have studied the magnetic properties of an Fe(II) spin-crossover complex near its high spin/low spin (HS/LS) phase transition in the emulsion polymerization of trifluoroethylmethacrylate (TFEMA) using poly(vinyl alcohol) (PVA) as a protective colloid, in comparison with sodium lauryl sulfate (SLS). Morphological analysis was used to establish that the nanodispersed spin-crossover complex was incorporated into the cores of polymer particles covered with PVA shells. The obvious bi-stability of the HS/LS phase transition was considered by the identification of multiplet states such as the triplet (S = 1) and quintet (S = 2) states, and the paramagnetic state (S = 1/2), by noting a gradual shift of g-value anisotropy in the electron spin resonance (ESR) spectrum at 5 K. This was thought to have arisen from the exchange interaction as a Jahn–Teller effect in the emulsion particles. Chemical modifications such as ligand substitution, and the nature of the central metal atom in the emulsion particle, especially influenced the HS/LS phase transition.     

Synthesis of polymeric core–shell particles using surface‐initiated living free‐radical polymerization

An easy and novel approach to the synthesis of functionalized nanostructured polymeric particles is reported. The surfactant‐free emulsion polymerization of methyl methacrylate in the presence of the crosslinking reagent 2‐ethyl‐2‐(hydroxy methyl)‐1,3‐propanediol trimethacrylate was used to in situ crosslink colloid micelles to produce stable, crosslinked polymeric particles (diameter size ～ 100–300 nm). A functionalized methacrylate monomer, 2‐methacryloxyethyl‐2′‐bromoisobutyrate, containing a dormant atom transfer radical polymerization (ATRP) living free‐radical initiator, which is termed an inimer (initiator/monomer), was added to the solution during the polymerization to functionalize the surface of the particles with ATRP initiator groups. The surface‐initiated ATRP of different monomers was then carried out to produce core–shell‐type polymeric nanostructures. This versatile technique can be easily employed for the design of a wide variety of polymeric shells surrounding a crosslinked core while keeping good control over the sizes of the nanostructures. The particles were characterized with scanning electron microscopy, transmission electron microscopy, optical microscopy, dynamic light scattering, and Raman spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1575–1584, 2007     

Electrical Properties and Stability of Poly(N-isopropylacylamide-co-methacrylic Acid) Core-Shell Microgel

Graphical Abstract: A doubly responsive microgel with core shell shape was prepared by seed polymerization. The electrical properties were characterized. The latex stability was evaluated and discussed according to the colloid theory.

A core-shell microgel of poly(N-isopropylacylamide-co-methacrylic acid) was prepared by seeded polymerization. Dynamic light scattering measurements indicated that the microgel had a narrow size distribution. Zeta potential decreased gradually with increasing ionic strength, and when salinity reached a certain concentration the surface charge was almost screened out. Further addition of salt led to the shrinking and final flocculation. For increasing temperature, the zeta potential under higher ionic strength exhibited an abrupt change for trending to zero. Total interaction energy between particles was calculated with colloid theory. Meanwhile, thermal stability was evaluated and interpreted the experimental phenomenons.     

HA/PDM自组装复合胶体粒子及其乳化性能

以阴离子天然大分子透明质酸(HA)和阳离子单体甲基丙烯酸二甲氨基乙酯(DM)组成带相反电荷的聚合物/单体复合体系, DM通过水相原位聚合可制备荷正电的聚甲基丙烯酸二甲氨基乙酯(PDM), PDM与HA间的静电作用可诱导两者在水溶液中进行自组装, 得到HA/PDM复合胶体粒子. 用傅里叶变换红外(FTIR)光谱仪对HA/PDM复合物结构进行了表征. 用动态激光光散射(DLS)研究了HA与PDM复合体系在水溶液中的自组装行为, 并表征了反应时间对HA/PDM复合胶体粒子粒径的影响. 利用透射电镜(TEM)表征了胶体粒子的形貌. 考察了溶液pH 对胶体粒子粒径及zeta 电位的影响, 并对胶体粒子的乳化性能进行初步探索. 结果表明:DM单体聚合前, 无HA/DM复合物聚集体形成; 而随着DM的逐步聚合, HA与PDM可通过静电作用逐渐组装形成球状HA/PDM复合胶体粒子, 其粒径随反应时间延长逐渐减小并趋于稳定. 同时, 该复合胶体粒子具有pH敏感性和乳化性, 乳化性能较纯HA和PDM有较大提高.     

Dextran stabilized poly(methyl methacrylate) latex particles and their potential application for affinity purification of lectins

 Stable poly(methyl methacrylate) latex particles (220–360 nm in diameter) using dextran as the protective colloid were prepared and characterized in this study. Such an emulsion polymerization system follows Smith–Ewart Case III kinetics (i.e., the average number of free radicals per particle is greater than 0.5) due to the relatively large latex particle size. The carbohydrate content of these dextran modified emulsion polymers shows a maximum around 5% dextran based on total monomer weight. The latex stability during polymerization is closely related to the carbohydrate content of these latex particles, and it is controlled by the ratio of the thickness of the dextran adsorption layer to that of the electric double layer of the latex particles. The critical flocculation concentration (CFC) of the latex products correlates well with the latex stability during polymerization. The greater the total scrap produced during polymerization (i.e., the stronger the bridging flocculation), the lower is the CFC of the latex products. The affinity precipitation of concanavalin A (a model lectin used in this study) by the dextran modified PMMA latex particles is also illustrated in this study. The specifically adsorbed concanavalin A increases with the carbohydrate content of the dextran modified latex particles. Received: 9 December 1996 Accepted: 8 April 1997     

钼体系催化丁二烯聚合反应催化剂相态的研究

钼体系催化丁二烯聚合反应催化剂相态的研究夏少武，夏树伟，赵菁，张平（青岛化工学院应化系，青岛，２６６０４２）关键词胶体催化剂，Ｔｙｎｄａｌｌ效应，陈化ＭｏＣｌ３（ＯＣ８Ｈ１７）２～（ｉ－Ｂｕ）２ＡＩＯＰｈＣＨ３（间）体系在加氢汽油溶液中具有较高的催化...     

Copolymerization of 2‐hydroxyethyl methacrylate with a comonomer with spiroacetal moiety

The study reports the synthesis of a copolymer based on 2‐hydroxyethyl methacrylate and 3,9‐divinyl‐2,4,8,10‐tetraoxaspiro[5.5]undecane (U) acquired through radical polymerization in the presence of 2,2′‐azobis(2‐methylpropionitrile). The attempt was to have a solid content as high as 10 wt %. The polymerization process was conducted in the presence of a classic ionic surfactant—sodium lauryl sulfate—and comparatively using two variants of protective colloid β‐cyclodextrin and poly(aspartic acid), respectively. The prepared dispersions were characterized from the viewpoint of their hydrodynamic radius, zeta potential, and conductivity evolution during syntheses. The mean particle size and size distribution and zeta potential and conductivity were also evaluated for the synthesized polymeric particles. The compositions of the polymers were confirmed by FTIR and ¹H NMR spectra, and also, the thermal stability of the polymeric compounds was evaluated. SEM and AFM investigations of the polymer morphology are also presented. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A unique transurf in styrene emulsion polymerization

The surface-active, chain transfer agent (‘transurf’) sodium ω-mercapto-decane sulfonate, SMDSo, was synthesized, purified, and its interfacial properties determined. The compound acted normally in styrene emulsion polymerization to produce extremely stable colloids containing only sulfonate ionic surface functional groups. It was then used to control the surface charge density of a model polystyrene colloid by means of seeded emulsion polymerization. Surface charge could thus be increased 16-fold over that of the seed particles, and was due solely to sulfonate groups introduced by the SMDSo. Unlike most conventional emulsion polymerizations, this technique allows one to control surface chemistry independently of particle size. To cite this article: C.C. Fifield, R.M. Fitch, C. R. Chimie 6 (2003).     

Effects of preparation conditions on the synthesis of nano-sized Ag metal particles by the wet-process using 3-mercapto-propionic acid

By the addition of sodium borohydride as a reducing agent into an aqueous solution of AgNO₃ mixed with 3-mercapto-propionic acid as a protective agent, nano-sized Ag metal particles could be synthesized. Using this advanced wet-process the synthesis of an aqueous Ag colloid system with a high density became possible, because the surfaces of the synthesized nano-sized Ag metal particles were covered and protected by the adsorbed 3-mercapto-propionic acid. By changing the mix ratio of AgNO₃ to 3-mercapto-propionic acid, the particle size of synthesized nano-sized Ag metal particles could be controlled; a higher 3-mercapto-propionic acid/AgNO₃ ratio was preferable in the synthesis of smaller Ag metal particles. From the relationship between the Ag metal particle size and the residual S content adsorbed on the metal particles, the mechanism of dispersion of Ag particles can be proposed as that the 3-mercapto-propionic acid having a thiol group adsorbs on Ag particles by forming Ag-S bonds as a protective agent.     

Effect of initiators on grafting in the initial stage of the emulsion polymerization of methyl methacrylate using poly(vinyl alcohol) as a protective colloid

 To make clear the reason of unsuitability of poly(vinyl alcohol) (PVA) protective colloid for the emulsion polymerization of conjugated monomers, a model experiment of emulsion polymerization of methyl methacrylate (MMA) was carried out with ammonium persulfate (APS) or azobis(isobutyronitrile) (AIBN) initiators, where a small amount of MMA (1/100th of the concentration compared with ordinary emulsion polymerization) was employed. This corresponds to the initial stage of the emulsion polymerization. Grafting of MMA onto PVA took place remarkably irrespective of the kind of the initiators. Formation of homo-poly(MMA) was observed to a small extent. The formation of new emulsion particles smaller than 100 nm continued to increase to almost the end of the polymerization. PVA molecules in the grafted polymer are supposed to act as stabilizers of newly formed particles. From kinetic treatment using the experimental data, the important issues were derived as follows. Firstly, the sulfate anion radical from APS is much more reactive than the isobutyronitrile radical from AIBN in terms of hydrogen abstraction from PVA. Secondly, high grafting ability of the latter initiator system, notwithstanding the much lower reactivity in the hydrogen abstraction compared with the APS system, is attributed to the relative reactivity of the primary radicals, i.e., hydrogen abstraction reaction from PVA to initiation reaction with MMA. The much slower rate of addition of the isobutyronitrile radical to the monomer compared with that of hydrogen abstraction from PVA facilitates the grafting, although the rate constant of hydrogen abstraction is far smaller than that with the sulfate anion radical by 10⁻⁴ times. Received: 26 April 2001 Accepted: 6 September 2001     

Nonaqueous dispersion polymerization of styrene in methanol with the ionomer block copolymer poly[(4‐methylstyrene)‐co‐(4‐vinyltriethylbenzyl ammonium bromide)]‐b‐polyisobutene as a stabilizer

The nonaqueous dispersion polymerization of styrene in methanol with poly[(4‐methylstyrene)‐co‐(4‐vinyltriethylbenzyl ammonium bromide)]‐b‐polyisobutene as a stabilizer was investigated. There was no observable inducing period or autoacceleration in the polymerization process. The conversion increased almost linearly with the polymerization time as high as 80%. The average sizes of the obtained polystyrene particles increased, and the size distributions of the polystyrene particles tended to become narrower, with increasing conversion. The mechanism of the dispersion polymerization in the presence of polyisobutene‐b‐poly[(4‐methylstyrene)‐co‐(4‐vinyltriethylbenzyl ammonium bromide)] was nucleation/growth. When the stabilizer/monomer ratio (w/w) was greater than 2.0%, the polystyrene dispersion was stable, and there was no observable polymer particle coagulation taking place during the whole polymerization process. The average diameter of the polymer particles can be mediated through changes in the polymerization conversion, monomer, and stabilizer. Nearly monodispersed polystyrene particles with average diameters of approximately 0.45–2.21 μm were obtained under optimal conditions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2678–2685, 2004     

Nitroxide-mediated photo-controlled/living radical dispersion polymerization of methyl methacrylate

The nitroxide-mediated photo dispersion polymerization of methyl methacrylate (MMA) was performed by irradiation at room temperature using (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator, (4-tert-butylphenyl)-diphenylsulfonium triflate as the photo-acid generator, and polyvinylpyrrolidone (PVP) as the surfactant in a mixed solvent of methanol/water = 3/1 (v/v). The MTEMPO-mediated photo dispersion polymerization produced spherical particles of PMMA, while the uncontrolled photo dispersion polymerization without MTEMPO provided nonspherical particles. The size distribution of the spherical particles decreased as the PVP concentration increased. The spherical particles showed a comparatively narrow molecular weight distribution of ca. 1.6. The livingness of the polymerization was confirmed on the basis of the linear correlations of the first-order time–conversion plots and conversion–molecular weight plots. The simultaneous control of the size distribution and molecular weight was possible as long as the light penetrates into the particles.     

Monodisperse polystyrene particles crosslinked with poly(dimethyl siloxane) diacrylate using dispersion polymerization and their monomer swelling capability

A flexible poly(dimethyl siloxane) diacrylate (PDMSDA) crosslinker was synthesized using different molecular weights of poly(dimethyl siloxane) (PDMS, M _n =550, 1,700, 4,000 g/mol). The monodisperse polystyrene (PS) particles crosslinked with various contents of PDMSDA were prepared by dispersion polymerization, and applied as seed particles in the seeded polymerization. The crosslinking density of the PS particles was determined from the rate of transport of the monomer molecules to the crosslinked seed particles. It was confirmed that the monomer swelling capacity of seed particles and final morphological changes of polymer beads were determined significantly by the crosslinking density of the seed particles. In addition, the morphological change was not observed without the oligomer swelling step in the seeded polymerization due to the hydrophobic property of PDMS. When highly crosslinked seed particles were used in the seeded polymerization, peculiar morphology (doublet structure) of polymer beads appeared.     

Ultrasonically assisted in situ emulsion polymerization: a facile approach to prepare conducting copolymer/silica nanocomposites

Ultrasonically assisted in situ emulsion polymerization was used to prepare electrically conducting copolymer poly(aniline‐co‐p‐phenylenediamine) [poly(Ani‐co‐pPD)] and silica (SiO₂) nancomposites. This approach can solve problems in the dispersion and stabilization of SiO₂ nanoparticles in the copolymer matrix. It was found that the aggregation of SiO₂ nanoparticles could be reduced under ultrasonic irradiation. Scanning transmission electron microscopy (STEM) confirmed that the resulting poly(Ani‐co‐pPD)/SiO₂ nanocomposite particles were spherical in shape, in which SiO₂ nanoparticles were well dispersed. The comonomer molecules were absorbed on the surface of SiO₂ particles and then polymerized to form core–shell nanocomposite. The incorporation of SiO₂ in the nanocomposite was supported by Fourier transform infrared spectroscopy (FT‐IR). UV‐visible spectra of the diluted colloid dispersion of nanocomposite particles were similar to those of the neat copolymer. Conductivity of nanocomposites was higher than the value obtained for the neat copolymer. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of spherical submicron-sized magnetite/silica nanocomposite particles

This paper describes a method for fabricating spherical submicron-sized silica particles that contained magnetite nanoparticles (magnetite/silica composite particles). The magnetite nanoparticles with a size of ca. 10 nm were prepared according to the Massart method, and were surface-modified with carboxyethylsilanetriol. The fabrication of magnetite/silica composite particles was performed in water/ethanol solution of tetraethoxyorthosilicate with ammonia catalyst in the presence of the surface-modified magnetite nanoparticles. The magnetite/silica composite particles with a size of ca. 100 nm were successfully prepared at 0.05 M TEOS, 15 M water, and 0.8 M ammonia with injection of the magnetite nanoparticle colloid at 2 min after the initiation of hydrolysis reaction of TEOS. Magnetite concentration in the composite particles could be raised to 17.3 wt.% by adjustment of the injected amount of the magnetite colloid, which brought about the saturation magnetization of 7.5 emu/g for the magnetite/silica composite particles.     

光敏共聚物P(St/VM-co-MA)自组装胶体粒子及其性能

以苯乙烯类光敏单体7-(4-乙烯基苄氧基)-4-甲基香豆素(VM)、苯乙烯(St)、马来酸酐(MA)为共聚单体,采用自由基聚合法制备了光敏性双亲共聚物P(St/VM-co-MA).在选择性溶剂(N,N-二甲基甲酰胺(DMF)/H2O)中对P(St/VM-co-MA)进行自组装,用透射电镜(TEM)和动态激光光散射(DLS)表征了自组装胶体粒子的形态、粒径大小及其分布.利用紫外光照使胶体粒子中香豆素基元发生光二聚反应,形成交联胶体粒子,并用紫外-可见光分光光度计(UV-Vis)跟踪其交联过程.用DLS研究了交联和未经交联胶体粒子的粒径和结构稳定性,用激光扫描共聚焦显微镜(LSCM)和光学显微镜考察了胶体粒子的乳化、包覆性能.结果表明:交联和未经交联胶体粒子均具有乳化性,且在乳化过程中可实现对油溶性染料的包覆.胶体粒子交联后,粒径有所减小,结构稳定性、乳化性能、包覆性能均有所提高.     

Surface modification of polystyrene latex particles via atom transfer radical polymerization

The atom transfer radical polymerization (ATRP) technique using the copper halide/ N,N′,N′,N″,N″‐pentamethyldiethylenetriamine complex was applied to the graft polymerization of methyl methacrylate and methyl acrylate on the uniform polystyrene (PS) seed particles and formed novel core‐shell particles. The core was submicron crosslinked PS particles that were prepared via emulsifier‐free emulsion polymerization. The crosslinked PS particles obtained were transferred into the organic phase (tetrahydrofuran), and surface modification using the chloromethylation method was performed. Then, the modified seed PS particles were used to initiate ATRP to prepare a controlled poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) shell. The final core‐shell particles were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, thermogravimetric analysis, and elementary analysis. The grafting polymerization was conducted successfully on the surface of modified crosslinked PS particles, and the shell thickness and weight ratio (PMMA and PMA) of the particles were calculated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 892–900, 2002; DOI 10.1002/pola.10160     

Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerization

Macroporous functionalized polymer beads of poly(4‐vinylpyridine‐co‐1,4‐divinylbenzene) [P(VPy‐co‐DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier‐free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy‐co‐DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10–50 μm, and the pore size was 0.1–1.5 μm. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 873–880, 2003