MICRON CORE-SHELL PARTICLES PREPARED BY GRAFTING POLYMERIZATION OF METHYL METHACRYLATE FROM NARROW DISPERSE SURFACE OF CHLOROMETHYLATED POLYDIVINYLBENZENE VIA ATRP

Grafting of poly(methyl methacrylate) from narrow disperse polymer particles by surface-initiated atom transfer radical polymerization (ATRP) was investigated. Polydivinylbenzene (PDVB) particles were prepared by dispersion polymerization with poly(N-vinyl pyrrolidone) (PVP) as the stabilizer. Chloromethylated PDVB was used as initiating core sites for subsequent ATRP of methyl methacrylate with CuBr/bpy as catalyst system. It was found that poly(methyl methacrylate) was grafted not only from the particle surfaces but also from within a thin shell layer, leading to particles size increases from 2.38-3.00μm with a core-shell structure particles. The grafted core-shell particles were characterized with FTIR, SEM, DSC.     

Influences of Electrolytes on the Soap-free Emulsion Copolymerization of St-MMA-AA

Monodisperse functional polymer microspheres with different particle size and with clean surface were prepared by batch soap-free emulsion polymerization of styrene, methyl methacrylate and acrylic acid in the presence of salts, and the influences of type and amount of electrolytes on polymerization process and particle morphology were investigated. Results showed that there was a critical concentration for different electrolyte to make polymerization process and the resultant emulsion stable, and the particle size increased with the increase of electrolyte concentration. The effect of metal ions was Ca^2＋〉〉K^＋〉Na^＋〉Li^＋, and the effect of haloids was Br〉Cl〉F. Keywords： Electrolyte, soap-free emulsion polymerization, polystyrene, latex particle morphology.     

Polymer-clay nanocomposites: chemical grafting of polystyrene onto Cloisite 20A

An account of the experiments on preparing polystyrene(PS) nanocomposites through grafting the polymer onto organophilic montmorillonite is reported.Cloisite 20A was reacted with vinyltrichlorosilane to replace the edge hydroxyl groups of the clay with a vinyl moiety.Because the reaction may liberate HC1,it was performed in the presence of sodium hydrogencarbonate to prevent the exchange of quaternary alkylammonium cations with H~+ ions.Only the silanol groups on the edge of the clay react with vinyltrichlorosilane.The radical polymerization of the product with styrene as a vinyl monomer leads to chemical grafting of PS onto the montmorillonite surface.The homopolymer formed during polymerization was separated from the grafted organoclay by Soxhlet extraction.Chemical grafting of the polymer onto Cloisite 20A was confirmed by infrared spectroscopy.The prepared nanocomposite materials and the grafted nano-particles were studied by XRD.Exfoliated nanocomposites may be obtained for 0.5 wt%-l wt%clay content.The nanocomposites were studied by thermogravimertic analysis(TGA) dynamic thermal analysis(DTA) and dynamic mechanical analysis (DMTA).     

PREPARATION OF Fe3O4/PSt MAGNETIC PARTICLES IN THE PRESENCE OF MAGNETIC FLUID IN ETHANOL/WATER MIXTURE*

Fe_3O_4/Polystyrene(PSt) magnetic particles with core/shell structure have been prepared in thepresence of Fe_3O_4 magnetic fluid in ethanol/water medium by dispersion polymeriation of styrene. A Fe_3O_4particle formation mechanism was proposed. According to this mechanism, the size of particle nuclei isdetermined by the extent of aggregation of Fe_3O_4 /oligomer. Magnetic particles with diameter ranging from 5to 200 μm were prepared under different reaction conditions. Some polymerization parameters such as theconcentration of monomer, stabilizer, initiator, and ethanol which affect particle size and size distribution arediscussed and their effect on particle formation are explained by the proposed mechanism.     

Preaparation of cationic latexes of poly(styrene-CO-butyl acrylate) and their properties evolution in latex dilution

Cationic latexes were prepared through emulsion copolymerization of styrene(St) and butyl acrylate(BA) with a cationic surfactant,cetyl trimethyl ammonium bromide(CTAB).Latex properties,including particle size,size distribution,ζpotential,surface tension and monomer conversion,were determined for latexes prepared with different CTAB amounts. Evolution of these properties during emulsion polymerization was followed in order to understand the mechanism of the particles formation.Results showed that both particle size andζpotential were function of polymerization time and latex solids.Parallel emulsion polymerizations with cationic,anionic charged initiator and charge-free initiators were also carried out,the latex properties were determined at different polymerization time.All these results were attentively interpreted based on the mechanisms of emulsion polymerization,surfactant adsorption and latex particle stabilization.     

INVESTIGATION OF POLYDL-LACTIDE-b-POLY（ETHYLENE GLYCOL）-b-POLYDL-LACTIDE MICROSPHERES CONTAINING PLASMID DNA

PolyDL-lactide (PDLLA) and the block copolymer, polyDL-lactide-b-poly(ethylene glycol)-b-polyDL-lactide (PELA) were used as the microsphere matrix to encapsulate plasmid DNA. The PDLLA, PELA, pBR322-1oaded PDLLA and pBR322-1oaded PELA microspheres were prepared by solvent extraction method based on the formation of multiple w1/o/w2 emulsion. The microspheres were characterized by surface morphology, mean particle size, particle size distribution and loading efficiency. The integrity of DNA molecules after being extracted from microspheres was determined by agarose gel electrophoresis. The result suggested that plasmid DNA molecules could retain their integrity after being encapsulated by PELA. The PELA microspheres could prevent plasmid DNA from being digested by DNase. The in vitro degradation and release profiles of plasmid DNA-loaded microspheres were measured in pH - 7.4 buffer solution at 37℃. The in vitro degradation profiles of the microspheres were evaluated by the deterioration in microspheres surface morphology, the molecular weight reduction of polymer, the mass loss of microspheres, the changes of pH values of degradation medium, and the changes of particle size. The in vitro release profiles of the microspheres were assessed by measurement of the amount of DNA presented in the release medium at determined intervals. The release profiles were correlation with the degradation profiles. The release of plasmid DNA from PELA microspheres showed a similar biphasic trend, that is, an initial burst release was followed by a slow, but sustained release.     

Preparation of well-defined polystyrene/silica hybrid nanoparticles by ATRP

Immobilization of the atom transfer radical polymerization (ATRP) macroinitiators at the silica nanoparticle surfaces was achieved through surface modification with excess toluene-2,4-diisocynate (TDI), after which the residual isocyanate groups were converted into ATRP macroinitiators. Structurally well-defined polystyrene chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polystyrene by ATRP, which was initiated by the as-synthesized silica-based macroinitiator. FTIR, NMR and gel permeation chro-matography (GPC) were used to characterize the polystyrene/silica hybrid particles.     

Preparation of POE/PS blends with fine particle sizes by diffusion and subsequent polymerization of styrene in POE pellets

Ethylene-α-octene copolymer(POE)/polystyrene(PS) blend pellets with fine particle sizes were prepared by diffusion and subsequent polymerization of styrene in POE pellets through a one-pot procedure.The effects of the amounts of styrene and BPO on PS content,monomer efficiency and monomer conversion were investigated.The blend pellets were characterized by Micro-FTIR and FESEM,showing homogeneous diametrical distributions of PS and particle size.After melt-processing into rods,the average particle sizes are almost doubled,but still in submicron scale.Compared to neat POE rods,the blend rods with PS content higher than 15% exhibit improved tensile modulus and tensile strength without significantly losing ductility,being attributed to the small sizes,complex nature of particles and the existence of POE-g-PS copolymer that result in good interfacial adhesion.POE/PS pellets were compared with the previously reported PP/PS pellets,and the differences between the two systems are attributed to the different morphology of the two matrices: POE is completely amorphous at the diffusion and polymerization temperature,while i PP is semicrystalline.Without efficient impediment of the crystal lamellae in POE pellets,styrene diffuses easily in POE pellets.     

Preparation of polystyrene/silica nanocomposites by radical copolymerization of styrene with silica macromonomer

A two-stage process has been developed to generate the silica-based macromonomer through surface-modification of silica with polymerizable vinyl groups. The silica surfaces were treated with excess 2,4-toluene diisocynate (TDI), after which the residual isocyanate groups were converted into polymerizable vinyl groups by reaction with hydroxypropylacrylate (HPA). Thus, polystyrene/silica nanocomposites were prepared by conventional radical copolymerization of styrene with silica macromonomer. The main effecting factors, such as ratios of styrene to the macromonomer, together with polymerization time on the copolymerization were studied in detail. FTIR, DSC and TGA were utilized to characterize the nanocomposites. Experimental results revealed that the silica nanoparticles act as cross-linking points in the polystytene/silica nanocomposites, and the glass transition temperatures of the nanocomposites are higher than that of the corresponding pure polystyrene. The glass transition temperatures of nanocomposites increased with the increasing of silica contents, which were further ascertained by DSC.     

Fischer–Tropsch synthesis on impregnated cobalt-based catalysts:New insights into the effect of impregnation solutions and pH value

The Co-based catalysts were prepared with different cobalt acetate solutions. Effects of p H value were studied deeply on Fischer–Tropsch synthesis(FTS) through a semi-batch reactor. Among all impregnation solutions(water, butanol, amyl alcohol, acetic acid, nitric acid and ammonium nitrate), the catalyst prepared by NH_4NO_3 solution showed the highest catalytic activity due to its small particle size and high reduction degree. However, the catalyst with the smallest particle size derived from water as impregnation solution exhibited low activity as well as high methane selectivity since it was difficult to be reduced and inactive in FTS. According to FT-IR spectra results, the low intensity of absorbed CO on the catalyst prepared from water solution resulted in low FTS activity. Whereas, the high activity of catalysts prepared from NH_4NO_3 solution could be explained by the high intensity of absorbed CO on the catalysts.The cobalt species on the catalysts prepared under lower p H conditions exhibited smaller particle size distribution as well as lower CO conversion than those prepared at higher p H value.     

Surface modification of polymeric microspheres using glycopolymers for biorecognition

We report the synthesis and characterization of sugar-containing microspheres consisting of poly(divinylbenzene) (PDVB) cores onto which chains of galactose- or mannose-bearing polymers have been grafted. PDVB particles prepared by distillation polymerization with a diameter of 2.4 μm containing residual surface vinyl groups were used as starting material. “Grafting from”, “grafting through” and “grafting to” techniques were performed and special interest was laid towards the resulting grafting densities. The surface modification via “grafting from” was conducted by reversible addition fragmentation chain transfer (RAFT) polymerization directly from the surface, whereas thiol-ene chemistry was used to affix glycopolymer chains onto the particle surface. The resulting sugar-covered microspheres were analyzed towards their protein recognition activity with a series of lectins.     

聚二乙烯基苯微球的合成及其表征研究

采用分散聚合方法制备了聚二乙烯基苯微球 ,研究了引发剂、稳定剂、单体 溶剂比例和溶剂种类对微球粒径及其分布的影响 ,在适当的条件下可以得到平均粒径较大、粒径分布较窄的微球 .用红外光谱法研究了聚合物微球内稳定剂、悬挂双键以及对位和间位二乙烯基苯含量随聚合过程的进行发生的变化 .测得的微球TG曲线表明 ,聚合物微球具有良好的热稳定性 .     

Hydrobromination of residual vinyl groups on divinylbenzene polymer particles followed by atom transfer radical surface graft polymerization

Rigid and monodisperse spherical polymer particles with 2.36 ± 0.18 μm diameter containing residual surface vinyl groups were prepared by photoinitiated precipitation polymerization of divinylbenzene. Anti‐Markovnikov addition of HBr to the surface vinyl groups yielded a 2‐bromoethyl functionality that was used as macroinitiator for atom transfer radical polymerization (ATRP), providing the possibility for further functionalization by controlled “grafting from” processes. This was demonstrated by grafting of glycidyl methacrylate brushes from the particle surface, using an ATRP system based on CuBr and pentamethyl diethylenetriamine. Existence of a methacrylic overlayer was verified by FTIR and XPS measurements, and the grafted particles were easily dispersed in water, confirming conversion of the particle surface from hydrophobic to hydrophilic. Hydrobromination of residual vinyl groups yields a macroinitiator that can be used for grafting of glycidyl methacrylate by ATRP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1259–1265, 2009     

Graft copolymers having hydrophobic backbone and hydrophilic branches. XI. Preparation and thermosensitive properties of polystyrene microspheres having poly (N-isopropylacrylamide) branches on their surfaces

Thermosensitive microspheres with 0.4–1.2 μm diameter consisting of a polystyrene core and poly(N-isopropylacrylamide) (polyNIPAAm) branches on their surfaces were prepared by the free radical polymerization of a polyNIPAAm macromonomer and styrene in ethanol. Electron spectroscopy for chemical analysis (ESCA) of the microsphere surface suggested that polyNIPAAm chains were favorably located on the surface of the microspheres. The morphology of the microspheres was observed by transmission electron micrograph (TEM) and the particle size of was estimated by submicron particle analyzer. The molecular weight of the polyNIPAAm macromonomer, the ratio of the macromonomer and styrene, and the polymerization temperature affected the particle size. Thermosensitive properties of polyNIPAAm-coated polystyrene microspheres were evaluated by the turbidity of their dispersion solutions and the hydrodynamic size of the miocrospheres. The transmittance in dispersion solutions changed clearly, similar to oligoNIPAAm and polyNIPAAm macromonomers. In addition, the particle size of microspheres decreased with rising temperature. These results were explained by the thermosensitivity of polyNIPAAm branches on the microsphere surface. © 1996 John Wiley & Sons, Inc.     

Narrow-disperse Highly Cross-linked “Living” Polymer Microspheres by Two-stage Precipitation Polymerization

Narrow-disperse, surface-functionalized "living" polymer microspheres with uniformly cross-linked structures were prepared by two-stage precipitation copolymerization of styrene and divinylbenzene. The two-stage precipitation polymerization is composed of an initial conventional precipitation polymerization for the nucleation followed by a reverse atom transfer radical polymerization(reverse ATRP) for the controlled polymerization process. The polymerization parameters(including reaction time for the first stage, AIBN amount and monomer loading) have been studied to show significant influences on the morphologies. Moreover, narrower size distribution and an ATRP initiator-functional surface of resulting particles can be obtained by applying reverse ATRP to conventional precipitation polymerization in the second stage. Furthermore, the "livingness" of the resulting polymer microspheres was testified by their surface modification of poly[2-(dimethylamino) ethyl methacrylate](PDMAEMA) brushes via surface-initiated ATRP(SI-ATRP).     

聚苯乙烯微球表面接枝丙烯腈的研究

采用分散聚合法制备出平均粒径为3.85 μm的窄分布聚苯乙烯微球， 并在此基础上引入第二单体丙烯腈进行共聚反应， 制备出平均粒径为4.02 μm的窄分布苯乙烯-丙烯腈共聚物微球. 对聚苯乙烯微球和苯乙烯-丙烯腈共聚物微球进行了形貌及粒径、红外光谱、差示扫描量热法(DSC)分析， 结果表明丙烯腈基团均匀分布在聚苯乙烯微球表面， 提高了聚苯乙烯微球表面的极性.     

原子转移自由基聚合制备聚(丙二醇-g-苯乙烯)

以氯甲基化苯氧基聚丙二醇 (CMPOPPG)为大分子引发剂 ,由CuCl/bpy催化的苯乙烯原子转移自由基聚合反应合成了聚 (丙二醇 g 苯乙烯 ) .CMPOPPG经环氧丙烷 (PO)与缩水甘油苯基醚 (GPE)的开环聚合和氯甲基化反应制得 .接枝聚合反应具有可控性 .用1H NMR和微库仑分析法对接枝共聚物进行了表征 .结果表明 ,支链分子量可控 ,接枝率可达 8.6.     

Further insight into the mechanism of poly(styrene‐co‐methyl methacrylate) microsphere formation

Polymeric microspheres have been used in a broad range of applications from chromatographic separation techniques to analysis of air flow over aerodynamic surfaces. The preparation of microspheres from many polymer families has consequently been extensively studied using a variety of synthetic approaches. Although there are a myriad of polymeric microsphere synthesis methods, free‐radical initiated emulsion polymerization is one of the most common techniques. In this work, poly(styrene‐co‐methyl methacrylate) microspheres were synthesized via surfactant‐free emulsion polymerization. The effects of co‐monomer composition and addition time on particle size distribution, particle formation, and particle morphology were investigated. Particles were characterized using dynamic light scattering and scanning electron microscopy to gain further insight into particle size and size distributions. Reaction kinetics were analyzed through consideration of characterization results. A particle formation mechanism for poly(styrene‐co‐methyl methacrylate) microspheres was proposed based on characterization results and known reaction kinetics. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2249–2259     

分散聚合法制备液相芯片聚苯乙烯磁性复合微球的研究

本文将丙烯酸基磁流体均匀分散到苯乙烯单体中,采用分散聚合法制备出了适于构建液相芯片微球载体的单分散性微米级磁性微球.考察了丙烯酸基磁流体预处理时间、加料顺序和单体量对微球形貌和粒径分布的影响及其条件优化.扫描电镜(SEM)显示磁性微球平均粒径为7.77 μm,具有良好的单分散性(多分散指数PDI为1.03),并且表面光滑致密;用超导量子干涉磁强计测量了Fe3O4纳米粒子的磁化曲线;用红外光谱(FT-IR)和热失重(TG)方法表征了磁性微球的化学结构及Fe3O4含量.