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     

Synthesis and characterization of saccharide‐based latex particles

The synthesis of new polymer colloids based on renewable resources, such as sugar‐derived monomers, is nowadays a matter of interest. These new polymeric particles should be useful in biomedical applications, such as drug delivery, because of their assumed biodegradability. In this work, two new families of polymer latex particles, based on a sugar‐derived monomer, 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D ‐glucofuranose (3‐MDG), were produced and characterized. The syntheses of poly(3‐MDG) crosslinked particles and those obtained by copolymerization with methacrylic acid (MAA), poly(3‐MDG‐co‐MAA) crosslinked particles, were prepared by surfactant‐free emulsion polymerization in a batch reactor. The average particle diameter evolutions, the effect of pH of the dispersion medium on the final average diameters, together with the microscopic and morphological analysis of the particle's surface and inner dominium, were analyzed. Poly(3‐MDG‐co‐EGDMA) stable particles were obtained by adding low amounts of initiator. The surface‐charge density of these particles corresponded to the sulfate groups coming from the initiator. In the second family of latices, poly(3‐MDG‐co‐MAA‐co‐EGDMA) particles, DCP measurements and SEM and TEM observations showed that the sizes and surface characteristics depended on the amounts of MAA and crosslinker used in the reaction mixture. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 443–457, 2006     

Tailored surface properties of monodispersed polymer particles with PCL hairy chains synthesized by hydroxyl‐initiated ring‐opening polymerization

Polymeric particles with hydrophobic PCL hairy chains were prepared by ring‐opening polymerization (ROP) from hydrophilic core particles, which were prepared by soap‐free emulsion polymerization of styrene, 2‐hydroxyethyl methacrylate, and divinylbenzene. Due to the incorporation of 2‐hydroxyethyl methacrylate in the core particles, hydroxyl groups on the surface of core particles could be obtained, and in the following ROP of ε‐caprolactone, the hydroxyl groups on the surface of the particles could effectively initiate the polymerization. Various reaction conditions were evaluated to produce hairy particles with optimal grafting efficiency. The presence of hydrophobic polymeric hairs on the surface of particles led to a dramatic improvement in their dispersibility in oil phase. By controlling the grafting amount of PCL on the surface of hydrophilic core particles, the surface properties of the hairy particles could be well tailored, represented the change of water contact angles from 75.0° to 114.6°. The prepared hairy particles were characterized by thermogravimetric analysis, scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4552–4563, 2007     

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.     

Effect of initiation site location on morphology of polymer microspheres via pickering polymerization

A novel way is introduced to control polymerization routes and morphology of final polymer microspheres during the Pickering polymerization. Cetyltrimethylammonium bromide (CTAB)‐modified silica and different initiators are used simultaneously to determine the initiation location, nucleation step, and morphology of final particles. As Pickering stabilizer, the CTAB‐modified silica is characterized by dynamic light scattering. The size and distribution of the oil droplets stabilized by the silica nanoparticles is observed by optical microscopy. The resulted silica/polymer composite microspheres are characterized by scanning electron microscopy and transmission electron microscopy. The silica content is measured by thermogravimetric analysis. It is proven that both surface property of inorganic particles and type of initiators can greatly affect the polymerization routes and the morphology of the obtained polymer microspheres. Detailed formation mechanisms of several kinds of polymer particles are also proposed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Block Copolymers in Emulsion and Dispersion Polymerization

Summary: This article deals with recent progress including the authors' work concerning the application of block copolymers as polymeric surfactants in heterophase polymerizations. The synthesis methods for preparing block copolymers by emulsion and dispersion techniques are outlined, with emphasis on recently developed controlled free radical polymerizations in aqueous media. Specific characteristics of amphiphilic block copolymers are described, for example, micellization and emulsifying effects. A general overview of emulsion and dispersion polymerization in an aqueous and organic medium with ionic and nonionic block copolymers is presented for the preparation of electrosteric and sterically stabilized latex particles. Typical examples of microemulsion, miniemulsion, oil‐in‐oil emulsion, and micellar polymerizations are provided. Current and potential developments of so‐called “hairy latexes”, inverse‐, multiple‐, and solid emulsions, as well as of nonaqueous polymeric dispersions are also discussed.

PS foam obtained by free radical polymerization of water‐in‐styrene, stabilized with a PS–PEO diblock copolymer.     

吴氏作图法的实验证明

"吴氏作图法"为高分子微球的大小和单体与稳定剂之比之间的关系提供了有效的定量数据分析方法.其基本点是,对于表面活性剂、离子基团或聚合物链所稳定的高分子微球,每个稳定剂所占有的高分子微球表面积(S)为一常数.过去的大量实验已证明,"吴氏作图法"适合应用于高分子纳米粒子.本文根据最近的实验结果,发现"吴氏作图法"同样适用于微米级高分子微球.这为分散聚合中设计和控制高分子微球的尺寸提供了理论依据.     

Surface grafting onto SiC nanoparticles with glycidyl methacrylate in emulsion

To improve the tribological performance of nano‐SiC particles filled epoxy composites, surface modification of the fillers is necessary. By means of soapless emulsion polymerization method, graft polymerization of glycidyl methacrylate (GMA) onto the surface of alkyl nano‐SiC was carried out, resulting in composite particles with SiC core and polymeric shell in which polyglycidyl methacrylate (PGMA) is chemically attached to the nanoparticles by the double bonds introduced during the pretreatment with a coupling agent. By analyzing the reaction mechanism, the emulsion polymerization loci were found to be situated at the SiC surface. Also, the factors affecting the grafting yielding of PGMA on the particles were investigated, including monomer concentration, initiator consumption, reaction temperature, reaction time, etc. Accordingly, an optimum grafting reaction condition was determined. It was shown that the grafted nanoparticles exhibit greatly improved dispersibility in good solvent for the grafting polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3842–3852, 2004     

Heterogeneous polymerization with polyaspartate macromonomer having vinyl pendant groups. I. Synthesis of macromonomer and dispersion copolymerization of styrene

Sodium polyaspartate (PAspNa) derivatives with vinylbenzyl pendant groups (VBA‐PAspNa) were synthesized by reaction of poly(succinimide) (PSI) and vinylbenzylamine (VBA), and hydrolysis by sodium hydroxide (NaOH) solution. VBA‐PAspNa is a macromonomer with multiple vinyl groups in the side chain. Submicron sized polymeric particles were prepared by dispersion copolymerization of styrene with VBA‐PAspNa in a mixture of ethanol and water. Particle diameter decreased with increasing concentration and vinyl group fraction of VBA‐PAspNa. When compared with the particle diameter prepared using PAspNa or benzylamine‐modified PAspNa (BA‐PAspNa) as a dispersion stabilizer without vinyl groups, the particles prepared with VBA‐PAspNa were an order smaller than those prepared with PAspNa or BA‐PAspNa. The particles after refinement show an adequate negative ζ‐potential. From this result, we clarified the presence of PAspNa chains anchored onto the particle surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 762–770, 2009     

乳液聚合的最新进展（下）

乳液聚合的最新进展（下）王群，府寿宽，于同隐（复旦大学高分子科学系，上海，２００４３３）２．５单分散聚合物微球的制备和应用自从５０年代，Ｖａｎｄｅｒｈｏｆｆ等人首次成功地制备单一尺寸的聚合物胶乳以来，对聚合物微球的兴趣日渐增长。乳液聚合是最早用于生产...     

Synthesis of polystyrene nanoparticles “armoured” with nanodimensional graphene oxide sheets by miniemulsion polymerization

Polystyrene particles “armoured” with nanosized graphene oxide (GO) sheets have been prepared by aqueous miniemulsion polymerization of styrene, exploiting the amphiphilic properties of GO in the absence of conventional surfactants. The nanoscale GO sheets were prepared from graphite nanofibers of diameter approximately 100 nm based on a novel procedure, thus effectively ensuring the absence of larger sheets. Polymerization proceeded to high conversion with minor coagulation, with final number‐average particle diameters of approximately 500 nm, but relatively broad particle size distributions. Scanning electron microscopy analysis revealed particles with a textured surface, consistent with the expected morphology. Interestingly, analysis of GO sheets recovered from the polymerization revealed that the GO sheets are partially reduced during the polymerization—approximately 50% of the initial carboxyl groups of the GO were lost, consistent with some loss in colloidal stability at high conversion. The overall approach offers a convenient and attractive synthetic route to novel graphene‐based polymeric nanostructures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Stereoselective Photopolymerization of Tetraphenylporphyrin Derivatives on Ag(110) at the Sub‐Monolayer Level

We explore a photochemical approach to achieve an ordered polymeric structure at the sub‐monolayer level on a metal substrate. In particular, a tetraphenylporphyrin derivative carrying para‐amino‐phenyl functional groups is used to obtain extended and highly ordered molecular wires on Ag(110). Scanning tunneling microscopy and density functional theory calculations reveal that porphyrin building blocks are joined through azo bridges, mainly as cis isomers. The observed highly stereoselective growth is the result of adsorbate/surface interactions, as indicated by X‐ray photoelectron spectroscopy. At variance with previous studies, we tailor the formation of long‐range ordered structures by the separate control of the surface molecular diffusion through sample heating, and of the reaction initiation through light absorption. This previously unreported approach shows that the photo‐induced covalent stabilization of self‐assembled molecular monolayers to obtain highly ordered surface covalent organic frameworks is viable by a careful choice of the precursors and reaction conditions.     

Fluorescence Self‐Reporting Precipitation Polymerization Based on Aggregation‐Induced Emission for Constructing Optical Nanoagents

Precipitation polymerization is becoming increasingly popular in energy, environment and biomedicine. However, its proficient utilization highly relies on the mechanistic understanding of polymerization process. Now, a fluorescence self‐reporting method based on aggregation‐induced emission (AIE) is used to shed light on the mechanism of precipitation polymerization. The nucleation and growth processes during the copolymerization of a vinyl‐modified AIEgen, styrene, and maleic anhydride can be sensitively monitored in real time. The phase‐separation and dynamic hardening processes can be clearly discerned by tracking fluorescence changes. Moreover, polymeric fluorescent particles (PFPs) with uniform and tunable sizes can be obtained in a self‐stabilized manner. These PFPs exhibit biolabeling and photosensitizing abilities and are used as superior optical nanoagents for photo‐controllable immunotherapy, indicative of their great potential in biomedical applications.     

Effect of temperature on styrene emulsion polymerization in the presence of sodium dodecyl sulfate. II

The batch emulsion polymerization kinetics of styrene initiated by a water‐soluble peroxodisulfate at different temperatures in the presence of sodium dodecyl sulfate was investigated. The curves of the polymerization rate versus conversion show two distinct nonstationary‐rate intervals and a shoulder occurring at a high conversion, whereas the stationary‐rate interval is very short. The nonstationary‐state polymerization is discussed in terms of the long‐term particle‐nucleation period, the additional formation of radicals by thermal initiation, the depressed monomer‐droplet degradation, the elimination of charged radicals through aqueous‐phase termination, the relatively narrow particle‐size distribution and constant polydispersity index throughout the reaction, and a mixed mode of continuous particle nucleation. The maximum rate of polymerization (or the number of polymer particles nucleated) is proportional to the rate of initiation to the 0.27 power, which indicates lower nucleation efficiency as compared to classical emulsion polymerization. The low activation energy of polymerization is attributed to the small barrier for the entering radicals. The overall activation energy was controlled by the initiation and propagation steps. The high ratio of the absorption rate of radicals by latex particles to the formation rate of radicals in water can be attributed to the efficient entry of uncharged radicals and the additional formation of radicals by thermally induced initiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1477–1486, 2000     

Semicontinuous seeded cationic emulsion polymerization of styrene: The effects of the concentration and type of cationic surfactant

The objective of this work was to analyze the effects of the concentration and type of cationic surfactant on the kinetic features (instantaneous and overall conversions) and colloidal characteristics [mean particle diameter, particle size distribution (PSD), and surface charge density] in the semicontinuous seeded cationic emulsion polymerization of styrene. 2,2′‐Azobis(N,N′‐dimethyleneisobutyramidine)dihydrochloride was used as an initiator. The surfactants were dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (HDTAB). So that the evolution of some polymeric and colloidal characteristics of the synthesized latices could be followed, the overall and instantaneous conversions were defined and determined gravimetrically. The PSDs and average particle diameters were determined by transmission electron microscopy and photon correlation spectroscopy. The surface charge density was determined by conductimetric titration. The evolution of the instantaneous conversions, the total number of particles, and the PSDs of the different reactions were related to the nucleation, growth, and coagulation processes taking place in the semicontinuous seeded emulsion polymerizations. The PSDs obtained from the reactions carried out with the emulsifier DTAB, at a concentration equal to its critical micelle concentration (cmc) and at a concentration twice its cmc, presented more and smaller particles than those obtained by the addition of HDTAB to the polymerization recipe. At lower emulsifier concentrations equal to half of the cmc, the system had lower colloidal stability with DTAB. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2322–2334, 2003     

Formation of Silica/Poly(p‐dioxanone) Microspheres by Surface‐Initiated Polymerization

A polymeric film of a biodegradable poly(p‐dioxanone) was grown from 490 nm silica particles by monolayer formation via self‐assembly of hydroxy‐terminated triethoxysilane and subsequent surface‐initiated ring‐opening polymerization of p‐dioxanone. The resulting silica/poly(p‐dioxanone) hybrid particles were characterized by means of ¹H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, field‐emission scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy.

     

Synthesis of colloidal superparamagnetic nanocomposites by grafting poly(ϵ‐caprolactone) from the surface of organosilane‐modified maghemite nanoparticles

Superparamagnetic and biodegradable/biocompatible core–corona nanocomposite particles were prepared by ring‐opening polymerization of ?‐caprolactone initiated from the surface of maghemite. As was done in a previous work, an aminosilane coupling agent was chosen as the coinitiator and immobilized at the surface of the maghemite particles to allow the growth of the poly(?‐caprolactone) (PCL) chains from the solid surface. Two different catalytic systems based on aluminum and tin alkoxides were investigated. Whatever the catalyst used, diffuse reflectance Fourier transform spectroscopy brought evidence for polymer anchoring through a covalent bond, whereas thermogravimetric analysis attested to the presence of high amounts of PCL around the maghemite. Magnetization measurements proved that the nanocomposites kept their superparamagnetic properties after coating. The polymer contents obtained by this grafting‐from route were compared with the results obtained by a more classical grafting‐to process. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3221–3231, 2005     

Surface modification of epoxy‐functionalized acrylate colloids

A synthetic route towards surface modified, monodisperse, spherical particles is presented. The precursor particles exhibit epoxy‐functionalities which can be opened afterwards with an appropriate nucleophile. Via this route, dye labeled particles are obtained. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of Latex Particles with Surface Functional Groups and Their Applications for the Fabrication of Porous Materials

In this study, monodisperse latex particles with specific surface functional groups were synthesized by emulsifier-free emulsion polymerization. Amidine or carboxylated polystyrene nanospheres with narrow size distribution were prepared by emulsion polymerization using AIBA (α,α′-zodiisobutyramidine dihydrochloride) as amine-containing initiator or acrylic acid as carboxyl-containing comonomer, respectively. Factors affecting the particle size and distribution were systemically studied by changing the amount of initiator or monomer, the polymerization temperature, and the stirring speed of emulsion polymerization reactor. Monodisperse polymethylmethacrylate beads were also synthesized by soapless emulsion polymerization using methacrylic acid or aminoethylmethacrylate hydrogen hydrochloride as comonomer for the surface functionalization of the particles. As applications of the latex beads, the polymeric particles were adopted as templating materials for the fabrication of macroporous titania film and meso-macroporous silica particles by colloidal templating method.