1. INTRODUCTION Hollow particles have been produced usually by the alkali swelling procedure (ASP), dynamic swelling method (DSM), and water-in-oil-in-water (w/o/w) emulsion polymerization [1]. Because particles can reserve various chemicals in their hollow, they could be used as reservoir and release material [2]. But almost all the work was to make hollow spheres. One kind of hollow particles, the bowl-shaped polymer particles have some advantages because of their special shape [3~6]… 相似文献
Poly(styrene-glycidyl methacrylate) particles having bowl-shaped hollow structures were synthesized by swollen seed emulsion polymerization. The PS emulsion synthesized through soap-free emulsion polymeri:ation was swollen by toluene, and then the mixture of second monomers was added under polymerization condition So a thin shell of poly(styrene-glycidyl methacrylate) cross-linked by triethylene glycol diacrylate was formed around the swollen PS particle. The bowl-shaped particles were obtained after the collapsing of the thin shell when the toluene emanated from the particles, but the shapes were effected by the degrees of cross-linking. The shape of the particles was observed by SEM. The release behavior of solvent from the particles was examined by TG 相似文献
Recently, the authors reported that micron-sized monodispersed cross-linked polymer particles having a single hollow in the
inside were produced by seeded polymerization for the dispersion of (toluene/divinylbenzene)-swollen polystyrene (PS) particles
prepared utilizing the dynamic swelling method which the authors had proposed. In this article, the particles at various conversions
of the seeded polymerization were observed with an optical microscope in detail. From the obtained results, the formation
mechanism of the hollow structure is suggested as follows. As seeded polymerization proceeds, poly-divinylbenzene (PDVB) molecules
precipitated in the swollen particle are trapped near the interface and gradually pile at the inner surface, which results
in a cross-linked PDVB shell. PS which dissolves in the swollen particles is repelled gradually to the inside. After the completion
of the polymerization, toluene in the hollow evaporates by drying, and PS clings to the inner wall of the shell uniformly.
Received: 14 February 1997 Accepted: 16 April 1997 相似文献
Monodisperse polar gradient particles were synthesized via a three‐step emulsion polymerization using poly(butyl acrylate‐methyl methacrylate‐methacrylic acid‐ethylene glycol dimethacrylate) (P(BA‐MMA‐MAA‐EGDMA)) as core, poly(methyl methacrylate‐methacrylic acid‐styrene) (P(St‐MMA‐MAA)) as interlayer and polystyrene (PSt) as shell. The particle growth and encapsulation in each emulsion polymerization step were followed by transmission electron microscopy (TEM), dynamic light scattering (DLS) and conductometric titration. Results indicated that the feeding mode and the interlayer were essential to prepare the polar gradient latex particles with hydrophilic core and hydrophobic shell. The morphologies of the two‐layer core/interlayer and three‐layer core/interlayer/shell particles were observed in TEM micrographs, and the sequential encapsulations of the carboxyl‐containing core and the core/interlayer particles were confirmed by an increase in the particle size as well as an increase in the buried carboxyl percentage. 相似文献
Monomeric emulsifiers with different copolymerization reactivities were used as stabilizers in emulsion polymerization of styrene initiated by 2,2′ azobisisobutyronitrile (AIBN). A significant change in emulsifier function was observed between equal micellar concentrations of surface-active sodium sulfopropyl alkyl maleates and the corresponding sodium sulfopropyl dodecyl fumarate. In the presence of less reactive maleates, copolymerization mainly occurs in the interface of the monomer swollen particles, while copolymerization with the fumarate in the first period of emulsion polymerization leads to polyelectrolyte formation in the water phase. 相似文献
4 μm-sized monodispersed cross-linked polymer particles having hollow structure were produced as follows. First, 1.7 μm-sized monodispersed polystyrene (PS) seed particles produced by dispersion polymerization were dispersed in ethanol/water (7/3, w/w) solution in which divinylbenzene (DVB), benzoyl peroxide (BPO), poly(vinyl alcohol), and toluene was dissolved. The PS seed particles were swollen with DVB, toluene and BPO maintaining high monodispersity throughout the dynamic swelling process where water was slowly added continuously. And then, the seeded polymerization of the (toluene/DVB)-swollen PS particles was carried out. 相似文献
Stable core‐shell latex was synthesized by semicontinuous seeded emulsion polymerization with core monomers consisting of styrene (St), butyl acrylate (BA), and shell monomers consisting of methyl methacrylate (MMA), eutyl acrylate (EA), and methacrylic acid (MAA). The effects of compound emulsifier amount, mass ratio of anionic/nonionic emulsifier, and initiator amount on latex performance were investigated. By particle size analysis and transmission electron microscopy (TEM) observation, results suggest that final latex particles have clearly core shell structures. 相似文献
PDMAAm microspheres have been obtained by inverse suspension, inverse emulsion, and dispersion polymerization. Conventional inverse suspension polymerization in toluene/trichloroethene is modified by the use of ultrasound. The resulting hydrogel microspheres are examined by dynamic light scattering and scanning electron microscopy to afford the morphology, dispersity, and size of the microspheres. Inverse suspension polymerization yields 100‐µm particles, while those obtained by inverse emulsion polymerization are 0.13–1 µm in diameter. While the inverse techniques produce particles of broad size distribution, monodisperse microspheres are obtained by the Kraton G 1650‐stabilized dispersion polymerization of DMAAm in a toluene/heptane medium. The particle size and polydispersity could be controlled by the addition of water into the dispersed phase, and by varying the cellulose acetate butyrate or Kraton G 1650 concentration and the toluene/trichloroethene or toluene/heptane ratio.
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. 相似文献
Summary : Monodisperse P(BA-MMA-MAA-EGDMA)/P(St-MAA-DVB) core/shell latex particles were first synthesized by a four-step emulsion polymerization, and a new kind of latex particles with “bowl-like” morphology were obtained by post-treating the resultant core/shell particles under alkali condition. Results indicated that the feeding rates of the monomer mixture and initiator aqueous solution were the key parameters to obtain monodisperse core/shell latex particles in the emulsion polymerization process, and the latex particles with “bowl-like” morphology could be generated only when the treatment temperature was equal or higher than 70 °C. 相似文献
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. 相似文献