单分散壳聚糖微囊的制备与表征

对水溶性壳聚糖和对苯二甲醛在水/油界面发生的交联反应进行了研究,考察了水相溶液的pH值和油相中对苯二甲醛的浓度对该界面交联反应的影响.采用微流控技术制备得到了单分散的壳聚糖微囊:首先通过毛细管同轴聚焦流微流控装置制备得到单分散的O/W/O乳液.乳液制备中,以Pluronic F-127作为水相乳化剂,羟乙基纤维素作为水相增稠剂,水溶性壳聚糖溶于中间水相;交联剂对苯二甲醛溶于内部油相;含乳化剂PGPR 90的大豆油作为外部油相.乳液制备完成后,以乳液为模板,对苯二甲醛通过油/水界面扩散进入水层,与壳聚糖的氨基发生交联反应,生成壳聚糖聚合物凝胶网络,从而构成微囊的囊壁.通过光学显微镜分析和扫描电镜观察发现:微囊具备良好的单分散性和球形度以及尺寸均一的内部空腔,微囊的囊壁致密无孔.所得单分散微囊在药物传递等领域具备潜在的应用价值.     

Preparation of monodisperse thermo-sensitive poly(N-isopropylacrylamide) hollow microcapsules

We successfully developed a novel and simple method for preparation of monodisperse thermo-sensitive poly(N-isopropylacrylamide) (PNIPAM) hollow microcapsules at the interface of water-in-oil (W/O) single emulsions at a temperature below the lower critical solution temperature (LCST) of PNIPAM. The prepared PNIPAM microcapsules are featured with hollow structures and thin membranes, high monodispersity, excellent reversible thermo-sensitivity and fast response to environmental temperature. This approach exhibits great interests in preparing monodisperse thermo-sensitive microcapsules for encapsulating bioactive materials or drugs requiring mild encapsulation conditions, because of the flexibility in choosing substances being dissolved in the aqueous phase. The preparation methodology demonstrated in this study provides a unique approach for preparing monodisperse hollow polymeric microcapsules with W/O single emulsions.     

复凝聚法辣椒油树脂微胶囊的制备

以辣椒油树脂为芯材,明胶和阿拉伯胶为壁材,采用复凝聚法制得辣椒油树脂微胶囊.考察了45℃、体系浓度为5%时,pH值、乳化剂的用量、搅拌速度等几个因素对微胶囊形成的影响.     

Preparation of porous crosslinked polymers with different surface morphologies via chemically induced phase separation

A novel and simple method for producing crosslinked polymers with controlled surface morphology is demonstrated in this study. The porous crosslinked polymers were made via stepwise polymerization of a mixture of epoxy resin, D.E.R. 331, and diethylene triamine in diisobutyl ketone (DIBK). Both the surface and bulk morphology of the cured polymers are dependent on the solvent fraction of the reactive solution. When the concentration of DIBK was more than about 30 vol %, chemically induced phase separation (CIPS) occurred during cure at 30 °C, and closed spherical pores, about 4 μm in diameter, appeared in the bulk of the crosslinked polymers, whose diameter increased to about 4.5 and 9 μm when the solvent was increased to 40% and 50%, respectively. The surface morphology of the epoxy networks is different from that of the bulk. Smaller pore size or dense skin was formed via the CIPS process, which can be tailored by covering the reactive solution with different contacting films during cure. The competition between the solvent‐rich and polymer‐rich phase absorbed onto the surface of contacting film could change the surface morphology. Therefore, the porous crosslinked polymers having similar bulk morphology could be prepared with a variety of surface structures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Highly monodisperse crosslinked polymethylmethacrylate microparticles by dispersion polymerization

Highly monodisperse polymethylmethacrylate (PMMA) microparticles crosslinked with carboxylic group-containing urethane acrylates (CUA) were produced by simple dispersion polymerization in methanol solution. In contrast to conventional crosslinkers, the CUA employed as a crosslinker was excellent for maintaining the monodispersity of PMMA microparticles even at moderate crosslinker concentrations (to about 5 wt%). It was believed that the CUA helped form the monomer-swellable surface of primary particles, because of the structurally long tetramethylene oxide groups in the molecule. Carboxylic groups in the molecular backbone resulted in larger primary particles by increasing the solubility of the monomer mixture in the medium. Owing to these larger primary particles, the crosslinked PMMA particles showed lower polymerization rates than the linear ones during particle growth. However, at high CUA concentrations (about 10 wt%), bimodal distributions were observed. This was attributed to the high crosslinking density of the primary particle surfaces. Therefore, monomer diffusion toward the polymer phase was restricted, resulting in more favorable secondary nucleation in the medium. Received: 12 May 1998 Accepted: 19 August 1998     

Highly monodisperse crosslinked polystyrene microparticles by dispersion polymerization

 Highly monodisperse polystyrene microparticles cross-linked with urethane acrylates were produced by dispersion polymerization in ethanol solution in the presence of 2,2′-azobis (isobutyronitrile) initiator, polyvinylpyrrolidone stabilizer, and Aerosol–OT costabilizer. Different from conventional crosslinkers, the urethane acrylates employed as a crosslinker showed an excellent effect on maintaining the monodispersity of polystyrene microparticles even in the moderate crosslinker concentration. This was believed that the urethane acrylate helped forming the monomer-swellable surface of primary particles, because of its structurally long tetramethylene oxide groups in its molecule. However, at high concentration of the urethane acrylate, the rough surface and the coagulum of particles were observed, which was attributed to the seriously decreased solubility of the monomer mixtures in ethanol solution. The solubility of the mixtures of styrene monomer and urethane acrylate in the media had a serious effect on the average particle size and morphology of the final particles. This could be confirmed by the measurement of cloud points and fractional conversions. Received: 21 February 1997 Accepted: 25 May 1998     

Preparation of micron-size monodisperse polymer microspheres having crosslinked structures and vinyl groups

Micron-size monodisperse polymer microspheres having crosslinked structures therein and vinyl groups thereon were prepared by seeded copolymerization of styrene and divinylbenzene with 2,2-azobisisobutyronitrile as initiator in ethanolwater medium in the presence of 2.1-m monodisperse polystyrene seed particles produced by dispersion polymerization. The optimum conditions of the seeded copolymerization for producing the microspheres with good monodispersity and colloidal stability were determined.Part CXXI of the series Studies on Suspension and Emulsion.     

The seed heterophase polymerisation as a method of forming crosslinked monodisperse microspheres

Crosslinked monodisperse microspheres of a diameter 3–10 μm were synthesized by a method of heterophase copolymerization of ethylene glycol dimethacrylate or styrene with divinylbenzene and methacrylic acid on seed nuclei produced by dispersion polymerization of styrene. The diameter and distribution of the microspheres by size, their morphology and surface structure were analyzed by SEM. Factors that control these characteristics of the microspheres in the polymerization process were determined. Swelling ability of the microspheres in toluene and dimethylformamide was evaluated using optical microscopy.     

Preparation of chitosan/alginate microcapsules by high-voltage electrostatic method

Chitosan and sodium alginate have the opposite charges; they can become a gelatin by the electrostatic attraction, High-voltage electrostatic droplet generator method was used to prepare chitosan-sodium alginate microcapsule. Multi-layer chitosan-sodium alginate microcapsule was prepared through layer-by-layer self-assembly, and the morphology was investigated. In addition, the release property of ofloxacin in microcapsules was studied by UV-Vis microscopy under different conditions such as pH value, layer number, etc. The results showed that the prepared microcapsules have a smooth surface with average particle size about 100 μm. The result of controlled release indicated that the prepared microcapsules are pH-independent, and the rate of release decreased when the layer number increases.     

Preparation of crosslinked epoxy microparticles via phase inversion

Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) studies have been performed to reveal a crosslinked epoxy nature of the spherical particles formed in cured epoxy/DDS/PMMA blends. An interesting phase inversion phenomenon was observed in cured DGEBA/DDS/PMMA blends, which occurred at a relatively low thermoplastic composition of 20 phr PMMA in blends. A unique method of preparing crosslinked epoxy spheres of controlled sizes based on cure-induced phase inversion is described in this report. Several factors have been found to affect the geometry of the formed epoxy spheres. The volume fraction of PMMA in the blends strongly dominates the influence. With the increase of PMMA volume fraction in the blends, the spheres not only become smaller in sizes, but also more regular in the spherical geometry due to less impingement. The crosslinking density (DDS phr in the blends) has been found to influence the average sizes of the spheres. The cure temperature has relatively limited effects only when the PMMA loadings in the blends are relatively small. Various potential applications for the epoxy microspheres may be investigated in future studies. © 1996 John Wiley & Sons, Inc.     

Preparation of micron-size monodisperse polymer particles having highly crosslinked structures and vinyl groups by seeded polymerization of divinylbenzene using the dynamic swelling method

Micron-size monodisperse polystyrene/polydivinylbenzene (PS/PDVB) composite particles having highly crosslinked structures and vinyl groups were prepared as follows. First, 1.9 m-size monodisperse PS seed particles produced by dispersion polymerization were dispersed in ethanol/water (70/30, w/w) solution which dissolved divinylbenzene (DVB) monomer, benzoyl peroxide as an initiator and poly(vinyl alcohol) as a stabilizer. The PS seed particles were swollen with a large amount of DVB monomers to 4.3 m in diameter while keeping good monodispersity by the dynamic swelling method, where water was slowly added, continuously, with a micro feeder into the dispersion. And then, the seeded polymerization of the absorbed DVB was carried out.Part CXXXV of the series Studies on Suspension and Emulsion     

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.     

A crosslinked chiral stationary phase for the separation of enantiomers by gas and supercritical fluid chromatography

Crosslinking experiments for the chiral stationary phase OV-225-L-Val-t-butylamide within both fused silica and glass capillary columns have been carried out. Amino acid enantiomers were separated on crosslinked columns by both GC and SFC methods. In SFC, the a values of amino acid enantiomers are independent of the density of the mobile phase, and they are hig her than those obtained by GC for the tested enantiomers with the same column due to the lower column temperature used in SFC.     

Oil core-polymer shell microcapsules prepared by internal phase separation from emulsion droplets. I. Characterization and release rates for microcapsules with polystyrene shells

Microcapsules with an oil core surrounded by a polymeric shell have been prepared by the controlled phase separation of polymer dissolved within the oil droplets of an oil-in-water emulsion. The dispersed oil phase consists of the shell polymer (polystyrene), a good solvent for the polymer (dichloromethane), and a poor solvent for the polymer (typically hexadecane). Removal of the good solvent results in phase separation of the polymer within the oil droplets. If the three interfacial tensions between the core oil, the shell-forming polymer, and the continuous phase are of the required relative magnitudes, a polymer shell forms surrounding the poor solvent. A UV-responsive organic molecule was added to the oil phase, prior to emulsification, to investigate the release of a model active ingredient from the microcapsules. This molecule should be soluble in the organic core but also have some water solubility to provide a driving force for release into the continuous aqueous phase. As the release rate of the active ingredient is a function of the thickness of the polymeric shell, for controlled release applications, it is necessary to control this parameter. For the preparative method described here, the thickness of the shell formed is directly related to the mass of polymer dissolved in the oil phase. The rate of volatile solvent removal influences the porosity of the polymer shell. Rapid evaporation leads to cracks in the shell and a relatively fast release rate of the active ingredient. If a more gentle evaporation method is employed, the porosity of the polymer shell is decreased, resulting in a reduction in release rate. Cross-linking the polymer shell after capsule formation was also found to decrease both the release rate and the yield of the active ingredient. The nature of the oil core also affected the release yield.     

Preparation of micron-size monodisperse polymer particles by seeded polymerization utilizing the dynamic monomer swelling method

Utilizing a new type of monomer swelling method, 6.1 m-size monodisperse polymer particles were prepared by seeded polymerization. 1.8 m-size monodisperse polystyrene (PS) seed particles (1.8 m in size) were prepared by dispersion polymerization in ethanol-water (80/20, v/v) medium in the presence of poly(acrylic acid) as stabilizer with 2,2-azobisisobutyronitrile as initiator. The PS seed dispersion was mixed with ethanol-water (60/40, v/v) solution dissolving styrene (S) monomer, benzoyl peroxide as initiator, and poly(vinyl alcohol) as stabilizer. By slow, continuous, dropwise addition of water with a micro feeder into the mixture, the PS particles absorbed the many S monomers, which were separated from the medium and swelled from 1.8 m to 8.4 m while keeping the monodispersity high. We named this procedure the dynamic swelling method. Then, the seeded polymerization of the absorbed S monomer was carried out in the presence of NaNO₂ as water-solube inhibitor.Part CXXII of the series Studies on Suspension and Emulsion.     

Preparation of hemispherical polymer particles via phase separation induced by microsuspension polymerization

Micrometer-sized, hemispherical polystyrene (PS) particles were successfully prepared by microsuspension polymerization of homogeneous styrene/hexadecane (HD) droplets dispersed in polyoxyethylene nonylphenyl ether (Emulgen 931) aqueous solution, followed by rapid removal of HD from formed PS/HD particles with a “Janus” structure. It was important for the formation of the morphology of Janus particles in thermodynamically stable state to carry out the polymerization slowly. The formation of by-product small PS particles by emulsion polymerization was suppressed by the additions of CuCl₂ as a water-soluble inhibitor and NaCl to decrease the solubility of styrene in the aqueous phase.     

Photochromic characteristics of monodisperse microcapsules containing azobenzene derivative-doped nematic liquid crystals

Highly mono-sized dye-doped liquid crystal (LC) microcapsules were prepared by the solute codiffusion method for application in photoswitchable devices. Azobenzene derivatives, which can be photoisomerized by irradiation with UV (366 nm) and visible (433 nm) light, were used as a photoresponsive dichroic dye. The microcapsules have a spherical shape and a single dye-doped LC domain. After UV light (366 nm) irradiation, PDLC films prepared using the microcapsules attained a photostationary state within 10 min and this state maintained stability. PDLC films made by employing a dichroic dye having electron donor and acceptor groups in the molecule showed especially good photoisomerization properties. The reversible trans-cis -photoisomerization occurred sharply by irradiating alternately with visible and UV light.     

Photochromic characteristics of monodisperse microcapsules containing azobenzene derivative-doped nematic liquid crystals

Highly mono-sized dye-doped liquid crystal (LC) microcapsules were prepared by the solute codiffusion method for application in photoswitchable devices. Azobenzene derivatives, which can be photoisomerized by irradiation with UV (366 nm) and visible (433 nm) light, were used as a photoresponsive dichroic dye. The microcapsules have a spherical shape and a single dye-doped LC domain. After UV light (366 nm) irradiation, PDLC films prepared using the microcapsules attained a photostationary state within 10 min and this state maintained stability. PDLC films made by employing a dichroic dye having electron donor and acceptor groups in the molecule showed especially good photoisomerization properties. The reversible trans-cis -photoisomerization occurred sharply by irradiating alternately with visible and UV light.     

Preparation of monodisperse polystyrene latices

Summary A series of monodisperse polystyrene latices was prepared by using the direct and the seeding emulsion polymerization methods. The recipes for their preparation are given in full detail. Best results were obtained when using Aerosol MA (a surfactant of the sulfosuccinate series) as the emulsifier. The particle size distributions were evaluated from electron microscopic data. The average size of latex particles ranged from 200 to 950 m. The polydispersity ratios being very near unity and modal frequencies about 95% indicate a very high monodispersity of latex preparations. The reproducibility of the particle size distribution parameters was remarkably good. Significant deviation from theSmith-Ewart mechanism was found. A possible mechanism of the emulsifier action in the formation of monodisperse latices is postulated.

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Zusammenfassung Es wurde eine Serie von monodispersen Polystyrollatices dargestellt. Die experimentellen Bedingungen, unter welchen monodisperse Latices entstehen, wurden untersucht. Die Vorschriften sind genau angegeben. Mit Aerosol MA (einem oberflächenaktiven Mittel der Sulfosuccinatserie) als Emulgator wurden die besten Ergebnisse erhalten. Mittels Elektronenmikroskopie wurde die Verteilung der Teilchengrößen ermittelt. Die durchschnittliche Größe der Latexteilchen lag zwischen 200 und 950 m. Die Polydispersitätsquotienten lagen in unmittelbarer Nähe von 1, und die modalen Frequenzen um 95% indizierten eine sehr hohe Monodispersität der Latexproben. Die Reproduzibilität der Teilchengröße-Verteilung-Parameter war besonders ausgeprägt. Es wurde eine Abweichung vomSmith-Ewart-Mechanismus beobachtet. Der mögliche Mechanismus der Emulgatorwirkung bei Entstehung der monodispersen Latices wurde diskutiert.

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With 7 figures and 8 tables