Pore size modification of macroporous crosslinked poly(dicyclopentadiene)

This article describes the pore size modification and in situ surface functionalization of macroporous crosslinked poly(dicyclopentadiene), produced by chemically induced phase separation, with norbornene‐functionalized poly(ethylene glycol) telechelic oligomers. The microstructure of the open porosity materials produced with this technique consisted of agglomerated particles. The incorporation of these telechelic oligomers allowed a substantial decrease in the pore size and a related increase in the internal surface area. These functionalized oligomers acted as stabilizers around the primary particles produced by phase separation and blocked their growth so that the materials resulting from the agglomeration of these smaller particles showed finer microstructures. The resulting porous materials were characterized by scanning electron microscopy, density measurements, nitrogen adsorption, and mercury porosimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2036–2046, 2003     

Selective pervaporation of water through a nonselective microporous titania membrane by a dynamically induced molecular sieving mechanism

Pervaporation experiments were performed on microporous titania membranes using several binary liquids containing 2-20 wt % water. The membrane was nonselective in the separation of water from alcohols and p-dioxane but showed a remarkably high selectivity in the separation of water from ethylene glycol/water mixtures with < or =15 mol % water. The absence of selectivity under most conditions is explained by the large pore size (0.9 nm) of microporous titania. The high selectivity for water in the separation from ethylene glycol can be explained by the formation of a hydrogen-bonded network of ethylene glycol in the micropores, which blocks transport of ethylene glycol, while water can still permeate through. These networks are disrupted by water at higher concentrations, leading to full loss of membrane selectivity.     

Use of hydrophilic hydroxypropyl methacrylate/ethylene glycol methacrylate packing material in size-exclusion chromatography

Spherical particles of hydroxypropyl methacrylate/ethylene glycol methacrylate copolymer were synthesized in-house for use in size-exclusion chromatography. The porous hydrophilic material was packed in glass and stainless steel columns to evaluate their chromatographic performance. The support particles were small (approximately 20 A), and the average pore size was in the low range of mesopores (approximately 100 A). The packed columns were calibrated by using polysaccharide dextrans, showing a good range of separation for molecular weights between 10000 and 600000 daltons. The packing material appears to separate the large molecules through the size-exclusion mechanism. Polysaccharides and polypeptides dissolved in adequate mobile phases were injected into the packed column. The separation of the macromolecules was consistent with the size-exclusion mechanism. Application of the packing material to the separation of small molecules (alkyl alcohols) was also investigated.     

Capillary zone electrophoresis for the characterization of latex particles

Capillary zone electrophoresis (CZE) was applied to the separation of acrylic styrene copolymer emulsion particles. Fast separations could be performed on samples containing chemically identical latex particles of different size, as well as on samples with particles of the same size but differing in chemical composition. The developed method was also used for the analysis of water soluble fractions of urethane dispersions. Additionally, the physical interaction between different particles (e.g., acrylic and urethane particles) could be studied using this method. The separation mechanism is based on the zeta potential of the particles and the relaxation effect under the applied analytical conditions.     

Atomic Force Microscopic Studies of Porous TiO2 Thin Films Prepared by the Sol-Gel Method

Porous titanium dioxide thin films were prepared from alkoxide solutions with and without polyethylene glycol (PEG) by the sol-gel method on soda-lime glass. The effects of PEG addition to the precursor solution on the microstructure and roughness of the resultant thin films were investigated by atomic force microscopy (AFM). It was found that TiO₂ films prepared from the precursor solution without PEG had granular microstructure and flat texture, and was composed of about 100 nm spherical particles. With an increase in the times of coating cycles, the roughness of films decreased and the size of TiO₂ particles increased. On the other hand, the larger the amount and molecular weight of the added PEG in precursor solutions, the larger the diameter and the depth of pores in the resultant films on the decomposition of PEG during heat-treatment. The surface of the films was also rougher, and fewer pores were produced during heat-treatment. The mechanism of porous structure formation in the TiO₂ films was explained using the principle of spinodal phase separation.     

Steric stabilization of thermally responsive N-isopropylacrylamide particles by poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) was used as a steric stabilizer for the dispersion polymerization of cross-linked poly(N-isopropylacrylamide) (PNIPAM) in water. A series of reactions were carried out using PVA of varying molecular weight and degree of hydrolysis. Under appropriate conditions, PNIPAM particles of uniform and controllable size were produced using PVA as the stabilizer. The colloidal stability was investigated by measuring changes in particle size with temperature in aqueous suspensions of varying ionic strength. For comparison, parallel colloidal stability measurements were conducted on PNIPAM particles synthesized with low-molecular-weight ionic surfactants. PVA provides colloidal stability over a wide range of temperature and ionic strength, whereas particles produced with ionic surfactants flocculate in moderate ionic strength solutions upon collapse of the hydrogel as the temperature is increased. Experimental results and theoretical consideration indicate that sterically stabilized PNIPAM particles resulted from the grafting of PVA to the PNIPAM particle surface. The enhanced colloidal stability afforded by PVA allows the temperature-responsive PNIPAM particles to be used under physiological conditions where electrostatic stability is ineffective.     

Production of micron-sized polystyrene particles containing PEG near the particles surface

Polystyrene (PS) particles in the size range of 1-7 µm, containing poly(ethylene glycol) or PEG on the particles surface, were prepared by multi-step seeded polymerizations. Micron-sized PS particles were first prepared by dispersion polymerization using 2,2'-azobisisobutyronitrile as initiator and polyvinyl pyrrolidone as stabilizer. Conventional swelling method was then used to increase the size of the PS particles with a large amount of styrene in presence of oil soluble initiator, benzoyl peroxide. In the final step, the PS particles have been used to carry out seeded polymerization with small amount of styrene in presence of poly(ethylene glycol)-azo or PEGA initiator with average molecular weights of the PEG chains of 200 and 3000 g mol^-1 , respectively. The average size, size distribution, and surface morphology indicate that seeded polymerization in the final step with small amount of styrene in presence of PEGA is the best way to produce monodisperse polystyrene particles containing PEG near the particles surface.     

In-vivo fluorescence imaging technique using colloid solution of multiple quantum dots/silica/poly(ethylene glycol) nanoparticles

This paper describes a method for producing silica particles containing multiple quantum dots (QD/SiO₂), a method for surface-modifying the particles with poly(ethylene glycol) (QD/SiO₂/PEG), and an in vivo fluorescence imaging technique using colloid solution of the QD/SiO₂/PEG particles. The QDs used were ZnS-coated CdSe_xTe_1?x nanoparticles surface-modified with carboxyl groups, and had an average size of 10.3 ± 2.1 nm. The QD/SiO₂ particles were fabricated by performing sol–gel reaction of tetraethyl orthosilicate using NaOH as a catalyst in the presence of the QDs. The produced particles formed core–shell structure composed of multiple QDs and silica shell, and had an average size of 50.2 ± 17.9 nm. Surface-modification of the QD/SiO₂ particles with PEG, or PEGylation of the particle surface, was performed by using methoxy polyethylene glycol silane. Fluorescence of QD colloid solution was not quenched even through the silica-coating and the PEGylation. Tissues of a mouse could be imaged by injecting the concentrated colloid solution into it and measuring fluorescence intensity emitted from the tissues.     

Use of Natural Monomer in the Synthesis of Nano- and Microparticles of Polyurethane by Suspension-Polyaddition Technique

Summary: Polyurethane nano- and microparticles were synthesized by suspension-polyaddition technique, using aqueous polymerization medium. Castor oil, a vegetable triglyceride possessing hydroxyl groups was used as natural polyol and methylene diphenyl diisocyanate (MDI) as isocyanate. The levofloxacin, an antibacterial drug was used as model drug to measure the particles encapsulation efficiency. The effect of the addition of a second polyol, the poly(ethylene glycol) (PEG), and the stirring rate on the mean diameter and morphology of particles was also investigated. The poly(ethylene glycol) has an important effect in the reduction of particles size and their porosity. On the other hand, the poly(ethylene glycol) reduced the yield of encapsulation from 70% for the formulation without PEG to 20% for formulations with PEG. FTIR analysis confirmed the polyurethane formation. Dynamic light scattering study, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to determine the nanoparticles size and shape. Spectrofluorimetric analysis was used to detect the levofloxacin.     

Silica particles encapsulated poly(styrene-divinylbenzene) monolithic stationary phases for micro-high performance liquid chromatography

In the paper we demonstrate a new approach for the preparation and application of continuous silica bed columns that involve encapsulation (entrapment) of functionalized silica microparticles, which can be used as packing material in micro high performance liquid chromatography (micro-HPLC) and capillary electrochromatography (CEC). Like traditional packed columns, these capillaries possess characterized silica particles that offer high phase ratio and narrow pore size distribution leading to high retention and separation efficiency, respectively. More importantly, immobilization of the microparticles stabilizes the separation bed and eliminates the need for retaining frits. The developed capillary columns were fabricated in exactly the same way as a packed capillary column (slurry packing) but with an additional entrapment step. This immobilization of the packed bed was achieved by in situ polymerization of styrene and divinylbenzene in presence of decanol as a porogen and azobisisobutyronitrile as thermal initiator. Silica particles with different particle sizes and pore sizes ranging from 60 to 4000 A were studied. In addition different modified silica was used, including C-18 reversed phase, anion exchange and chiral stationary phases. Efficient separation of polyphenolic compounds, peptides, proteins and even DNA mutation were achieved using the developed technique depending on the properties of the silica particles used (particles pore size). For example, using 3 microm ProntoSIL C-18 particles with 300 A pore size, separation efficiencies in the range of 120,000-200,000 plates/m were obtained for protein separation, in a 6 cm x 200 microm i.d. capillary column. Using encapsulated silica C-18 with 1000 A pore size, separation of DNA homo and hetero duplexes were achieved under denaturing HPLC conditions for mutation detection. In addition, nucleotides were separated using anion exchange material encapsulated with poly(styrene-divinylbenzene) (PS/DVB), which indicated that the chromatographic properties of the silica packing material were still active after polymerization. The prepared capillary columns were found to be stable and could easily be operated continuously up to a pressure of 350 bar without column damage and capillary can be cut to any desired length.     

Size-exclusion separation of proteins using a biocompatible polymeric monolithic capillary column with mesoporosity

Biocompatible poly(ethylene glycol methyl ether acrylate-co-polyethylene glycol diacrylate) monoliths were prepared for size exclusion chromatography (SEC) of proteins in the capillary format using Brij 58P in a mixture of hexanes and dodecanol as porogens. The monolithic columns provided size separation of four proteins in 20 mM sodium phosphate buffer (pH 7.0) containing 0.15 M NaCl, and there was a linear relationship between the retention times and the logarithmic values of the molecular weights. Compared to SEC monoliths previously synthesized using a triblock copolymer of polyethylene oxide and polypropylene oxide, an increase in mesoporosity was confirmed by inverse size exclusion chromatography. As a result, improved protein separation in the high molecular weight range and reduced column back-pressure were observed.     

重力场流分离系统用于聚苯乙烯颗粒的分离条件优化

重力场流分离是最简单的场流分离(gravitational flow-field fractionation,GrFFF)技术,常用于分离粒径几微米到几十微米的颗粒及生物样品。利用自组装加工的重力场流分离仪器分离3种不同粒径(3、6、20μm)的聚苯乙烯(PS)颗粒。自制了一种混合表面活性剂,并与商品化的表面活性剂FL-70进行了比较。通过均匀设计优化流速、混合表面活性剂中聚乙二醇辛基苯基醚(Triton X-100)的质量分数、载液黏度、停流时间等分离条件,以分离度(Rs)和保留比(R)为评价指标,发现FL-70的分离效能略优于自制的混合表面活性剂,可实现3种PS颗粒的完全分离(Rs1为1.771,Rs2为2.074)。结果表明该系统具有良好的分离性能。     

Silica-based diffusion probes for use in FRAP and NMR-diffusometry

Development of multi-purpose probes for mass transport measurements is of importance to gain knowledge in diffusional behaviour in heterogeneous structures such as food, hygiene or pharamceuticals. By combining different techniques, such as Fluorescence Recovery After Photobleaching (FRAP) and Nuclear Magnetic Resonance Diffusometry (NMR-d), information of both local and global diffusion can be collected and used to gain insights on for example material heterogeneities and probe-material interactions. To obtain a FRAP-responsive probe, fluorescent silica particles were produced using fluorescent preconjugates added in a modified Stöber process. A NMR-d responsive moiety was introduced by derivatizing the fluorescent silica particles with polyethylene glycol. The particle size distributions were determined by dynamic light scattering and transmission electron microscopy and these measurements were compared to value extrapolated from diffusion measurements using FRAP and NMR-d. The good agreement between the FRAP and NMR-d measurements demonstrates the potential of multi-purpose probes for future applications concerning mass transport at local and global scale simultaneously.     

Comparison of newly developed hydroxyl-functionalized monodisperse HILIC columns new HILIC column

In this study, new hydroxyl-functionalized monodisperse polymeric hydrophilic interaction chromatography (HILIC) columns were developed using different derivatization agents. In addition, the influences of derivatization temperature of the best agent and polymer composition on the separation were investigated under HILIC conditions. Monodisperse–porous hydrophilic particles were synthesized by the seeded polymerization method using 3-chloro-2-hydroxypropile methacrylate (HPMA-CL) and ethylene glycol dimethacrylate (EGDMA) monomers. The chloropropyl terminal ends of the poly(HPMA-Cl-co-EGDMA) particles were derivatized with amine group of ethanolamine (EA), diethanolamine, and triethanolamine (TEA) at 80°C through nucleophilic reaction. The performance of synthesized particles was evaluated with the amount of ligand on the particle surfaces, column backpressure, and separation power under HILIC condition. TEA was found to be the best derivatization agent for the separation of toluene, acrylamide, thymine, adenine, and cytosine in respect to resolution factors (>1.5 for all analytes) and theoretical plate numbers (64.562?N/m for acylamide). Upon determination of the best ligand, then the effect of different derivatization temperatures and polymer composition on TEA performance was investigated. Of all the tested polymer compositions, the chromatographic performance of TEA-M-80 (the derivatization of TEA at 80°C together with M polymer composition) was found to be the best.     

Effect of the synthesis conditions on the size of magnetite nanoparticles produced by high-temperature reductive hydrolysis

A study was made into the effect of the conditions (synthesis temperature, water content, iron salt(III) concentration, and nature of precipitant) of the synthesis of magnetite nanoparticles by high-temperature reductive hydrolysis of iron(III) salts in an ethylene glycol medium on their size and morphology. It was shown that is basically possible to carry out the direct synthesis of spherical particles with an average size of 55–170 nm while varying synthesis conditions. The obtained particles were characterized by X-ray powder diffraction analysis, and their magnetic properties were explored. The synthesized particles are ferrimagnets. The magnetic moments, numbers, and sizes of domains in magnetite particles of various sizes were found.     

基于硅胶整体材料研磨颗粒的多功能聚乙二醇键合固定相的制备及其在高效液相色谱多模式分离中的应用

研究通过对溶胶-凝胶法制备的硅胶整体材料进行研磨、浮选、假晶相转换和水热处理，最终获得了粒径为2~5 μm、孔径为20~60 nm的硅胶颗粒。利用部分含氟的阴离子表面活性剂Capstone FS-66和常用的阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）组成的双胶束模板体系对硅胶基质进行假晶相转换处理；再采用碳酸钠溶液水热处理的方式，进一步扩大孔径。用扫描电镜（SEM）和N₂吸附-解吸等温线测量对扩孔处理前后的硅胶整体材料研磨颗粒进行表征，结果清楚地显示了处理前后的形貌变化和差异。随后将含有长链聚乙二醇（PEG）的硅烷键合到扩孔后的硅胶颗粒表面，分别利用元素分析、红外光谱以及热重分析对固定相进行表征，并对固定相进行色谱性能评价。对键合固定相的元素分析和热重分析数据进行分析表明，硅胶表面键合PEG的含量约为8%。研究揭示了利用假晶相转换法与碳酸钠溶液水热处理和长链PEG硅烷修饰的硅胶整体材料颗粒在尺寸排阻色谱分离蛋白质方面的良好分离效果。同时进一步的高效液相色谱评价结果表明，该键合固定相还可用于疏水作用色谱模式分离核糖核酸酶A和溶菌酶，以及可用于亲水作用色谱模式分离吡啶甲酸、左旋多巴、三聚氰胺和邻苯二酚等极性比较强的化合物。研究显示了PEG键合固定相具有多功能性，及其在多模式高效液相色谱分离中的应用潜力。     

Improved liquid chromatographic separation of different proteins by designing functional surfaces of cattle bone-originated apatite

Spherical particles of cattle bone-originated hydroxyapatite (r-HAp) were prepared by dissolution-precipitation, spray-drying using a two fluid-nozzle apparatus, and subsequent heat treatment. The product had effective pore structures for liquid chromatographic separation of albumin, myoglobin, ribonuclease, lysozyme and cytochrome c. The activated surfaces of the r-HAp particles were easily prepared with desired proportions of P- and C-sites and appropriate acid-basic strength for selective protein adsorption by optimizing the synthesis conditions. Liquid chromatography columns packed with the particles exhibited high resolution and durability in protein separation, reflecting stable distribution of pore size.     

Separation of cationic polymer particles and characterization of avidin-immobilized particles by capillary electrophoresis

Cationic polymer microparticles have received much attention especially in the field of biotechnology, such that their analysis and separation have become important. So far, the separation of cationic polymer particles with different size using CE has not been achieved and the cationic particles migrated as if they are negatively charged, probably due to electrostatic interaction between capillary wall and cationic polymer particles. In this paper, the separation of cationic polymer microparticles by CE was investigated in detail. The separation of cationic particles with different size was achieved in CE by taking into account the interaction between sample particles and the inner surface of capillaries. By employing a poly(vinyl alcohol)-coated capillary, a better size separation of amine-modified latex particles was obtained compared to a Polybrene-coated capillary. It was elucidated that the composition, concentration, and pH of the background solution were also important factors in the separation of colloidal particles to avoid the surface adsorption and the characteristic aggregation of polymer particles. Furthermore, the CE analysis was applied to the characterization of cationic protein-immobilized particles.     

A novel method for encapsulation of a liquid crystal in monodisperse micron-sized polymer particles

Liquid crystals (LCs) encapsulated in monodisperse micron-sized polymer particles were prepared to control the size and size distribution of LC droplets in polymer-dispersed LCs. The poly(methyl methacrylate) (PMMA) seed particles were swollen with the mixture of liquid crystal, monomers (methyl methacrylate and styrene) and initiator by using a diffusion-controlled swelling method. A single LC domain was produced by the phase separation between PMMA and LC through polymerization. The optical microscopy and scanning electron microscopy showed that the particles are highly monodisperse with core–shell structure. Moreover, monodisperse LC core domains were confirmed from polarized optical microscope observations. The final particle morphology was influenced by the cross-linking of the seed particle. When linear PMMA particles, which are not cross-linked, were used as a seed, the microcapsules were distorted after annealing for a few days; however, in the case of cross-linked PMMA particles, the core–shell structure was sustained stably after annealing. Received: 22 November 2000 Accepted: 12 March 2001     

Formulation design of taste-masked particles, including famotidine, for an oral fast-disintegrating dosage form

In this study, the taste-masking of famotidine, which could apply to any fast-disintegrating tablet, was investigated using the spray-dry method. The target characteristics of taste-masked particles were set as follows: the dissolution rate is not to be more than 30% at 1 min and not less than 85% at 15 min, and the particle size is not to be more than 150 microm in diameter to avoid a gritty feeling in the mouth. The target dissolution profiles of spray-dried particles consisting of Aquacoat ECD30 and Eudragit NE30D or triacetin was accomplished by the screening of formulas and the appropriate lab-scale manufacturing conditions. Lab-scale testing produced taste-masked particles that met the formulation targets. On the pilot scale, spray-dried particles with attributes, such as dissolution rate and particle size, of the same quality were produced, and reproducibility was also confirmed. This confirmed that the spray-dry method produced the most appropriate taste-masked particles for fast-disintegrating dosage forms.