Shirasu Porous Glass Emulsification Research Articles

Synthesis of poly(N-isopropylacrylamide)/poly(ethyl-2-cyanoacrylate) composite hollow particles

Recently, synthesis of hollow particles has received great interest due to their potential applications in controlled drug delivery, cosmetics, paint, electronic inks, heterogeneous catalytic or enzymatic reactions. In most cases, however, the syntheses include sacrificial templates and subsequent delicate removal steps, and which leads to detrimental effects such as, uses of toxic solvents, high impurities, and collapsed shell morphology. In order to resolve such drawbacks, several techniques have been developed. Among the techniques, the Shirasu Porous Glass (SPG) membrane emulsification seems not new but promising due to versatility in material selection, morphology control, energy cost, and mass productions. Herein, we aimed to fabricate monodisperse composite hollow particles of poly(N-isopropylacrylamide)/poly(ethyl-2cyanoacrylate) (namely, poly(NIPAAm)/ poly(E2CA)) by using SPG emulsification, ionic, and photo-polymerization techniques. Poly(NIPAAm) is well known biocompatible polymer exhibiting volume phase transition temperature (VPTT) near lower critical solution temperature (LCST) around 35 C. Poly(E2CA), known as one of ‘instant’ adhesive family, is both biocompatible and biodegradable. In this work, we found that shell morphology of the composite hollow particles was changed from semi-interpenetrating network (semi-IPN) to double shell structure depending on the mass ratio of NIPAAm and E2CA monomers.

The effects of acrylate monomers and polystyrene addition on the morphology of DOP‐plasticized styrene–acrylate polymer particles prepared by SPG emulsification and suspension polymerization

AbstractFairly uniform copolymer particles of methyl acrylate (MA), butyl acrylate (BA), or butyl methacrylate (BMA) were synthesized via Shirasu porous glass (SPG) membrane and followed by suspension polymerization. After a single‐step SPG emulsification, the emulsion composed mainly of the monomers. Hydrophobic additives of dioctyl phthalate (DOP), polystyrene molecules, and an oil‐soluble initiator, suspended in an aqueous phase containing poly(vinyl alcohol) (PVA) stabilizer and sodium nitrite inhibitor (NaNO2), were subsequently subjected to suspension polymerization. Two‐phase copolymers with a soft phase and a hard phase were obtained. The composite particles of poly(St‐co‐MA)/PSt were prepared by varying the St/PSt ratios or the DOP amount. The addition of PSt induced a high viscosity at the dispersion phase. The molecular weight slightly increased with increasing St/PSt concentration. The multiple‐phase separation of the St‐rich phase and PMA domains, observed by transmission electron microscopy, was caused by composition drift because the MA reactivity ratio is greater than that of St. The addition of DOP revealed the greater compatibility between the hard‐St and soft‐MA moieties than that without DOP. The phase morphologies of poly(St‐co‐MA), poly(St‐co‐BMA), and their composites with PSt were revealed under the influence of DOP. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1195–1206, 2006

Synthesis and property behavior of dioctyl phthalate plasticized styrene–acrylate particles by Shirasu porous glass emulsification and subsequent suspension copolymerization

AbstractTwo‐phase model styrene–acrylate copolymers were synthesized with a soft phase consisting of methyl acrylate, butyl acrylate, and butyl methacrylate. Besides the styrenic copolymers, copolymers containing a hard phase of methyl methacylate and methyl acrylate were also synthesized. Comonomer droplets with a narrow size distribution and fair uniformity were prepared using an SPG (Shirasu porous glass) membrane having pore size of 0.90 μm. After the single‐step SPG emulsion, the emulsion droplets were composed mainly of monomers, hydrophobic additives, and an oil‐soluble initiator, suspended in the aqueous phase containing a stabilizer and inhibitor. These were then transferred to a reactor, and subsequent suspension polymerization was carried out. Uniform copolymer particles with a mean diameter ranging from 3 to 7 μm, depending on the recipe, with a narrow particle size distribution and a coefficient of variation of about 10% were achieved. Based on the glass‐transition temperatures, as measured by differential scanning calorimetry, the resulting copolymer particles containing a soft phase of acrylate were better compatibilized with a hard phase of methyl methacrylate than with styrene with dioctyl phthalate (DOP) addition. Glass‐transition temperatures of poly(MMA‐co‐MA) particles were strongly affected by the composition drift in the copolymer caused by their substantial difference in reactivity ratios. Incorporation of DOP in the copolymer particles does not significantly affect the glass‐transition temperature of MMA‐ or MA‐containing copolymer particles, but it does affect the St‐containing copolymer and particle morphology of the copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3037–3050, 2003

Microencapsulation of oil with poly(styrene- N,N-dimethylaminoethyl methacrylate) by SPG emulsification technique: Effects of conversion and composition of oil phase

Microcapsules with narrow size distribution, in which hexadecane (HD) was used as a oily core and poly(styrene-co- N,N-dimethylaminoethyl methacrylate) [P(St-DMAEMA)] as a wall, were prepared by a Shirasu porous glass (SPG) emulsification technique and a subsequent suspension polymerization process. That is, a mixture of St monomer, DMAEMA monomer, HD, and N,N′-azobis(2,4-dimethylvaleronitrile) initiator was permeated through the uniform pores of an SPG membrane into a continuous phase containing a poly(vinylpyrrolidone), sodium lauryl sulfate, and sodium nitrite water-soluble inhibitor by applying a pressure, to form uniform droplets. Then, the droplets were polymerized at 70 °C. It was found that HD was encapsulated completely only when conversion was quite high, irrespective of whether a DMAEMA hydrophilic monomer was incorporated into the polymer. As the amount of HD increased, HD was more easily encapsulated by the polymer. In order to clarify the reason for such unique behavior, a simulation was carried out, taking the St monomer partition in the HD phase and PSt wall phase into the consideration. It was found that the main reason HD could not be encapsulated completely by PSt when conversion was lower was that the interfacial tension of the HD phase with water and the PSt phase with water got closer. As a result, both HD and PSt can come in contact with the water phase.

Synthesis and characterization of polyurethaneurea-vinyl polymer (PUU-VP) uniform hybrid microspheres by SPG emulsification technique and subsequent suspension polymerization

Uniform polyurethaneurea–vinyl polymer (PUU–VP) hybrid microspheres of about 20 μm were prepared by a Shirasu porous glass (SPG) membrane emulsification technique and a subsequent radical suspension polymerization process, that is, a mixture of a 40 wt % urethane prepolymer (UP) solution of xylene and a vinyl monomer (VP) containing an initiator was permeated through the uniform pores of the SPG membrane into a continuous phase containing a stabilizer to form uniform droplets. Then, the droplets were allowed to stand for chain extension at room temperature with di- or triamines for 2 h in the absence or presence of ethyl acetate (EA), followed by suspension polymerization at 70°C for 24 h. The effect of the type and the amount of the monomer composition, crosslinker, and chain extender on the monomer conversion, particle morphology, and stability of the dispersion was investigated. A strong relationship was found between the compatibility of PUU with VP and the stability of the dispersion. The monomer conversion increased and the stability of the dispersion was improved as the amount of the crosslinker was increased. Solid and spherical PUU–VA hybrid particles with a smooth surface and a higher destructive strength were obtained when a trifunctional crosslinker and a chain extender were used together. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 163–178, 2003

Morphology development of 10‐μm scale polymer particles prepared by SPG emulsification and suspension polymerization

Classicalparticle morphologies, core-shell, hemisphere, sandwich, and so on, were all reproducible by starting from ca. 10-μm uniform droplets composed of monomers, initiator, solvents, and polymer, and polymerizing them by subsequent suspension polymerization. SPG (Shirasu porous glass) membrane was employed to form uniform size droplets having the coefficient of variation (CV) around 10%. Styrene (ST) and acrylic monomers were used as monomers, and their polymers were dissolved in the droplets to investigate the development of phase separation. When hydrophilic methyl methacrylate (MMA) was polymerized in the droplets with a mixed solvent consisting of hydrophilic hexanol (HA) and hydrophobic benzene and hexadecane (HD), the resulting morphology shifted from hemisphere to sandwich and eventually to PMMA/solvent core-shell with increasing hydrophilicity of the mixed solvent. The sandwich was converted to the core-shell after several weeks elapsed. As styrene was added to MMA, the morphology shifted from hemisphere core/solvent shell to raspberry core/solvent shell as the fraction of ST increased. The domain of the mixed solvent in the raspberry core was reduced with increasing the hydrophilicity of the mixed solvent. All these morphologies were eventually converted to the copolymer core/solvent shell. When a mixed monomer of styrene and MMA dissolving polystyrene (PS) was polymerized, the resulting morphology shifted from salami to core-shell with increasing the MMA fraction in the comonomer. The salami particles were then swollen with toluene, and after the swelling, toluene was removed under the different temperature and pressure. The final particle morphology converted to the core-shell with a milder rate of toluene removal which was predicted from the thermodynamic model. When styrene and cyclohexyl acrylate (CHA), a pair with widely different reactivity ratios, were copolymerized, salami morphologies, with tiny CHA-rich domains dispersed in the matrix, were obtained even at a higher fraction of CHA in comonomer. Effects of glass transition temperature of the polymers, molecular weight, and the composition of copolymers were taken in consideration whenever the final morphologies were discussed. By these experiments, the authors tried to demonstrate an advantage of using large uniform spheres for the particle morphology studies. SPG emulsification technique was a potential tool because of its free formulation of the droplets, and the subsequent polymerization could undergo without the breakup or coalescence of the droplets. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2200–2220, 2001

Morphology development of 10-?m scale polymer particles prepared by SPG emulsification and suspension polymerization

Classicalparticle morphologies, core-shell, hemisphere, sandwich, and so on, were all reproducible by starting from ca. 10-μm uniform droplets composed of monomers, initiator, solvents, and polymer, and polymerizing them by subsequent suspension polymerization. SPG (Shirasu porous glass) membrane was employed to form uniform size droplets having the coefficient of variation (CV) around 10%. Styrene (ST) and acrylic monomers were used as monomers, and their polymers were dissolved in the droplets to investigate the development of phase separation. When hydrophilic methyl methacrylate (MMA) was polymerized in the droplets with a mixed solvent consisting of hydrophilic hexanol (HA) and hydrophobic benzene and hexadecane (HD), the resulting morphology shifted from hemisphere to sandwich and eventually to PMMA/solvent core-shell with increasing hydrophilicity of the mixed solvent. The sandwich was converted to the core-shell after several weeks elapsed. As styrene was added to MMA, the morphology shifted from hemisphere core/solvent shell to raspberry core/solvent shell as the fraction of ST increased. The domain of the mixed solvent in the raspberry core was reduced with increasing the hydrophilicity of the mixed solvent. All these morphologies were eventually converted to the copolymer core/solvent shell. When a mixed monomer of styrene and MMA dissolving polystyrene (PS) was polymerized, the resulting morphology shifted from salami to core-shell with increasing the MMA fraction in the comonomer. The salami particles were then swollen with toluene, and after the swelling, toluene was removed under the different temperature and pressure. The final particle morphology converted to the core-shell with a milder rate of toluene removal which was predicted from the thermodynamic model. When styrene and cyclohexyl acrylate (CHA), a pair with widely different reactivity ratios, were copolymerized, salami morphologies, with tiny CHA-rich domains dispersed in the matrix, were obtained even at a higher fraction of CHA in comonomer. Effects of glass transition temperature of the polymers, molecular weight, and the composition of copolymers were taken in consideration whenever the final morphologies were discussed. By these experiments, the authors tried to demonstrate an advantage of using large uniform spheres for the particle morphology studies. SPG emulsification technique was a potential tool because of its free formulation of the droplets, and the subsequent polymerization could undergo without the breakup or coalescence of the droplets. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2200–2220, 2001

Effect of Lauryl Alcohol on Morphology of Uniform Polystyrene–Poly(methyl methacrylate) Composite Microspheres Prepared by Porous Glass Membrane Emulsification Technique

Fairly uniform poly(styrene)–poly(methyl methacrylate) (PST–PMMA) composite microspheres were prepared by employing an SPG (Shirasu Porous Glass) membrane emulsification technique. A mixture of PST, PMMA, and cosurfactant [lauryl alcohol (LOH)] dissolved in dichloromethane (DCM) was used as the dispersed phase, and an aqueous phase containing poly(vinyl alcohol) and sodium lauryl sulfate was used as the continuous phase. It is necessary to add LOH to obtain uniform particles with the SPG emulsification technique. The effects of the volume of LOH on the morphology of the final particles were investigated by varying the volume of LOH from 0 to 2 ml (per 1.2 g polymer). A three-component model was developed for different PMMA/PST ratios and LOH/polymer ratios, based on Sundberg's theory; and the calculation on morphology was carried out by using the three-component model. Agreement was obtained between experimental and calculated results. When 2 ml of LOH was added, it was found that LOH can engulf the polymer particles completely; a hemicore (HCP1P2P3) morphology, where PST and PMMA formed a hemisphere core inside a LOH shell, was observed when the PMMA/PST ratio was high, while core–shell–shell (CSP1P2P3) morphology, where PMMA formed a core and PST and LOH formed an inner shell and an outer shell, respectively, was observed when the PMMA/PST ratio was low. When the volume of LOH was below 1 ml (per 1.2 g polymer), however, LOH could not always engulf the inner polymer particles completely; cored hemisphere (CHSP3P2P1), core–shell–shell (CSP2P1P3), and hemicore (HCP1P2P3) morphologies were observed, depending on the PMMA/PST ratio and volume of LOH.

Preparation of uniformly sized polymeric separation media potentially suitable for small-scale high-performance liquid chromatography and/or capillary electrochromatography

Uniformly sized polymer particles were prepared by either a two-step swelling and polymerization method or a Shirasu porous glass (SPG) emulsification technique to compare their suitability as a uniformly sized packing material for small-scale high-performance liquid chromatography (HPLC) or capillary electrochromatography (CEC). The SPG emulsification technique afforded slightly worse size uniformity compared to the two-step swelling and polymerization technique. However, fairly nice spherical shapes with reproducible outward appearance and internal pore size distribution were obtained for both of 3- or 6-μm sized particles. On the other hand, the two-step swelling and polymerization method afforded broken particles with quite different outward appearances due to the polymeric porogen effects of seed polymer utilized as the shape template. In HPLC, the column packed with the 3-μm particles prepared with the SPG emulsification technique proved to have a fairly high column efficiency with good column stability, as assessed under repeated use in gradient elution. On the other hand, the column packed with the packing material obtained through the two-step swelling and polymerization method showed much poorer column stability, while initial column efficiency was compatible to that obtained using the SPG emulsification method. In addition, the packing material prepared with the SPG emulsification technique could be modified with ion-exchangeable monomers and showed fairly good column efficiency in the CEC mode.

Synthesis of monodisperse polymeric microspheres including polyimide prepolymer by using SPG emulsification technique

An occlusion of a functional material, polyimide prepolymer (PIP), into uniform polymeric microspheres was attempted in order to demonstrate the versatility of the SPG (Shirasu porous glass) membrane emulsification technique. An oil phase consisting of hydrophobic monomers (styrene and acrylates with a longer side chain) and, although not necessarily, a water-insoluble reagent (lauryl alcohol) dissolved PIP up to 50 wt.%, and also an initiator (ADVN). An aqueous phase contained polyvinyl alcohol (PVA) and a small amount of sodium lauryl sulfate (SLS) as a stabilizing pair. The former was permeated through a SPG membrane, and uniform droplets were suspended in the latter. The seed droplets were swollen with the hydrophilic components, MMA and EGDMA, with a selective addition of isoamyl acetate, hexanol or octanol. After the swelling, an additional amount of the stabilizer solution was added. Polymerization was carried out at 343 K for 24 h. Uniform polymeric spheres, the coefficient of variation approximately 10% and occluding a maximum 28.4 wt.% of PIP were obtained. The entrapment of PIP was improved when the matrix polymer chains were crosslinked with EGDMA (but not with DVB), and an employment of the acrylates with a longer side chain, implying that the presence of ester groups are favored for a stable occlusion. A co-monomer system composed of MMA, 2-ethylhexyl acrylate and butyl acrylate plus octyl alcohol was able to occlude almost 100% of PIP in a stable condition without the presence of EGDMA.

Synthesis of 100 ?m uniform porous spheres by SPG emulsification with subsequent swelling of the droplets

mm porous p(styrene-co-divinylbenzene) (PS-DVB) microspheres were synthesized by employing a particular membrane emulsification technique, and subse- quent swelling of the seed droplets. DVB dissolving a water-insoluble substance, hexa- decane (HD), and an initiator was permeated through a SPG (Shirasu porous glass) membrane, and the uniform (seed) droplets were released to a stabilizer solution acting as the continuous phase. The average droplet size was around 30 mm, and this emulsion was mixed with a secondary emulsion of much smaller size consisting of more hydro- philic components, a mixture of styrene, middle chain alcohol (C6 to C8), dichloroben- zene, and isoamyl acetate, which promotes the degradative diffusion process of the components. After all the droplets in the secondary emulsion virtually disappeared, the seed droplets were swollen to a maximum 110 mm. Polymerization was carried out at 348 K under a nitrogen atmosphere. Uniform porous spheres of 100 mm with the coefficient of variation less than 10% were obtained. Specific surface area was 350 m 2 / g. Careful controlling of the specific gravity of swollen droplets and the choice of solvents balancing between the good solvency for the polymer and polarity (solubility in water) proved vital in order that the polymerization may proceed without an extensive phase separation in the early stage, which eventually induces breakup of the droplets. The three component system, isoamyl acetate-hexanol-o-dichlorobenzene, provided an ade- quate cosolvent for these purposes. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 931-942, 1997

Synthesis of 100 μm uniform porous spheres by SPG emulsification with subsequent swelling of the droplets

100 μm porous p(styrene-co-divinylbenzene) (PS-DVB) microspheres were synthesized by employing a particular membrane emulsification technique, and subsequent swelling of the seed droplets. DVB dissolving a water-insoluble substance, hexadecane (HD), and an initiator was permeated through a SPG (Shirasu porous glass) membrane, and the uniform (seed) droplets were released to a stabilizer solution acting as the continuous phase. The average droplet size was around 30 μm, and this emulsion was mixed with a secondary emulsion of much smaller size consisting of more hydrophilic components, a mixture of styrene, middle chain alcohol (C6 to C8), dichlorobenzene, and isoamyl acetate, which promotes the degradative diffusion process of the components. After all the droplets in the secondary emulsion virtually disappeared, the seed droplets were swollen to a maximum 110 μm. Polymerization was carried out at 348 K under a nitrogen atmosphere. Uniform porous spheres of 100 μm with the coefficient of variation less than 10% were obtained. Specific surface area was 350 m2/g. Careful controlling of the specific gravity of swollen droplets and the choice of solvents balancing between the good solvency for the polymer and polarity (solubility in water) proved vital in order that the polymerization may proceed without an extensive phase separation in the early stage, which eventually induces breakup of the droplets. The three component system, isoamyl acetate-hexanol-o-dichlorobenzene, provided an adequate cosolvent for these purposes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 931–942, 1997

Preparation of GPC Packed Polymer Beads by a SPG Membrane Emulsifier.

Monodispersed porous polystyrene beads crosslinked with divinylbenzene were prepared by in situ polymerization. For this objective, the preparation of uniform oil microdroplets in water was successfully achieved by using a Shirasu Porous Glass (SPG) membrane emulsifier (POEM® from Reika Kogyo Co. Ltd.). Separation abilities for a gel permeation chromatograph (GPC) column were discussed with polymer microbeads obtained by changing key experimental factors such as the pore sizes of the SPG membrane and diluents. Consequently, it was evident from gel permeation chromatography that the porous beads prepared by SPG emulsification can be used for the effective separation of a molecular weight range of 102 to 106.