Phase separation in polystyrene latex interpenetrating polymer networks

Polystyrene/polystyrene latex interpenetrating polymer networks (IPNs) were prepared by seeded emulsion polymerzation of styrene–divinylbenzene mixtures in crosslinked monodisperse polystyrene seed latexes. The resulting latexes comprised uniform nonspherical particles, which were formed by separation of the second-stage monomer from the crosslinked seed network during swelling and polymerization. The kinetics of phase separation were investigated by examining the changes in particle morphology using optical microscopy, which revealed that the phase separation was induced by the relaxation of the polymer chains before polymerization began and was enhanced by increased conversion. The thermodynamics of phase separation were investigated by analysis of the free-energy changes during swelling and polymerization, and the phase separation was described by a nucleation-and-growth mechanism. The results of this study have been applied to the design and synthesis of a series of uniform nonspherical particles of different morphology.     

Monodisperse polystyrene particles crosslinked with poly(dimethyl siloxane) diacrylate using dispersion polymerization and their monomer swelling capability

A flexible poly(dimethyl siloxane) diacrylate (PDMSDA) crosslinker was synthesized using different molecular weights of poly(dimethyl siloxane) (PDMS, M _n =550, 1,700, 4,000 g/mol). The monodisperse polystyrene (PS) particles crosslinked with various contents of PDMSDA were prepared by dispersion polymerization, and applied as seed particles in the seeded polymerization. The crosslinking density of the PS particles was determined from the rate of transport of the monomer molecules to the crosslinked seed particles. It was confirmed that the monomer swelling capacity of seed particles and final morphological changes of polymer beads were determined significantly by the crosslinking density of the seed particles. In addition, the morphological change was not observed without the oligomer swelling step in the seeded polymerization due to the hydrophobic property of PDMS. When highly crosslinked seed particles were used in the seeded polymerization, peculiar morphology (doublet structure) of polymer beads appeared.     

Poly(2-acetoxyethyl methacrylate)/polystyrene latex interpenetrating polymer networks with well-defined phase-separated structure

A series of poly(2-acetoxyethyl methacrylate)/polystyrene(PAEMA/PS) latex interpenetrating polymer networks(LIPNs) were prepared by seeded soap-free emulsion polymerization of styrene on the crosslinked PAEMA seed particles using an oil-soluble initiator.These PAEMA/PS LIPNs showed a well-defined phase-separated structure with PS phase dispersing in continuous PAEMA phase.The domain size of PS phase was found to depend on the crosslinking degree of PAEMA seed particles and the amount of second-stage styrene monomer.     

Effect of second monomer and initiator type, mixing method, and stabilizer content on the shape of the particles produced by seeded dispersion polymerization in the presence of saturated hydrocarbon droplets

In this work, the preparation of micron-sized polymer particles with nonspherical shapes via seeded dispersion polymerization of 2-ethylhexyl methacrylate with polystyrene seed particles in the presence of hydrocarbon droplets and evaporation of hydrocarbon after the polymerization under various polymerization conditions was discussed. The effect of second monomer and initiator type, mixing method, and stabilizer content on the shape of the obtained particles was investigated. It was observed that particles with more nonspherical shapes were obtained with increasing the alkyl chain length of ester group of the methacrylate of the second monomer which is because of increasing the absorption amounts of hydrocarbon by second polymer domains. Moreover, the experimental results showed that shape of the particles which was produced by shaking is more nonspherical than the shape of the particles which was obtained from tumbling. Furthermore, particles with different nonspherical shapes were prepared by changing the initiator type and stabilizer content.     

Synthesis of nonspherical colloidal particles with anisotropic properties

We describe a promising and flexible technique for fabricating uniform nonspherical particles with anisotropic phase and surface properties. Our approach is based on the seeded polymerization technique in which monomer-swollen particles are polymerized. The polymerization causes a phase separation to occur, giving rise to two-phase nonspherical particles. We show that the elastic contraction of the swollen polymer particles induced by elevated polymerization temperatures plays an important role in the phase separation. Moreover, chemical anisotropy of nonspherical particles can be obtained by using immiscible polymer pairs and by employing surface treatments. Furthermore, we are able to produce amphiphilic dumbbell particles consisting of two different bulbs: hydrophilic poly (ethylene imine)-coated polystyrene and hydrophobic polystyrene. Controlled geometries of these amphiphilic nonspherical particles will allow a wide range of potential applications, such as engineered colloid surfactants.     

Synthesis of polymeric particles by seeded growth technique for the applications of particle self-assembly

In this study, shape-anisotropic polymeric particles were synthesized by seeded growth technique for the applications of particle self-assembly. First, cross-linked seed particle dispersion was prepared by emulsifier-free emulsion polymerization with divinylbenzene as cross-linker. Then, seeded growth scheme was applied to the seeds by swelling the particles with monomer and subsequent polymerization. The morphologies of the nonspherical particles could be controlled by adjusting the size and the amount of monomer during the swelling step or the cross-linking density of the seed particles, enabling the synthesis of prolate ellipsoids, lobed spheres with triangular shape, snowman-shaped particles, and dumbbell particles. As a demonstrative application, the cross-linked particles could be used as templates for the synthesis of porous materials, whereas dumbbell-shaped particles could be self-organized into colloidal clusters using toluene emulsions as confining geometries. Collectively, shape-anisotropic particles were found to be efficient building blocks to prepare the unique packing structures other than simple spherical colloids.     

Crosslinked polystyrene latexes prepared with 12-(o-styryloxy)dodecyltrimethylammonium bromide

Crosslinked polystyrene latexes with high surface charge densities have been prepared with 1, 3, and 5 mol% divinylbenzene and 0.5–5.0 mol% of 12-(o-styryloxy)dodecyltrimethylammonium bromide ( 1 ). Within experimental error all of surfactant 1 was incorporated into the particles. Analysis of the latex particles by transmission electron microscopy showed nonspherical shapes, aggregates, and number average diameters ranging from 22 to 95 nm. The particle size decreases and the polydispersity increases with increasing amounts of surfactant 1 and of divinylbenzene in the monomer mixture. A mechanism is proposed for particle formation by precipitation of crosslinked polymer from monomer droplets to form primary particles, coagulation of the primary particles to colloidally stable aggregates, and growth by further polymerization.     

Understanding and preventing the formation of deformed polymer particles during synthesis by a seeded polymerization method

Uniformly sized porous polymer particles with different polarity namely poly(divinylbenzene), poly(vinyl acetate‐co‐divinylbenzene), poly(ethylene dimethacrylate), and poly (glycidyl methacrylate‐co‐ethylene dimethacrylate) were prepared in the micron‐size range by a seeded polymerization method. Parameters affecting the particle morphologies including monomer mixture content, porogen content, and polystyrene (PS) seed latexes were varied, and the morphologies of the resulting particles were investigated by scanning electron and confocal microscopy. The results obtained indicated that the particle shape depended dominantly on the molecular weight of the PS seed template. Deformed particles, including collapsed spheres and spheres with holes were obtained when high molecular weight PS seeds were used, whereas well‐defined polymer particles were produced easily by using low molecular weight seeds. The use of 1,1‐diphenylethylene as a chain terminator during seed polymerization is proposed in this work as an efficient method to lower molecular weight of PS in seed particles while keeping seed size small. This low molecular weight seed template retained its spherical geometry after swelling and polymerization with different second stage monomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of anisotropic nanoparticles by seeded emulsion polymerization

Anisotropic polystyrene nanoparticles of diameters below 0.5 microm were prepared by coating the surface of cross-linked polystyrene latex particles with a thin hydrophilic polymer layer prior to swelling the particles with styrene and then initiating second-stage free-radical polymerization. Conditions were found so that all particles had uniform asymmetry. The effect of surface chemistry on the development of particle anisotropy during seeded emulsion polymerization of sub-0.5 microm diameter particles was studied. The extent and uniformity of the anisotropy of the final particles depended strongly on the presence of the hydrophilic surface coating. Systematic variation of the degree of hydrophilicity of the surface coating provided qualitative insight into the mechanism responsible for anisotropy. Conditions were chosen so that the surface free energy favored the extrusion of a hydrophobic bulge of monomer on the hydrophilic surface of the particle during the swelling phase: the presence of a hydrophilic layer on the particle surface causes this asymmetry to be favored above uniform wetting of the particle surface by the monomer. Kinetic effects, arising from the finite time required for the seed to swell with the monomer, also play a role.     

Synthesis of the raspberry‐like PS/PAN particles with anisotropic properties via seeded emulsion polymerization initiated by γ‐ray radiation

We herein report a facile method to prepare the submicron‐sized raspberry‐like polystyrene/polyacrylonitrile particles with anisotropic properties and controllable structure via γ‐radiation‐induced seeded emulsion polymerization under ambient pressure and at room temperature, in which the monodisperse crosslinked styrene‐divinylbenzene‐acrylic acid terpolymer (P(S‐DVB‐AA)) particles were used as seed particles and acrylonitrile (AN) as the second monomer. The influence of the weight ratio of polymer/monomer, the absorbed dose rate, the absorbed dose, and the dispersion medium on the morphology of the as‐prepared particles was investigated. The final products were thoroughly characterized by Fourier transform infrared spectroscopy (FTIR), field‐emission scanning electron microscopy, and transmission electron microscopy. The results showed that the raspberry‐like particles could be fabricated in high yield. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Production of micron-sized monodispersed cross-linked polymer particles having hollow structure

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.     

Morphologies of micron-sized monodispersed composite polymer particles having crosslinked structures produced by seeded polymerizations

Three kinds of micron-sized monodispersed polystyrene (PS)/ poly(styrene - divinylbenzene) composite particles were produced by two kinds of seeded copolymerizations of styrene (S) and divinylbenzene (DVB) (PS seed/ (S+DVB)=2/1, wt. ratio; S/DVB=1/1, molar ratio) in the presence of about 2 μm-sized monodispersed PS particles, and their morphologies were examined. One was produced by a seeded dispersion copolymerization where almost monomers and initiators exist in an ethanol/water (12.6/4.0, w/w) medium. The others two were produced by seeded copolymerizations with the dynamic swelling method where almost monomers exist in the monomer-swollen particles using 2, 2'-azobisisobutyronitrile in monomer-swollen PS seed particles or using 4, 4'-azobis (4-cyanopentanoic acid) in an ethanol/water (7/43, w/w) medium. In the former polymerization, the produced composite particles had a high dense crosslinked shell, whereas in the latter two polymerizations, they did the comparatively homogeneous crosslinked structures.     

Synthesis and characterization of micrometer‐sized particles of narrow size distribution with chloromethyl functionality on the basis of single‐step swelling of uniform polystyrene template microspheres

Polystyrene template microspheres of 1.4 ± 0.1 μm were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. These template particles were then swelled at room temperature in a single step with emulsion that was prepared in sodium dodecyl sulfate aqueous solution from a swelling solvent (dibutyl phthalate) containing the initiator (benzoyl peroxide) and monomer(s) (chlormethylstyrene, divinylbenzene, or ethylene dimethacrylate). Composite uniform particles composed of the template polystyrene and noncrosslinked or crosslinked polychloromethylstyrene were prepared by polymerizing the monomer(s) within the swelled particles at 73 °C. Crosslinked uniform polychloromethylstyrene particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. The influence of various reaction parameters, such as dibuthyl phthalate concentration, chloromethylstyrene concentration, crosslinker type and concentration, and so forth on the molecular weight, size, size distribution, shape, morphology, surface area, and decomposition temperature of the particles was investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1342–1352, 2002     

Hollow latex particles as submicrometer reactors for polymerization in confined geometries

A method was developed for free‐radical polymerization in the confines of a hollow latex particle. Hollow particles were prepared via the dynamic swelling method from polystyrene seed and divinylbenzene and had hollows of 500–1000 nm. So that these hollow poly(divinylbenzene) particles could function as submicrometer reactors, the particles were filled with a monomer (N‐isopropylacrylamide) via the dispersion of the dried particles in the molten monomer. The monomer that was not contained in the hollows was removed by washing and gentle abrasion. Free‐radical polymerization was then initiated by γ radiolysis in the solid state. Transmission electron microscopy showed that poly(N‐isopropylacrylamide) formed in the hollow interior of the particles, which functioned as submicrometer reactors. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5706–5713, 2004     

Preparation of nonspherical particles via dual-seeded dispersion polymerization in the presence of saturated hydrocarbon droplets

In this study, the effect of various polymerization conditions on the shape of the particles produced by dual-seeded dispersion polymerization of a second monomer with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed particles in the presence of saturated hydrocarbon droplets in a polar media was discussed. It was observed that with changing the affinity between the hydrocarbon and PS seed particles, second monomer type, polarity, and alcohol type of the medium nonspherical particles with a variety of shapes can be produced. Furthermore, we suggested that the presence of PMMA seed particles in the medium affects the distribution of the second polymer domains on the surface of the PS seed particles in addition to the absorbed amount of the hydrocarbon by PS particles and second polymer domains and the distribution of the hydrocarbon between them. Moreover, the experimental results showed that almond shell-like PS particles can be prepared under certain conditions.     

Preparation of micron-sized nonspherical polystyrene/poly(styrene-<Emphasis Type="Italic">co</Emphasis>-ethyleneglycol dimethacrylate) particles by seeded soap-free emulsion polymerization

Micron-sized nonspherical polymer particles having different morphologies were synthesized by seeded soap-free emulsion polymerization of styrene(St) and ethyleneglycol dimethacrylate(EGDMA,used as a crosslinker) on spherical, linear polystyrene(PS) seed particles.The morphology of the resulting PS/poly(St-co-EGDMA) particles was dependent on the crosslinker concentration and polymerization temperature.     

Preparation and characterization of core-shell polystyrene/polychloromethylstyrene and hollow polychloromethylstyrene micrometer-sized particles of narrow-size distribution

Polystyrene core microspheres of narrow-size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Polystyrene/polychloromethylstyrene and polystyrene/poly(chloromethylstyrene-divinylbenzene) core-shell microspheres of narrow-size distribution were prepared by seeded emulsion polymerization of chloromethylstyrene or chloromethylstyrene and divinylbenzene in the presence of the polystyrene core microspheres at 71 °C. Core-shell particles with different properties (size, surface morphology, and composition) have been prepared by changing various parameters belonging to the emulsion polymerization process, e.g., volume of the chloromethylstyrene and the volume ratio of chloromethylstyrene to divinylbenzene. Dissolution of the polystyrene core of the polystyrene/poly(chloromethylstyrene-divinylbenzene) core-shell particles resulted in the formation of crosslinked hollow polychloromethylstyrene microspheres, broken crosslinked polychloromethylstyrene shells, or particles containing voids, depending on the composition of the polystyrene/poly(chloromethylstyrene-divinylbenzene) particles.     

Surface modification of crosslinked poly(styrene-divinyl benzene) micrometer-sized particles of narrow size distribution by ozonolysis

Micrometer-sized polystyrene template particles of narrow size distribution were prepared by dispersion polymerization of styrene in 2-methoxyethanol. Uniform micrometer-sized polystyrene/crosslinked poly(styrene-divinyl benzene) composite particles were formed by a single-step swelling process of the template particles with styrene, divinyl benzene and benzoyl peroxide, followed by polymerization at 70 degrees C. Uniform micrometer-sized crosslinked poly(styrene-divinyl benzene) particles of higher surface area were produced by dissolution of the template polystyrene part of the former composite particles with N,N-dimethylformamide. Hydroperoxide conjugated crosslinked poly(styrene-divinyl benzene) particles were produced by ozonolysis of these particles. The effect of ozonolysis conditions, such as exposure time and flow rate of the ozone, on the hydroperoxide conjugation to the crosslinked particles was also studied. Functionalization of the crosslinked poly(styrene-divinyl benzene) particles was performed by graft polymerization of vinylic monomers such as acrylonitrile and chloromethylstyrene on the hydroperoxide conjugated crosslinked particles. This was accomplished by raising the temperature (e.g., 70 degrees C) of deairated acetonitrile dispersions containing the hydroperoxide conjugated particles and the vinylic monomers. The influence of various polymerization parameters on the grafting yield, e.g., monomer concentration, conjugated hydroperoxide concentration, and temperature, was also elucidated.     

Morphological investigations of crosslinked polystyrene microspheres by seeded polymerization

 Crosslinked polystyrene microspheres with novel surface and inner morphologies were synthesized by seeded polymerization following a seed-swelling method, using uncrosslinked polystyrene microspheres as seeds and a mixture of toluene, styrene (St), and divinylbenzene (DVB) as the swelling agent. With the increasing toluene/ (St+DVB) ratio, the crosslinked particles changed from smooth-surfaced spheres to deformed spheres with dimples or heavy dents at the surface. A single hole inside the spherical particles was produced at low St/DVB ratio, while higher St/DVB ratios gave irregular dented or dimpled particles. Ultrathin cross-section observation by TEM revealed a non-uniformly crosslinked inner structure. Received: 20 January 1998 Accepted: 14 April 1998     

Thermotropic liquid-crystal/polymer microcapsules prepared by in situ suspension polymerization

In this study, thermotropic liquid-crystal/polymer microcapsules were produced via in situ suspension polymerization. The phase separation between cholesteryl liquid crystal (CLC) and poly(methyl methacrylate) (PMMA) in the droplets was induced by polymerization, resulting consequently in uniform liquid-crystal-containing polymer microcapsules. The phase behavior of the microcapsules was dependent on the loading amount of the liquid crystals and the degree of cross-linking of the polymer phase. Above 30% loading amount of CLC, the liquid crystals started to appear clearly. It was found that the spherical morphology of the microcapsules was achieved within a slight degree of cross-linking of the PMMA phase. At a high degree of cross-linking, nonspherical particles with a rough surface and deeper dents were obtained, which was due to the elastic-retractive force of the cross-linked network. The liquid-crystal/polymer microcapsules produced in this study could find great applicability in pharmaceutics and electronics as a smart drug carrier.