Synthesis and characterization of spherical and hemispherical polyepoxide micrometer‐sized particles of narrow size distribution by a single‐step swelling of uniform polystyrene template microspheres with glycidyl methacrylate

Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. Spherical and hemispherical polystyrene/poly(glycidyl methacrylate) microspheres of narrow size distribution were prepared by a single‐step swelling of the polystyrene template microspheres with the swelling solvent monomer glycidyl methacylate, followed by polymerization of the monomer within the swollen template microspheres at 73 °C. Uniform polystyrene/poly(glycidyl methacylate‐ethylene glycol dimethacrylate) polyepoxide composite microspheres were synthesized similarly, substituting glycidyl methacylate for glycidyl methacylate and ethylene glycol dimethacrylate. Uniform crosslinked poly(glycidyl methacylate‐ethylene glycol dimethacrylate) polyepoxide microspheres have been prepared by dissolution of the PS template polymer of the former composite microspheres. Particles with different properties, for example size, size distribution, shape, surface morphology, surface area, and so forth, were prepared by changing various parameters belonging to the swelling and/or polymerization steps, for example, volume of the swelling monomer/s and/or the swelling solvent dibutyl phthalate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4612–4622, 2007     

Synthesis and characterization of micrometer‐sized homo and composite polyacrylonitrile particles of narrow size distribution on the basis of single‐step swelling of uniform polystyrene template microspheres

Polyacrylonitrile/polystyrene micrometer‐sized composite particles of narrow size distribution were prepared by a single‐step swelling of uniform polystyrene template microspheres with emulsion droplets of methylene chloride containing the monomer acrylonitrile and the initiator benzoyl peroxide. Methylene chloride was then evaporated carefully, followed by polymerization of acrylonitrile at 70 °C within the shrunken template particles. Polymerization of acrylonitrile also occurred at the particles' surface due to the interaction of surface polyacrylonitrile oligoradicals with acrylonitrile dissolved in the aqueous phase. Uniform polyacrylonitrile particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, TGA‐DSC, XRD, XPS, advancing contact angle, light microscope, SEM and cross‐sectional TEM. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4847–4861, 2004     

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.     

Poly(2‐hydroxyethyl methacrylate‐co‐N,O‐dimethacryloylhydroxylamine) particles by dispersion polymerization

Poly(2‐hydroxyethyl methacrylate‐co‐N,O‐dimethacryloylhydroxylamine) particles were prepared by dispersion polymerization in toluene/2‐methylpropan‐1‐ol medium using cellulose acetate butyrate and dibenzoyl peroxide (BPO) as a steric stabilizer and initiator, respectively. The particle size was reduced with decreasing solvency of the reaction medium (more nuclei were generated) because the critical chain length of the precipitated oligomers decreased with an increasing toluene content, which is a poorer solvent for the polymer than 2‐methylpropan‐1‐ol. There is an optimum initiator concentration (2 wt % BPO relative to monomers) for producing low‐polydispersity particles under given conditions. Additionally, discrete spherical particles were obtained at a low monomer concentration and/or higher polymerization temperature. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1625–1632, 2002     

Morphology of micron‐sized,monomer‐adsorbed,crosslinked polymer particles having snowmanlike shapes prepared by the dynamic swelling method

A series of monomer‐adsorbed, crosslinked polystyrene/polydivinylbenzene composite particles having snowmanlike shapes were prepared by the dynamic swelling method that the authors had proposed in 1991. The morphology of the snowman‐shaped particles was estimated with the contact angle of the monomer phase on the polymer particle. Influences of the kind of monomers and polyvinyl alcohol colloidal stabilizer on the morphology were obviously observed and discussed from the viewpoint of thermodynamic stability. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3106–3111, 2001     

Effects of the reaction parameters on the properties of thermosensitive poly(N‐isopropylacrylamide) microspheres prepared by precipitation and dispersion polymerization

Poly(N‐isopropylacrylamide) (PNIPAAm)‐based microspheres were prepared by precipitation and dispersion polymerization. The effects of several reaction parameters, such as the type and concentration of the crosslinker (N,N′‐methylenebisacrylamide or ethylene dimethacrylate), medium polarity, concentration of the monomer and initiator, and polymerization temperature, on the properties were examined. The hydrogel microspheres were characterized in terms of their chemical structure, size and size distribution, and morphological and temperature‐induced swelling properties. A decrease in the particle size was observed with increasing polarity of the reaction medium or increasing concentration of poly(N‐vinylpyrrolidone) as a stabilizer in the dispersion polymerization. The higher the content was of the crosslinking agent, the lower the swelling ratio was. Too much crosslinker gave unstable dispersions. Although the solvency of the precipitation polymerization mixture controlled the PNIPAAm microsphere size in the range of 0.2–1 μm, a micrometer range was obtained in the Shellvis 50 and Kraton G 1650 stabilized dispersion polymerizations of N‐isopropylacrylamide in toluene/heptane. Typically, the particles had fairly narrow size distributions. Copolymerization with the functional glycidyl methacrylate monomer afforded microspheres with reactive oxirane groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 968–982, 2006     

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     

Monodisperse polystyrene microspheres prepared by dispersion polymerization with microwave irradiation

Monodisperse polystyrene microspheres with diameters of 200–500 nm were prepared by dispersion polymerization with microwave irradiation with poly(N‐vinylpyrrolidone) as a steric stabilizer and 2,2′‐azobisisobutyronitrile as a radical initiator in an ethanol/water medium. The morphology, size, and size distribution of the polystyrene microspheres were characterized with transmission electron microscopy and photon correlation spectroscopy, and the formed films of the polystyrene dispersions were characterized with atomic force microscopy. The effects of the monomer concentration, stabilizer concentration, and initiator concentration on the size and size distribution of the polystyrene microspheres were investigated. The polystyrene microspheres prepared by dispersion polymerization with microwave irradiation were smaller, more uniform, and steadier than those obtained with conventional heating. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2368‐2376, 2005     

Facile preparation of monodisperse hollow cross‐linked chitosan microspheres

We have successfully prepared biocompatible and biodegradable hollow microspheres using carboxyl‐functionalized polystyrene particles as core template and the chitosan cross‐linked with glutaraldehyde as the shell. The monodisperse carboxyl‐functionalized polystyrene particles were made by emulsifier‐free emulsion polymerization. The structure, morphology, and constitution of the carboxyl‐functionalized polystyrene particles were characterized by FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS). The structure, morphology, and formation process of the hollow cross‐linked chitosan microspheres were characterized by FTIR, SEM, and TEM. The results revealed that the latex particles were removed by exposed to solvent and the microspheres exhibited the hollow structure. This work confirmed that the hollow microspheres were accomplished by fabricating on the basis of chemical cross‐linking on the surface of the carboxyl‐functionalized polystyrene particles and then removing off the cores of particles. Moreover, with the increase of carboxyl‐functionalization degree at the surface of latexes and the increase of cross‐linking period, the thicker and firmer monodisperse hollow microspheres were obtained. In addition, a water‐soluble drug, salicylic acid, encapsulated in the microcapsules slowly released at pH 1.2. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 228–237, 2008     

Preparation of non‐spherical particles from amphiphilic block copolymers

Simple self‐assembly techniques to fabricate non‐spherical polymer particles, where surface composition and shape can be tuned through temperature and the choice of non‐solvents was developed. A series of amphiphilic polystyrene‐b‐poly(2‐ethyl‐2‐oxazoline) block copolymers were prepared and through solvent exchange techniques using varying non‐solvent composition a range of non‐spherical particles were formed. Faceted phase separated particles approximately 300 nm in diameter were obtained when self‐assembled from tetrahydrofuran (THF) into water compared with unique large multivesicular particles of 1200 nm size being obtained when assembled from THF into ethanol (EtOH). A range of intermediate structures were also prepared from a three part solvent system THF/water/EtOH. These techniques present new tools to engineer the self‐assembly of non‐spherical polymer particles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 750–757     

Pore size in one‐step swelling and polymerization of monodisperse polymer beads

Crosslinked polystyrene beads were prepared at low swelling ratios by one‐step swelling and polymerization method. Pore size of the beads was observed based on the GPC calibration curves. It is found that: (1) the pore size increases as the swelling ratio decreases; (2) when a good solvent is used as the porogen the pore size increases with the crosslinking monomer content; and (3) at high crosslinking monomer content the pore size does not depend on the porogen solubility. The effects are discussed in terms of polymer miscibility, including phase separation between the seed and bead polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3270–3277, 2000     

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     

Fully crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization and their superior thermal properties

Fully crosslinked, stable poly(styrene‐co‐divinylbenzene) microspheres, which are composed of various concentrations of divilylbenzene from 5 to 75 mol % based on styrene monomer, were prepared without a significant particle coagulation by the precipitation polymerization. The number‐average particle diameter ranged from 3.5 to 2.8 μm and decreased with an increasing concentration of divinylbenzene in monomer. In addition, the coefficient of variation of the microspheres was slightly reduced with the increasing concentration of divinylbenzene. The circularity and the measured specific surface area indicated that lesser particles are coagulated because of the improved stability of individual particles at a high divinylbenzene concentration and that the resulting particles have a smooth surface without micropores. The glass‐transition temperature was not observed for all microspheres formed from the range of divinylbenzene concentrations. In addition, the onset of the thermal‐degradation temperature was increased from 339.8 to 376.9 °C upon higher contents of divinylbenzene. On the basis of the DSC and thermogravimetric data, the polymer microspheres prepared by the precipitation polymerization possessed a fully crosslinked structure and highly enhanced thermal stability. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 835–845, 2004     

Polymerizable Molecular Silsesquioxane Cage Armored Hybrid Microcapsules with In Situ Shell Functionalization

We prepared core–shell polymer–silsesquioxane hybrid microcapsules from cage‐like methacryloxypropyl silsesquioxanes (CMSQs) and styrene (St). The presence of CMSQ can moderately reduce the interfacial tension between St and water and help to emulsify the monomer prior to polymerization. Dynamic light scattering (DLS) and TEM analysis demonstrated that uniform core–shell latex particles were achieved. The polymer latex particles were subsequently transformed into well‐defined hollow nanospheres by removing the polystyrene (PS) core with 1:1 ethanol/cyclohexane. High‐resolution TEM and nitrogen adsorption–desorption analysis showed that the final nanospheres possessed hollow cavities and had porous shells; the pore size was approximately 2–3 nm. The nanospheres exhibited large surface areas (up to 486 m² g^?1) and preferential adsorption, and they demonstrated the highest reported methylene blue adsorption capacity (95.1 mg g^?1). Moreover, the uniform distribution of the methacryloyl moiety on the hollow nanospheres endowed them with more potential properties. These results could provide a new benchmark for preparing hollow microspheres by a facile one‐step template‐free method for various applications.     

Monodisperse superparamagnetic pH‐sensitive single‐layer chitosan hollow microspheres with controllable structure

Facile strategy was developed for the fabrication of the monodisperse superparamagnetic pH‐sensitive single‐layer chitosan (CS) hollow microspheres with controllable structure. The carboxyl group‐functionalized polystyrene microspheres prepared by soap‐free emulsion polymerization were used as the templates. After the Fe₃O₄ nanoparticles were in situ formed onto the surface of the templates, the single‐layer CS was self‐assembled and cross‐linked with glutaraldehyde subsequently. Then, the magnetic single‐layer CS hollow microspheres were obtained after the templates were removed. It was found that the feeding ratio of the monomer acrylic acid in the soap‐free emulsion polymerization had played an important role on the particle size and surface carboxyl group content of the templates, which determined the particle size and shell thickness of the magnetic single‐layer CS hollow microspheres in the proposed strategy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and characterization of temperature‐ and pH‐sensitive hydrogels based on poly(2‐ethyl‐2‐oxazoline) and poly(D,L‐lactide)

A novel series of temperature‐ and pH‐sensitive hydrogels based on poly(2‐ethyl‐2‐oxazoline) and three‐arm poly(D,L ‐lactide) were synthesized via photocopolymerization. For the creation of polymeric networks, two types of macromers terminated with methacrylate groups were prepared: poly(2‐ethyl‐2‐oxazoline) dimethacrylate and three‐arm poly(D,L ‐lactide) trimethacrylate. The chemical structures were analyzed with ¹H NMR and Fourier transform infrared techniques. The thermal behaviors, morphologies, and swelling properties were measured for the characterization of the polymeric networks. All the poly(2‐ethyl‐2‐oxazoline)/three‐arm poly(D,L ‐lactide)hydrogels provided high water retention capacity and exhibited reversible swelling–shrinking behavior in response to temperature and pH variations. The hydrogels with higher poly(2‐ethyl‐2‐oxazoline) dimethacrylate contents were more effective in raising the swelling ratio and temperature and pH sensitivity. However, higher contents of three‐arm poly(D,L ‐lactide) trimethacrylate produced larger particles and pore sizes in the hydrogels. This study effectively proves that this unique combination of water swellability and biodegradability provides hydrogels with a much wider range of applications in biomedical fields. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1112–1121, 2002     

Synthesis,swelling properties,and network structure of new stimuli‐responsive poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels

Poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels were prepared by thermal free‐radical copolymerization of N‐acryloyl‐N′‐ethyl piperazine (AcrNEP) and N‐isopropylacrylamide (NIPAM) in solution using N, N′‐methylene bisacrylamide as the crosslinking agent. The gels were responsive to changes in external stimuli such as pH and temperature. The pH and temperature responsive character of the gels was greatly dependent on the monomer content, namely AcrNEP and NIPAM, respectively. The gels swelled in acidic (pH 2) and de‐swelled in basic (pH 10) solutions with a response time of 60 min. With increase in temperature from 23 to 80 °C the swelling of the gels decreased continuously and this effect was different in acidic and basic solutions. The temperature dependence of equilibrium water content of the gels was evaluated by the Gibbs–Helmholtz equation. Detailed analysis of the swelling properties of these new gels in relation to molecular heterogeneity in acidic (pH 2) and basic (pH 10) solutions were performed. Water transport property of the gels was studied gravimetrically. In acidic solution, the diffusion process was non‐Fickian (anomalous) while in basic solution, the diffusion was quasi‐Fickian. The effect was more evident in solution of pH 2 than in pH 10. Various structural parameters of the gels such as number‐average molar mass between crosslink (M_c), the crosslink density (ρ_c), and the mesh size (ξ) were evaluated. The mesh sizes of the hydrogels were between 64 and 783 Å in the swollen state in acidic solution and 20 and 195 Å in the collapsed state in basic solution. The mesh size increased between three to four times during the pH‐dependent swelling process. The amount of unbound water (free water) and bound water of the gels was also evaluated using differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Poly(N,N‐diethylacrylamide) microspheres by dispersion polymerization

Poly(N,N‐diethylacrylamide)‐based microspheres were prepared by ammonium persulfate (APS)‐initiated and poly(vinylpyrrolidone) (PVP)‐stabilized dispersion polymerization. The effects of various polymerization parameters, including concentration of N,N′‐methylenebisacrylamide (MBAAm) crosslinker, monomer, initiator, stabilizer and polymerization temperature on their properties were elucidated. The hydrogel microspheres were described in terms of their size and size distribution and morphological and temperature‐induced swelling properties. While scanning electron microscopy was used to characterize the morphology of the microspheres, the temperature sensitivity of the microspheres was demonstrated by dynamic light scattering. The hydrodynamic particle diameter decreased sharply as the temperature reached a critical temperature ～ 30 °C. A decrease in the particle size was observed with increasing concentration of both the APS initiator and the PVP stabilizer. The microspheres crosslinked with 2–15 wt % of MBAAm had a fairly narrow size distribution. It was found that the higher the content of the crosslinking agent, the lower the swelling ratio. High concentration of the crosslinker gave unstable dispersions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6263–6271, 2008     

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.     

Positron annihilation studies of poly(N‐isopropyl acrylamide) gel in mixed solvents

Positron annihilation lifetime spectroscopy was used to characterize the reentrant volume‐phase‐transition behavior of poly(N‐isopropyl acrylamide) hydrogel in an ethanol/water mixed solvent. The polymer gel was synthesized with γ irradiation. The ortho‐positronium lifetime (τ₃) in the gel slowly increased with an increase in the ethanol content in the mixed solvent. τ₃ was not influenced by the volume phase transition. The ortho‐positronium intensity decreased with the collapse of the gel in an approximately 10% ethanol/water mixture. When swelled in pure ethanol, τ₃ initially increased with the solvent amount in the gel, showing the destruction of intramolecular hydrogen bonding and the relaxation of polymer chains. The lower critical solution temperature of the gel in the 10% ethanol/water mixture was lower than that in pure water, and τ₃ for various solvent contents showed behavior similar to that seen in pure solvent. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1028–1036, 2002