Synthesis of monodisperse polystyrene microspheres by dispersion polymerization using sodium polyaspartate

We prepared monodisperse polystyrene microspheres by dispersion polymerization using sodium polyaspartate (PAspNa) as a dispersion stabilizer in an ethanol/water medium. The influence of reaction parameters, i.e., the volume fraction of ethanol in the medium, stabilizer concentration, and the monomer concentration, on the average diameter of the prepared polystyrene microspheres and its distribution were investigated. Polystyrene microspheres were successfully prepared, and the average diameter of the prepared monodisperse polystyrene microspheres was controlled by adjusting the reaction parameters. The zeta potential of the microspheres and the time course of conversion, the particle diameter and its distribution, and particle numbers were also examined. It was found that PAspNa as a dispersion stabilizer provides an environmentally benign process for the preparation of monodisperse polymer microspheres by dispersion polymerization.     

Synthesis of polystyrene microspheres by dispersion polymerization in supercritical carbon dioxide using a poly(dimethylsiloxane)-based macroazoinitiator

The synthesis of polystyrene microspheres was achieved by the dispersion polymerization of styrene in supercritical carbon dioxide using azobisisobutylonitrile (AIBN) and a poly(dimethylsiloxane) (PDMS)-based macroazoinitiator, VPS-1001. VPS-1001 contained seven to nine molecules of the azo groups and the PDMS blocks with a molecular weight of 10,000 per molecule. The polymerization in the presence of both VPS-1001 and AIBN produced polystyrene microspheres with a diameter below 4 μm in over 85% yields, whereas the polymerization with VPS-1001 in the absence of AIBN provided a nonspecific polystyrene in only 20% yield. The particle size decreased as a result of increasing the concentration of VPS-1001. It was confirmed that the polystyrene particles were stabilized by the PDMS-block-polystyrene formed through the polymerization initiated by VPS-1001 because the polymerization using a PDMS homopolymer provided nonspecific polystyrene as a precipitate during the polymerization.     

Morphology of micron-sized monodispersed poly(butyl methacrylate)/polystyrene composite particles produced by seeded dispersion polymerization

In order to develop the seeded dispersion polymerization technique for the production of micron-sized monodispersed core/shell composite polymer particles the effect of polymerization temperature on the core/shell morphology was examined. Micron-sized monodispersed composite particles were produced by seeded dispersion polymerizations of styrene with about 1.4-μm-sized monodispersed poly(n-butyl methacrylate) (Pn-BMA) and poly(i-butyl methacrylate) (Pi-BMA) particles in a methanol/water (4/1, w/w) medium in the temperature range from 20 to 90 °C. The composite particles, PBMA/polystyrene (PS) (2/1, w/w), consisting of a PBMA core and a PS shell were produced with 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) initiator at 30 °C for Pn-BMA seed and with 2,2′-azobis(isobutyronitrile) initiator at 60 °C for Pi-BMA seed. The polymerization temperatures were a little above the glass-transition temperatures (T _g) of both Pn-BMA (20 °C) and Pi-BMA (40 °C). On the other hand, when the seeded dispersion polymerizations were carried out at much higher temperatures than the T _g of the seed polymers, composite particles having a polymeric oil-in-oil structure were produced. Received: 14 October 1998 Accepted in revised form: 2 June 1999     

Gas phase PVT properties and second virial coefficients of dimethyl ether

Dimethyl ether (DME) is an important chemical material and gets more and more attention as a clean alternative fuel and refrigerant nowadays. The gas phase PVT properties of dimethyl ether were measured using the Burentt-isochoric coupling method in the temperature range of 328–403 K with two Burnett expansions at 383 and 403 K. A total of 126 experimental points have been obtained. The experimental measurement uncertainties were estimated to be within ±10 mK for temperature and ±0.7 kPa for pressure. The second virial coefficients along 16 isotherms were derived using the present data.     

Preparation of poly(vinyl pivalate) microspheres by dispersion polymerization in an ionic liquid and saponification for the preparation of poly(vinyl alcohol) with high syndiotacticity

We report here a successful free-radical dispersion polymerization of vinyl pivalate (VPi) in an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][TFSI]) using poly(vinyl pyrrolidone) (PVP) as a stabilizer. Morphological analysis by FE-SEM revealed that poly(vinyl pivalate) (PVPi) obtained from dispersion polymerizations were in the form of spherical particles. Micron-sized, PVPi particles with a number-average molecular weight (M_n) of 166,400 g/mol could be obtained using 5% stabilizer (w/w to monomer) at 65 °C for 20 h. The effects of varying concentration of stabilizer, initiator and monomer upon polymer yield, molecular weight, and morphology of PVPi were also investigated. Analogous polymerizations in dimethyl sulfoxide (DMSO) and bulk served as references. In addition, the preparation of poly(vinyl alcohol) (PVA) by saponification of the resultant PVPi was described.     

Magnetic poly(N‐isopropylacrylamide) microspheres by dispersion and inverse emulsion polymerization

The aim of this study was to develop novel thermally responsive polymer microspheres with magnetic properties. Dispersion and inverse emulsion copolymerization of N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm) was investigated in the presence of γ‐Fe₂O₃ nanoparticles. The resulting microspheres were characterized in terms of morphology, size, polydispersity, iron content, and temperature‐dependent swelling using optical microscopy, transmission electron microscopy, scanning electron microscopy, QELS, and AAS. The effects of several variables, such as the concentration of γ‐Fe₂O₃, MBAAm crosslinking agent, Span 80 surfactant, 2,2′‐azobis(2‐methyloctanenitrile) (AMON) initiator, and polymerization temperature on the properties of the microspheres were studied. Swelling and thermoresponsive behavior of the microspheres containing γ‐Fe₂O₃ nanoparticles were also investigated. The microspheres contained about 8 wt % of iron. The presence of magnetic nanoparticles and their concentration changes did not have any significant effect on the temperature sensitivity of the composites. The particles gradually shrink into an increasingly collapsed state when the temperature is raised to 40 °C since the increase in temperature weakens the hydration and PNIPAAm chains gradually become more hydrophobic, which leads to the collapse of the particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5884–5898, 2007     

Synthesis of tert-butyl-substituted poly (ether ketone) by nickel-catalyzed coupling polymerization of aromatic dichloride

tert-Butyl substituted poly (aryl ether ketone)s with relatively high molecular weights were prepared by the Ni-catalyzed polymerization of tert-butyl substituted aromatic dichlorides containing ether ketone unit. These polymers were amorphous and soluble in common organic solvents, such as THF, dichloromethane, and chloroform. De-tert-butylation of the polymer by the treatment of trifluoromethanesulfonic acid in the presence of toluene proceeded smoothly and produced crystalline poly (aryl ether ketone). © 1994 John Wiley & Sons, Inc.     

Reactive poly(glycidyl methacrylate) microspheres prepared by dispersion polymerization

Poly(glycidyl methacrylate) [poly(GMA)] microspheres of narrow size distribution were prepared in a simple one‐step procedure by dispersion radical polymerization. Depending on the solvent used, poly(GMA) particle size could be controlled in the range of 0.5–4 μm by changing the solubility parameter of the reaction mixture. In N,N′‐dimethylformamide (DMF)/methanol mixture, the particle size increased and the size distribution broadened with decreasing initial solubility parameter. While in the DMF/methanol solvent system, hydroxypropyl cellulose (HPC) or cellulose acetate butyrate (CAB) were taken as steric stabilizers of the dispersion polymerization, poly(vinylpyrrolidone) (PVP) was used in alcoholic media. Contrary to the DMF/methanol system, narrow particle size distributions were obtained with PVP‐stabilized polymerizations in ethanolic, methanolic, propan‐1‐olic or butan‐1‐olic medium. Both the particle size and polydispersity were reduced with increasing stabilizer concentration. If lower molecular‐weight PVP was used, larger microspheres were obtained. Poly(GMA) samples prepared in a neat alcoholic medium virtually quantitatively retained oxirane group content after the polymerization. Reactivity of the poly(GMA) microspheres was confirmed by their hydrolysis and aminolysis. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3855–3863, 2000     

Vapor–liquid equilibria of the 1,1,1-trifluoroethane (HFC-143a) + dimethyl ether (DME) system

Binary vapor liquid equilibrium data were measured for the 1,1,1-trifluoroethane (HFC-143a) + dimethyl ether (DME) system at temperatures from 313.15 K to 363.15 K. These experiments were carried out with a circulating-type apparatus with on-line gas chromatograph analysis. The experimental data were correlated well by the Peng-Robinson equation of state using the Wong-Sandler mixing rules.     

Dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) using siloxane-based surfactant in supercritical carbon dioxide and in compressed liquid dimethyl ether

The free radical dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) has been carried out in supercritical carbon dioxide (scCO₂) and compressed liquid DME using several surfactants. The polymerization are performed in the presence of fluorine-based poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl acrylate) [poly(HDFDA)], poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate) [poly(HDFDMA)], or poly(HDFDMA-co-MMA) and siloxane-based PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA™) or PDMS modified surfactants, SS-5050K™ and KF6017™ as polymerization surfactants. When scCO₂ was used as a polymerization medium, the PHEMA were heavily agglomerated. However, the spherical and relatively uniform poly(2-hydroxyethyl methacrylate) (PHEMA) particles could be produced even at 20 bar, with a narrow particle size distribution in compressed liquid DME. It was observed that fluorine-based surfactants were not a good surfactant as siloxane-based surfactants for the dispersion polymerization of HEMA. The average particle size of PHEMA was shown to be dependent on the type of the surfactant, the amount of the surfactant and initiator added to the system. The effect of two continuous phases, which are scCO₂ and compressed liquid DME, as a polymerization medium, the surfactant types and the concentration, initiator concentration, and monomer concentration on the morphology and size of the polymer particles was also investigated.     

Synthesis of large-sized monodisperse polystyrene microspheres by dispersion polymerization with dropwise monomer feeding procedure

Highly monodisperse polystyrene (PS) microspheres in the size range of 3.75–7.09 μm were synthesized by dispersion polymerization with dropwise monomer feeding procedure. The morphology, size, and particle size distribution (PSD) of the PS microspheres obtained by different monomer feeding modes, including batch polymerization and various feeding rates, were investigated. The PSD of particles showed a close dependence on feeding rate. The PS microspheres with low coefficient of variation (CV) values all less than 4.8% obtained by the optimum feeding rates revealed better uniformity than those by batch polymerization (CV values all more than 8.2%). According to the time courses of monomer conversion and particle numbers, the effects of monomer feeding modes on the polymerization reaction of the large-sized PS microspheres were clarified. It is found that the dropwise monomer feeding procedure is promising for the synthesis of large-sized monodisperse PS particles in 3.75–7.09 μm.     

Preparation of narrow or monodisperse poly(ethyleneglycol dimethacrylate) microspheres by distillation-precipitation polymerization

Highly crosslinked narrow or monodisperse poly(ethyleneglycol dimethacryltae) (polyEGDMA) microspheres were prepared by distillation-precipitation polymerization in neat acetonitrile with 2,2′-azobis(2-methyl propinitrile) (AIBN) as an initiator. The polymer microspheres with clean surfaces due to the absence of any added stabilizer in the reaction system were formed simultaneously through a precipitation manner during the distillation of acetonitrile off the reaction system. The effects of the solvent, initiator concentration, monomer concentration and comonomer (divinylbenzene, DVB) fraction on the formation of the microspheres were investigated. Narrow- or monodisperse particles with spherical shape and smooth surface were obtained with diameters between 1.18 and 2.50 μm with monomer loading lower than 3.13 vol%. The surfaces of the microspheres became rougher, some elliptic particles and doublet or triplet appeared with the increase of monomer concentration (as high as 3.75 vol%). The yield of polymer microspheres was increased from 31% to 75% with the increase of EGDMA fraction from 0 to 100% when EGDMA was copolymerized with DVB. The resulting polymer microspheres were characterized with scanning electron microscope (SEM) and Fourier transform-IR spectra.     

Magnetic polyglycidylmethacrylate microspheres by dispersion polymerization

Composite polyglycidylmethacrylate [poly(GMA)] spherical microparticles capable of responding to magnetic fields were prepared by dispersion polymerization of GMA in the presence of iron oxides. The polymerization reaction was carried out in aqueous alcoholic media (methanol, ethanol, propan‐1‐ol, and butan‐1‐ol) using poly‐(N‐vinylpyrrolidone) and 2,2′‐azobisisobutyronitrile as a steric stabilizer and initiator, respectively. Quaternary ammonium salt (Aliquat 336) acting as an electrostatic costabilizer favorably affected dispersity. The solubility parameter of the reaction mixture determined the size of the resulting microspheres. In addition to the particle size distribution, the addition of iron oxide to the polymerization medium also caused a shift of the particle size to higher values. The results show that poly(GMA) particles contained up to 25 wt % iron oxide. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3707–3715, 2001     

Preparation of biodegradable microspheres by anionic dispersion polymerization with PLA copolymeric dispersion stabilizer

We prepared poly(d,l-lactide) (PLA) microspheres by anionic dispersion polymerization of d,l-lactide. The polymerization was carried out in xylene/heptane (1:2 in v/v) mixture solution at 368 K for 9 h, with poly(dodecyl methacrylate)-co-poly[α-methacryloxyethoxy-poly(l-lactide)] (PDMA-co-P(MA-PLLA)) synthesized in this study, as a dispersion stabilizer. The number-averaged diameter and diameter distribution (coefficient of variation) of obtained PLA microspheres ranged from 180 to 800 nm and 14–40%, respectively, depending on the preparation condition. Furthermore, the time courses of monomer conversion, particle diameter, and particle number were investigated to clarify the formation mechanism of microspheres with PDMA-co-P(MA-PLLA) as a dispersion stabilizer. From this experiment, we found that the aggregation of primary particles occurred in anionic dispersion polymerization, and the particle diameter of obtained PLA microspheres decreased with increasing PDMA-co-P(MA-PLLA) concentration. In conclusion, we clarified that PDMA-co-P(MA-PLLA) effectively contributed to the stability of primary particles.     

Synthesis of monodisperse poly(methacrylic acid) microspheres by distillation-precipitation polymerization

Monodisperse poly(methacrylic acid) (PMAA) microspheres were prepared by distillation-precipitation polymerization in acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as initiator. The polymeric microspheres were formed simultaneously via a precipitation polymerization manner during the distillation of the solvent out of the reaction system in the absence of any surfactant and crosslinker. Monodisperse PMAA microspheres with spherical shape and smooth surface were synthesized with diameters ranging from 60 to 290 nm below the glass transition temperature of PMAA without any stabilizer. The particle size increased with increasing monomer concentration, which may be resulted from the higher molecular weight for the polymerization. To investigate the growth procedure of PMAA microspheres, the morphology of microspheres over the distillated acetonitrile volume was conducted by monitoring the morphologies with TEM. GPC and FTIR provide key insights into the particle growth mechanism. The PMAA microspheres may be formed by an internal contraction due to the marginal solvency of the continuous phase with the aid of the hydrogen-bonding interaction between the carboxylic acid unit, in which the particles were stabilized by the steric effect of the pendent chains and surface gel as well as the electrostatic repulsion from the carboxylic acid group.     

Synthesis of highly sulfonated poly(arylene ether sulfone) random (statistical) copolymers via direct polymerization

Novel biphenol‐based wholly aromatic poly (arylene ether sulfones) containing pendant sulfonate groups were prepared by direct aromatic nucleophilic substitution polycondensation of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenyl sulfone (SDCDPS), 4,4′‐dichlorodiphenylsulfone (DCDPS) and biphenol. Copolymerization proceeded quantitatively to high molecular weight in N‐methyl‐2‐pyrrolidinone at 190°C in the presence of anhydrous potassium carbonate. Tough membranes were successfully cast from the control and the copolymers, which had a SDCDPS/DCDPS mole ratio of either 40:60 or 60:40 using N,N‐dimethylactamide; the 100% SDCDPS homopolymer was water soluble. Short‐term aging (30 min) indicates that the desired acid form membranes are stable to 220°C in air and conductivity values at 25°C of 0.110 (40%) and 0.170 S/cm (60%) were measured, which are comparable to or higher than the state‐of‐the art fluorinated copolymer Nafion 1135 control. The new copolymers, which contain ion conductivity sites on deactivated rings, are candidates as new polymeric electrolyte materials for proton exchange membrane (PEM) fuel cells. Further research comparing their membrane behavior to post‐sulfonated systems is in progress.     

Polyepichlorohydrine stabilized core shell microspheres by dispersion polymerization

Polystyrene microspheres ranging in diameter from 2 to 10 μm were prepared by dispersion polymerization in the presence of polyepichlorohydrine as the steric stabilizer precursor in alcoholic media. To clarify the effects of the solvent mixture composition, initiator concentration and steric stabilizer amount on the microsphere characteristics, including the molar mass parameters of the polymeric material, the microsphere size, and the steric stabilizer surface density, a three-factor full factorial design involving two levels of each of the factors and replicate experiments was employed. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 681–688, 1997     

Monodisperse and isolated microspheres of poly(N-methylaniline) prepared by dispersion polymerization

Monodisperse and isolated microspheres of poly(N-methylaniline) were successfully prepared through chemical polymerization of N-methylaniline by in adipic acid containing poly(vinylpyrrolidone) (PVP). Mean diameters of the microspheres with smooth surfaces changed from 320 to 100 nm by increasing the reaction temperature from 25 to 75 °C. The concentration of PVP did not affect much the size of microspheres, but the increased PVP concentration led to longer induction times for the onset of dispersion polymerization.     

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     

Magnetic poly(glycidyl methacrylate) microspheres prepared by dispersion polymerization in the presence of electrostatically stabilized ferrofluids

Fine magnetite nanoparticles, both electrostatically stabilized and nonstabilized, were synthesized in situ by precipitation of Fe(II) and Fe(III) salts in alkaline medium. Magnetic poly(glycidyl methacrylate) (PGMA) microspheres with core‐shell structure, where Fe₃O₄ is the magnetic core and PGMA is the shell, were obtained by dispersion polymerization initiated with 2,2′‐azobisisobutyronitrile (AIBN), 4,4′‐azobis(4‐cyanovaleric acid) (ACVA), or ammonium persulfate (APS) in ethanol containing poly(vinylpyrrolidone) or ethylcellulose stabilizer in the presence of iron oxide ferrofluid. The average microsphere size ranged from 100 nm to 2 μm. The effects of the nature of ferrofluid, polymerization temperature, monomer, initiator, and stabilizer concentration on the PGMA particle size and polydispersity were studied. The particles contained 2–24 wt % of iron. AIBN produced larger microspheres than APS or ACVA. Polymers encapsulating electrostatically stabilized iron oxide particles contained lower amounts of oxirane groups compared with those obtained with untreated ferrofluid. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5827–5837, 2004