The kinetics of poly(N-isopropylacrylamide) microgel latex formation

Conversion versus time curves were measured for poly(N-isopropylacrylamide) microgel latexes prepared by polymerization in water with sodium dodecyl sulfate, SDS. Polymerization rates increased with temperature with methylenebisacrylamide crosslinking monomer consumed faster thanN-isopropylacrylamide. The particle diameter decreased with increasing concentrations of SDS in the polymerization recipe and there was evidence that the rate of polymerization increased somewhat with SDS concentration. Particle formation occurred by homogeneous nucleation as micelles were absent.Comparison of particle size distributions from dynamic light scattering to those from a centrifugal sizer led to the conclusion that larger particles within a specific latex were less swollen with acetonitrile than were the smaller ones. This was interpreted as evidence for the polymer in larger particles having a higher crosslink density. Particle swelling was estimated from swelling ratios defined as the particle volume at 25 °C divided by the volume at 50 °C. In the absence of crosslinking poly(N-isopropylacrylamide) linear chains would disolve at 25 °C. The swelling results indicated that the average crosslink density in the particles decreased with conversion. This was explained by the observation that the methylenebisacrylamide was consumed more quickly and is typical of crosslinking in emulsion polymerization where polymer particles have high polymer concentrations at their birth.     

Agitation requirement for synthesis of micron-sized monodisperse polymer particles in soap-free polymerization method

Single-stage polymerization recently proposed for producing micron-sized polymer particles in aqueous media by Gu, Inukai and Konno (2002) was carried out under the control of agitation with styrene monomer, an amphoteric initiator, 2,2′-azobis [N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate and a pH buffer NH₃/NH₄Cl at a monomer concentration of 1.1 kmol/m³ H₂O, an initiator concentration of 10 mol/m³ H₂O and a buffer concentration of [NH₃] = [NH₄Cl] = 10 mol/m³ H₂O. In the polymerizations, impeller speed was ranged from 300 to 500 rpm to satisfy complete dispersion of the monomer phase and not to introduce the gas phase from the free surface. Polymerization experiments under steady agitation indicated that impeller speed was an important factor for size distribution of polymer particles. An increase in impeller speed promoted particle coagulation during the polymerization to enlarge the average size of polymer particles but widen the size distribution. To produce polymer particles with narrow size distribution, stepwise reduction in impeller speed was examined in the polymerization experiments. It was demonstrated that this method was more effective than the steady agitation. The impeller speed reduction could produce highly monodisperse particles with an average size of 2 μm and a coefficient of variation of size distributions of 2.2% that was much smaller than typical monodispersity criterion of 10%.     

无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究

无乳化剂乳液聚合法合成单分散大粒径高分子微球的研究朱世雄杜金环金熹高陈柳生（中国科学院化学研究所北京１０００８０）关键词无乳化剂乳液聚合，单分散，均相成核，低聚物胶束微米级大粒径单分散高分子微球在标准计量、情报信息、分析化学等许多领域都有广泛的...     

Influence of the swelling state of seed polymer particles with monomer on the morphology of micron-sized monodispersed composite polymer particles produced by seeded polymerization utilizing the dynamic swelling method

 Micron-sized mono-dispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles (PS/PBMA=2/1 by weight) having a heterogeneous structure in which many fine PBMA domains dispersed in a PS matrix near the particle surface were produced by seeded polymerization of n-butyl methacrylate (BMA) of which almost all had been absorbed by 1.8 μm-sized monodispersed PS seed particles utilizing the dynamic swelling method. The morphology was varied by changing the PS/BMA ratio and polymerization temperature. It was concluded that the swelling state of 2 μm-sized BMA-swollen PS particles in the seeded polymerization process is one of the important factors to control the morphology of the composite particles. Received: 27 November 1996 Accepted: 21 March 1997     

Preparation of two kinds of chloromethylated polystyrene particle using 1,4-bis (chloromethoxy) butane as chloromethylation reagent

By adopting “grafting from” manner, polystyrene was grafted onto the surface of silica gel particles with an average size of 125 μm in a solution polymerization system, and grafted particle PSt/SiO₂ was prepared. Using 1,4-bis (chloromethoxy) butane (BCMB, it is nontoxic.) as chloromethylation reagent, chloromethylation reaction for the grafted particle PSt/SiO₂ was performed in the presence of Lewis acid catalyst SnCl₄. At the same time, cross-linked styrene-divinylbenzene copolymer (CPS) microsphere also was chloromethylated with the same reagent as PSt/SiO₂, so that two kinds of chloromethylated polystyrene particles were obtained, and they are chloromethylated grafted particle (CMPS/SiO₂) and chloromethylated cross-linked polystyrene (CMCPS) microsphere, respectively. The chemical structures and compositions of the two particles were characterized using Fourier transform infrared and Volhard method. The effects of various factors on the chloromethylation reactions were mainly investigated. The experimental results show that the process to prepare the two kinds of chloromethylated polystyrene particles not only has the character of environment friendness and low cost but also is convenient to control via adjusting various reaction conditions. The main reaction conditions affecting the chloromethylation reactions are reaction time, the added amount of BCMB, and the used amount of solvent and catalyst. They influence the reaction in two respects: (1) the chloromethylation degrees of polystyrene are different under different conditions; (2) Friedel–Crafts cross-linking reaction between polystyrene macromolecules is accelerated or inhibited under different conditions (for CPS microsphere, this cross-linking reaction also is called the additional cross-linking). Under suitable conditions, the two kinds of chloromethylated polystyrene particles with a high chlorine content (about 17%, this chlorine content was calculated based on polystyrene weight) can be gained using SnCl₄ as catalyst and CH₂Cl₂ as solvent at room temperature for 10 h and basically without cross-linking or additional cross-linking.     

Laser Emission from Dye-Doped Organic-Inorganic Particles of Microcavity Structure

Interaction between laser light and a micrometer-size spherical particle causes an optical resonance in its interior since a spherical wall acts as a cavity. The present work seeks to investigate the preparation of organicinorganic particles containing laser dyes and demonstrate their lasing behavior. Rhodamine 6G was incorporated into organic-inorganic spherical particles of micrometer-size using sol-gel technique. Phenyl triethoxy silane was used as a starting material for particles. Particle size was 1–10 μm and dye content was 1–7 × 10⁻⁵ mol/g. A particle was set on a glass plate in air and pumped by a second harmonic pulse ofQ-switched Nd-YAG laser (532 nm wavelength). From a particle of 6 μm in diameter, a strong laser emission peak was observed at 598 nm wavelength which corresponded to the whispering-gallery mode resonance.     

Design of polylactide-grafted copolymeric stabilizer for dispersion polymerization of D,L-lactide

Poly(D,L-lactide) (PDLLA) microspheres with narrow diameter distribution were prepared by dispersion polymerization of D,L-lactide in xylene/heptane (1:2, v/v) using poly(dodecyl methacrylate)-g-poly(D,L-lactide) (PDMA-g-PDLLA) as a dispersion stabilizer. The particle diameters of PDLLA microspheres were controlled from 200 nm to 5 μm by altering the concentration and the graft chain number of PDMA-g-PDLLA. The effect of the copolymer composition on the particle diameter was investigated to clarify an important factor of the copolymer structure for the control of the particle diameter. As a result, it was necessary for anchor block in diblock copolymer as a dispersion stabilizer to have low solubility in the solution rather than the compatibility with particles. Moreover, we confirmed by dynamic light scattering measurement that PDMA-g-PDLLA formed micelles in the solution. In conclusion, it was clarified that PDLLA microspheres with a wide range of particle diameter were prepared due to the different kinetic stability of micelles.     

Synthesis of polyhedral particles by dispersion polymerization in supercritical carbon dioxide

The novel synthesis of polyhedral particles was attained by the dispersion polymerization of styrene in supercritical carbon dioxide using a polydimethylsiloxane-based macroazoinitiator as a precursor of the surfactant. The macroazoinitiator, VPS-1001, composed of poly(dimethylsiloxane) and 6-8 molecules of the azo groups served as a precursor of the surfactant for the dispersion polymerization by azobisisobutylonitrile as an initiator to produce 0.8-4 μm polyhedral particles. The size of the particles decreased as a result of increasing the VPS-1001 concentration. Too high a concentration of VPS-1001 caused coagulation of the particles. A decrease in the temperature increased the particle size and size distribution, while a decrease in the pressure produced particles with nonspecific shapes. An increase in the stirring rotation speed tended to increase the size and size distribution. However, too high a speed of rotation also caused coagulation of the particles.     

Desulfurization of pittsburgh coal by microbial column flotation

Microbial column flotation usingThiobacillus ferrooxidans was applied for desulfurization of Pittsburgh coal of CWM (Coal-Water Mixture) size between 38 μm and 75 μm. The coal contained ferrous ion which would interfere separation of pyrite from coal by microbial flotation. The wash-out of ferrous ion with 0.5N HC1 solution enabled pyrite removal from coal. The coal was divided into two parts, the small-size coal between 38 μm and 53 μm, and the large-size coal between 53 μm and 75 μm. The pyritic sulfur content was decreased from 2.88% of the feed coal to 0.98% of the product coal for the largesize coal and from 2.77% of the feed coal to 1.12% of the product coal for the small-size coal by microbial flotation. The decrease was based on removal of liberated pyrite particles (between 20 μm and 70 μm). However, the fine particles (less than 20 μm) could not be removed even though the pyrite particles were liberated from coal particles. The microbial column flotation was more effective for desulfurization of the large liberated pyrite particle than that of the small. It was not effective for desulfurization of the locked pyrite particles that were buried in coal particles. Both the pyrite liberation from coal and its particle size are important factors for the pyrite removal by microbial column flotation.     

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     

Effect of reaction parameters on the dispersion polymerization of 1‐vinyl‐2‐pyrrolidone

Nonporous hydrogel microspheres 0.1–1.3 μm in diameter were prepared by the dispersion copolymerization of 1‐vinyl‐2‐pyrrolidone and ethylene dimethacrylate as a crosslinking agent. The crosslinking was evidenced by solid state ¹³C NMR and elemental analysis. The effect of various parameters including selection of solvent (cyclohexane, butyl acetate), initiator (4,4′‐azobis(4‐cyanopentanoic acid), 2,2′‐azobisisobutyronitrile, dibenzoyl peroxide) and stabilizer on the properties of resulting microspheres has been studied. Dynamic light scattering and photographic examination were used for determination of the diameter and polydispersity of microspheres. Increasing concentration of steric stabilizer in the initial polymerization mixture decreased the particle size. The particle size depended on the molecular weight of polystyrene‐block‐hydrogenated polyisoprene stabilizer, but not on the number of PS and polybutadiene blocks in the styrene–butadiene block copolymer stabilizers. Dibenzoyl peroxide used as an initiator resulted in agglomeration of particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 653–663, 2000     

Size control of polystyrene nodules formed on silica particles in soap-free emulsion polymerization with amphoteric initiator

An amphoteric initiator of 2,2′-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was applied to fabrication of raspberry-shaped composite particles in soap-free emulsion polymerization of styrene in the presence of silica particles surface-modified with 3-methacryoxypropyltrimethoxysilane. In the polymerizations, pH of the solution was ranged from 7.9 to 9.9 to alter dissociation degree of ionizable groups in the initiator. Raspberry-shaped particles were obtained in a pH range of 8.0 to 9.3 followed by a tendency in which average size of polystyrene (PSt) nodules adsorbed onto the silica particles decreased with pH. This tendency was similar to that of polymer particles formed in conventional soap-free emulsion polymerization in the absence of the silica particles. An increase in silica particle concentration led to a decrease in the final size in PSt nodules. The decrease was caused by the stabilization of polymer particles fixed to the silica surface against polymer particle aggregation in water phase.     

Emulsion copolymerization of styrene and methacrylic acid in the presence of a polyethylene oxide based-polymerizable stabilizer with a shorter chain length

The emulsion copolymerization of styrene and methacrylic acid (MAA) was performed in the presence of a relatively new macromonomer, poly(ethylene glycol) ethyl ether methacrylate (PEG-EEM) as a stabilizer. In contrast to similar studies, a macromonomer having relatively shorter polyethylene oxide chain length (i.e., M_n:246, n ≈ 3.0) was selected for this study. Highly uniform and carboxyl functionalized latex particles in the size range of 0.16–0.50 μm were obtained by changing MAA, PEG-EEM, total monomer, and initiator concentrations. The use of PEG-EEM as a stabilizer resulted in larger monodisperse particles relative to those obtained by the emulsifier-free emulsion copolymerization of styrene and MAA. The particle size decreased and the polymerization rate increased with the increasing MAA feed concentration. The application of power law model indicated that MAA concentration was more effective in the presence of PEG-EEM for control of particle size relative to similar systems. The latex particles with higher numbers of surface-carboxyl groups were obtained with the higher MAA feed concentrations. Although the particle size decreased and the polymerization rate increased with the increasing PEG-EEM concentration in the emulsion polymerization of styrene, both of them remained roughly constant with the increasing PEG-EEM concentration in the presence of MAA. Received: 21 December 2000 Accepted: 13 July 2000     

Preparation of monodisperse polystyrene microspheres: effect of reaction parameters on particle formation,and optical performances of its diffusive agent application

There are three monodisperse polystyrene (PSt) microspheres, 1.10, 3.13, and 5.21 um in diameter were prepared by dispersion polymerization in ethanol/iso-propanol media. 2,2′-azobis(isobutyronitrile) (AIBN) and poly(acrylic acid) (PAA) were utilized as initiator and steric stabilizer, respectively. The effects of the PAA stabilizer, AIBN initiator, St monomer, and EtOH solvent on particle size and size distribution were reviewed in this article. Besides, optical properties including total transmittance (T%) and transmittance haze (H%) were performed when these three monodisperse PSt microspheres were applied as diffusive agents. The results were examined in terms of total interface area in a system, and came up an optimal situation between transmittance haze (H _max% = 65%) and T% when total surface area of particles is around 45,000 cm².     

Morphology of micron-sized monodispersed composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

 Monodispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles having 9.4 μm in diameter were produced by seeded polymerization for the dispersion of highly n-butyl methacrylate (BMA)-swollen PS particles, and their morphologies were examined. The highly BMA-swollen PS particles (about 150 times the weight of the PS seed particles) were prepared by mixing monodispersed 1.8 μm-sized PS seed particles and 0.7 μm sized BMA droplets prepared with an ultrasonic homogenizer in ethanol/water (1/2, w/w) medium at room temperature. After NaNO₂ aqueous solution as inhibitor was added in the dispersion, the seeded polymerization was carried out at 70 °C. In an optical microscopic observation, one or two spherical high contrast regions which consisted mainly of PS were observed inside PS/PBMA composite particles. In the PS domain, there were many fine spherical PBMA domains. Such morphologies were based on the phase separation of PS and PBMA within the homogeneous swollen particles during the seeded polymerization. Received: 04 June 1997 Accepted: 27 August 1997     

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.     

Visual microscopic studies on hetero-aggregation and selective aggregation

 An optical video microscopic technique was used to study hetero-aggregation and selective aggregation phenomena among n-hexadecane oil drops (40–110 μm in diameter) and two types of polystyrene latex particles (6.76 and 30.2 μm, in diameter), suspended inside an aqueous medium with pH varying between 1.1 and 12.9. A single drop was produced in situ using a micropipette inside the aqueous phase-filled glass microcapillary (100–160 μm i.d.) containing the particles. Interactions between the drop and the solid particles and among the solid particles was achieved by movement of the aqueous medium in and out of a second micropipette. Drop–particle interactions were distinctly different from particle–particle interactions. It was observed that the latex particles aggregated irreversibly with the oil drop in all cases except two, viz. for 6.76 μm particles at around neutral pH whereas the irreversibility of aggregation in particle–particle interactions was only seen at the ends of the pH spectrum. At around neutral pH, the flocs or clusters of small particles were very weak. Visual observations at each pH are explained on the basis of the classical DLVO (Derjaguin–Landau–Verwey–Overbeek) theory. Partial wetting of particles surfaces by oil appears to be a key factor in the irreversibility of drop– particle hetero-aggregation. Results indicate that the display of reversible, irreversible or weak aggregation depends on the location and depth of the secondary minimum and that the long-range, attractive, London–van der Waals force is responsible for the initial formation of an aggregate. Received: 4 July 1996 Accepted: 5 December 1996     

Kinetics analysis of colloidal crystallization of silica spheres modified with polymers on their surfaces in acetonitrile

 The nucleation and growth rates in the colloidal crystallization of silica spheres (136 nm in diameter) modified with polymers on their surface were measured by time-resolved reflection spectroscopy. The polymers were poly(maleic anhydride-co-styrene) [P(MA-ST)] and poly(methyl methacrylate) (PMMA). The induction period for nucleation decreased sharply when the sphere concentration increased. The crystal growth process consisted of a fast growing step leading to metastable crystals (rate v ₁) and a slow growth rate accompanied by the formation of stable crystals. The crystal size of the P(MA-ST)/SiO₂ particles decreased from 0.4 to 0.06 mm, whereas v ₁ increased from 13 to 37 μm/s, when the particle concentration increased. The slow step was also observed for almost all the samples but was not analyzed since the rate was too small. For PMMA/SiO₂ dispersions, the crystal size (0.17–0.3 mm) and v ₁ (43–166 μm/s) did not show any relation to the particle concentration but showed a linear relationship with the molecular weight of PMMA. These results suggest the important role of the excluded-volume effects of the polymer layers around the silica surface. The contribution of the repulsion due to the electrical double layers is still effective in the colloidal crystallization in acetonitrile. Received: 6 June 2001 Accepted: 20 September 2001     

Synthesis of porous titaniaspheres for HPLC by polymerization-induced colloid aggregation (PICA) using <Emphasis Type="Italic">tert-n</Emphasis>-butyl titanate

Porous titanic microspheres with a very narrow particle size distribution (PSD) which are useful as chromatographic packing materials for high performance liquid chromatography (HPLC), were synthesized by an improved process of polymerization-induced colloid aggregation method using tert-n -butyl titanate. Porous titania particles obtained after polymer combustion and sintering of the aggregates are 3.5 μm in diameter with a surface area of 9.6 m² g⁻¹ and an average pore diameter of 18.9 nm. The particles are strong enough to withstand the high packing pressure for a HPLC column. The article is published in the original.     

Influence of particle diameter on the morphology of micron-sized, monodispersed composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

 Micron-sized, monodispersed polystyrene (PS)/poly (n-butyl methacrylate) (PBMA) composite particles, in which the PS domain(s) were dispersed in a PBMA continuous phase, were produced by seeded polymerization for dispersions of n-butyl methacrylate (BMA) swollen PS particles in a wide range of PS/BMA ratios in the presence of NaNO₂ as a water-soluble inhibitor. Moreover, in order to change the diameter of the composite particles at same PS/BMA ratio, PS/PBMA (1/150 w/w) composite particles were produced using five kinds of PS particles in a range of diameters from 0.64 to 3.27 μm as seeds. The percentages of the PS/PBMA composite particles having double and triple and over PS domains, which were thermodynamically unstable morphologies, increased with the increase in the diameter of BMA swollen PS particles. There was a clear influence of the size of the swollen particles on the morphology of the PS/PBMA composite particles produced. Received: 30 September 1999/Accepted: 18 April 2000