Emulsifier‐free miniemulsion polymerization of styrene and the investigation of encapsulation of nanoparticles with polystyrene via this procedure using an anionic initiator

Emulsifier‐free miniemulsion polymerization of styrene was investigated in the presence of potassium persulfate (KPS) as an anionic initiator and cetyl alcohol as a costabilizer using ultrasonic irradiation and comparison of this procedure with conventional emulsifier‐free emulsion polymerization showed that this method has a remarkably higher polymerization rate (R_p), smaller size of particles, and narrower molecular weight distribution via gravimetric measurement, transmission electron microscopy (TEM), and gel permeation chromatography techniques, respectively. Then, the encapsulation of magnetite (Fe₃O₄) and titanium dioxide (TiO₂) nanoparticles with polystyrene was investigated using this procedure. Attempt to encapsulate magnetite nanoparticles failed; however, the encapsulation of titanium dioxide nanoparticles was successfully carried out via this procedure using KPS in both cases. TEM proved the presence of TiO₂ nanoparticles in polymer particles, and thermogravimetric analysis was used to determine the percentage of TiO₂ in the products. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Kinetic studies of semibatch emulsion copolymerization of methyl methacrylate and styrene in the presence of high intensity ultrasound and initiator

The present work deals with kinetic studies of copolymerization of methyl methacrylate and styrene using ultrasound assisted semibatch emulsion copolymerization in the presence of sodium dodecyl sulfate (emulsifier) and potassium persulfate (external initiator). The effect of temperature, acoustic intensity, initiator loading, surfactant concentration and monomer concentration on the extent of conversion has been investigated. The extent of polymerization was observed to increase with an increase in the temperature, and concentrations of initiator, monomer and surfactant. Further, the initial polymerization rate increased with an increase in the acoustic intensity from 11.2 to 23.1 W cm⁻² and then it was found to decrease with a further increase to 33.80 W cm⁻². The novelty of this work lies in the fact that there have been only limited kinetic studies for the approach of ultrasound assisted emulsion copolymerization. It has been also established in the present work that the formation of fine and stable monomer droplets, due to the cavitational activity at/near the interface of immiscible monomer phase and subsequent disruption by micro jets, leads to the smaller final polymer particle size and under optimized conditions, it was found to be about 40 nm.     

十八烷/PSt相变微胶囊的制备及其热性能研究

细乳液法制备了十八烷/聚苯乙烯(PSt)相变微胶囊,用TEM、DLS和DSC等对微胶囊进行了表征。研究了十二烷基硫酸钠(SDS)的加入量、亲水性单体丙烯酸的加入量、引发剂类型以及苯乙烯与十八烷的加料比对产物形态的影响。研究表明:低的SDS浓度有利于微胶囊结构的形成,产物粒子的平均粒径随SDS加入量的增大而减小;加入亲水性共聚单体丙烯酸可以改善微胶囊的形态,但产物中PSt均相微球增多;使用油溶性引发剂AIBN比使用KPS更加有利于微胶囊的形成;苯乙烯与十八烷的投料比为1∶1时,制备的微胶囊相变焓为111.6 J/g。     

Kinetics of magnetite nanoparticles formation in a one step low temperature hydrothermal process

In the present study, a one step hydrothermal process was employed to synthesize magnetite nanoparticles using oleic acid as surfactant agent at 140 °C. Effects of reaction time and alkalinity were studied on particles size and morphology. By changing these parameters, some monodisperse spherical nanoparticles with mean particle size between 2.71 and 13.88 nm were synthesized and characterized via TEM, XRD, VSM, TGA and FT-IR techniques. Assuming the Avrami behavior of particles formation, a kinetics equation was proposed for the transformation rate at 140 °C. Using some simplifying assumptions, nucleation and growth rates were calculated for the hydrothermal formation of magnetite nanoparticles at 140 °C.     

Nonionic surfactant-stabilized raspberry-like polymer/silica nanoparticles latex with film formability

Raspberry-like P(St-BA)/SiO₂ nanoparticle latexes were prepared via miniemulsion polymerization of styrene (St) and butyl acrylate (BA) in the presence of 20 nm glycerol-modified SiO₂ sol as a Pickering emulsifier and octaphenyl polyoxyethylene (CA-897) as a nonionic surfactant, using 2,2-azobis (isobutyronitrile) (AIBN) as an initiator. 2-(Methacryloyl) ethyltrimethylammonium chloride (MTC) was introduced to act as an auxiliary monomer to enhance the attraction of SiO₂ sol onto latex nanoparticles (NPs) via increasing their electrostatic interaction with negative-charged SiO₂ sol. The average particle sizes of the latex particles can be well controlled from 200 to 360 nm by variation of the SiO₂ sol content as well as soft monomer BA component. The latex NPs displayed a good colloidal stability with excellent resistance to both strong acidic and basic environment. Furthermore, the nanosized latexes exhibited good film formability. The influence of reaction parameters, e.g., the initial silica amount and soft monomer BA content was systematically investigated on the film performances, such as hardness, abrasive resistance, water absorption, gloss. The results indicated that the increase of SiO₂ sol content can contribute to the increase of the film hardness and water absorption ability, while increasing BA component is beneficial to the improvement of the film gloss.     

Unsaturated polyester resins based on rosin maleic anhydride adduct as corrosion protections of steel

Unsaturated polyester resin (UP), based on 1 mol maleopimaric adduct (MPA), 1 mol maleic anhydride, 1 mol isophthalic acid, 1 mol adipic acid, 1 mol propylene glycol, and 1 mol diethylene glycol, were obtained at various times during polyesterification. They were characterized by ¹H NMR and chemical titration. Increasing the reaction time to 8 h led to an increase in (a) the number-average molar mass (Mn), (b) the glass transition temperature (T_g) and (c) the compatibility with styrene. Several of these fractions were cured with styrene, in amount of UP/ST = 2.5 (weight of styrene, ST, and unsaturated polyester, UP), using initiator and activator. The curing behaviors of cured UP resins with styrene were evaluated by DSC measurements. The prepared UP curable resins were evaluated in the field of steel coating by measuring their mechanical properties and chemical resistance. The corrosion resistance of cured films was evaluated using salt fog resistance test.     

On the mechanical and biological properties of bredigite-magnetite (Ca7MgSi4O16-Fe3O4) nanocomposite scaffolds

The aim of the present study was to study the mechanical and biologocal properties of the bredigite-magnetite (Ca₇MgSi₄O₁₆-Fe₃O₄) nanocomposite with various amounts of magnetite (0, 10, 20 and 30 wt%). According to the obtained results, the properties of the constructed scaffolds have an extreme dependence on the magnetite content. In this research, the bredigite-30 wt% magnetite as the optimum sample showed a fracture toughness of 2.69 MPa m^1/2 and a Young's modulus of 29 GPa. Increasing bredigite content led to the increase of pH values in the SBF solution. This was originated from the interchange/interaction of Ca²⁺ ion on the scaffold surface. The sample containing 10 wt% magnetite presented a rocky and irregular surface while that of 30 wt% illustrated a smooth and flat outer layer with coarse projections. The results confirmed that the biodegradation rate of the pure bredigite is more than that of 20 wt% sample. The event is originated from the dissolution of the Si ions of the bridigite particles in the absence of magnetite.     

Preparation and characterization of CuS hollow spheres

CuS hollow spheres have been successfully prepared using styrene–acrylic acid copolymer (PSA) latex particles as template. The process involved the deposition of inorganic coatings on the surface of PSA latex particles and subsequent removal of the latex particles by dispersing in toluene. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and UV–vis absorption spectroscopy. The results showed the wall thickness of CuS shell to be about 20 nm and the pore diameter to be about 150 nm. The possible formation mechanism of CuS hollow spheres has been proposed.     

Preparation and Characterization of magnetic latexes using Styrene monomer

Summary Preparation of magnetic latexes using styrene as monomer was carried out via miniemulsion polymerization. Magnetite (Fe₃O₄), with an average size of 12nm was used as magnetic particles. An organic phase is prepared dispersing the magnetite in styrene where bis(2-ethyl, hexyl) sulphosuccinate (AOT) is used as dispersant of the particles. The dispersion is miniemulsified in water using Cethyltrimethylammonium bromide (CTAB) as second emulsifier forming a stable emulsion. The miniemulsion polymerization was carried out at 60° C and was initiated with 2,2 Azo-bis-iso-butyronitrile (AIBN). The latexes obtained were characterized by X-ray diffraction, Magnetometry and Transmission Electronic Microscopy.     

Influence of the Initial pH on the adsorption behaviour of dispersant on nano zirconia powder

The quantitative adsorption behaviour of ammonium salt of poly(acrylic acid) onto zirconia powder in aqueous solution is characterized by using UV adsorption spectrum. Adsorption isotherms of dispersant on the zirconia surface, electrophoretic mobility of zirconia particles as a function of the dispersant concentration have been investigated. The adsorption behaviour of PAA-NH₄ is dependent on the pH of the suspension and the concentration of the ammonium salt of poly(acrylic acid). The maximum amount of PAA-NH₄ adsorbed on the zirconia surface, 6·3 mg m⁻² at pH 2·62, decreases to 2·1 mg m⁻² at pH 12·20. The adsorption of PAA-NH₄ causes a highly negatively charged powder surface and almost same final pH value.     

Particle number and size of polystyrene‐dependent micellar crosslinking polymerization of acrylic acid

The effect of the number and size of polystyrene particles and the concentration of ammonium persulfate used as the initiator on the micellar crosslinking polymerization of acrylic acid was studied by real‐time monitoring of the storage modulus (G ′), the damping factor (tanδ), and the ratio of the complex modulus (G*) to the maximum G* (G*_max) during 1 h of polymerization. The molar ratio (5.83 × 10^?4) of N,N′‐methylenebis‐acrylamide to acrylic acid was fixed. Polystyrene particles were prepared by emulsifier‐free emulsion polymerization. The diameter of the particles ranged from 233 to 696 nm. The results show that crosslinking polymerization was most effective when 1.31 × 10¹² particles were incorporated into the system, while crosslinking polymerization was less effective in the particle‐filled system than in the unfilled polymerization system if the particle number was 50% lower or higher. Crosslinking was also more effective with the use of uncrosslinked firmer and larger particles at the fixed particle number, except for the anomalous behavior observed with 696 nm polystyrene particles. Increasing the feed concentration of the initiator resulted in more efficient crosslinking up to a limiting concentration of 0.765 mg mL^?1 (the molar ratio of initiator to monomer was 8.52 × 10^?4). When this initiator concentration was doubled, the rate of increase of G ′ in the deceleration phase was slower after the network was formed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42851.     

Synthesis of high-stability acidic Ce3 + (La3 + or Sm3 +)~β/Al-MCM-41 and the catalytic performance for the esterification of oleic acid

Ce^3 + (La^3 + or Sm^3 +)~β/Al-MCM-41 molecular sieves were synthesized by impregnation and used to catalyze the esterification of oleic acid with short chain alcohols, such as methanol, ethanol, isopropanol, and isobutanol, to obtain biodiesel. Ce^3 +(La^3 + or Sm^3 +)~β/Al-MCM-41 was found to exhibit excellent catalytic activity and stability. The effect of rare earth elements on the acidity of catalysts was examined in detail by NH₃-TPD and Py-FTIR. The optimum conditions for the esterification of oleic acid with methanol were determined. Moreover, the kinetics of the esterification showed that the average reaction order (n) was 1.92, with an activation energy of 51.46 kJ/mol.     

Double‐miniemulsion preparation of Fe3O4/poly(methyl methacrylate) magnetic latex

Magnetic poly(methyl methacrylate) (PMMA) microspheres were prepared by double‐miniemulsion polymerization. First, oleic acid coated magnetite particles synthesized by means of coprecipitation were dispersed into octane to obtain a ferrofluid. The ferrofluid and MMA were emulsified to form O/W emulsion, respectively. Subsequently two miniemulsions were mixed together for polymerization. The obtained magnetic polymer particles were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, X‐ray powder diffraction, and thermogravimetry. The results showed that oleic acid coated magnetite particles were well encapsulated in PMMA. The effects of initiator dosage and monomer concentration on the conversion of MMA were also investigated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Particle formation mechanism in radical polymerization in miniemulsion based on in situ surfactant formation without high energy homogenization

Conventional radical polymerization of styrene at 70 °C in aqueous miniemulsion generated using the in situ surfactant technique, without use of high energy mixing, has been investigated in detail. The surfactant potassium oleate was formed in situ by reaction between oleic acid and potassium hydroxide at the styrene/water interface. The particle formation mechanism was investigated by use of pyrene as a probe, revealing that under suitable conditions with an oil-phase initiator, particle formation occurs primarily via monomer droplet nucleation. The droplet/particle stability is however inferior to that in a typical miniemulsion generated employing ultrasonication, as manifested by a marked increase in droplet/particle size with conversion and a bimodal droplet/particle size distribution by weight. The droplet/particle stability increases with increasing amount of oleic acid, hexadecane, water, and the ratio potassium hydroxide:oleic acid, respectively.     

Preparation of Fe-BEA zeolites by isomorphous substitution for oxidehydration of glycerol to acrylic acid

The preparation by post-synthesis isomorphous substitution of Fe_X-BEA-Y in one step was investigated for the oxidehydration of pure glycerol. TPR and DR UV–vis highlighted the presence of Fe^(+ III) species in the framework of zeolites. Iron allows the activation of the catalyst by the reduction by glycerol of part of Fe^(+ III) into Fe^(+ II) species, which stabilizes the glycerol conversion. Total glycerol conversion is obtained with 4 wt% of iron and acrylic acid yield reaches 23% over this catalyst. The Fe^(+ III) tetrahedral species are thought to be the main active redox sites for the formation of acrylic acid.     

Flow improver additives for gas condensate

This paper describes synthesis and evaluation of polymeric additives for improving the flow properties of gas condensate. The additives were prepared by the free-radical initiated polymerization of methacryl esters with styrene and acrylic or methacrylic acid. Polymerization was performed by initiator azo-bis isobutyronitrile in toluene or xylene at 80 °C. The influence of additives structure, composition and molar weight, as well as gas condensate properties on its flow properties was studied. Gas condensate samples from the fields of Kalinovac, Stari Gradac and Molve located in the northern Croatia were used for evaluation of the prepared additives. It was found that the additives efficiency was considerably influenced by their properties and by condensate n-paraffin content and distribution.     

Studies on graft copolymerization of chitosan with acrylonitrile by the redox system

Graft copolymers of chitosan with acrylonitrile (AN) were prepared by free radical polymerization using initiator pair of ammonium persulfate and sodium thiosulfate as redox system firstly. Graft copolymerization was confirmed by FTIR spectra, X-ray diffraction and ¹H NMR spectra measurements. The mechanism of graft copolymerization and factors affected graft reaction were explored in details, and the optimum reaction conditions were obtained at [AN] 0.9 mol/L, [CS] 13.3 g/L, [Initiator] 0.006 mol/L, 62 ± 1 °C and 2 h. Then the solubility of chitosan-g-PAN was investigated by using several solvents. The concentrated nitric acid solution and NaSCN solution are good solvents for the graft product. It's confirmed that composites of graft copolymer and PAN had a good film-forming property, and it is suggested that the graft copolymer is promising for fabrication of acrylic fibers as a kind of functional additive.     

The effect of the surfactants on the formulation of UV-curable SLA alumina suspension

Stereolithography (SLA) has been regarded as the most promising rapid prototype (RP) production method for ceramic parts recently because of its better precision in size and site control. The rheological behavior and curing behavior of suspensions are controlling factors for ceramic stereolithography. In this work, oleic acid (OA), stearic acid (SA) and Poly(Acrylate Ammonium) (PAA-NH₄) were studied as the surfactant for HDDA-based suspension formulation. Modified alumina particles exhibit different wettability with HDDA monomer and thus the different rheology behavior and stability between the formulated suspensions. OA shows the best performance among all three dispersants. 40 vol% alumina suspensions with a viscosity ˂3 Pa s at 30 s⁻¹ shear rate were successfully formulated with OA and SA. A sintering density of 95% can be reached for the OA- and SA-modified alumina UV-curable resins.     

Synthesis of amphiphilic copolymers by ATRP initiated with a bifunctional initiator containing trichloromethyl groups

Bifunctional polystyrene macroinitiators, having various molecular weights, were prepared by atom transfer radical polymerization (ATRP), initiated with bifunctional initiator 1,3-bis{1-methyl-1[(2,2,2-trichloroethoxy) carbonylamino]ethyl}benzene in conjunction with CuCl catalyst and polyamine ligands. These macroinitiators were subsequently used for ATRP of tert-butyl acrylate (t-BuA), giving BAB triblocks poly[(t-BuA)-b-(Sty)-b-(t-BuA)] as precursors of amphiphilic copolymers. Both the polymerization steps proceeded as controlled processes with linear semi-logarithmic conversion plots and lengths of the blocks following theoretical predictions. Hydrolysis of outer poly(t-BuA) blocks led to triblock copolymers with the central polystyrene block and outer blocks of poly(acrylic acid), the molecular weights of which ranged from ca. 5 × 10³ to almost 1 × 10⁵ Da.     

Efficient carbon-based solid acid catalysts for the esterification of oleic acid

A series of carbon-based solid acid catalysts was prepared by the sulfonation of mesoporous carbon substrates with thin pore walls, and catalytic activity for the esterification of oleic acid with methanol was tested. The highest turnover frequency (TOF) observed was 78 h^− 1, five times that of Amberlyst-15. The high catalytic activity may be attributed to the good dispersion of the catalysts in methanol. Catalysts with improved dispersion were obtained by a modified preparation, after which the highest TOF observed was 109 h^− 1, seven times that of Amberlyst-15.