Nucleation mechanism and morphology of polystyrene/Fe3O4 latex particles via miniemulsion polymerization using AIBN as initiator

In this study, oil‐based magnetic Fe₃O₄ nanoparticles were first synthesized by a coprecipitation method followed by a surface modification using lauric acid. Polystyrene/Fe₃O₄ composite particles were then prepared via miniemulsion polymerization method using styrene as monomer, 2,2′‐azobisisobutyronitrile (AIBN) as initiator, sodium dodecyl sulfate (SDS) as surfactant, hexadecane (HD) or sorbitan monolaurate (Span20®) as costabilizer in the presence of Fe₃O₄ nanoparticles. The effects of Fe₃O₄ content, costabilizer, homogenization energy during ultrasonication, and surfactant concentration on the polymerization kinetics (e.g., conversion), nucleation mechanism, and morphology (e.g., size distributions of droplets and latex) of composite particles were investigated. The results showed that at high homogenization energy, an optimum amount of SDS and hydrophobic costabilizer was needed to obtain composite particles nucleated predominately by droplet nucleation mechanism. The morphology of the composite particles can be well controlled by the homogenization energy and the hydrophobicity of the costabilizer. The magnetic composite particles can be made by locating Fe₃O₄ inside the latex particles or forming a shell layer on their PS core surface depending on the aforementioned polymerization conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

The formation of asymmetric polystyrene/saponite composite nanoparticles via miniemulsion polymerization

The synthesis of asymmetric spherical nanoparticles has attracted great interest because their anisotropic structure can be used as unique building blocks for constructing advanced materials. In this article, we report the formation of hemispherical or truncated polystyrene/nanosaponite composite particles via one‐pot miniemulsion polymerization. It was found that the morphology of final composite latex particles strongly depends on the size of the nanoclay and its surface properties. Hemisphere or truncated sphere is the dominant morphology if the size of the nanoclay is larger than 100 nm. With the increase of the nanoclay content (up to 30 wt %), the fraction of hemispherical or truncated polystyrene/nanosaponite composite latex particles increased accordingly. The formation of hemispherical particles is possibly attributed to either the asymmetric growth of polymer chains on one side of the hydrophobically modified clay or the mechanical peeling‐off of large spherical particles between polymer and saponite. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Nanocomposite particles with core‐shell morphology. I. Preparation and characterization of Fe3O4–poly(butyl acrylate‐styrene) particles via miniemulsion polymerization

Colloidal particles with magnetic properties have become increasingly important both technologically and for fundamental studies. Here, chemical initiator‐free miniemulsion polymerization of styrene and butyl acrylate has been performed for preparation of magnetic nanocomposite particles with the diameter of 81–150 nm in the presence of sodium dodecyl sulfate as surfactant, span 80 as stabilizer, and hexadecane as hydrophobe. The polymerization reaction was initiated and progressed under ultrasonic irradiation, generated by immersed probe into the latex. The key point in achievement of encapsulation of modified Fe₃O₄ nanoparticles was preparation of a stable colloidal dispersion at the end of the reaction. The obtained products in each step were characterized by FTIR spectroscopy. Dynamic light scattering analysis was used to follow particle size diameter of the samples. Morphology of the particles and formation of core‐shell structure were analyzed by SEM and TEM micrographs, respectively. TGA and magnetometry of the polymeric films confirmed the extent of insertion of used magnetite and their corresponding behavior. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of PSt/SiO2 nanoparticles with raspberry-like structure via nonionic surfactant miniemulsion polymerization

Preparation of inorganic/organic nanoparticles (NPs) with special morphology, controllable size, and good stability is important for widening their applications. In this study, a series of polystyrene (PSt)/SiO₂ NPs with a raspberry-like structure was synthesized via a miniemulsion polymerization approach, using octaphenyl polyoxyethylene (CA-897) as a nonionic surfactant. To increase silica loading capacity, methacryloyloxyethyl trimethyl ammonium chloride (MTC) was introduced as an auxiliary monomer. The results indicate that the combinative employment of CA-897/SiO₂ NPs/MTC could contribute to the formation of raspberry-like PSt/SiO₂ nanohybrids with controlled size of 130–370 nm as well as adjustable silica inorganic content of 17–31 wt%, respectively. The raspberry structure played a significant role on the stabilization of PSt/SiO₂ NPs in both electrolytic and strong basic/acidic environments.     

磁场引发苯乙烯分散聚合反应的研究

本文采用苯乙烯的分散聚合反应体系为研究对象,在无外加温度、压力及其它物理手段的前提下,直接利用磁场在室温条件下引发苯乙烯的分散聚合反应,成功制备出了聚苯乙烯微球。研究结果表明,交变磁场作用引发苯乙烯分散聚合生成了聚苯乙烯,其重均分子量Mw=96856,数均分子量Mn=13162。所制备的聚苯乙烯微球的粒径为1—2μm,恒定磁场条件下制备的聚苯乙烯微球重含有部分不成形的杂质,而交变磁场条件下制备的聚苯乙烯微球的球形度规整,表面光滑,无缺陷和杂质。     

Particle nucleation and growth mechanisms in miniemulsion polymerization of styrene

Styrene miniemulsion polymerizations stabilized by sodium lauryl sulfate in combination with a reactive costabilizer, lauryl methacrylate (LMA) or stearyl methacrylate (SMA), were studied. A small amount of extremely hydrophobic dye was incorporated into monomer droplets (10² nm in diameter) to investigate particle nucleation and growth mechanisms. In addition to monomer droplet nucleation, particle nuclei generated in the aqueous phase (homogeneous nucleation) also play an important role in both LMA‐ and SMA‐containing polymerization systems. The way that these two nucleation mechanisms compete with each other is closely related to the water solubility of the costabilizer (LMA > SMA). The fraction of latex particles originating from homogeneous nucleation increases with decreasing hydrophobicity of the costabilizer. Zeta potential data of latex particles and the molecular weight and molecular weight distribution of emulsion polymers provide supporting evidence for the proposed competitive particle nucleation and growth mechanisms. © 2002 Society of Chemical Industry     

Preparation of poly(styrene‐co‐hexylacrylate)/cellulose whiskers nanocomposites via miniemulsion polymerization

A stable aqueous nanocomposite dispersion containing cellulose whiskers and a poly(styrene‐co‐hexylacrylate) matrix was prepared via miniemulsion polymerization. We were able to prepare a stable dispersion with a 20 wt % solid content and a cellulose whiskers content ranging from 1 up to 5 wt % based on polymer content. To avoid particle agglomeration leading to coagulum formation, the addition of a low amount of reactive silane, i.e., methacryloxypropyl triethoxysilane revealed to efficiently stabilize the dispersion. The nanocomposite dispersion was characterized using dynamic light scattering, transmission electron microscopy, and atomic force microscopy. Films obtained by casting followed by water evaporation and particle coalescence were analyzed by differential scanning calorimetry, dynamic mechanical analysis, and tensile testing. At 5 wt % whiskers loading, an enhancement by 500% of the storage modulus above the glass transition was determined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

细乳液聚合制备含氟丙烯酸酯聚氨酯共聚物

采用细乳液聚合法,制备了稳定的含氟丙烯酸酯聚氨酯细乳液。用FT-IR表征了丙烯酸酯聚氨酯预聚体及其共聚物的结构组成;考查了细乳液的稳定性;用透射电子显微镜(TEM)观察了乳胶粒的形态;用接触角法表征了乳胶膜对水和正十六烷的接触角。     

Radical styrene polymerization in the presence of trace levels of sulfonic acids

The bulk polymerization of styrene in the presence of the vinyl functional sulfonic acid 2‐sulfoethylmethacrylate (SEM) was found to have utility for making polystyrenes with narrow polydispersity, bimodal polydispersity, and ultrahigh molecular weight at fast polymerization rates. Narrow polydispersity polymers were made by the addition of SEM to nitroxide‐mediated polymerizations. Bimodal polydispersity polymers were made by the ultrahigh molecular weight component being made in the presence of SEM in the absence of an initiator and the low molecular weight component being made in the presence of an initiator and/or chain‐transfer agent. Ultrahigh molecular weight monomodal polystyrenes were prepared at much faster polymerization rates than possible via spontaneous polymerization in the absence of SEM. SEM was found to be more effective, by an order of magnitude, than camphor sulfonic acid on a weight basis and, because it is copolymerized into the polymer chain, should not lead to corrosion problems during fabrication of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 869–875, 2003     

Modeling for primary radical desorption in miniemulsion polymerization initiated by oil‐soluble initiator

Primary radical (PR) desorption in the miniemulsion polymerization initiated by oil‐soluble initiator was investigated. Both the aqueous phase inhibition experiments and the theoretical predictions, which combined the two film theory and aqueous phase mass balance, were performed to evaluate the PR desorption process quantitatively. The theoretical predictions agreed well with the experiment results. It was found that the organic phase diffusion, particle size, surfactant layer, aqueous phase resistance, and different initiator type affected the PR desorption. The desorption rate of PR was faster than its reaction rate at the early stage of polymerization, while the former decreased to a comparable level as the latter at the high conversion. PR was prone to desorb in the polymerization and the desorption of PR played a critical role in the miniemulsion polymerization initiated by oil‐soluble initiator. It is concluded that the PR desorption–reabsorption is a process to generate effective radicals in the miniemulsion polymerization initiated by oil‐soluble initiator. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3276–3285, 2014     

Emulsion and miniemulsion polymerization of isobornyl acrylate

Isobornyl acrylate, a highly hydrophobic monomer, was batch‐polymerized in both emulsion and miniemulsion recipes. Surfactant levels above and below the critical micelle concentration were used, as were two different initiator types: ionic (potassium persulfate) and nonionic (t‐butyl hydroperoxide) Samples were analyzed for degree of conversion, molecular weight, and particle size. The effects of reaction type (emulsion versus miniemulsion), surfactant level, type of initiator (ionic versus nonionic) of the polymer properties are discussed. Issues of monomer transport across the aqueous phase, and mechanisms of nucleation, especially at very low surfactant concentrations are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 819–833, 2007     

Particle morphology development in hybrid miniemulsion polymerization

Incompatibility between polymer phases resulting from hybrid minienulsion polymerization of acrylic monomers in the presence of alkyd resin leads to interesting particle morphologies. In this paper, morphology was deduced through crosscomparison of results from several forms of microscopy. For the combination of methyl methacrylate and alkyd, a derivative of core/shell morphology was observed through the combination of transmission electron microscopy, scanning electron microscopy, and spin diffusion NMR. A raspherry-like shell was found to form on the hybrid particle surface consisting of a full coverage of small (roughly 25 nm) polymethyl methacrylate spheres anchored to the particle surface through grafting with the alkyd core. Migration of the spheres to tha surface is thought to be induced by phase separation, and the size of the spheres precludes their origin from homoparticles from homogeneous nucleation. Homopolymethyl methacrylate particles were also detected in the particle distribution, resulting from the aqueous-phase initiator and hydrophilicity of methyl methacrylate monomer. For copolymer/alkyd systems (either methyl methacrylate/butyl acrylate/acrylic acid/alkyd or methyl methacrylate/butyl acrylate/alkyd), more traditional core/shell morphologies were observed with a lesser degree of homonucleated particles. A significantly different result was found in the combination of butyl acrylate and alkyd, resulting in a continuous particle-phase of polylbutyl acrylate and small internally dispersed island domains of alkyd. This is likely due to the lesser incompatibility between polybutyl acrylate and alkyd along with their similar hydrophobicity and glass transition temperatures. A higher degree of grafting between the alkyd and polybutyl acrylate also contributed to the compatibility between the two components, when compared to hybrid methyl methyl methacrylate/alkyd systems.     

Kinetic study on the ring-opening polymerization of octamethylcyclotetrasiloxane (D4) in miniemulsion

A kinetic study on the ring-opening polymerization (ROP) of octamethylcyclotetrasiloxane (D4) in miniemulsion is presented in this work. The polymerization is initiated by dodecylbenzenesulfonic acid (DBSA) which also serves as the surfactant (inisurf). The influence of the size of monomer droplet and the concentration of DBSA on the polymerization rate were studied. Since the main place for the ROP of D4 was confirmed to be at the oil/water interface, a three-layer interface model was proposed to analyze the distribution of molecules at the interface and the effects of DBSA. A kinetic equation is then developed based on this model. In the equation, the polymerization rate (R_p) is related to the initial monomer concentration ([D4]₀), the droplet radius (r), the coverage of DBSA on monomer droplets surface (x). The polymerization rate can be predicted from the kinetic equation feeding all parameters with their experimental values. Finally, the equation gave a good accordance between the predicted polymerization rate data and the experimental results under different polymerization conditions.     

Bulk polymerization of styrene in the presence of organomodified montmorillonite

The effect of montmorillonite (Cloisite 6A) on the bulk polymerization of styrene initiated by benzoyl peroxide (BPO) was studied by the dilatometric determination of the polymerization rates. The bulk polymerization rates increased as the montmorillonite input quantity increased. The effect became greater when the BPO concentration decreased. Under the assumption that clay participated in the radical initiation reaction of the chains, the reaction orders for clay and BPO were determined to be approximately 1.0 and 0.5, respectively. X‐ray diffraction and thermogravimetric analysis studies showed that the structure and properties of the obtained polystyrene (PS)/montmorillonite nanocomposites were greatly affected by the BPO concentration. With lower BPO concentrations, a larger interlayer distance and a higher extent of delamination for the clay were observed in the obtained PS/montmorillonite nanocomposites. The nanocomposites prepared with lower BPO concentrations also showed higher heat‐decomposition‐resistance temperatures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1146–1152, 2005     

Challenges for industrialization of miniemulsion polymerization

Miniemulsion polymerization facilitates the synthesis complex materials that cannot be produced otherwise. These materials have a broad range of potential applications including among others adhesives, coatings, anticounterfeiting, textile pigments, bio-based polymer dispersions, gene and drug delivery, anti-viral therapy, tissue engineering, catalyst supports, polymeric photoresists, energy storage and self-healing agents. However, 40 years after the pioneering work of Ugelstad, El-Aasser and Vanderhoff the promises have not been fulfilled and the presence of miniemulsion polymerization in commercial products is scarce. This article reviews the advances in the field, discusses the reasons for this delay and analyzes the challenges that have to be overcome in order to fully use this process in commercial practice.     

Graft polymerization synthesis and application of magnetic Fe3O4/polyacrylic acid composite nanoparticles

Fe₃O₄ magnetic nanoparticles were prepared by coprecipitation using NH₃ · H₂O as the precipitating agent, and were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X‐ray powder diffraction (XRD). The compatibility between the Fe₃O₄ nanoparticles and water were enhanced by grafting acrylic acid onto the nanoparticle surface. FTIR, XRD, thermogravimetry (TG), and differential scanning calorimetry (DSC) were used to characterize the resultant sample. The effects of initiator dosage, monomer concentration, and reaction temperature on the characteristics of surface‐modified Fe₃O₄ nanoparticles were investigated. Moreover, magnetic fluids (MF), prepared by dispersing the PAA grafted Fe₃O₄ nanoparticles in water, were characterized using UV–vis spectrophotometer, Gouy magnetic balance, and laser particle‐size analyzer. The rheological characteristics of magnetic fluid were investigated using capillary and rotating rheometers. The MF was added to prepare PVA thin film to improve mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

细乳液聚合制备改性硅溶胶／聚丙烯酸酯复合乳液

常温下一步法制备改性硅溶胶,并通过细乳液聚合制备改性硅溶胶／聚丙烯酸酯复合乳液。考查了温度对聚合速率和单体转化率的影响以及不同乳化剂含量下聚合过程中乳胶粒粒径的变化情况;测试了乳胶膜的吸水率,并用接触角法表征了乳胶膜的表面自由能。     

Encapsulation of magnetic particles via miniemulsion polymerization of styrene. II. Effect of some parameters on the polymerization of styrene

Effects of some parameters on the polymerization of Styrene (St) during encapsulation of iron oxide particles via miniemulsion polymerization have been investigated. At the early stage of reaction, polymerization rate increased slightly with the increase of sonicating time, and then it leveled off. The polymerization rate increased with the increase of KPS at the early stage of polymerization, which tendency is analogous to the result of polymerization of St in miniemulsion without the presence of iron oxide particles. The increase of iron oxide not only decreased the polymerization rate but also resulted in poorer monodisperse of the particles when keeping the amount of dispersant constant. The dispersant played an important role in the encapsulation of magnetic particles via miniemulsion polymerization of St. It not only made the iron oxide disperse well in monomer droplets but also led to a much faster polymerization than that of no dispersant in system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Fe3O4/P(St/ACPA)磁性高分子纳米球的制备与磁性能研究

采用化学共沉淀方法制备Fe_3O_4磁性粒子,并使用油酸和十一烯酸对其进行表面改性,然后采用一步细乳液聚合法制备含有羧基官能团的Fe_3O_4/P(St/ACPA)磁性高分子纳米球,对磁流体和磁性高分子纳米球进行性能表征。结果表明,改性的Fe_3O_4磁流体分散性好,粒径均一,在室温下呈超顺磁性,磁含量为68.5%(w),饱和磁化强度为51.3emu/g;Fe_3O_4/P(St/ACPA)磁性高分子纳米球成球性好,粒径为70 nm,磁含量为39%(w),饱和磁化强度为27.9 emu/g。