Convenient method for removing and concentrating hydrophobic organic compounds from water with amphiphilic polymers

A stable fluoroacrylate copolymer emulsion was successfully prepared by miniemulsion polymerization with fluoroacrylate, lauryl methylacrylate, and methyl methacrylate as monomers. Extremely hydrophobic fluoroacrylate, instead of conventional cosurfactants, was used as a reactive cosurfactant to stabilize the miniemulsions. The results indicated that fluoroacrylate retarded Ostwald ripening and allowed the production of stable miniemulsions. The chemical compositions of the copolymer were studied with Fourier transform infrared and ¹H‐NMR. The average composition of the copolymers prepared with miniemulsions was in good agreement with the feed ratio according to ¹H‐NMR from the integration ratios corresponding to typical protons of the individual monomers. The particle size distribution and morphology of the latex particles were determined with laser particle analysis and transmission electron microscopy. The particle size of the latex underwent no change in the process of miniemulsion polymerization, but the particle size distributions were broader than those of conventional emulsion polymerization. The effects of various reaction parameters, including the temperature and concentrations of the emulsifier and initiator, on the miniemulsion polymerization were also investigated, and the polymerization rate and conversion increased with increasing concentrations of nonylphenol polyethoxylate (with an average of 40 ethylene oxide units per molecule), cetyltrimethylammonium, and 2,2′‐azobisisobutyronitrile. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 641–647, 2007     

Miniemulsion copolymerization of styrene and butyl acrylate initiated by redox system at lower temperature-preparation and polymerization of miniemulsion

Miniemulsions of styrene and butyl acrylate with sodium dodecyl sulfate (SDS) as the surfactant and hexadecane (HDE) and cetyl alcohol (HDL) as cosurfactants were prepared under high-speed stirring or ultrasonification. Results indicate that the stability of miniemulsions produced with HDE is more stable than that with HDL, when the feeding method, in which the cosurfactant is mixed with monomers, is used. There is an optical ratio (¼) of the surfactant to the cosurfactant for maximum stabilization of the miniemulsions. The miniemulsions prepared by ultrasonification are much more stable than those by high-speed stirring. Also, a stable miniemulsion can be prepared at lower temperature (45°C) when homogenizing way of ultrasonification is used. The emulsions were of a droplet-size range common to miniemulsions and some of them exhibited long-term stabilities (3 months). When these emulsions were initiated, particle formation occurred predominantly by monomer droplet nucleation. The effects of temperature, ultrasonification time, ratio of monomers, and concentrations of surfactant, cosurfactant, and initiator on the polymerization rate, conversion, and particle size were determined. It was found that the miniemulsion copolymerization of styrene and butyl acrylate with a midial amount of a redox initiator ((NH₄)₂S₂O₈/NaH SO₃) at lower temperature (45°C) can be carried out successfully by using a suitable amount of the surfactant SDS (10 mM) and the cosurfactant HDE (40 mM), when a homogenizing way of ultrasonification is applied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2029–2039, 1998     

Seeded emulsion polymerization of n-butyl acrylate utilizing miniemulsions

Nucleation of polymer particles in the seeded emulsion polymerization of n-butyl acrylate (BuA) was studied through experiments designed to control the amount of new particles formed. The results show that for the batch and semicontinuous seeded polymerization of BuA, a small amount of new particles was formed in the system in which the monomer was added neat, whereas a singificant amount of new particles was formed when the monomer was added as a miniemulsion. This suggests that new particles formed in the miniemulsion process were from nucleation of the monomer droplets. These experiments also showed that monomer-droplet nucleation decreased with increasing seed concentration in the reactor. For the seeded semicontinuous polymerizations, monomer-droplet nucleation decreases with decreasing BuA miniemulsion feed rate. The results also show that monomerdroplet nucleation takes place whenever miniemulsion droplets exist in the reactor. This study suggests that miniemulsions can be used to control the particle size distribution of a polymer latex system.     

Relative shear stability of mini- and macroemulsion latexes

The shear stability of mini- and macroemulsion latexes is compared and quantitatively evaluated with respect to their particle-size distributions. The effect of a few externally added large particles on the shear stability of these two types of latexes was also investigated. All the latexes selected were in the colloidal size range (less than 1 micron). The original particle sizes for the macroemulsion latexes ranged from 141 to 241 nm, and those for the miniemulsion latexes ranged from 96 to 209 nm. The miniemulsion latexes were found to be more shear stable than were their macroemulsion latex counterparts over the particle-size range investigated. This trend was repeated even in the presence of a few large particles. Additionally, seeding experiments suggest that mini- and macroemulsion latexes incur different levels of shear aggregation due to inherent differences in their particle-size distributions. The shear rate used along with the particle size and number were quantitatively shown to significantly influence the aggregation process. Finally, a quantitative method for evaluating relative shear stability in emulsion polymerization was demonstrated, which, although not very rigorous, could serve as a starting point for further quantitative isolation and investigation of the various parameters that affect the shear aggregation process. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1317–1324, 1997     

Robust nucleation in polymer-stabilized miniemulsion polymerization

The addition of a monomer soluble polymer to an emulsion was found to slow the effects of Ostwald ripening and impart diffusional stability to the droplets. Droplet nucleation was found to be the dominant nucleation mechanism in the polymerization of these polymer-stabilized miniemulsions (as distinguished from true miniemulsions). As a result these nucleations were more robust, and the polymerizations were less sensitive to variations in the recipe or contaminants levels. This was evident in the rates of polymerization and in the particle numbers. The miniemulsion polymerizations were subjected to changes in initiator concentration, a water-phase retarder, an oil-phase inhibitor, and agitation. Particle number was found to vary with each of these factors to the powers of 0.002, 0.02, 0.0031, and −0.026, respectively. The corresponding exponents for conventional emulsion were one to two orders of magnitude greater. These results demonstrate the potential of miniemulsion polymerization to greatly reduce the variability in particle number found in conventional emulsion polymerizations. © 1996 John Wiley & Sons, Inc.     

Predominant droplet nucleation in emulsion polymerization

Emulsions stabilized against diffusional degradation by incorporating a polymeric cosurfactant have been produced and polymerized. The presence of large numbers of small droplets shifts the nucleation mechanism from micellar or homogeneous nucleation, to droplet nucleation. When an efficient cosurfactant is used, this process is referred to as miniemulsion polymerization. Polymer, however, is known to be a poor cosurfactant. Its advantage is that, unlike most cosurfactants, it is innocuous in the recipe. Results indicate that even a poor cosurfactant (polymer) is adequate to stabilize small droplets against diffusional degradation long enough to nucleate them into polymer particles. The dependence of the concentration and molecular weight of the cosurfactant on the droplet size and distribution is investigated. Droplet diameters range from 19.5 to 141.2 nm with polydispersities of about 1.023. The polymeric cosurfactant is found to affect the mechanism of nucleation. On-line conductance measurements are used to successfully differentiate between nucleation mechanisms. The observed reaction rates are dependent on the amount of polymeric cosurfactant present. In addition, the latexes prepared with the polymeric cosurfactant have lower polydispersities (1.006) than either latexes prepared from classical emulsions (1.049) or from alkane-stabilized miniemulsions (1.037). © 1996 John Wiley & Sons, Inc.     

Miniemulsion copolymerization of styrene and butyl acrylate initiated by redox system at lower temperature: Reaction kinetics and evolution of particle‐size distribution

The kinetics of the miniemulsion copolymerization of styrene (St) and butyl acrylate (BA) initiated by redox initiators, (NH₄)₂S₂O₈/NaHSO₃, at lower temperature (45°C) was studied. The polymerization rate in miniemulsion copolymerization is lower than that of the corresponding conventional emulsion copolymerization. In regard to the rate of polymerization, the initiator concentration plays a more important role in miniemulsion copolymerization than in conventional emulsion polymerization, while the surfactant concentration has a more important role in conventional emulsion polymerization than in miniemulsion polymerization. These are attributed to their different nucleation mechanisms, which are the same as those found in the miniemulsion polymerization carried out at higher temperatures. While by eliminating nucleation via micelle and ensuring against homogeneous nucleation, miniemulsion polymerization can be carried out by the sole nucleation mechanism—monomer droplet nucleation—at lower temperature. Because of this, the particles become narrower during the polymerization and, finally, monodisperse polymer particles are obtained. The result of the particle numbers indicated that a continuous nucleation will cease at about 60% conversion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 315–322, 1999     

Elucidation of the miniemulsion stabilization mechanism and polymerization kinetics

Styrene/hexadecane miniemulsions were polymerized at 50°C using a redox initiator. The miniemulsions and their corresponding latexes were characterized in terms of size, polymerization rate, and surface properties. The resulting data were analyzed to elucidate the miniemulsion stabilization and polymerization mechanisms. It was found that the free surfactant concentration exceeded the critical micelle concentration when large amounts of surfactant (60 mM sodium lauryl sulfate) were used, resulting in simultaneous micellar and droplet nucleation. Most surfactant was on the surface of the droplets (85%) or particles (95%). The fractional surface coverage was proportional to the surfactant concentration to the 0.55 power. Using a particle diameter equation, the number of particles was calculated to be proportional to the surfactant concentration to the 1.35 power. Through direct particle size measurements, a power of 1.38 was confirmed. The rate of polymerization was determined by reaction calorimetry to be proportional to the number of particles to the 0.59 power, in contrast to classical Smith–Ewart kinetics for conventional emulsions (1.0 power). The average number of radicals per particle was estimated from the rate and number data, and varied with the particle diameter to the 0.97 power. The observed kinetic dependencies were validated through an extension of Smith–Ewart theory. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3987–3993, 2003     

Kinetics and effect of surfactant and cosurfactant on miniemulsion polymerization of acrylate monomers

The effects of the type and amount of the surfactant and cosurfactant on the miniemulsion polymerization of acrylate monomers were studied, and the comparison of the kinetics between miniemulsion polymerization and conventional emulsion polymerization was discussed in the presence of reactive surfactant allyloxy nonylphenol propyl polyoxyethylene (10), ether sulfate (DNS-86), and reactive cosurfactant stearyl methacrylate (SMA). The results showed that the obtained polyacrylate miniemulsion had a high monomer conversion rate and a low coagulum fraction, which were affected little by the surfactant and cosurfactant type. When the surfactant and cosurfactant amounts were all 2 wt%, the contact angle of the prepared polyacrylate miniemulsion with DNS-86/SMA and the water absorption fraction of the latex film were 39° and 8.3 wt%, respectively. FTIR results confirmed that DNS-86 and SMA took part in the polymerization of acrylate monomers. In the miniemulsion polymerization of acrylate monomers with DNS-86/SMA, monomer droplet nucleation was the main nucleation style.     

Miniemulsion and conventional emulsion copolymerization of styrene and butadiene: A comparative kinetic study

The kinetics of conventional and miniemulsion copolymerizations of styrene and butadiene were compared using the Mettler RC1 calorimeter. A two‐step homogenization procedure was applied to obtain miniemulsions of these monomers with hexadecane as the costabilizer. The results indicated that the miniemulsion polymerizations proceeded mainly by nucleation in the monomer droplets, while in the conventional emulsion polymerizations, particle formation occurred by a combination of micellar and homogeneous nucleation. The overall rate of miniemulsion polymerization was faster than the corresponding conventional emulsion system if the surfactant concentration was below the critical micelle concentration (cmc) and slower if the surfactant concentration was above the cmc. The homogenization process is important for making stable miniemulsion systems, but had no effect on the conventional emulsion system (without hexadecane), most likely because of the second stage addition of the butadiene monomer. The dependencies of the rate of polymerization (heat of reaction) and number of particles on the surfactant concentration differed for the two types of polymerization systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2304–2312, 2006     

In situ surfactant generation as a means of miniemulsification?

In situ emulsification, where the surfactant is synthesized spontaneously at the oil/water interface, has been put forth as a simpler method for the preparation of miniemulsions‐like systems. Miniemulsions are relatively stable oil‐(e.g., monomer)‐in‐water emulsions having droplet sizes anywhere in the range of 50–500 nm, and are typically created with high shear and stabilized by the combination a surfactant and a costabilizer. Using the in situ method of preparation, emulsion stability and droplet and particle sizes were monitored and compared with conventional emulsions and miniemulsions. Styrene emulsions prepared by the in situ method do not demonstrate the stability of a comparable miniemulsion. Upon polymerization, the final particle size generated from the in situ emulsion did not differ significantly from the comparable conventional emulsion polymerization; the reaction mechanism for in situ emulsions is more like conventional emulsion polymerization rather than miniemulsion polymerization. Similar results were found when the in situ method was applied to controlled free radical polymerizations (CFRP), which have been advanced as a potential application of the method. Molecular weight control was found to be achieved via diffusion of the CFRP agents through the aqueous phase owing to limited water solubilities. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

CONTINUOUS MINIEMULSION POLYMERIZATION: KINETIC INVESTIGATIONS

Experimental data on the dynamic behavior of the miniemulsion polymerization of methyl methacrylate in a CSTR are presented. These data are contrasted with those for similar conventional emulsion polymerizations. The dominance of nucleation in monomer droplets in miniemulsion systems is shown to be responsible for the absence of the decaying oscillatory transients observed in continuous emulsion polymerization. Rates of polymerization for the miniemulsion system are reported to be twice those of the equivalent emulsion system. In addition, the polymer produced in this study is of high molecular weight, indicating a high degree of segregation within the polymer particles. These last two observations are attributed to the extremely small monomer droplets produced by the combination of the addition of a cosurfactant and the high shear to which the unpolymerized emulsion is subjected     

Effect of ionic liquids on stability of O/W miniemulsion for application of low emission coating products

Room temperature ionic liquids (RTILs) are non-volatile organic salts. They may replace conventional coalescing agents in latex coating thus reducing volatile organic compounds (VOCs) emission as well as improving performance of latex coating products such as better thermal stability, conductivity, and antifouling property. The formation of latex coating containing RTILs can be achieved by encapsulation of RTILs inside particles via miniemulsion polymerization. In this study, the role of RTILs and its concentration on stability of miniemulsion during storage and polymerization were investigated. It has been found that, above a critical concentration (10 wt%), adding more RTILs to oil phase may weaken miniemulsion stability during storage aswell as polymerization. Such observations were consistent with the zeta potential measurement for miniemulsions prepared at the similar conditions. The results obtained here would be a useful guideline for the development of new waterborne coating products with desirable functions and particle sizes.     

Miniemulsion polymerization—a comparative study of preparative variables

Variations in the conditions used to prepare miniemulsions of monomers in water have resulted in substantial differences in polymerization kinetics and final particle sizes and distributions. These variations have included (1) surfactant amount and type; (2) cosurfactant amount and type; (3) monomer (s) type; (4) temperature of preparation and polymerization; (5) means and conditions of homogenization; and (6) degree of aging of the emulsion. In an effort to unify some of the disparate information of previous work, a systematic study of some of the above variables was undertaken using styrene as the oil phase with sodium lauryl sulfate as surfactant. Based on the polymerization kinetics and particle sizes obtained, the following conclusions are drawn: The finest droplet size miniemulsions are obtained by (1) using a cosurfactant; (2) homogenizing at elevated temperature; (3) homogenizing using a uniform high shear device (Microfluidizer); and (4) limiting the aging time prior to polymerization.     

Kinetics of miniemulsion polymerizations of ethylene glycol dimethacrylate and/or methyl methacrylate

Two types of reactive acrylic microgel particles of methyl methacrylate (MMA)/ethylene glycol dimethacrylate (EGDMA) (66.4/33.6 and 0/100 (mol/mol)) were prepared by miniemulsion polymerization with 2,2′‐azobisisobutyronitrile as the initiator in the temperature range 60–80 °C. Ostwald ripening occurred during the very early stage of polymerization. In addition to the predominant droplet nucleation, homogeneous nucleation was also observed. The polymerization rate for MMA/EGDMA miniemulsion was higher than that for EGDMA miniemulsion. By contrast, comparable apparent limiting conversions were observed for the polymerizations of MMA/EGDMA and EGDMA. The mole fractions of MMA and EGDMA units incorporated into the copolymer product were estimated to be 0.62 and 0.38, respectively, for the polymerization of MMA/EGDMA at 70 °C. The mole fraction of the EGDMA unit containing one ? C?C? within the MMA/EGDMA microgel particle product was estimated to be 0.23, which was comparable to that (0.22) of the EGDMA unit containing one ? C?C? within the EGDMA microgel particle product. © 2015 Society of Chemical Industry     

High pressure semibatch emulsion and miniemulsion copolymerization of vinyl acetate and ethylene

This study presents the experimental study of semibatch emulsion and miniemulsion copolymerization of vinyl acetate (VAc) and ethylene to vinyl acetate-ethylene (VAE) copolymer at 60°C and 80–300 psig. In the miniemulsion copolymerization, a water-soluble initiator (K₂S₂O₈) is used and VAc miniemulsion is prepared in presence of surfactant and cosurfactant using a sonicator or a high-shear homogenizer. Then, ethylene gas is supplied to the reactor at constant partial pressure. In a miniemulsion process, the mass transfer limitations of VAc from monomer droplets to the aqueous phase, and to micelles or polymer latex particles that are present in conventional macro-emulsion polymerization can be eliminated and the transfer of ethylene dissolved in the aqueous phase to the miniemulsion droplets is the major ethylene transport process for the polymerization. The experimental data show that the amount of ethylene incorporation into the copolymer is higher in miniemulsion polymerization than in emulsion polymerization. The ethylene pressure has been found to have a strong impact on the ethylene incorporation into the copolymer phase in both emulsion and miniemulsion copolymerizations but the increase is more pronounced in miniemulsion case. The VAE copolymer latex particles prepared by miniemulsion polymerization exhibited higher storage stability than those prepared by macro-emulsion polymerization.     

Particle nucleation and growth in seeded semibatch miniemulsion polymerization of hybrid CeO2/acrylic latexes

CeO₂/acrylic hybrid coatings with high solids content and with nanoparticle percentages up to 5 wt% have been successfully synthesized by seeded semibatch miniemulsion polymerization process. The droplet nucleation efficiency has been assessed by Capillary Hydrodynamic Chromatography and TEM analysis. The effect of the stability of the miniemulsion, the type of initiator and the number of particles of the seed on the efficiency of the nucleation of the nanodroplets fed has been investigated. It was found that the less stable the hybrid miniemulsion, the higher the diffusion of the monomer out of the droplets and hence, the seed latex particles grew in size. However, the CeO₂ nanoparticles did not diffuse out with the monomer and remained in very small droplets that eventually nucleate leading to a bimodal population. When stable miniemulsions were produced by using a polymer as hydrophobe, droplet size increased reducing the number of particles in the seed and monomer diffusion was minimized enhancing nucleation of droplets with larger sizes that produced broad PSDs. Coalescence of droplets was negligible because the size distribution of the nanoceria particles did not change from the seed particles to the final latex. The UV–Vis absorption capacity of the films prepared with increasing the amount of CeO₂ increased, but scattering effects were observed at high loading of CeO₂ due to the large size of the CeO₂ aggregates.     

Styrene miniemulsion polymerization stabilized by carboxylated polyurethane. II. Kinetics

A styrene miniemulsion was prepared using carboxylated polyurethane as the sole costabilizer and sodium dodecyl sulfate as the surfactant. The effects of the amount of carboxylated polyurethane, the amount of the initiator and surfactant, the presence of a water‐phase inhibitor (sodium nitrite), and the reaction temperature on the kinetics of the miniemulsion polymerization were investigated. The evolution of the particle size during the polymerization was measured. The results show that the polymerization rate was proportional to the 0.21 power of the surfactant concentration and the 0.30 power of azobisisobutyronitrile. The droplet nucleation and homogeneous nucleation were found to be coexistent in the polymerization. The hydrophility of the particle surface plays a key role in the nucleation of the particle and, therefore, has an important effect on the kinetics of the polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1941–1947, 2003     

苯乙烯-有机硅烷共聚物作为助稳定剂的细乳液聚合研究

以苯乙烯(St)与甲基丙烯酰氧基丙基三乙氧基硅烷(TEPM)的共聚物P(St-TEPM)为助稳定剂,用于不同亲水性单体的细乳液聚合.考察了P(St-TEPM)助稳定剂在不同亲水性单体(St、甲基丙烯酸甲酯MMA、醋酸乙烯酯VAc)的细乳液聚合过程中对单体转化率、聚合物粒子粒径的影响及成核机理.结果表明,P(St-TEPM)单独作为助稳定剂用于不同单体(St、MMA、VAc)的细乳液聚合,亲油性较好的St和亲水性较好的VAc的聚合转化率分别为90.6%和63.8%,聚合物粒子的最终数目和单体液滴的起始数目(N pf/Nmi )分别为1.06和0.10.通过以上分析认为P(St-TEPM)可以作为细乳液聚合的助稳定剂使用,亲油性单体St聚合机理以单体液滴成核为主体.     

Emulsion and miniemulsion copolymerization of acrylic monomers in the presence of alkyd resin

Emulsion and miniemulsion copolymerizations were carried out with acrylic monomers (methyl methacrylate, butyl acrylate, and acrylic acid) in the presence of an alkyd resin. Poly(methyl methacrylate) was used as a hydrophobe or cosurfactant in the miniemulsion reactions. The results demonstrate that miniemulsion polymerization is the preferred process, probably because of mass transport limitations of the alkyd in the conventional emulsion polymerization reactions. The monomer emulsions prepared for the miniemulsion reactions were much more stable and the polymerizations were free of coagulum. Reaction rates, particle size characteristics, grafting efficiencies, and some film properties were measured. © 1996 John Wiley & Sons, Inc.