Miniemulsion polymerization of styrene with polymeric costabilizers

The polymeric costabilizers poly(stearyl methacrylate‐co‐2‐hydroxyethylmethacrylate) (PSH) and poly(lauryl methacrylate‐co‐2‐hydroxyethylmethacrylate) (PLH), composed of a hydrophilic backbone and several hydrophobic alkyl (stearyl or lauryl) side chains, were prepared by the free‐radical copolymerization of stearyl methacrylate (SMA) or lauryl methacrylate (LMA) with 2‐hydroxyethylmethacrylate and evaluated in the miniemulsion polymerization of styrene (ST). For comparison, the reactive costabilizers SMA and LMA were also included in this work. The hydrophobicity of costabilizers in increasing order was PLH < PSH < LMA < SMA. Only a small amount of these comb‐like copolymers was capable of producing kinetically stable ST emulsion droplets. The more hydrophobic the costabilizer was, the more effective was the costabilizer in the retardation of Ostwald ripening. About 30–40% of the monomer droplets were successfully converted into latex particles during the polymerization. The degree of monomer droplet nucleation increased with increasing hydrophobicity of the costabilizer. The formation of particle nuclei in the continuous aqueous phase played a crucial role in the polymerization kinetics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1961–1969, 2004     

Miniemulsion copolymerizations of styrene and reactive alkyl methacrylate costabilizers

Miniemulsion copolymerizations of styrene (ST) and stearyl methacrylate (SMA) or lauryl methacrylate (LMA) were investigated. Miniemulsions comprising ST and various levels of SMA showed very good storage stability against the diffusional degradation of monomer droplets (Ostwald ripening), whereas miniemulsions comprising ST and various levels of LMA exhibited significant Ostwald ripening. In subsequent miniemulsion copolymerizations of ST and SMA, particle nucleation occurring in the continuous aqueous phase (homogeneous nucleation) plays an important role in the particle formation process in addition to monomer droplet nucleation. The final overall conversion and the individual conversions of ST and SMA all decrease with increasing SMA concentration. Furthermore, at a particular reaction time, the individual conversion of SMA is always greater than that of ST. Monomer droplet nucleation was retarded severely for the monomer pair ST/LMA, presumably due to the very strong Ostwald ripening effect. As a result, relatively slow rates of copolymerization of ST and LMA were attained compared with the ST/SMA counterpart. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Miniemulsion copolymerizations of methyl methacrylate and butyl acrylate in the presence of reactive costabilizer

The storage stability and free radical polymerizations of miniemulsions comprising methyl methacrylate (MMA), butyl acrylate (BA), and a reactive costabilizer stearyl methacrylate (SMA) were investigated. The Ostwald ripening rate increases with increasing MMA content in the monomer mixture. Both the pseudo‐two‐component model and empirical equation with one adjustable parameter k adequately predicted the Ostwald ripening rate data. For the empirical model, the least‐squares best fit technique gave a value of k equal to 677.5 and values of Ostwald ripening rate and water solubility equal to (8.8 ± 0.2) × 10^?21 cm³/s and 1.8 × 10^?9 cm³/cm³ for SMA, respectively. These two models were combined to impart some physical insight to the parameter k. The kinetic studies showed that the polymerization rate increased with increasing MMA content. This is closely related to the nature of the constituent monomers MMA and BA and the particle nucleation mechanisms. The reactive costabilizer SMA is not hydrophobic enough to completely eliminate the Ostwald ripening effect, thereby increasing the probability of polymer reactions in the continuous aqueous phase. Thus, in addition to monomer droplet nucleation, particle nuclei can be generated in the aqueous phase via homogeneous nucleation. The extent of homogeneous nucleation increased with increasing MMA content and, as a result, the number of reaction loci available for the major polymerization to take place followed the same trend. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Particle Nucleation Loci in Styrene-Butyl Acrylate Miniemulsion Copolymerization

Summary Miniemulsion polymerizations of styrene and butyl acrylate in the presence of sodium dodecyl sulfate (SDS) as the surfactant and stearyl methacrylate (SMA) as reactive cosurfactant were carried out by using water-soluble (potassium persulfate) and oil-soluble (2,2-azobisisobutyronitrile) (AIBN) initiators respectively. Effects of the two initiators on the particle nucleation mechanisms are investigated. By comparison with the mean diameter of monomer droplets and polymer particles, it is shown that both homogeneous nucleation and monomer droplets nucleation coexist in the presence of a water-soluble initiator but homogeneous nucleation becomes less significant with SDS concentration increasing. Meanwhile, using oil-soluble initiator, the possibility of homogeneous nucleation is depressed effectively. As a result, monomer droplets are definitely the main loci of particle nucleation.     

Semibatch emulsion copolymerization of methyl methacrylate and butyl acrylate

The concentration of sodium lauryl sulfate (SLS) in the initial reactor charge is the most important parameter in determining the particle size of a semibatch emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The number of particles formed is proportional to the concentration of SLS to the 0.5–1.2 power and it is proportional to the concentration of the nonyl phenol–40 mol ethylene oxide adduct to the 0.014–0.72 power. The number of particles is almost independent of the concentration of the initiator. The solubility of monomer in water has an important effect on the nucleation mechanism according to the literature. However, the ratio of MMA to BA does not show any significant effect on the latex particle size in our laboratory. The particle size also increases with increasing ionic strength or agitation speed. Experimental data of particle-size distribution and molecular weight distribution support the coagulative nucleation mechanism when the concentration of SLS is way below its critical micelle concentration (CMC). © 1995 John Wiley & Sons, Inc.     

Kinetic study of emulsion copolymerization of ethyl methacrylate/lauryl methacrylate in propylene glycol,stabilized with poly(ethylene oxide)–block–polystyrene–block–poly(ethylene oxide) triblock copolymer

The kinetics of emulsion copolymerization of ethyl methacrylate (EMA)/lauryl methacrylate (LMA) in propylene glycol is very similar to the emulsion copolymerizations of water‐soluble monomers in water because of the high solubility of EMA/LMA in propylene glycol. The initial rate of polymerization depends only on initiator concentration and is not affected by either monomer concentration or stabilizer concentration. The overall rate of polymerization is only slightly dependent on monomer concentration and stabilizer concentration and is independent of initiator concentration. The final particle number density increases with increasing amount of stabilizer and decreases with increasing monomer concentration. The total surface area increases with stabilizer concentration and is not governed by either initiator concentration or monomer concentration. Homogeneous nucleation is the dominant mechanism of particle nucleation, as shown by the kinetic data on seeded polymerization and monomer partition behavior. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1691–1704, 2001     

Miniemulsion copolymerizations of styrene and methyl methacrylate in the presence of reactive costabilizer

Miniemulsion stability of three‐component disperse phase systems comprising styrene [ST (1)], methyl methacrylate [MMA (2)], and stearyl methacrylate [SMA (3)] was investigated. The Ostwald ripening rate (ω) increases with increasing MMA content in the monomer mixture. The empirical equation 1 /ω = k(φ₁/ω₁ + φ₂/ω₂) + φ₃/ω₃ was proposed to adequately predict the miniemulsion stability data. The empirical parameter k was determined to be 555.77, and the Ostwald ripening rate (ω₃) and water solubility of SMA were estimated to be 8.77 × 10^?21 cm³/s and 1.90 × 10^?9 mL/mL, respectively. A water‐insoluble dye was used as a molecular probe to study particle nucleation mechanisms in the miniemulsion copolymerizations. In addition to the primary monomer droplet nucleation, homogeneous nucleation also plays an important role in the formation of particle nuclei, and this mechanism becomes more important for the polymerization systems with higher MMA contents as a result of the enhanced aqueous phase polymer reactions. The polymer composition data suggest that, during the early stage of polymerization, MMA is consumed more rapidly by free radical polymerization compared with ST. The final latex particle surface potential data also support this conclusion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Isothermal emulsion polymerization of n-butyl methacrylate with KPS and redox initiators: Nucleation

Nucleation is a very important stage of emulsion polymerization due to its significant influence on the latex particle diameter, particle diameter distribution, and molecular weight. In this study, we evaluated the effect of thermal and redox initiators on the nucleation and reaction kinetics with a model emulsion system comprised of n-butyl methacrylate, sodium lauryl sulfate, water, initiators, and other additives. Our previous study has demonstrated that a micellar nucleation mechanism plays a role in both initiator systems. In the present study, we further explored secondary nucleation using these two types of initiator systems, that is, homogeneous nucleation, which exists in the redox-initiated process, and micellar nucleation which is the main nucleation mechanism for the thermal-initiated system. The investigation also illustrates that coagulative nucleation in the redox-initiated emulsion system results in a greater extent of monodispersed particle diameter distributions, much smaller particle diameters, and lower molecular weights for the final latex. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48275.     

Kinetics of emulsifier–free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 10⁶ to 1.2 × 10⁶ g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.     

Solvent effect on the emulsion copolymerization of methyl methacrylate and lauryl methacrylate in aqueous media

Aqueous emulsion homo- and copolymerization of lauryl methacrylate (LMA), a highly hydrophobic, almost water-insoluble monomer, is quite challenging. Due to the addition of ethanol to the aqueous phase the solvency for LMA is increased and it is possible to successfully produce LMA-methyl methacrylate (MMA) copolymer particles. The incorporation of LMA is confirmed by ¹H NMR spectroscopy. Coagulation at higher ethanol content in the continuous phase could be avoided by polymeric steric stabilizers such as poly(vinyl pyrrolidone) or poly(vinyl alcohol). The conversion–time curves exhibit, independent of the stabilizer, an initially high rate where predominantly MMA is polymerized and a second period with slower rate dominated by LMA consumption as proven by ¹H NMR spectroscopy and DSC data. The morphology of the copolymer particles changes with increasing ethanol content from solid sphere - like to porous. For medium PVP - stabilizer concentrations the particles possess a single pore and appear almost bowl-shaped. The large difference between the hydrodynamic and the hard sphere particle diameter indicates a high degree of swelling of the copolymer particles with the water–ethanol mixture of the continuous phase.     

Preparation of hydrophobic polymer particles by radical polymerization and subsequent modification into magnetically doped particles

The application potential of hydrophobic polymer is numerous. Lauryl methacrylate (LMA) having long alkyl chain is a commercially available hydrophobic monomer. In this investigation, poly‐LMA (PLMA) latex particles were prepared by suspension polymerization in aqueous media using 2,2′‐azobis(isobutyronitrile) (AIBN) in presence of poly(vinyl alcohol) (PVA) as steric stabilizer. The preparation kinetics was studied in detail in terms of percentage yield and particle size variation. Low glass transition temperature (～ ?65°C) associated with high flexibility did not allow electron micrographic observation though ¹H‐NMR and particle size measurement confirmed the formation of PLMA latex. To improve the glass transition temperature, aqueous emulsion copolymerization of LMA with methyl methacrylate (MMA) was carried out. The solubility of LMA was improved by adding ethanol to the aqueous phase. Two types of polymeric stabilizers, PVA and poly(vinyl pyrrolidone) (PVP) were used to stabilize the colloidal particles. The nature of the stabilizer affected both morphology and final rate of polymerization. The hydrophobic P(LMA‐MMA) copolymer particles were subsequently modified by nanosized magnetic (Fe₃O₄) particles by two different methods. The in situ formation of Fe₃O₄ particles in presence of P(LMA‐MMA) was found to be suitable for the preparation of magnetic latex particles. Scanning electron microscope (SEM), FTIR, transmission electron microscope (TEM), X‐ray diffraction (XRD) and energy‐dispersive X‐ray spectroscopy (EDX) were used for the characterization of magnetically doped particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

SEMICONTINUOUS EMULSION COPOLYMERIZATION OF BUTYL ACRYLATE-STYRENE†

Butylacrylate (BA)-Styrene (St) copolymers have been synthesized via a semicontinuous emulsion process in which the monomers feeding rate and weight ratios (BA/St) were varied. The feed consisted of only pure monomers which were added to an aqueous solution that contained the emulsifier and initiator

The experimental results show that monomer consumption is governed by the feeding rate as well as by the monomer's reactivity, The average molecular weight decreased as the feeding rate increased independent of the BA/St ratio

Measurement of the latex average particle size and particle number, as a function of the reaction time. showed a complex sequence of particle formation and agglomeration. In general, the average particle diameter increased in direct proportion to the feeding rate. This fact suggests that most probably homogeneous nucleation is preferred over monomer diffusion to the previously formed particles. Additionally, the monomer reactivity ratios (r ₁, r ₂) decreased as the monomer feeding rate was increased

The experimental copolymer compositions determined by gas chromatography and NMR-H⁺ showed that the resulting copolymers were closely homogeneous.     

High solids content emulsions. III. Synthesis of concentrated latices by classic emulsion polymerization

Two different methods of producing bi‐ and trimodal latices of a mixture of methyl methacrylate, butyl acrylate, and small amounts of acrylic acid were tested. It is shown that a combination of concentrating blends of seed particles by semibatch reaction, followed by a nucleation of small particles plus a second semibatch phase allowed us to obtain stable latices with solids contents over 65% and viscosities of below 2500 mPa s^?1 with little coagulum formation. The key parameter in determining latex stability, coagulum formation, and viscosity appears to be the the particle size distribution, and especially its modification attributed to secondary nucleation. Because it is not possible to eliminate water‐soluble monomers from the polymerization recipe, secondary (homogeneous) nucleation must be minimized by careful addition of the free‐radical initiator and choice of monomer feed flow rates. The nucleation of the third population in the trimodal latices is best accomplished with a mixed surfactant system because renucleation by anionic surfactant alone leads to detrimental changes in the particle size distribution (PSD) resulting from excessive flocculation of particles. In addition, it was found that the viscosity of the final products was not sensitive to small changes in the ionic strength of the latex, although neutralization to a pH of 6 effectively doubles the final latex viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1916–1934, 2002; DOI 10.1002/app.10513     

Monomer Effects on Emulsion Polymerization with ASR as the Surfactant

In this paper, alkali soluble resin (ASR) was evaluated as a surfactant in the emulsion polymerizations of methyl methacrylate (MMA), ethyl methacrylate (EMA), and butyl methacrylate (BMA). It was found that the number of particles formed was proportional to the hydrophilicity of monomer and the concentration of initiator. Kinetic analysis indicated that the monomer concentration within the latex particle influences the average number of radicals per latex particle. The increase of monomer concentration within the particle enhances radical desorption from the particle and reduces the average number of radicals per particle. Experimental results show that the grafting reaction of ASR is proportional to the concentration of initiator or ASR. But the hydrophilicity of monomer is the major factor which influences the grafting reaction. This phenomenon is due to the fact that particle nucleation is different between the hydrophilic and hydrophobic monomer.     

Characterization and properties of gradient polyacrylate latex particles by gradient emulsion polymerization

In this study, gradient acrylate latex particles were synthesized by gradient copolymerization. n-Butyl acrylate (BA) and methyl methacrylate (MMA) were used as co-monomers, dodecyl diphenyl ether sodium disulfonate as the emulsifier, and potassium persulfate as the initiator. The technique involved the continuous addition of one monomer mixture into a stirred tank containing another monomer mixture. Their microstructure and properties were analyzed by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), atomic force microscopy (AFM), transmission electron microscopy (TEM), and particle size analysis. ¹H-NMR spectra show a gradual change in the chemical composition with the growth of molecular chains. The gradient polymer latexes, the instantaneous copolymer composition of which varies as the polymerization proceeds, are obtained. GPC analyses show that the aggregated molecular chain in the BA-centered latex particle experiences a process from dominant BA to MMA with changes in the monomer's feed composition during the polymerization. Particle size and TEM analyses show that the increasing latex size agrees well with the gradient growth pattern. DSC analyses show that the gradient latex particles exhibit only one broadened and ambiguous glass transition region. AFM analyses indicate no obvious microphase segregation occurs in the gradient latex particles, further verifying that the gradient microstructure is obtained.     

Synthesis of Fe3O4/PMMA composite latex particles: Kinetic modeling

In this work, a generalized mathematical model was developed to estimate the variation of particle concentration during the entire course of soapless emulsion polymerization of methyl methacrylate with ferrofluid. Two mechanisms for the nucleation and growth of particles throughout the polymerization reaction were discussed: Mechanism I – seeded polymerization; and Mechanism II – self‐nucleation polymerization. Here, the self‐nucleation included homogeneous nucleation and micelle nucleation. Coagulation between particles, which came from different nucleation mechanisms during the course of polymerization, was considered and included in this model. When appropriate parameters were selected, this model could be successfully used to interpret the variation of particle concentration during the entire reaction. Under different conditions, rate of polymerization, number of radicals in each particle, average molecular weight of polymers, and rate constant of termination were also calculated. All of them explained the experimental results quite well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4925–4934, 2006     

Synthesis of poly(butyl methacrylate) in three-component cationic microemulsions

The polymerization of butyl methacrylate in three-component microemulsions prepared with the cationic surfactant dodecyltrimethlammonium bromide is reported here as a function of monomer and surfactant content in parent microemulsions, type and concentration of initiator, and temperature. Fast reaction rates and high conversions are achieved in all cases. Final latexes are bluish-opaque and stable, and contain spherical particles with diameters in the range of 20 to 30 nm, depending on composition of the parent microemulsions and reaction conditions. Each of these particles is composed of a few macromolecules of high molecular weight (2 to 4 × 10⁶ Dalton). Both particle size and average molecular weight remain constant throughout the reaction, suggesting a continuous nucleation mechanism. Analysis of the molecular weight distribution indicates that the controlling termination mechanism is chain-transfer to monomer. © 1996 John Wiley & Sons, Inc.     

Preparation and characterization of imidazole‐functionalized microspheres

The preparation of imidazole‐functionalized latex microspheres by a two‐stage emulsion copolymerization process and their characterization are reported on. Emulsifier‐free emulsion copolymerization of styrene (St) and 1‐vinyl imidazole (VIMZ) exhibited bimodal particle size distributions caused by secondary homogeneous nucleation process. However, secondary nucleation can be avoided by using cetyltrimethylammonium bromide (CTAB) as a stabilizer at a concentration below its cmc (critical micelle concentration). This would result in the formation of monodisperse latex particles. The final particle size diameter depended on the concentration of CTAB as well as the amount of VIMZ. To control the amount of the functional imidazole groups on the latex particle surfaces, independent of the latex diameters, without secondary nucleation of particles, the seeded emulsion copolymerization of styrene and VIMZ was explored as a second‐stage polymerization at different concentrations and ratios of monomers in the presence of the previously prepared monodisperse poly(styrene‐co‐1‐vinyl imidazole) seed latex particles. The concentration of imidazole functional groups on the surface of the latex particles could also be varied through the rearrangement of hydrophilic imidazole groups by varying the second‐stage monomer addition process such as the utilization of monomer‐swollen seed particles or a shot addition of monomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 120:5753–5762, 2006     

Facile synthesis of one‐to‐one copy of monomer droplet to latex particle via equilibrium stabilized miniemulsion polymerization

Miniemulsion polymerization has been traditionally used to synthesize latex particles with a high homogenization energy to prepare an oil/water miniemulsion followed by further polymerizations. However, the exact copy of monomer droplets to latex particles depends critically on emulsion formulation, homogenization condition as well as the stability of the miniemulsified droplets after homogenization. In this study, we demonstrated experimentally for the first time that one‐to‐one copy of monomer droplets to latex particles can be synthesized via polymerization of a miniemulsion prepared from a less stringent preparation process including formulation without costabilizer and low homogenization energy. The criterion to obtain narrow size distribution of monomer droplets was established by equilibration of a low energy homogenized emulsion for different keeping time and the bulk homogenized emulsion subsequently phase separated into two layers. Top layer is the polydispersed monomer‐rich phase. The bottom layer is the equilibrium‐stabilized monomer droplet emulsion, in which the size distribution of droplets is narrow. The equilibrium‐stabilized emulsion is stable for days and subsequent polymerization exhibits nearly 100% droplet nucleation. Furthermore, the effect of surfactant/costabilizer and initiator on the one‐to‐one feature for the synthesis of latex particles was investigated in details. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

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