Study on ultrasonic induced encapsulating emulsion polymerization in the presence of nanoparticles

In this paper, the ultrasonic induced encapsulating emulsion polymerization technique was used to prepare polymer/inorganic nanoparticle composites. The main affecting factors in ultrasonic induced encapsulating emulsion polymerization were studied systematically. The experimental results suggested that the pH value, the type of monomers, the type, content, and surface properties of nanoparticles, the type and concentration of surfactant have great influence on the ultrasonic induced encapsulating emulsion polymerization and the obtained latex stability. If selecting cationic emulsifier (such as cetyl trimethylammonium bromide), low water soluble monomer (such as n‐butyl acrylate and styrene), and hydrophobic nano silica, the inorganic nanoparticles could be encapsulated by polymers through ultrasonic irradiation successfully under alkalescent condition, forming a novel polymer/inorganic nanoparticles composite. The mechanism of ultrasonic induced encapsulating emulsion polymerization and the composite latex stabilization are proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1130–1139, 2001     

Polystyrene latex synthesized in presence of ultrasonic initiation

The low water solubility of styrene (St) monomer increase the need for a good initiator system to speed up the emulsion polymerization and remove unreacted monomers. Polymerization of styrene monomer in water was performed at 30, 50, and 70°C under ultrasonic irradiation using sodium dodecyl sulfate as surfactant and ammonium persulfate as initiator. Ultrasonic energy was used as a tool to speed up the polymerization. Combining ultrasonic and ammonium persulfate led to a higher conversion and higher rate of polymerization. Ultrasonic energy has an effect on the particle size distribution. The particle size distribution increases with an increase in the monomer conversion of styrene for ultrasonic polymerization, whereas the particle size distribution did not change with an increase in the monomer conversion compared with the conventional thermal polymerization results. Higher molecular weights were obtained under ultrasonic irradiation. FE‐SEM and TEM pictures show different morphology with changing temperature polymerization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

高分子表面活性剂存在下超声辐照引发苯乙烯乳液聚合的研究

采用高分子表面活性剂(CMC-A9)和十二烷基硫酸钠(SDS)做乳化剂,用超声辐照乳液聚合方法制备了相对分子质量高(>106)的寡链聚苯乙烯纳米粒子。研究结果表明,在适当的反应条件下,CMC-A9的加入使反应速率大大提高,反应60min单体转化率能达到85%,制得直径30～60nm的聚苯乙烯胶乳粒子,乳胶粒子中含平均分子链数为3～20。CMC-A9或SDS质量浓度提高,能降低乳胶粒径和乳胶中所含的平均分子链数,增加聚合物相对分子质量。超声波输出功率对乳胶粒径影响不大。     

Polymerization of methyl acrylate initiated by V(V)-cyclohexanone redox system in micellar phase

The kinetics of methyl acrylate (MA) polymerization initiated by a V(V)-Cyclohexanone redox system, in the presence of surfactant, over a temperature range of 30–50°C in acidic medium are analyzed. The anionic surfactant (SDS) enhances the rate of polymerization (R_p) as well as the rate of V(V) consumption (−R_v). The cationic surfactant, cetyl trimethylammonium bromide (CTAB), decreases both the rates. The effect of variation of the concentration of surfactant, monomer, substrate, and acid have been examined. A suitable free radical mechanistic scheme has been proposed for the above process. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2081–2088, 1997     

Emulsifier‐free miniemulsion polymerization of styrene using a cationic initiator

Polystyrene latex particles were synthesized using a method based on emulsifier‐free miniemulsion polymerization under ultrasonic irradiation in the presence of 2,2′ azobis (2‐amidinopropane) dihydrochloride (V‐50) as a cationic ionizable water‐soluble initiator and cetyl alcohol as costabilizer. The optimized conditions were obtained by using various parameters, such as the amounts of monomer and initiator, and the time and power of ultrasonic irradiation. In optimal conditions, the latex particles appeared to be about 250 nm in diameter through scanning electron microscopy (SEM). The SEM and gel permeation chromatography (GPC) analyses and monomer conversions of emulsifier‐free miniemulsion polymerization were compared with those of conventional emulsifier‐free emulsion polymerization using V‐50 as initiator in both cases. The results showed that in the miniemulsion polymerization, the rate of polymerization (Rp) was significantly higher, and latex particles were significantly smaller than those in the conventional emulsion polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Preparation and characterization of monodisperse magnetic poly(styrene butyl acrylate methacrylic acid) microspheres in the presence of a polar solvent

Magnetic poly(styrene butyl acrylate methacrylic acid) [P(St–BA–MAA)] microspheres were prepared by emulsifier‐free emulsion polymerization in the presence of a polar solvent and a ferrofluid prepared by a coprecipitation method. The effects of some polymerization parameters, such as the medium polarity, reaction temperature, initiator content, and surfactant content in the ferrofluid, on the particle diameter and particle size distribution of magnetic P(St–BA–MAA) microspheres were examined in detail. The results showed that the electrostatic repulsion in the polymerization system significantly affected the monodispersity of the resulting magnetic polymer microspheres. The proper electrostatic repulsion, achieved through changes in the medium polarity and amount of surfactant in the polymerization system, improved the monodispersity, but a higher or lower repulsion led to a decrease in the monodispersity. Although the existence of surfactant and magnetite particles reduced the monodispersity more or less, the polymerization behavior of an emulsifier‐free emulsion polymerization in the presence of the ferrofluid was analogous to that of a conventional emulsifier‐free emulsion polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1733–1738, 2003     

Ultrasonically initiated free radical‐catalyzed emulsion polymerization of methyl methacrylate (i)

The emulsion polymerization of methyl methacrylate initiated by ultrasound has been studied at ambient temperature using sodium lauryl sulfate as the surfactant. The investigation includes the: (1) nature and source of the free radical for the initiation process; (2) effects of different types of cavitation; and (3) dependence of the polymerization rate, polymer particle number generated, and the polymer molecular weight on acoustic intensity, argon gas flow rate, surfactant concentration, and initial monomer concentration. It was found that the polymerization could be initiated by ultrasound in the emulsion systems containing methyl methacrylate, water, and sodium lauryl sulfate at ambient temperature in the absence of a conventional initiator. The source of the free radical for the initiation process was found to come from the degradation of the sodium lauryl sulfate, presumably in the aqueous phase. The weight average molecular weight of the poly(methyl methacrylate) obtained varied from 2,500,000 to 3,500,000 g mol⁻¹, and the conversion for polymerization was up to 70%. Deviations from the Smith–Ewart kinetics were observed. The polymerization rate was found to be proportional to the acoustic intensity to the 0.98 power; to the argon gas flow rate to the 0.086 power; to the surfactant concentration to the 0.08 power, with the 0.035M–0.139M surfactant concentration range; and to the surfactant concentration to the 0.58 power, with the 0.139M–0.243M surfactant concentration range. The polymerization rate was found to increase with increasing initial monomer concentration up to a point where it became independent of initial monomer concentration. The polymer particle number generated per milliliter of water was found to be proportional to the acoustic intensity to the 1.23 power; to the argon gas flow rate to the 0.16 power; to the surfactant concentration to the 0.3 power, with the 0.035M–0.139M surfactant concentration range; and to the surfactant concentration to the 1.87 power, with the 0.139M–0.243M surfactant concentration range. The polymer weight average molecular weight was found to be proportional to the acoustic intensity to the 0.21 power, and to the argon gas flow rate to the 0.02 power. It was found to be inversely proportional to the surfactant concentration to the 0.12 and 0.34 power, with the 0.035M–0.139M and the 0.139M–0.243M surfactant concentration ranges, respectively. The polymer yield and polymerization rate were found to be much larger than those obtained from an ultrasonically initiated bulk polymerization method. The polymerization rates obtained at ambient temperature were found to be similar to or higher than those obtained from the conventional higher temperature thermal emulsion polymerization method. This investigation demonstrated the capability of ultrasound to both initiate and accelerate polymerization in the emulsion system, and to do this at a lower temperature that could offer substantial energy savings. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 797–825, 1999     

Ionic liquid as surfactant in microwave‐assisted emulsion polymerization

The aim of this work is to study the use of an ionic liquid (IL) as surfactant in emulsion polymerization reactions and to evaluate its effect when these reactions are heated under microwave irradiation. The IL 1‐n‐dodecyl‐3‐methylimidazolium chloride was chosen to replace the surfactant dodecyltrimethylammonium bromide (DTAB) in methyl methacrylate emulsion polymerizations. The conversion evolutions and the final average diameter of polymeric particles were quite similar for reactions using the surfactant DTAB or the IL, showing that the IL acted efficiently as surfactant in emulsion polymerizations. Comparing the polymerization reactions performed under microwave irradiation and conventional heating, reaction rate enhancements were obtained for both DTAB and IL. Using a pulsed scheme, under high‐power microwave irradiation, slightly higher reaction rates and molecular weights were obtained in reactions using IL, in comparison with surfactant DTAB, indicating the existence of some specific effects linked to IL–microwaves interaction. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of poly(butyl methacrylate)/γ‐Al2O3 nanocomposites via ultrasonic irradiation

A new technique (ultrasonic irradiation) has been employed to prepare poly(n‐butyl methacrylate) PBMA/γ‐Al₂O₃ nanocomposites, taking advantages of the multiple effects of ultrasonic irradiation, such as dispersion, pulverization and activation. When subjected to ultrasonic irradiation, n‐butyl methacrylate (BMA) is polymerized to form poly(n‐butyl methacrylate) (PBMA) latex without any chemical initiators, and the monomer conversion reaches 72.5% in 25 min. At an appropriate pH, surfactant bilayers are formed through electrostatic interactions between γ‐Al₂O₃ nanoparticles and the anionic surfactant sodium dodecyl sulfate (SDS), which adsorb BMA. After ultrasonic induced polymerization of BMA in the presence of nanoparticles of γ‐Al₂O₃, the γ‐Al₂O₃ nanoparticles are encapsulated by PBMA shells formed. The influence of factors such as pH, surfactant concentration and the nanoparticle content is investigated. The FTIR spectra show that there are still polymers tightly adsorbed by nanoparticles even after extraction by acetone for 72 h. The difference observed in the XPS spectra of nanocomposite residues and the pure γ‐Al₂O₃ nanoparticles may indicate some interactions between γ‐Al₂O₃ nanoparticles and the PBMA matrix. Furthermore, the feasibility of SDS bilayer formation and encapsulating polymerization is proven by XPS characterization. © 2001 Society of Chemical Industry     

超声波作用下反应体系组成对苯乙烯分散聚合反应规律的影响

研究了超声波作用下反应体系组成对苯乙烯(St)分散聚合反应规律的影响,表明超声波作用下的分散聚合反应并非一般的热引发分散聚合反应,超声波的空化作用可有效地、多途径地生成更多的自由基。掌握了聚合反应规律,可初步实现根据聚苯乙烯(PS)粒径及分布和聚合反应速率要求进行反应体系的配方设计。     

Desorption of free radicals in semibatch emulsion polymerization of methyl acrylate

Desorption of free radicals from particles can cause an emulsion polymerization system to deviate from Smith–Ewart case II kinetics. A mechanistic model has been developed to predict the effect of desorption of radicals from particles on the kinetics of semibatch emulsion polymerization of methyl acrylate under the monomer-starved condition. Experimental data available in the literature are used to assess the proposed kinetic model. The model predicts the experimental data reasonably well for a wide range of monomer feed rates. The rate of polymerization increases with an increase in the rate of monomer addition. The kinetic data are also useful in evaluating the desorption rate constant (K′_d) for methyl acrylate. The best fitted value of K′_d at 50°C is 4 × 10^-12 cm²/s, which is in good agreement with the theoretical values predicted by desorption theory. © 1995 John Wiley & Sons, Inc.     

Study on bulk polymerization of methyl methacrylate initiated by low intensity ultrasonic irradiation

Methyl methacrylate (MMA) was polymerized in bulk solutions using low intensity ultrasonic radiation of 0.25 W/cm². The polymerization occurred after 1 h of irradiation time was applied. The polymerization rate was greatly accelerated either by increasing the amount of poly (methyl methacrylate) (PMMA) granular added into the system or by elongating the irradiation time. However, it was found that the reaction rate increased with the decreasing of the ultrasonic frequencies when the exposure time of the polymerization under the irradiation was less than 3 h. Experimental results verified that the polymerization was initiated by free radicals, which were mainly generated from the degradation of PMMA macromolecular chains, the friction between the polymer macromolecular chains and the solvent monomer. These findings were obviously different from those obtained when high intensity ultrasonic irradiation was used. The polymers fabricated in this study by using ultrasound irradiation have a narrower molecular weight distribution compared to those obtained from the polymerizations induced by the conventional initiators. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of surfactants on acrylonitrile polymerization initiated by a Cr(VI)–cyclohexanone redox system: A kinetic study

The polymerization of acrylonitrile (AN) was kinetically studied with a Cr(VI)–cyclohexanone (CH) redox system as an initiator from 25 to 45° C in the presence of a surfactant. The rate of polymerization and the percentage of the monomer conversion increased as the concentration of the anionic surfactant [sodium dodecyl sulfate (SDS)] increased above its critical micelle concentration. However, the cationic surfactant (cetyltrimethylammonium bromide) reduced the rate considerably at higher concentrations, whereas the nonionic surfactant (TX‐100) had no effect on the rate. The effects of the Cr(VI), CH, AN, and H⁺ concentrations and the ionic strength on the rates were also examined. The presence of 0.015M SDS reduced the overall activation energy of the polymerization by 5.55 kcal/mol with respect to that in the absence of the surfactant. With increasing SDS concentration, the viscosity‐average molecular weight also increased. A suitable mechanistic scheme was proposed for the polymerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1147–1153, 2004     

Effects of alkali soluble resin on the emulsion polymerization of butyl methacrylate

In this work, alkali soluble resin (ASR) was evaluated as a surfactant in the emulsion polymerization of butyl methacrylate (BMA). Kinetic analysis indicated that the ASR surfactant retarded the reaction rate and reduced the average number of radicals per latex particle. Since the particle nucleation period proceeds until the disappearance of droplets, Interval II does not exist in this system. Experimental results show that the particle number depends on the 0.31 and 0.51 powers of the ASR and KPS concentration, respectively. The particle size distribution of the latex becomes broad with the increase of the ASR concentration in the emulsion polymerization. This phenomenon explains why the period of the particle nucleation is proportional to the ASR concentration used in the reaction.     

Emulsion polymerization of styrene: Simulation the effects of mixed ionic and non-ionic surfactant system in the presence of coagulation

A detailed model was developed for emulsion polymerization of styrene in batch reactor to predict the evolution of the product particle size distribution. The effect of binary surfactant systems (ionic/non-ionic surfactants) with different compositions was studied. The zero–one kinetics was employed for the nucleation rate, with the model comprising a set of rigorously developed population balance equations. The modeling incorporated particle formation by both nucleation and coagulation phenomena. The partial differential equations describing the particle population were discretized using finite volume elements. Binary surfactant systems, comprising sodium dodecyl sulfate (SDS) as anionic, and a commercial polyether polyol (Brij35^®) as non-ionic surfactants, were examined with different mass ratios. Increasing non-ionic surfactant mass fraction in binary surfactant system showed the decrease of particle number due to intensifying the coagulation between particles. Broader particle size distributions with greater average particle size were obtained with non-ionic surfactant comparing those obtained with anionic one.     

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     

Entry in emulsion polymerization using a mixture of sodium polystyrene sulfonate and sodium dodecyl sulfate as the surfactant

A mixture of sodium polystyrene sulfonate (NaPSS) and anionic surfactant, sodium dodecyl sulfate (SDS), was used as the emulsifier in the emulsion polymerization of styrene at 60 °C. The latexes prepared were stable, bearing the better resistance to the addition of electrolyte, and have the larger values in particle size and the higher polymerization rates than those counterparts prepared using SDS only. The NaPSS was prepared by a series of process: a concentrated cyclohexane solution of an anionically polymerized polystyrene (PS) was sulfonated with sulfuric acid at 80 °C, and then neutralized and purified through dialysis. The data of average polymer number per particle (n_p) were found useful in investigating the surfactant content effect on the entry of radicals into particles, where the latex particle size plays an important role.     

Modification of PTFE latex with P4VP/Surfactant complexes at nanoscale

Polytetrafluoroethylene (PTFE) latex nanoparticles were subjected to modification with Poly (4‐vinylpyridine) (P4VP) by in situ seeded emulsion polymerization technique using regular [sodium dodecyl sulfate (SDS)] and fluorinated [Potassium heptadecafluoro‐1‐octanesulfonate (PFS)]surfactants. The as prepared PTFE‐ (P4VP/surfactant complex) composite latex nanoparticles were characterized for structure, morphology, and thermal properties and a comparison of particles obtained by PFS and SDS was done with different W/W ratios of PTFE and 4VP monomer. The composites have shown a multistep degradation pattern that may be attributed to the P4VP, surfactant and PTFE backbone degradation. Lowering of crystal–crystal transition temperature of PTFE and increase in the glass transition temperature of the P4VP/PFS or SDS complexes was noticed in all the composites suggesting a homogeneous modification. Thus, a simple and easy way to modify PTFE has been reported which could be subsequently complexed with metal salts such that stringent high energy pretreatment methods like plasma, ozone, or irradiation techniques could be avoided. POLYM. ENG. SCI., 55:499–505, 2015. © 2014 Society of Plastics Engineers     

Inferential closed-loop control of particle size distribution for styrene emulsion polymerization

In this work, a new control strategy for controlling the particle size distribution (PSD) in emulsion polymerization has been proposed. It is shown that the desired PSD can be achieved by controlling the free surfactant concentration which in turn can be done by manipulating the surfactant feed rate. Simulation results show that the closed-loop control of free surfactant concentration results in a better control of PSD compared to open-loop control strategy, in presence of model mismatch and disturbances. Since the on-line measuring of ionic free surfactant concentration is difficult, conductivity which is related to it is measured instead and used for control purposes. The closed-loop control of conductivity also results in a better control of PSD compared to open-loop control strategy, but its performance is not as good as controlling free surfactant concentration in presence of model mismatch.     

Reaction kinetics of vinyl acetate emulsion polymerization

Transport of free radicals out of latex particles into the aqueous phase plays an important role in the emulsion polymerization of vinyl acetate. This so-called “desorption” process involves chain transfer to monomer which generates a mobile and rather stable monomer-unit free radical followed by the diffusion of this free radical out of the latex particle. A kinetic model is developed based on the reaction mechanisms of such an emulsion system. The experimental data available in the literature are used to test the model under various polymerization conditions. Reasonable agreement between the model predictions and experimental data is observed.