Microemulsion polymerization of acrylamide and styrene: Effect of the structures of reaction media

Isothermal phase diagrams of the system cetyltrimethylammonium bromide (CTAB)/n‐butanol/n‐octane/water were constructed, and the effect of the oil (n‐octane) contents on the microemulsions was studied at 40 °C. We determined the microemulsion structures of two systems, CTAB/n‐butanol/10% n‐octane/water and sodium dodecyl sulfonate (As)/n‐butanol/20% styrene/water, by conductivity measurements to investigate the polymerization of acrylamide and styrene in the two microemulsion systems. The polymerization kinetics of the water‐soluble monomer acrylamide in CTAB micelles and the different CTAB/n‐butanol/10% n‐octane/water microemulsion media [water‐in‐oil (W/O), bicontinuous (BC), and oil‐in‐water (O/W)] were studied with water‐soluble sodium bisulfite as the initiator. The maximum polymerization rate in CTAB micelles was found at the second critical micelle concentration. A mechanism of polyacrylamide formation and growth was proposed. A connection between the structures of the microemulsions and the polymerization rates was observed; the maximum polymerization rate occurred at two transition points, from W/O to BC and from BC to O/W, and the polyacrylamide molecular weights, which depended on the structures of the microemulsions, were also found. A square‐root dependence of the polymerization rates on the initiator concentrations was obtained in CTAB micelles and O/W microemulsion media. The polymerization of the oil‐soluble monomer styrene in different As/n‐butanol/20% styrene/water microemulsion media (W/O, BC, and O/W) was also investigated with different initiators: water‐soluble potassium persulfate and oil‐soluble azobisisobutyronitrile. A similar connection between the structures of the microemulsions and the conversions of styrene in CTAB/n‐butanol/10% n‐octane/water for the polymerization of acrylamide was observed again. The structures of the microemulsions had an important role in the molecular weights and sizes of polystyrene. The polystyrene particles were 10–20 nm in diameter in BC microemulsion media and 30–60 nm in diameter in O/W microemulsion media according to transmission electron microscopy. We determined the solubilization site of styrene in O/W microemulsion drops by ¹H NMR spectra to analyze the results of the microemulsion polymerization of styrene. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3320–3334, 2001     

微乳液催化苯乙烯聚合反应

微乳液催化苯乙烯聚合反应１）郝京诚汪汉卿２）（中国科学院兰州化学物理研究所兰州７３００００）石元昌李干佐（山东大学胶体与界面化学研究所济南２５０１００）关键词微乳液催化苯乙烯聚合微乳液［１］是油、水、表面活性剂和助表面活性剂在适当比例下自发形成的热力...     

微乳液中苯乙烯聚合反应的研究

测定了十二烷基磺酸钠(As)/正丁醇/20%苯乙烯/水体系相平衡。用油溶性偶氮二异丁腈(AIBN)和水溶性过二硫酸钾(K~2S~2O~8)为引发剂,研究了油包水(W/O)、双连续(BC)和水包油(O/W)型微乳液介质中苯乙烯的聚合反应。得到了苯乙烯转化率和聚苯乙烯分子量与体系水含量之间的关系,讨论了微乳液结构对聚合作用的影响。并通过电镜观察了聚苯乙烯的形貌,求得了聚苯乙烯的粒径,同时用^1HNMR研究了苯乙烯在微乳液液滴中的增溶位置,分析了聚合作用的实验结果。     

微乳液结构的研究

测定了十二烷基磺酸钠／正丁醇／２０％苯乙烯／水体系的相平衡，用冷冻刻蚀、ＥＳＲ、ＦＴ－ＩＲ研究了上述体系微乳液的结构，研究表明，苯乙烯含量恒定时，随着体系中水含量增加，电导确定的双连续结构的微乳液经历着从油包水到以连续再到水包油变化，ＦＴ－ＩＲ测定表明，Ｗ／Ｏ微乳兴较Ｏ／Ｗ微乳液的ＯＨ伸缩振动和弯曲振动频率有显著减小，说明Ｗ／Ｏ微乳兴中氢键缔合要比Ｏ／Ｗ强得多。ＥＳＲ测定表明Ｏ／Ｗ微乳液的旋转相关     

反相微乳液模板法合成介孔聚苯乙烯

提出并实施了反相微乳液为模板合成介孔聚合物的新方法. 通过考察氯仿/CTAB/水三元系反相微乳液的稳定性, 以及均相微乳液粒径变化规律, 得到了三元反相微乳液体系的稳定区域. 以(NH4)2S2O8为引发剂, 利用此反相微乳液为模板合成得到介孔聚苯乙烯材料. 产物的XRD图谱中有两个明显的衍射峰, 对应的晶面间距离d分别为2.6和1.3 nm, 1/d值之比等于1:2, 为层状结构. N2气吸附/脱附曲线表明大部分孔径为1.7 nm, 与动态光散射测得的微乳液液滴的尺寸相一致.     

Effect of short-chain alcohols on the oil-in-water microemulsion polymerization of styrene

The influence of short-chain alcohols, 1-butanol (C₄OH), 2-pentanol (C₅OH) and 1-hexanol (C₆OH), on the formation of oil-in-water styrene microemulsions and the subsequent free-radical polymerization was studied. Sodium dodecyl sulfate was used as the surfactant. The overall performance of C₄OH as the cosurfactant is quite different from C₅OH and C₆OH. The range of the microemulsion region in decreasing order is C₄OH > C₅OH > C₆OH. The primary parameters selected for the microemulsion polymerization study were the concentrations of cosurfactant and styrene. Only a small fraction of microemulsion droplets initially present in the reaction system can be successfully transformed into latex particles and the remaining droplets serve as a reservoir to supply the growing particles with monomer. Limited flocculation of latex particles also occurs during polymerization and the degree of flocculation is most significant for the C₄OH system. Received: 24 August 1999/Accepted in revised form: 22 October 1999     

Characteristics of microemulsion polymerized styrene with water-soluble versus oil-soluble initiators

The effect of oil-soluble versus water-soluble free-radical generators in the polymerization of styrene in oil-in-water (O/W) micromulsions were investigated by photon correlation spectroscopy. The microemulsions were formed by styrene, brine, sodium dodecyl sulfate (SDS), and pentanol. The polymerizations were carried out in two microemulsions that contained droplets differing by a factor of 2.4 in volume. Under the conditions of ? = 0.019 and NaCl/SDS > 2 the microemulsions were stable and the droplets were independent of one another. Both oil-soluble and water-soluble initiators produced polystyrene that contained fractions of two different sizes. In the case of the oil-soluble initiator the droplet size in the microemulsion seemed to be correlated to the size of the product whereas in the case of the water-soluble initiator, there seemed to be little relation.     

乙酰水杨酸在微乳液中水解动力学研究

用紫外分光光度法研究了乙酰水杨酸在十六烷基三甲基溴化铵(CTAB)/正丁醇/25%正辛烷/H2O微乳液体系中水解动力学, 探讨了反应机理。结果表明,微乳液结构和结构转变点对乙酰水杨酸水解有影响。水解速率在油包水(W/O)微乳液结构介质中较大, 且随水含量增加而减小。而水解反应速率转变点发生在微乳液结构由W/O到B. C. 再到O/W转变点处, 认为是水解反应机理不同和界面膜极性改变造成的。     

Microenvironment Effect on the Location Distribution of Phenothiazine in Cetyltrimethylammonium Bromide/<Emphasis Type="Italic">n</Emphasis>-Pentanol/H<Subscript>2</Subscript>O W/O and Bi-continuous Microemulsions

In cetyltrimethylammonium/n-pentanol/H₂O W/O (W/O = water in oil microemulsion) mixtures and bi-continuous microemulsions, phenothiazine (PTZ) molecules exist in the membrane phase of the dispersion either with the N atom or with the S atom pointed toward the polar head of cetyltrimethylammonium (CTAB). Cyclic voltammetry has been used to investigate the effects of the compositions and structures of the microemulsions, pH, and the salt on the location distribution of PTZ in the membrane phase of the dispersion in CTAB/n-C₅H₁₁OH/H₂O W/O and bi-continuous microemulsions. The results show that the location distribution of PTZ in the membrane phase of the dispersion in microemulsions is mainly dependent on the hydrogen bond between PTZ and n-C₅H₁₁OH (or the counterion), and on the electrostatic attractive interaction between the N atom in PTZ and the polar head of CTAB.     

Evaporation from microemulsions

The composition of W/O microemulsions during slow evaporation at room temperature and at 90°C was determined by chemical analysis. One series of microemulsions was stabilized by pentanol combined with sodium dodecyl sulfate, the other one was combined with hexadecyltrimethylammonium bromide.The hydrocarbon was styrene and the evaporation in the microemulsion was compared to that of the corresponding styrene/pentanol solutions.The results showed significant influence on the evaporation by the microemulsion structure; especially for water contents close to the minimum for stability     

Effect of monomer water solubility on cationic microemulsion polymerization of three components (water,surfactant, and monomer)

Here, we present the oil/water (O/W) microemulsion polymerization in three‐component microemulsions of n‐butyl acrylate, ethyl acrylate, and methyl acrylate, monomers with similar chemical structures but different water solubilities using the cationic surfactant dodecyl trimethyl ammonium bromide. The effects of monomer water solubility, initiator type and initial monomer concentration on the polymerization kinetics were studied. Reaction rates were high with final conversions between 70 and 98% depending on the monomer and reaction conditions. The final latexes were bluish, with a particle size ranging between 20 and 50 nm and polymer with molar masses in the order of 10⁶ g mol^?1. Increasing monomer water solubility resulted in a slower reaction rate, larger particles and a lower number density of particles. A higher reaction rate, larger average particle size and higher particle number density were obtained by increasing the monomer concentration. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Solubilization of Styrene and Acrylamide Monomers in Microemulsions

Abstract

Phase diagrams of sodium dodecyl sulfonate (DS)/n‐butanol/styrene/water systems with variable amounts of styrene were constructed at 40°C, and the effects of styrene on microemulsion stability were studied. The solubilization of styrene in these O/W microemulsion systems was investigated by ¹H NMR methods. The results show that the solubilization site shifts from the palisade layer to the inner core of microemulsion droplets when the molar fraction of styrene reaches 0.312. The solubilization of acrylamide in cetyltrimethylmethyl ammonium bromide (CTAB)/n‐butanol/10% n‐octane/water reverse microemulsions (W/O) was studied with a ¹³C NMR method. It was found that the acrylamide was mainly solubilized in the Stern layer of droplets at low acrylamide levels. However, when the mole fraction of acrylamide approaches 0.428, the acrylamide penetrates into the palisade layer and is distributed along the hydrocarbon chain of the surfactant.     

The Inhibition of the Hydrolysis of Cephanone by CTAB/n‐C5H11OH/H2O Microemulsion

Abstract

The hydrolysis of cephanone in water, cetyl trimethyl ammonium bromide (CTAB) micelle, and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion was studied through UV‐VIS absorption spectroscopy. The mechanism of the hydrolysis and the effects of both the acidity of the media and the composition of O/W microemulsion on the hydrolysis were studied. The results show that the hydrolysis rate of cephanone increases with the acidity. Compared with water, CTAB micelle and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion suppress this hydrolysis. The inhibition of the hydrolysis of cephanone by CTAB micelle and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion is related to the location of cephanone in the interphases of CTAB micelles and CTAB/n‐C₅H₁₁OH/H₂O O/W microemulsion droplets.     

Middle-phase microemulsions of green surfactant alkyl polyglucosides

Microemulsions are important organized molecular assembles in surfactant solutions and are used in various fields such as tertiary oil recovery, pharmaceutics, cosmetics, nanoparticle synthe-sis and chemical engineering. The more commonly used nonionic surfactants to produce micro- emulsions are the ethylene oxide-based compounds (CiEj). In recent years alkyl polyglucosides have been received considerable attention in producing microemulsions[17]. Alkyl polyglucosides (APG), which are widely…     

Microemulsion polymerization of styrene

Initiation of polymerization in styrene oil-in-water microemulsions by water-soluble potassium persulfate of oil-soluble 2,2′-azobis-(2-methyl butyronitrile) at 70°C gave stable latexes which were bluish and less translucent than the original microemulsions. The effects of initiator concentration, polymerization temperature, and monomer concentration on the kinetics, particle size distributions, and molecular weight distributions were investigated. The kinetics of polymerization were measured by dilatometry. In all cases, the polymerization rate shows only two intervals, which increased to a maximum and then decreased. There was no apparent constant rate period and no gel effect. A longer nucleation period was found for polymerizations initiated by potassium persulfate as compared to 2,2′-azobis-(2-methyl butyronitrile). The small latex particle size (20–30 nm) and high polymer molecular weight (1–2 × 10⁶) implies that each latex particle consists of two or three polystyrene molecules. The maximum polymerization rate and number of particles varied with the 0.47 and 0.40 powers of potassium persulfate concentration, and the 0.39 and 0.38 powers of 2,2′-azobis-(2-methyl butyronitrile) concentration, respectively. This is consistent with the 0.4 power predicted by Smith–Ewart Case 2 kinetics. Microemulsion polymerizations of styrene–toluene mixtures at the same oil-water phase ratio gave lower polymerization rates and lower molecular weights, but the same latex particle size as with styrene alone. A mechanism is proposed, which comprised initiation and polymerization in the microemulsion droplets, by comparing the kinetics of microemulsion polymerization with conventional emulsion and miniemulsion polymerization systems.     

Studies on the Phase Properties of Winsor Ⅰ-Ⅲ Type Microemulsions with Dielectric Relaxation Spectroscopy

The dielectric relaxation spectroscopy (DRS) of Winsor Ⅰ～Ⅲ microemulsions for nonionic surfactant octyl polyglucoside C8G1.46/1-butanol/cyclohexane/water system was studied.The experiment shows that the permittivity decreases with the increase in the frequency and clear dielectric relaxation phenomena were observed. Permittivity obviously decreases with the change of the microstructure of the microemulsion, W/O, B.C. and O/W can be distinguished by the permittivity.     

THE HYDROLYSIS OF PHOSPHATIDYLCHOLINE BY PHOSPHOLIPASE A2 IN MICROEMULSION AS MICROREACTOR

Phosphotipase A₂ (PLA₂) was used to hydrolyze phosphatidylcholine (PC) in microemulsions. Phase diagrams were constructed for mixtures of alcohols (C₂-C₆), medium chain triglycerides (tricaprylin, TC) or vegetable oils, PC and water, and areas corresponding to isotropic systems were identified. The PC hydrolysis was carried out with high yields at various PC/(TC+alcohol) compositions within the areas of isotropic systems at increasing amounts of solubilized water.

The initial reaction rates depended on the aggregation state of the PC (size and nature of microemulsion structures), as well as on temperature and mode of calcium addition.

At low enzyme concentrations, hydrolysis was preceded by a “lag phase” followed by an abrupt increase in rate. By contrast, no latency was observed at higher PLA₂ PC ratios and the rate was significantly higher.

The easy access of the enzyme to the substrate in the curved phospholipid-containing microemulsion particles facilitate activation of the enzyme and “pushes” the reaction to completion. Hence, these microemulsions can serve as microreactors for the enzymatic high yield hydrolysis.     

Preparation of inorganic nanoparticles in oil-in-water microemulsions: A soft and versatile approach

In this review, the synthesis of inorganic nanoparticles using oil-in-water (O/W) microemulsions as confined reaction media is discussed. Synthesis using (O/W) microemulsions has been demonstrated for a great variety of inorganic nanoparticles: metallic (Pt, Pd, Rh, Ag), single metal oxides (CeO₂, ZrO₂, TiO₂, Fe₂O₃), mixed and doped metal oxides (Ce_0.5Zr_0.5O₂, Ce_0.99Eu_0.01O₂, Zr_0.99Eu_0.01O₂, and Fe₂Mn_0.5Zn_0.5O₄), semiconductors (PbS, CdS, Ag₂S, ZnS, CdSe, PbSe, Ag₂Se), fluorides (CaF₂, YF₃, NdF₃, PrF₃), phosphates (CePO₄, HoPO₄), and chromates (BaCrO₄ and PbCrO₄). There are two synthetic strategies: 1) the use of oil-in water (O/W) microemulsions, in which the precursor is an ionic salt which is dissolved in the continuous aqueous phase; and 2) use of O/W microemulsions, in which the precursor is an organometallic salt dissolved in the oil droplets of the microemulsion. The latter approach keeps more resemblance to the typical W/O microemulsion reaction method, as it has the greatest level of precursor confinement.     

Study of nano-emulsion formation by dilution of microemulsions

The influence of different dilution procedures on the properties of oil-in-water (O/W) nano-emulsions obtained by dilution of oil-in-water (O/W) and water-in-oil (W/O) microemulsions has been studied. The system water/SDS/cosurfactant/dodecane with either hexanol or pentanol as cosurfactant was chosen as model system. The dilution procedures consisted of adding water (or microemulsion) stepwise or at once over a microemulsion (or water). Starting emulsification from O/W microemulsions, nano-emulsions with droplet diameters of 20 nm are obtained, independently on the microemulsion composition and the dilution procedure used. In contrast, starting emulsification from W/O microemulsions, nano-emulsions are only obtained if the emulsification conditions allow reaching the equilibrium in an O/W microemulsion domain during the process. These conditions are achieved by stepwise addition of water over W/O microemulsions with O/S ratios at which a direct microemulsion domain is crossed during emulsification. The nature of the alcohol used as cosurfactant has been found to play a key role on the properties of the nano-emulsions obtained: nano-emulsions in the system using hexanol as cosurfactant are smaller in size, lower in polydispersity, and have a higher stability than those with pentanol.