Surfactant concentration effects on the microemulsion polymerization of vinyl acetate

The polymerization of vinyl acetate in oil-in-water microemulsions stabilized with cetyltrimethylammonium bromide (CTAB) is reported here as a function of surfactant concentration. Reaction rate decreases as the CTAB/water ratio is increased in the parent microemulsions. Polymer particles in the latexes grow with conversion; they also become bigger as the initial surfactant content is increased. Number-average molar masses are smaller than those expected by termination by chain transfer to monomer, but weight-average molar masses increased as the surfactant concentration in the parent microemulsion is raised. However, the latter are much smaller than those obtained by polymerization in an emulsion stabilized with the same surfactant. Possible explanations to this unusual behavior are provided here.     

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     

Polymerization of vinyl acetate in microemulsions stabilized with a mixture of dodecyltrimethylammonium bromide and didodecyldimethylammonium bromide

Summary Polymerization of vinyl acetate (VA) in three component oil/water (o/w) microemulsions stabilized with a mixture of two cationic surfactants (DTAB/DDAB in a weight ratio of 3), was carried out at 40, 50 and 60°C using a water soluble initiator, V-50. In all cases studied, stable latexes containing particles with diameters between 70 and 110 nm were obtained. Particle size increased with conversion yielding uncommonly large particles for microemulsion polymerization, probably because particle coagulation. Multimodal molar mass distributions with average molar masses between 1.2 to 2.0×10⁶ g/mol were obtained. Chain transfer to polymer and bimolecular termination reactions play important roles in the microemulsion polymerization of this monomer. Received: 5 October 1998/Revised version: 12 February 1999/Accepted: 12 February 1999     

十二烷基三甲基溴化铵/醇/庚烷/水微乳化作用研究

以铁氰化钾为电化学探针,用循环伏安法测定了十二烷基三甲基溴化铵(DTAB)/醇/庚烷/水体系微乳液的扩散系数,同时用电导率法研究了微乳液的结构及结构转变。绘制了不同条件下DTAB微乳体系的拟三元相图,探讨了体系的微乳化作用规律,考察了醇的种类、含量对微乳区形成的影响。结果表明,当醇(正丁醇)固定时,随着醇含量增加,微乳区面积先增大后减小;醇的链长不同,体系的微乳区类型及面积分数均不同,随着醇碳链的增长,微乳区面积先增大后减小。     

Radiation-induced admicellar polymerization of isoprene on silica: Effects of surfactant's chain length

This research compared radiation-induced admicellar polymerization with the traditional thermal process and studied the influence of the hydrocarbon chain length of different surfactants on film formation. Three types of surfactants were used in this study: dodecyl trimethyl ammonium bromide (DTAB), tetradecyl trimethyl ammonium bromide (TTAB) and cetyl trimethyl ammonium bromide (CTAB). Isoprene was used as a monomer for the formation of thin film inside the surfactant bilayers, called admicelle, adsorbed on silica surface. The results showed that an optimum dose can lead to a better film formation on silica, compared with the thermal method. However, when the dose was over the optimum value, the formation of polyisoprene film was diminished. The formation of polyisoprene film was found to depend not only on the hydrocarbon chain length of the surfactant, but also on the density of adsorbed surfactant on silica surface.     

溴化苯乙烯/苯乙烯/丙烯腈乳液聚合试验条件探索

以过硫酸钾为引发剂,十二烷基硫酸钠为乳化剂,叔十二烷基硫醇为链转移剂,通过乳液法对溴化苯乙烯、苯乙烯、丙烯腈进行共聚得到溴化苯乙烯-丙烯腈共聚物.考察了引发剂、乳化剂、链转移剂的添加量,反应温度,反应时间,水和单体比例等对聚合反应收率的影响.研究表明：较适宜的反应条件为反应温度80℃,反应时间6h,水与单体质量比4∶1,引发剂质量为单体总质量的0.4％,乳化剂质量为单体总质量的4％,叔十二烷基硫醇为单体总物质的量的2％;上述条件下的产物收率高,相对分子质量4万左右,热分解温度高于350℃.     

阳离子改性蒙脱土插层脲醛树脂胶粘剂的性能研究

以十六烷基三甲基溴化铵(CTAB)、十二烷基三甲基溴化铵(DTAB)和CTAB/DTAB分别作为蒙脱土(MMT)的改性剂,制成了相应的有机插层剂(如CTAB-MMT、DTAB-MMT和OMMT等);然后采用复合插层法制成了压制胶合板用有机插层剂/脲醛树脂(CTAB-MMT/UF、DTAB-MMT/UF和OMMT/UF)复合胶粘剂。结果表明:OMMT的层间结构最优;当w(OMMT)=3%时,相应的OMMT/UF复合胶粘剂的综合性能最好,由其压制而成的胶合板的粘接强度和游离甲醛释放量均满足相关标准要求。     

Modeling analysis of chain transfer in reversible addition‐fragmentation chain transfer polymerization

The validity of simplifying the reversible addition‐fragmentation chain transfer (RAFT) polymerization as a degenerative chain transfer process was verified in this work. The simplified chain transfer mechanism enabled the direct modeling investigation of chain transfer coefficient in the RAFT polymerization. It also gave the analytical expressions for concentration, chain length, and polydispersity of various chain species. The comparison between the simulations based on chain transfer mechanism and those from general RAFT mechanism showed that this simplified mechanism can accurately predict RAFT polymerization in the absence of side reactions to adduct radicals other than fragmentation. However, significant errors are introduced at high conversion when side reactions to adduct are present. The chain transfer coefficient of RAFT agent is the key factor in RAFT polymerization. The polydispersity is more sensitive to chain transfer coefficient at low conversion. At high conversion, however, the polydispersity is mainly determined by termination, which can be controlled by RAFT agent concentration and the selection of initiator. At last, an analytical equation is derived to directly estimate chain transfer coefficient of RAFT agent from the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Aggregation and Adsorption Behavior of Cationic Surfactants (Cetyltrimethylammonium Bromide and Dodecyltrimethylammonium Bromide) in Aqueous Solutions of Antibiotic Drug (Amikacin Sulphate) at Different Temperatures

Conductivity and spectroscopy techniques have been accomplished to comprehend the mechanism of supramolecular assembly of cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) in aqueous solution of amikacin sulphate (0.001, 0.005, and 0.010 mol kg⁻¹). For CTAB, the normal boost of the CMC value with rise in temperature manifests the significant role of aquaphilic dehydration. However, the aquaphobic dehydrations become prominent with temperature and depict typical U-shaped behavior of CMC for DTAB. The thermodynamic parameters of micellization have been derived from CMC values. The outcomes have been conferred in terms of solvation of hydrophobic part of surfactants by hydrophobic part of amikacin sulphate and micellization becomes more favorable for surfactant with more hydrophobic character in the presence of drug. The alteration in micro-environment of the ternary (drug/surfactant/water) system has been explained in terms of fluorescence emission intensity of surfactant solutions which has been found to decrease by the addition of drug. The obtained absorbance spectrum by varying concentrations of surfactant/drug affords noteworthy information regarding the diverse interactions in studied systems. Moreover, the exhaustive understanding of surfactant micellar behavior have been discussed in consideration of use of surfactants as drug delivery agents and hence to amplify drug bioavailability consequently remodeling its treatment efficacy.     

ABS乳液接枝聚合反应中影响接枝率的因素

采用乳液聚合法合成ABS接枝聚合物,通过改变反应过程中聚丁二烯、引发剂和分子量调节剂的用量,改变反应温度及增量反应时间,考察ABS接枝聚合物接枝率的变化。结果表明：在实验范围内,接枝率随着聚丁二烯或分子量调节剂用量的增加迅速减小;随着引发剂用量的增加或增量反应时间的增长而增大;随着反应温度的升高而增大,但变化不大。     

Radical thermo‐ and sonopolymerization of methyl methacrylate initiated by iodobenzene 1,1‐diacetate

The efficiency of iodobenzene 1,1‐diacetate or (diacetoxyiodo)benzene (DAIB) as a thermo‐ and sono‐initiator of methyl methacrylate (MMA) in radical bulk polymerization is tested. The polymerization kinetics and molecular‐mass characteristics support an assumption for a combined polymerization mechanism including a classical bimolecular termination with chain transfer reaction and iniferter quasi‐living polymerization. In addition to the equilibrium formation and degradation of the ‘dormant’ polymer ends, other possible decomposition reactions of the hypervalent iodine bond are the probable reason for the deviation of this polymerization from the iniferter polymerization mechanism. These reactions bear some similarity to the two‐step addition–fragmentation chain transfer mechanism of controlled radical polymerization. The application of the poly(MMA) obtained as a macroinitiator is evidence of ‘dormant’ chain end formation. © 2001 Society of Chemical Industry     

Controlled synthesis of vinyl-functionalized homopolymers and block copolymers by RAFT polymerization of vinyl methacrylate

Reversible addition-fragmentation chain transfer (RAFT) polymerization of an asymmetrical divinyl monomer, vinyl methacrylate (VMA), was investigated under various conditions. RAFT polymerization of VMA using a dithioester-type chain transfer agent (CTA) under suitable conditions afforded soluble polymers with a high content of pendant vinyl ester side chains in sufficient yields (>70%). The monomer concentration, the nature of the CTA, and the CTA/initiator ratio were found to affect the polymerization reaction and the structure of the resulting polymers; this behavior is attributed to the relative propensities for intermolecular propagating/cross-linking reactions and intramolecular cyclization. A kinetic study of the RAFT polymerization of VMA with the dithioester-type CTA 1 suggested that the propagation reaction of the methacryloyl group proceeded predominantly with a certain level of intramolecular cyclization during the early stage of the polymerization and intermolecular cross-linking during the final stage of the polymerization. Block copolymers with one segment featuring pendant vinyl functionality were synthesized by RAFT polymerization of VMA using poly(methyl methacrylate) as a macro-chain transfer agent (macro-CTA).     

Interaction between 4-chloro-(2′-hydroxylphenylazo)rhodanine and cetyltrimethyl ammonium bromide

The interaction between 4-chloro-(2′-hydroxylphenylazo)rhodanine (ClHPAR) and cationic surfactant cetyltrimethyl ammonium bromide (CTAB) was investigated by surface tension, absorption spectra, resonance light scattering (RLS) spectra and transmission electron microscopy. It can be concluded from the experimental results that the hydrophobic forces cannot be neglected, even though the electrostatic interaction between ClHPAR and CTAB plays an important role. The RLS spectral behavior of ClHPAR changes in the presence of CTAB. The efficiency and the effectiveness of ClHPAR–CTAB mixture to decrease the surface tension of water are higher than those of any single component, i.e. CTAB and ClHPAR. As one might expect, NaCl and urine have different effects on the interaction between ClHPAR and CTAB and their interaction also depends on pH.     

Interfacial Dynamic Properties and Dilational Rheology of Sulfonate Gemini Surfactant and its Mixtures with Quaternary Ammonium Bromides at the Air–Water Interface

The dynamic interfacial properties and dilational rheology of gemini sulfonate surfactant (SGS) and its mixtures with quaternary ammonium bromides (DTAB, CTAB) at the air–water interface were investigated using drop shape analysis. Results suggest that the adsorption process of these surfactants is diffusion-controlled at dilute concentrations, whereas the adsorption mechanism gradually shifts to a mixed kinetic-diffusion control with increasing surfactant concentration. The mixed surfactant system possesses the best surface activity when the molar ratios of SGS/DTAB and SGS/CTAB mixtures are 9:10. The formation of catanionic complexes shields the electrostatic repulsion between surfactant molecules and lowers the electrostatic adsorption barrier. Therefore, SGS/DTAB and SGS/CTAB mixtures exhibit higher adsorption rates than either component alone. The effects of oscillating frequency and surfactant concentration on the surface dilational properties of SGS, DTAB, CTAB, SGS/DTAB, and SGS/CTAB mixtures were also determined. As the oscillating frequency increases, the dilational elasticity of these surfactants gradually increases. The dilational elasticity peaks at a certain concentration, which is less than the critical micelle concentration (CMC). Results show that the dilational elasticity of SGS/DTAB and SGS/CTAB mixtures is higher than that of either component, resulting from the formation of a denser monomolecular adsorption layer at the air–water interface. Our study provides a basis for understanding the interaction mechanism of catanionic surfactant mixtures containing Gemini surfactant at the air–water interface.     

Interaction of cetyltrimethylammonium bromide with cefixime trihydrate drug at different temperatures and compositions: Effect of different electrolytes

Herein,conductivity measurements have been carried out to explore the interaction between cetyltrimethylammonium bromide(CTAB,a cationic surfactant) and antibiotic drug(cefixime trihydrate(CMT)) in water and also in occurrence of inorganic salts(NaCl,Na_2 SO_4 and Na_3 PO_4) over the temperature range of 303.15-323.15 K with an interval of 5 K.In all cases,two critical micelle concentrations(c~*) were achieved for the CMT-surfactant system.Addition of CMT drug to CTAB solution decreases the values of c~*which indicates the interaction between CMT and CTAB.Both values of c~*for CMT-CTAB mixture in the presence of salts are lower in magnitude compared to the aqueous medium which indicates that micellization of the CMT-CTAB mixed system is favorable in salt solution.The values of △G_m~0 were obtained to be negative indicating the spontaneity of the micellization process and the extent of spontaneity further increases by means of rising temperature.The obtained outcomes from the ΔHm0 and ΔSm0 values disclose that the interactions between CMT and CTAB are mostly electrostatic along with hydrophobic in nature.The thermodynamic parameters of transfer and enthalpy-entropy compensation phenomenon were also determined and discussed in detail.     

Organometallic mediated radical polymerization

Controlled radical polymerization has become increasingly important over the past decade and a half, allowing for the facile synthesis of specific macromolecular architectures with excellent control over the chemical and physical properties. This article presents an organized and detailed review of one particular CRP technique, organometallic mediated radical polymerization (OMRP), focusing on the individual catalysts developed, their efficacy and monomer scope. Rhodium, cobalt, molybdenum, osmium, iron, palladium, titanium, chromium and vanadium mediated radical polymerizations are presented alongside organo-main group mediated reactions. A separate section reviews the types of copolymers which have been synthesized using OMRP techniques. An attempt is made to unify the many disparate names which have previously been used for OMRP by virtue of the common mechanistic aspects displayed by the different catalyst systems. A mechanistic discussion highlights the similarities and differences between these systems and examines the interplay between reversible termination and degenerative transfer OMRP and competing 1-electron redox processes.     

Preparation of poly(methyl methacrylate) by ATRP using initiators for continuous activator regeneration (ICAR) in ionic liquid/microemulsions

In this study, we reported the synthesis of poly(methyl methacrylate) (PMMA) polymers via initiators for continuous activator regeneration atom transfer radical polymerization using CCl₄ as initiator, FeCl₃·6H₂O/hexamethylene tetramine as catalyst complex, and 2,2′-azobis(isobutyronitrile) (AIBN) as reducing agent. The polymerization was conducted at 60 °C in the ionic liquid based microemulsion with hexadecyl trimethyl ammonium bromide (CTAB) as surfactant. Kinetics experimental results showed that the polymerization proceeded in a controlled/‘living’ process. The effects of the molar ratio of [CCl₄]/[FeCl₃·6H₂O], the concentration of AIBN, temperature and the concentration of CTAB on the polymerization was investigated. The effect of CTAB concentration on the resulting PMMA particle size was also investigated. The obtained polymer was characterized by proton nuclear magnetic resonance and gel permeation chromatography. The living characteristics were demonstrated by chain extension experiment.     

Spontaneous polymerization and chain microstructure evolution in high-temperature solution polymerization of n-butyl acrylate

This study concerns understanding of the underlying mechanistic pathways in high temperature solution polymerization of n-butyl acrylate (nBA) in the absence of added thermal initiators. The particular system of interest is the batch polymerization of nBA in xylene at temperatures between 140 and 180 °C with initial monomer content between 20 and 40 wt%. A mechanistic process model is developed to capture the dynamics of the polymerization system. Postulated reaction mechanisms include chain-initiation by monomer (self-initiation), chain-initiation by unknown impurities, chain-propagation by secondary and tertiary radicals, intra-molecular chain-transfer to polymer (back-biting), chain-fragmentation (β-scission), chain-transfer to monomer and solvent, and chain termination by disproportionation and combination. The extent of the reactions is quantified by estimating the reaction rate constants of the initiation and the secondary reactions, based on a set of process measurements. The set of measurements considered in the parameter estimation includes monomer conversion, number- and weight-average molecular weights, and average number of chain-branches per chain (CBC). Effect of temperature on chain microstructures was observed to be most evident when microstructures are expressed in terms of their quantities per chain. The evolution of other microstructural quantities such as average number of terminal double bonds per chain (TDBC) and average number of terminal solvent groups per chain (TSGC) was then also investigated. Microstructural quantities per polymer chain (TDBC, TSGC, CBC) are defined based on combinations of ¹³C, ¹H NMR and chromatographic measurements. This study presents (i) a mechanistic explanation for the competing nature of short-chain-branch and terminal double bond formation (i.e. as temperature increases, number of chain branches per chain decreases and number of terminal double bonds per chain increases), (ii) quantitative insights into dominant modes of chain-initiation and chain-termination reactions, and (iii) mechanistic explanations for the observed spontaneous polymerization. The study also reports estimated Arrhenius parameters for second-order self initiation, tertiary radical propagation, secondary radical backbiting and tertiary radical β-scission reaction rate constants. Validation of the mechanistic process model with the estimated Arrhenius parameters and comparison of estimated parameter values to recently reported estimates are also presented.     

Surface activity of mixtures of dodecyl trimethyl ammonium bromide with sodium perfluorooctanoate and sodium octanoate

In this study, the surface tension of mixtures of cationic surfactant dodecyl trimethylammonium bromide (DTAB) and anionic surfactant sodium perfluorooctanoate (SPFO) was evaluated as a function of DTAB-SPFO composition and total surfactant concentration, with and without added electrolyte. It was found that the critical micelle concentration (CMC) of these mixtures was reduced by more than two orders of magnitude when compared to the CMC of SPFO and DTAB alone. The surface tension, after CMC, of the mixtures was close to that of SPFO with added electrolyte and even lower than that of SPFO without added electrolyte. Using the appropriate, combination of SPFO and DTAB, surface tensions near 18 mJ/m² were obtained using a concentration 1/500 of that required for SPFO alone. When these results were compared to those obtained for DTAB-sodium octanoate (SOCT) mixtures, it was evident that the DTAB-SPFO system shows a larger degree of synergism than the DTAB-SOCT system. Contact angle measurements on Teflon^® surfaces corroborates that the lower surface tension of DTAB-SPFO mixtures improves wetting on these hydrophobic surfaces. Using the regular solution theory to interpret the data of CMC and C45mJ/m² (monolayer formation) versus DTAB-SPFO composition, it was concluded that even when small concentrations of SPFO are introduced in the mixture, the composition of the micelles (at the CMC) and monolayer adsorbed at the air-water interface tends to be equimolar in SPFO and DTAB.     

Inhibition of copper corrosion in acidic chloride solution by methionine combined with cetrimonium bromide/cetylpyridinium bromide

Methionine (MET) is non-toxic and easily biodegradable so that it is an alternative corrosion inhibitor in the water treatment and industrial pickling process. In this article, the inhibition behavior of MET combined with cetrimonium bromide (CTAB) and cetylpyridinium bromide (CPB) for copper corrosion in 0.5 M HCl solution has been investigated by using the electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and polarization curve methods. It shows that combination of MET with CTAB or CPB improves the inhibition performance effectively, and produces strong synergistic inhibition effect. The combined inhibitors suppress cathodic reaction and shift the corrosion potential toward more negative values. The mixed CTAB/MET has a better synergistic effect compared with the mixed CPB/MET. The quantum chemical parameters were calculated by PM3 semi-empirical quantum method. The better synergistic inhibition between MET and CTAB is attributed to their stronger electrostatic interaction.