Comparison of oil-soluble and water-soluble initiation of styrene polymerization in a three-component microemulsion

The polymerization of styrene in three-component oil-in-water microemulsions made with the cationic surfactant dodecyltrimethylammonium bromide is studied by dilatometry and quasielastic light scattering as a function of type and concentration of initiator. Fast polymerization rates, high conversions, and high molecular weight polymers are achieved with both oil-soluble (AIBN) and water-soluble (potassium persulfate) initiators. The rate of polymerization shows initiation and termination intervals, but no constant-rate interval is observed. Stable monodisperse microlatexes are obtained with both types of initiators. For both AIBN and potassium persulfate, polystyrene molecular weight is proportional to initiator concentration [I]^–0.4 and particle radii decrease as [I]^–0.2. Polymerization initiation occurs in or at the microemulsion droplets, and polymer particles grow by recruiting monomer and surfactant from uninitiated swollen micelles.     

Contribution of Na counterions to H-AOT&Na-AOT-based W/O microemulsion formation using aqueous NaOH solutions as estimated by pyranine absorbance

The objective of this study is to estimate the contribution of Na⁺ as a counterion in the formation of H-AOT&Na-AOT-based W/O microemulsions using aqueous NaOH solution by pyranine absorbance measurements. A mixture of an aqueous NaOH solution containing pyranine/H-AOT&Na-AOT/isooctane was emulsified by changing the mixing ratio of Na-AOT (X_Na-AOT = 0–1) and the mole fraction of NaOH (X_NaOH = [NaOH]/the AOT⁻ concentration in the water pool = 0–1). The phase behavior of the emulsified mixture was evaluated from the absorbance of pyranine at the isosbestic point and by visual observations. W/O microelumsions are formed at the mid-range of X_Na-AOT, whereas the emulsified mixture separates into two phases at lower X_Na-AOT and higher X_Na-AOT. The two phase boundaries shift toward lower X_Na-AOT as with increasing X_NaOH. The phase behavior depends on the degree of screening of electrostatic repulsions between the polar headgroups of AOT⁻ by the Na⁺ counterion. Interestingly, nano-sized W/O microemulsions are formed without phase separation using a highly concentrated NaOH aqueous solution when the Na-AOT mixing ratio is appropriately adjusted. The phase behavior was plotted as X_NaOH versus X_Na-AOT, and the correlation equations for the two phase boundaries were obtained by fitting the points. The contribution of the Na⁺ counterion from NaOH to W/O microemulsion formation was estimated by the correlation equations. The absorbance of pyranine and the size of W/O microemulsions, as measured by DLS, were plotted as a function of X_Na⁺=(x[Na⁺   from   NaOH]+[Na⁺   from   Na-AOT])/[AOT⁻], in which x is the ratio contributed by NaOH. The absorbance and size correlates well with X_Na⁺, indicating that X_Na⁺ is a meaningful parameter for quantitatively estimating phase behavior and size variation.     

Ionic Equilibria of Chromophoric Reagents in Microemulsions

Protolytic equilibria of twenty chromophoric acid–base indicators from different classes, namely, sulfophthaleins, hydroxyxanthenes, azo compounds, and others, were studied in direct microemulsions of benzene–pentanol-1–surfactant–water at volume fractions of the dispersed phase of up to 13%. Cetylpyridinium chloride, sodium dodecylsulfate, and certain nonionic surfactants were used. Apparent acidity constants (pK _a) of indicators were determined under the conditions of their complete binding by microdroplets (pK _a ^ac). The strong differentiating effect of the dispersed phase of microemulsions of different types on the acid–base properties of indicators was revealed. The effect of the ionic strength of the continuous phase (0.025–1.0) on the values of pK _a ^ac was studied. The partition constants of Bromothymol Blue anions between water and negatively charged microdroplets were estimated. Similarities and differences were revealed in the action of microemulsions and micellar solutions of the corresponding surfactants on the state of the studied chromophoric reagents.     

Effect of solution components on the termination mechanism in acrylamide microemulsion polymerizations

A study of the effect of the various solution components on the kinetics of the polymerization of acrylamide in water/oil (w/o) microemulsions has been performed. For the polymerizations with toluene as the continuous phase, both the rate of polymerization, R_p, and the molecular weight of the polyacrylamide were found to be first order in monomer concentration. Furthermore, for the low temperatures (10°C) involved in these experiments, nondegradative chain transfer to monomer appears to be insignificant. When the continuous-phase solvent was changed, an exponential dependence, X, of R_p on the incident light intensity in the order of toluene (X = 1.06) > heptane (X = 0.73) > benzene (X = 0.55) was found. Thus, the monoradical termination found in the toluene microemulsions is likely due to degradative transfer to toluene, forming a stable benzyl radical, while polymerization in benzene (no labile hydrogen atoms) leads to biradical termination     

Ambient temperature Atom Transfer Radical copolymerization of tetrahydrofurfuryl methacrylate and methyl methacrylate: Reactivity ratio determination

Tetrahydrofurfuryl methacrylate (THFMA), a heterocyclic monomer was polymerized by ambient temperature Atom Transfer Radical Polymerization (AT ATRP) using CuX/PMDETA/EBiB system. THFMA was found to undergo very rapid polymerization, in bulk. For a target DP > 200, bulk polymerization results in cross-linking as evidenced by (CH₂)_n,wag peaks (IR spectroscopy). Atom Transfer Radical copolymerization (ATRcP) of THFMA with MMA was performed and the reactivity ratios were calculated from the copolymer composition, as determined by ¹H NMR, using Fineman–Ross and Kelen–Tudos methods. The reactivity ratios determined for ATRP were found to be significantly different from the literature values for conventional free radical polymerization (CFRP). This may be due to the coordination of copper catalytic system with the oxygen atom of the tetrahydrofurfuryl group that could lead to the variation in reactivity ratios. ¹H NMR evidence for catalyst–monomer interaction is also provided.     

Polymerization of butyl acrylate in anionic microemulsion

Butyl acrylate was initiated with KPS or BPO to polymerize at high monomer concentration in the microemulsions with SBOA (sodium 12-butinoyloxy-9-octadecenate) as emulsifier. The microemulsion remained clear or reddish. It was found that the constant polymerization period appeared in most microemulsions and the length of it varied with the concentration of monomer and the initiating rate. When microemulsions were initiated with KPS, the overall polymerization rate increased with the emulsifier concentration; while initiator was BPO, it showed the inverse tendency. It was attributed to the difference between the initiating mechanism of the two initiators. © 1996 John Wiley & Sons, Inc.     

Formations of polyvinyltoluene microlatexes in quaternary oil in water cetyltrimethylammonium bromide microemulsions

Polymerization of vinyltoluene (VT) in quaternary microemulsions containing cetyltrimethylammonium bromide (CTAB) as the cationic surfactant is studied using laser Raman spectroscopy (LRS) and dilatometry. The influences of water soluble (potassium peroxodisulphate, ammonium peroxodisulphate) and oil soluble (azobisisobutyronitrile, benzoyl peroxide) initiators, monomer, surfactant, cosurfactants (n-alcohol and bifunctional alcohols) and temperature on the rates of polymerization (R _p), energy of activation (Ea), particle diameter (D), number of polymer particles (N _p), molecular weight of polyvinyltoluene (M _v) and number of polymer chains per latex particle (N _pc) are investigated. The dependencies of the kinetic and latex size parameters on the initiators and cosurfactants are discussed in terms of the efficiency of the initiators in initiating the polymerization and on the interfacial partitioning behavior of various cosurfactants. The polymerization mechanism seems to follow Smith Ewart Case II hypothesis with two distinct rate regions. Final polymer microlatexes are found to lie within 10–50 nm as observed by transmission electron microscopy (TEM). Molecular weights are in the range of (1 to 5)×10⁶. Each latex particle contains one to three polymer chains.     

Aqueous polymerization of acrylonitrile initiated by manganese(III) pyrophosphate-thiocyanate redox system: a kinetic study

Summary The kinetics of aqueous polymerization of acrylonitrile monomer (M) initiated by the Mn^III-KNCS redox system have been studied under deaerated conditions in the temperature range 26–40 °C at constant ionic strength. The overall rates of polymerization and the disappearance of Mn^III were determined. The polymerization was initiated by the free radicals arising from the Mn^III-thiocyanate redox reaction. The rate of polymerization was investigated at various concentrations of monomer and initiator. The effects of varying [Mn^III], [NCS^–], pH, total [P₂O _inf7 ^sup4– ], added [Mn^II], metal ions, ClO _inf4 ^sup– , Cl^– and SO _inf4 ^sup2– were examined. Dependence of the rate of polymerization on temperature was studied and activation parameters were computed from an Arrhenius plot. A suitable kinetic scheme consistent with the observed results is proposed and discussed.     

KINETICS AND MECHANISM OF PHASE TRANSFER CATALYZED FREE RADICAL POLYMERIZATION OF METHYL ACRYLATE

The kinetics of free radical polymerization of methylacrylate (MA) was investigated using benzyltributylammonium chloride (BTBAC) as phase transfer catalyst and potassium peroxydisulfate as initiator at aconstant temperature, 60°C, in an inert atmosphere under unstirred condition. The effect of concentrations of the monomer, initiator and the catalyst on polymerization was discussed and a mechanism of polymerization has been proposed. The order with respect to the monomer, initiator, and phase transfer catalyst was found to be 2, 0.5, and 0.5, respectively.     

Polymerization in nonaqueous microemulsions

Nonaqueous microemulsions containing formamide, the anionic surfactant AOT (bis(2-ethyl-hexyl)sulfosuccinate sodium salt), sodium bromide (NaBr), and either of the monomers hexyl methacrylate or styrene are polymerized at 60°C. For both monomers, the final product is a stable, bluish dispersion of particles of ca. 80 nm diameter. Based on phase behavior studies as a function of NaBr concentration, we describe how a systematic variation of composition and monomer causes changes in reaction rates and latex characteristics. The monomer solubility in the continuous phase plays an important role in determining the final polymer characteristics. Decreasing monomer solubility shifts the mechanism from one similar to solution polymerization to one closer to traditional emulsion polymerization.     

Macrocyclic Polyether Phase Transfer Catalysts for Free Radical Polymerization of Acrolein

Macrocyclic polyethers, e.g., crown ethers and cryptands, were prepared and employed as phase transfer catalysts for free radical polymerization of acrolein, a vinyl monomer, with persulfates (S₂O₈^2–) as initiators. The catalytic abilities of various macrocyclic polyethers as catalysts for the free radical polymerization of acrolein were found to be in the order: benzo‐15‐crown‐5 > dibenzo‐18‐crown‐6 > 12‐crown‐4 > 15‐crown‐5 > 18‐crown‐6 > cryptand‐22 with sodium persulfate (Na₂S₂O₈) as initiator. Sodium persulfate proved to be a better initiator than ammonium persulfate or potassium persulfate with benzo‐15‐crown‐5 as a catalyst. Effects of solvents and temperature on the catalytic polymerization were also investigated. The polymerization rates in various solvents were in the order: dioxane > benzene > acetonitrile > acetone > dichloromethane > hexane > water. Comparison between bulk polymerization and solution polymerization was also made. Higher polymerization rate was observed at higher temperature. The molecular weights of polyacrolein and the conversion of monomer in reaction period were determined with gel permeation chromatography and ultra‐violet spectrophotometry, respectively. Concentration effects of crown ether and initiator were also investigated and discussed.     

Aqueous polymerization of ethyl acrylate initiated by ceric ion-reducing agent system in sulphuric acid medium

Kinetic study of aqueous polymerization of ethyl acrylate (EA) is carried out at 30 °C in dilute sulphuric acid medium by employing ammonium ceric sulphate–methyl ethyl ketone (MEK) as redox initiator system. The ceric ion consumption is found to be first order with respect to ceric ion and half order with respect to reducing agent concentrations. No complex formation between ceric ion and reducing agent is observed. The orders with respect to ceric ion, reducing agent and monomer concentrations are evaluated for the aqueous polymerization of EA by Ce(IV)–MEK redox initiator system, and are found to be 0.5, 0.5 and 1.4, respectively . The overall activation energy, E _overall, for aqueous polymerization of EA in the temperature region of 27–40°C is found to be 20.27 kJ/mol. A kinetic scheme for the aqueous polymerization of EA initiated by Ce(IV)–MEK redox initiator system is presented.This revised version was published online in June 2005 with corrections to figure legends as well as small corrections within text.     

Synthesis and characterization of PAni–SiO2 and PTh–SiO2 nanocomposites' thin films by plasma polymerization

In the present work, we explore the possibility to deposit polyaniline–silicon dioxide (PAni–SiO₂) and polythiophene–silicon dioxide (PTh–SiO₂) nanocomposites through a plasma polymerization route. The films were generated by spraying of mixtures of nano-sized silica particles dispersed in the liquid monomer into a plasma stream of the DC-plasma discharge reactor. The silica in the resulted polymer matrix changes the conduction mechanisms varying from ohmic to ballistic and traps inducing the space charged limited currents (SCLC). The silica modifies the morphology and composition of the deposited films.     

丙烯酰胺双水相聚合体系稳定性研究

通过浊点滴定法测定了不同温度下PAAmPEGH2O双水相体系相图,发现分相浓度随着温度的升高先增后降,55℃时分相浓度最低.双水相聚合体系微观结构显示,分散相以砾状液滴形式均匀分散在连续相中.研究了聚合过程中聚合体系粘度的变化,以及聚合温度、分散介质、单体、引发剂及乳化剂等对聚合体系最终粘度的影响,聚合体系最终粘度在一定范围内随分散介质和单体浓度增加变化不大,但是超过某一浓度后聚合体系粘度急剧增加;聚合体系中加入少量乳化剂对体系粘度影响不大,但加入大量乳化剂后体系稳定性变差,聚合体系粘度急剧增加;聚合体系最终粘度随着聚合温度升高先降后增,与相图的预测结果一致.     

Understanding the synthesis of DEGVE pulsed plasmas for application to ultra thin biocompatible interfaces

There is interest in the development of novel surface treatments for biocompatibility and non-fouling behaviors on various surfaces of in vivo devices. Polyethylene glycol thin films have shown promise as non-fouling passivation layers for such devices. Studies of the surface chemistry and non-fouling effectiveness of plasma deposited di(ethylene glycol) vinyl ether (DEGVE) films have observed that non-fouling performance is maximized when plasma deposition occurs at low values of average power, (<5 W). [Y.J. Wu, R.B. Timmons, J.S. Jen, Frank E. Molock, Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer, Colloids and Surfaces B: Biointerfaces 18 (2000) 235–248.] Chemical properties of plasma deposited films were directly attributed to the complex interactions occurring within the gas phase. In order to better understand the deposition process, as well as the significance of the conclusions drawn by Wu et al. [Y.J. Wu, R.B. Timmons, J.S. Jen, Frank E. Molock, Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer, Colloids and Surfaces B: Biointerfaces 18 (2000) 235–248.] an investigation of the gas phase behavior in DEGVE pulsed plasma discharges was performed. Infrared spectra were used to characterize the chemical composition and dissociative behavior of DEGVE plasmas across a range of average powers. This allowed for the construction of a dissociative model of the DEGVE monomer in the plasma discharge. Analysis of the observed dissociative pattern demonstrates the presence of key daughter species which would account for the observations made on deposited DEGVE films by Wu et al. [Y.J. Wu, R.B. Timmons, J.S. Jen, Frank E. Molock, Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer, Colloids and Surfaces B: Biointerfaces 18 (2000) 235–248.].     

Radiation-induced copolymerization of styrene/n-butyl acrylate in the presence of ultra-fine powdered styrene–butadiene rubber

Styrene (St)/n-butyl acrylate (BA) copolymers were prepared by two-stage polymerization: St/BA was pre-polymerized to a viscous state by bulk polymerization with initiation by benzoyl peroxide (BPO) followed by ⁶⁰Co γ-ray radiation curing. The resultant copolymers had higher molecular weight and narrower molecular weight distribution than conventional methods. After incorporation of ultra-fine powdered styrene–butadiene rubber (UFSBR) with a particle size of 100 nm in the monomer, the glass transition temperature (T_g) of St–BA copolymer increased at low rubber content. Both the St–BA copolymer and the St–BA copolymer/UFSBR composites had good transparency at BA content below 40%.     

Aggregation phenomena in the suspension polymerization of VCM

In the suspension polymerization of VCM, insoluble polymer particles are formed inside the monomer droplets. The growth and aggregation of these particles are responsible for important polymer properties, such as porosity. It is well established that the most characteristic polymer particles, the primary particles, are of a narrow distribution with a size (diameter) ranging from 0.10–0.20 m. This work studied the formation of primary particles based on the aggregation phenomena that take place inside a monomer droplet. This was done by formulating a population balance equation, which was based on the following considerations: a) polymerization occurs in both the monomer and the polymer phases; b) there is continuous formation of the basic particles in the monomer phase; c) the growth of the polymer particles occurs as a result of both polymerization in the polymer phase and aggregation of the particles; d) the colloidal properties of the particles that are responsible for the aggregation phenomena were considered to be the net result of attraction and repulsion energies.It was shown that for particles carrying a constant charge it was not possible to predict the formation of primary particles of size 0.10–0.20 m. The particle size distribution had a mode diameter equal to the diameter of the basic particles. Consequently, the particle charge was allowed to vary in a way proportional to the particle radius raised to a power coefficient. For values of the coefficient greater than zero, i. e., when the particle charge increased during polymerization, the aggregation of the basic particles was efficient enough to result in the formation of large primary particles.     

相互缠结的聚甲基丙烯酸甲酯/磺化聚苯乙烯复合水基微乳液Ⅰ:制备及影响因素

将聚苯乙烯制成磺化聚苯乙烯离聚体 (SPS) ,利用相反转技术 ,将磺化聚苯乙烯离聚体加水制成具有纳米级的稳定的水基微乳液。利用SPS纳米微粒核内部作为反应场所 ,用引发剂引发亲油性单体甲基丙烯酸甲酯聚合 ,制备具有相互缠结结构的PMMA/SPS复合水基微乳液。研究了引发剂的用量、MMA的用量、溶剂极性对聚合反应及复合水基微乳液的影响     

Synthesis and Characterization of Hydrogel Nanoparticles Through Inverse Microemulsion Polymerization of 2-Acrylamido-2-methyl-1-propanesulfonic Acid

Nanosized hydrogel particles prepared through inverse microemulsion polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid, using the combination of an oil soluble emulsifier (SPAN80) with a water soluble emulsifier (TWEEN 80), and precise determination of HLB range related to the formation of stable single phase microemulsions.

The effect of crosslink density, water phase to oil phase ratio, and the hydrophilic-lipophilic balance (HLB) value on polymerization rate, particle size, and swelling ratio were investigated. It found that polymerization rate and particle size are strongly dependent on the water phase to oil phase ratio. Hydrogel samples prepared using oil soluble and water soluble initiators and the results showed that the initiator type had a great influence on monomer conversion and particle size. Effect of pH on equilibrium swelling of hydrogels was studied by dynamic light scattering and hydrogels showed pH-independent swelling behavior in a broad range of pH values. We also reported and discussed the crosslink density distribution in nanogels prepared by inverse microemulsion polymerization.     

Particle nucleation and monomer partitioning in styrene O/W microemulsion polymerization

Particle nucleation in the polymerization of styrene microemulsions was found to take place throughout the polymerization as indicated by measurements of the particle number as a function of conversion. A mechanism based on the nucleation in the microemulsion droplets was proposed to explain the experimental findings although homogeneous nucleation and coagulation during polymerization were not completely ruled out. A thermodynamic model was developed to simulate the partitioning of monomer in the different phases during polymerization. The model predicts that the oil cores of the microemulsion droplets were depleted early in the polymerization (4% conversion). Due to the high monomer/polymer swelling ratio of the polymer particles, most of the monomer resides in the polymer particles during polymerization. The termination of chain growth inside the polymer particles was attributed to the chain transfer reaction to monomer. The low n? (less than 0.5) of the microemulsion system was attributed to the fast exit of monomeric radicals.