An experimental investigation on the evolution of the molecular weight distribution in styrene emulsion polymerization

Styrene ab initio emulsion polymerizations were conducted at 70°C in an automated reaction calorimeter. Two polymerizations were performed, one above and the other below the critical micelle concentration (CMC) of the surfactant, thus ensuring differing polymerization kinetics between the two: the system below the CMC gave large particles that were expected to follow pseudobulk kinetics, while that above the CMC gave small particles that were expected to follow zero-one kinetics. The evolutions of the molecular weight distributions (MWDs) were characterized by removing samples periodically during the course of the reactions and analyzing with gel permeation chromatography. Interpretation of the data used average molecular weights, the GPC MWDs, and the number MWDs, as functions of conversion. It was found that all of the number MWDs (plotted as ln (number of polymer chains) vs. molecular weight of polymer chains) were concave-up at low molecular weights and become nearly linear at molecular weights (≥3−4 × 10⁶); this linearity is expected from theory. The slope of the high molecular weight region was consistent with theory for the dominant mode for chain stoppage: termination and transfer for the pseudobulk system and (predominantly) chain transfer to monomer for the zero-one system. The most likely explanation for the concavity of the number MWDs is a heterogeneity of radicals: some surface anchored with sulfate end groups and others (with hydrogen end groups arising from transfer to monomer and/or reentry) being more mobile. Thus, two types of termination are proposed: slow reaction-diffusion for the less mobile surface anchored chains, and rapid short-long (center of mass) termination for the more mobile hydrogen-terminated chains. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 989–1006, 1997     

A mass spectrometric investigation of the water-soluble oligomers remaining after the emulsion polymerization of methyl methacrylate

A “surfactant-free” emulsion polymerization of methyl methacrylate was conducted at 80°C with ammonium persulfate initiator. The water-soluble MMA-based oligomers re-maining were isolated and analyzed both as-produced and after hydrolysis. NMR analysis revealed that the mole ratio of MMA repeat units to sulfate end groups in the former is 6.5. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and gel permeation chromatography both showed that the mean number of MMA repeat units comprising the extracted material is 8–9. The hydrolysis procedure rids the oligomers of their terminal groups and converts some of the methyl ester groups to acid, greatly sim-plifying the mass spectrum. This appears to be the first direct measurement of “surfactants” produced in situ from monomer and persulfate initiator. © 1995 John Wiley & Sons, Inc.     

Experimental study on high-pressure rheology of water/crude oil emulsion in the presence of methane

The crude oil is in most cases accompanied with water and natural gas. For this reason, it is important to understand the rheology of the oil emulsion. There are already many works relating to rheology of the oil/water emulsion. However, studies on high-pressure rheology of water/crude oil emulsion in the presence of CH₄ are rare. In this work, light crude oil with characteristics of high wax content, which is typical in Northwest China, was studied. The rheology of water/crude oil emulsion in the presence of CH₄ under various conditions were fully studied. The results show that the crude oil emulsion showed obvious characteristics of non-Newtonian fluid at a lower temperature. Before water fraction reached a certain limit, the viscosity increases with the increase of water fraction, when water fraction reaches and exceeds the limit the emulsion viscosity drops with the increase of water fraction. The shear stress–shear rate curves become similar as the increase of temperature, indicating the decreasing effect of temperature on the relation between shear stress and shear rate. When the pressure reaches 8 MPa, the shear stress measured with CH₄ in the system surpasses that measured without CH₄. At higher pressure, CH₄ shows obvious influence on the rheology.     

A novel way to study the initial stages of soap-free emulsion polymerizations: The intercalation of polystyrene oligomers into hydrotalcite

The dominant species in the early stages of an emulsifier-free emulsion polymerization of styrene has been found to be an oligomer of two to three monomer units using a novel trapping technique. This involved the intercalation of charged primary oligomers between the layers of a hydrotalcite, [Mg₄Al₂(OH)₁₂]²⁺[A]^2- (where A = dianion). Hydrotalcites are an important class of lamellar, inorganic compounds whose interlayer spacing can be mod-ified by anion exchange. Our approach first involved preparing a hydrotalcite precursor in which the layers were propped apart by an organic dianion (terephthalate = TA). This material was then used to capture the negatively charged polystyrene oligomers from the emulsion polymerization reaction mixture. We found that TA was rapidly ion-exchanged for the charged oligomers. The resulting pillared hydrotalcite material was characterized using XRD and SEC. We found that the interlayer spacing between the hydroxide layers increased to 23.2 Å on exposure to the emulsion reaction mixture. This represents an interlayer expansion of 18.3 Å (after subtraction of the hydroxide layer contribution), which is cnsistent with intercalation of oligomers with two to three monomer units arranged in a bilayer. This size estimate was confirmed by the results of size exclusion chromatography. © 1995 John Wiley & Sons, Inc.     

Preparation and characterization of pure polyacrylate polymer colloid through emulsion polymerization using a novel initiator

A series of acrylic polymer colloids were prepared via semi-continuous seeded emulsion polymerization of BA and MMA in water phase when OP-10 and AIBI is used to be emulsifier and initiator, respectively. FTIR spectrum identifies the formation of copolymers of P (MMA-co-BA). DSC confirms that the colloid is a kind of random copolymer and the consistency among the chain segment is fairly good. The emulsion polymerization conditions of preparing acrylic polymer colloid are optimized. Results show that the conversion rate is high and the coagulum is low and the particle size of the acrylic polymer colloids is small when the amount of AIBI is 0.75 g. The polymerization temperature is 70 °C, which is lower than the one that the emulsion polymerization is initiated with the persulfate.     

Annurca peel extract: from the chemical composition,through the functional activity,to the formulation and characterisation of a topical oil-in-water emulsion

The aim of this study was to produce a hydro-alcoholic safe antioxidant Malus pumila Miller cv Annurca peel extract (APE) useful as functional ingredient in an oil-in-water emulsion. Results showed that APE contains a hydroxycinnamic acid (chlorogenic acid), flavonol glycosides (quercetin derivatives) and a dihydrochalcone, phloridzin (phloretin-2-O-glucoside). The isoquercitrin (quercetin-3-O-glucoside) content was quantified in 0.3% w/w of extract. APE showed a significant and concentration-dependent free-radical scavenging activity correlated to its polyphenols content. No cytotoxic effect was observed in primary human epidermal keratinocyte adults and dermal fibroblast cell lines. The formulative approach led to produce a stable emulsion able to load a high amount of APE, up to 6.0% w/w. The homogenous distribution of APE in the emulsion was clearly demonstrated by fluorescence microscopy analysis. The emulsion resulted able to enhance the in vitro release rate of APE through synthetic membranes with respect to the raw material.     

Kinetics of the batch cationic emulsion polymerization of styrene: A comparative study with the anionic case

An in‐depth study on the kinetics of the cationic emulsion polymerization of styrene in a batch reactor is presented. This study is focused on the effect of the amount of the cationic surfactant dodecyltrimethylammonium bromide (DTAB), using two different cationic initiators: 2,2′‐azobisisobutyramidine dihydrochloride (AIBA), 2,2′‐azobis (N,N′‐dimethyleneisobutyramidine) dihydrochloride (ADIBA), on kinetics and colloidal features such as conversion, number of particles, number average of radicals per particle, mean particle diameter, and particle size distribution (PSD) of the polystyrene latices obtained by emulsion polymerization in a batch reactor. Furthermore, the results of the cationic emulsion polymerization were compared with its homologous anionic case. Using DTAB as cationic surfactant an expected increase in the total rate of polymerization was observed when the DTAB concentration increased. However, the total number of particles increased much more than in the anionic system. On the other hand, a dependence on the particle size of the rate of polymerization per particle together with the average number of radicals per particle was found. These differences between cationic and anionic emulsion polymerizations were explained taking into account the limited particle coagulation observed with cationic surfactants, and the high rate of radical formation of cationic initiators. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4461–4478, 2006     

Application of the response surface methodology for modeling demulsification of crude oil emulsion using a demulsifier

The main objective of this research is to determine the capability of four surface-active compounds namely poly(ethylene glycol) distearate, N,N-dimethyldodecylamine N–oxide solution, polyoxyethylene (10) tridecyl ether, and polyethylene glycol sorbitan monooleate as demulsifier agents in breaking water-in-crude oil emulsion through the bottle test method. The influence of temperature, concentration, water content, and pH on demulsification efficiency of the studied demulsifiers was investigated via the response surface methodology (RSM) and the central composite design method (CCD) was applied to design the experiments. The optimum values of input variables to obtain the maximum water separation efficiency were determined based on the developed model by analyze of variance (ANOVA). The R-squared values demonstrate that the developed models could appropriately predict the experimental results of all demulsifier agents.     

Multivariate optimization of the determination of zinc in diesel oil employing a novel extraction strategy based on emulsion breaking

This paper describes the extraction/pre-concentration of Zn from diesel oil and its determination by Flame Atomic Absorption Spectrometry (FAAS), proposed as a novel approach for these kinds of analyses and the multivariate optimization of the proposed procedure. The extraction of Zn is based on the emulsification of an aqueous solution containing Triton X-114 and HNO₃ with diesel oil samples followed by breaking of the emulsion by heating. The aqueous phase obtained after the emulsion breaking was collected and used for Zn quantification by FAAS. The methodology was optimized using a Doehlert design and the system variables were the concentrations of surfactant and HNO₃ in the solution employed in the emulsification and the temperature used in the emulsion breaking. The ratio between absorbance and the time required to break the emulsions was taken as response. Two sets of experiments, using different emulsifier agents, were run: the first one using Triton X-100 and the second one using Triton X-114. At optimized conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 5% w/v of Triton X-114 and 15% v/v of HNO₃ and broken by heating at 80 °C. The proposed analytical procedure was applied in the analysis of six real samples of diesel oil and a recovery test was carried out by spiking the samples with known amounts of Zn (25 and 50 μg L⁻¹), added as organometallic oiled standard. Recovery percentages achieved in this test were between 92 and 109%.     

The effect of brine salinity on water-in-oil emulsion stability through droplet size distribution analysis: A case study

Water-in-oil emulsion usually forms during waterflooding in some heavy oil reservoirs. The composition and salinity of the injected water critically affect the w/o emulsion droplet size distribution, which control the emulsion stability and emulsion flow in porous media. The aim of the present work is to assess the effect of different sea water salinities on w/o emulsion stability through microscopic imaging. Therefore, w/o emulsions were prepared with different sea water samples, which were synthesized to resemble Persian Gulf, Mediterranean, Red Sea, and North Sea water samples. The results showed that log-normal distribution function predicts very well the experimental data to track the emulsion droplet size distribution, and then it was used for the emulsion stability analysis. It was found that among the four emulsion samples, North Sea emulsion with the lowest NaCl and TDS concentration of 24.12?g/L and 34.44?g/L remained stable up to almost 24 hours, while Red sea emulsion with the highest NaCl and TDS concentration of 32.39?g/L and 41?g/L became unstable after 6-hour period. This indicated that as the brine concentration increases, the w/o emulsion droplets would be larger due to the higher rate of aggregation and coalescence, and the emulsion stability decreases.     

A kinetic investigation of surfactant‐free emulsion polymerization of styrene using laponite clay platelets as stabilizers

We report the kinetics and mechanism of soap‐free emulsion polymerization of styrene using laponite platelets as stabilizers. The polymerization was initiated by potassium persulfate and the latex particles were stabilized by laponite platelets dispersed in water. Laponite adsorption on the polymer particles was enhanced by the addition of poly(ethylene glycol) monomethylether methacrylate (PEGMA). Particle nucleation can be described using the classical homogeneous nucleation mechanism followed by coagulation of unstable precursors. Oligomeric radicals formed in the water phase become insoluble and precipitate on the laponite surface leading to primary precursor particles composed of a few polymer chains and one or several clay platelets. Mature latex particles are then generated by coagulation and growth of the previously formed precursor particles. Both the nucleation and initial aggregation rates increased in the presence of PEGMA. Calorimetric monitoring of the polymerization allowed estimating the heat produced by the reaction and the monomer conversion. Hence, using the monomer material balance, the number of radicals in the polymer particles could be estimated precisely. The average number of radicals per particle, $ \bar n $ , was found to be high in the range 3–6. This result was attributed to strong attractive interactions between the growing radicals and the clay surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Determination of water,ammonium nitrate and sodium nitrate content in ‘water-in-oil’ emulsions using TG and DSC

The main component of an emulsion explosive is a water-in-oil emulsion consisting of a supersaturated ammonium nitrate (AN) water phase, finely dispersed in an oil phase. Quantitative determination of nearly all the components in a W/O emulsion is possible using thermogravimetry (TG) and differential scanning calorimetry (DSC). Isothermal TG measurements enable determination of water content, while cycled DSC measurements allow the amount of ammonium nitrate to be determined. In the case that sodium nitrate (SN) is also added to AN as an oxidizing agent, it is necessary to quantitatively separate both salts from organic matter with diethyl ether. On the basis of the TG curve of the precipitated salts, the amount of AN can then be calculated, and that of SN is obtained from TG measurement of the original sample.     

A novel method for the spectrophotometric determination of nitrite in water

A rapid, simple, selective and sensitive method for the spectrophotometric determination of nitrite in water has been developed and optimum reaction conditions along with other analytical parameters have been evaluated. Nitrite reacts with barbituric acid in acidic solution to give the nitroso derivative, violuric acid. At analytical wavelength of 310 nm, Beer's law is obeyed over the concentration range 0.00–3.22 ppm of nitrite. The molar absorptivity is 15330 ± 259.7 (95%) with pooled standard deviation of 355.57 and R.S.D. of 2.32%. As well as the method is sensitive (2.99 × 10⁻³ μg NO₂ cm⁻²) and selective, it tolerates most of the potential interferents. It has been successfully applied to nitrite determination in natural waters by use of a calibration graph with determination limit of 1.66 μg NO₂ in 100 mL working solution corresponding to minimum 9.5 ppb NO₂–N in water samples. Lower concentrations of nitrite (3.0 μg NO₂/L sample) is precisely analyzed by using the method of dilution with sample, with R.S.D. of lower than 0.5%. The results were compared with standard N-(1-naphtyl)ethylenediamine dihydrochloride method and very good agreement between the data was observed. The method can easily be applied in the field.     

Model prediction of batch emulsion copolymerization as a function of conversion: A sensitivity analysis

Recently a model has been developed capable of predicting absolute monomer concentrations and their ratios in the polymer, aqueous, and monomer droplet phases as a function of conversion in batch emulsion copolymerizations without using any adjustable parameters. In this article the sensitivity of model predictions of composition drift toward deviations of 10% in all model parameters (maximum swellabilities of monomer in the polymer phase, water solubilities, reactivity ratios, and monomer and polymer densities) was estimated using the monomer combination methyl methacrylate-styrene as an example. From the sensitivity analysis it can be concluded that the reactivity ratios are the most important parameters affecting composition drift. The effects of deviations in maximum swellabilities and monomer and polymer densities on composition drift can be neglected, while the water solubility is important only in those cases where the amount of monomer in the aqueous phase cannot be neglected as compared with the total monomer amount. © 1994 John Wiley & Sons, Inc.     

An experimental study of asymmetry in an argon inductively coupled plasma torch using a relaxation method

A relaxation method is used to undertake an experimental study of the degree of cylindrical symmetry present in an argon inductively coupled plasma torch, ICP. This technique, in effect a direct comparison between two different parameters, the electron (T_e) and gas (T_g) temperatures in the torch, is shown to be a very sensitive indicator of axisymmetry. Measurements using this technique delineate areas of axisymmetry in the ICP, and show that axisymmetry is significantly dependent on the observation height and coolant gas flow-rate.     

A new method for determining droplet size distribution of an unstable dispersion

The droplet size distribution (DSD) of unstable water/oil dispersions has been studied with a new technique. The technique is based on a fast dilution of the dispersion injected into an analysis vessel where the DSD is analyzed with a video camera and a image analyzing tool. Dispersions generated with no pressure drop in the flow rig were compared to those generated with a pressure drop over a needle valve. The latter dispersion showed a much narrower DSD and a lower average droplet diameter. The results are from preliminary experiments in order to evaluate the method.     

Microparticles for Drug Delivery Based on Functional Polycaprolactones with Enhanced Degradability: Loading of Hydrophilic and Hydrophobic Active Compounds

Microparticle drug carriers made of biodegradable functional polyesters were produced. The polyesters consist of a poly(ε‐caprolactone) backbone bearing pendant acryloyloxy and methacryloyloxy groups. Stable microparticles were prepared via an oil/water emulsion‐solvent evaporation technique eventually combined with a simultaneous crosslinking procedure. Crosslinked particles were obtained via photo‐crosslinking and Michael type addition using diamines as crosslinking agents. Encapsulation of a hydrophobic fluorescent dye and a hydrophilic protein, as model drugs, were performed and confirmed by optical microscopy and Raman spectroscopy. The presence of the functional groups allow for not only the tuning of the degradation rate, but also for further processing and (bio)functionalization.

     

Emulsion polymerization of vinyl acetate using a polymerizable surfactant. III. Mathematical model

A mathematical model was developed to aid in the further understanding of the growth of latex particles in the emulsion polymerization of vinyl acctate using a polymerizable surfactant, sodium dodecyl allyl sulfosuccinate (TREM LF-40). The model incorporates the main features of the system observed experimentally: copolymerization in the aqueous phase, at the particle surface, and chain transfer to TREM LF-40. The reactions at the particle/water interface and, more specifically, the chain transfer to TREM LF-40 leading to a decrease in the average number of radicals per particle, was found to be the most significant mechanism for explaining the difference in kinetic results found for TREM LF-40 and its nonpolymerizable counterpart. The copolymerization of vinyl acetate with TREM LF-40 was also shown to slow the overall polymerization rate. However, the copolymerization alone was not sufficient to account for the decreased polymerization rates observed experimentally. A combination of copolymerization and chain transfer to TREM LF-40 was found to provide a good fit of the experimental results. © 1993 John Wiley & Sons, Inc.     

An experimental investigation of polyacrylamide and sulfonated polyacrylamides based gels crosslinked with cr(III)-acetate for water shutoff in fractured oil reservoirs

Abstract

Water injection as one of the most efficient and worldwide extensively employed approach in homogenous oil reservoirs suffers from early water breakthrough time as well as low oil sweep efficiency values in fractured oil reservoirs. This study investigates the potential application of Cr(III)-acetate based gel polymer system in a typical water injection process using one fractured micromodel. For this purpose, three sulfonated polyacrylamides, different in solfunation degree, and one hydrolyzed polyacrylamide were studied regarding gelation time, gel strength and stability to find the optimized conditions in terms of polymer type and concentration, and polymer/Cr(III)-acetate ratio, which were subsequently used for one dynamic test. Results illustrated the optimized conditions as AN 105 polymer with concentration of 5000?ppm and polymer/Cr(III) ratio of 5. Moreover, results showed that implementing such gel system yields an increased oil recovery value of 24.46% OOIP at 1.55 PV and delays the breakthrough time from 0.47 PV to 0.51 PV.