In-Line Monitoring of Particle Size during Emulsion Polymerization under Different Operational Conditions using NIR Spectroscopy

In the present work, the sensitivity of NIR spectroscopy toward the evolution of particle size was studied during emulsion homopolymerization of styrene (Sty) and emulsion copolymerization of vinyl acetate-butyl acrylate conducted in a semibatch stirred tank and a tubular pulsed sieve plate reactor, respectively. All NIR spectra were collected online with a transflectance probe immersed into the reaction medium. The spectral range used for the NIR monitoring was from 9 500 to 13 000 cm(-1), where the absorbance of the chemical components present is minimal and the changes in the NIR spectrum can be ascribed to the effects of light scattering by the polymer particles. Off-line measurements of the average diameter of the polymer particles by DLS were used as reference values for the development of the multi-variate NIR calibration models based on partial least squares. Results indicated that, in the spectral range studied, it is possible to monitor the evolution of the average size of the polymer particles during emulsion polymerization reactions. The inclusion of an additional spectral range, from 5 701 to 6 447 cm(-1), containing information on absorbances (""chemical information"") in the calibration models was also evaluated.

Influence of Granulometry and Organic Treatment of a Brazilian Montmorillonite on the Properties of Poly(styrene-co-n-butyl acrylate)/Layered Silicate Nanocomposites Prepared by Miniemulsion Polymerization

The influence of granulometry and organic treatment of a Brazilian montmorillonite (MMT) clay on the synthesis and properties of poly(styrene-co-n-butyl acrylate)/layered silicate nanocomposites was studied. Hybrid latexes of poly(styrene-co-butyl acrylate)/MMT were synthesized via miniemulsion polymerization using either sodium or organically modified MMT. Five clay granulometries ranging from clay particles smaller than 75 mu m to colloidal size were selected. The size of the clay particles was evaluated by Specific surface area measurements (BET). Cetyl trimethyl ammonium chloride was used as an organic modifier to enhance the clay compatibility with the monomer phase before polymerization and to improve the clav distribution and dispersion within the polymeric matrix after polymerization. The sodium and organically modified natural clays as well as the composites were characterized by X-ray diffraction analysis. The latexes were characterized by dynamic light scattering. The mechanical, thermal, and rheological properties of the composites obtained were characterized by dynamical-mechanical analysis, thermogravimetry, and small amplitude oscillatory, shear tests, respectively. The results showed that smaller the size of the organically modified MMT, the higher the degree of exfoliation of nanoplatelets. Hybrid latexes in presence of Na-MMT resulted in materials with intercalated structures. (C) 2009 Wiley, Periodicals, Inc. J Appl Polym Sci 112: 1949-1958, 2009

Influence of the Type of Quaternary Ammonium Salt Used in the Organic Treatment of Montmorillonite on the Properties of Poly(Styrene-co-Butyl Acrylate)/Layered Silicate Nanocomposites Prepared by In Situ Miniemulsion Polymerization

Hybrid latices of poly(styrene-co-butyl acrylate) were synthesized via in situ miniemulsion polymerization in the presence of 3 and 6 wt % organically modified montmorillonite (OMMT). Three different ammonium salts: cetyl trimethyl ammonium chloride (CTAC), alkyl dimethyl benzyl ammonium chloride (Dodigen), and distearyl dimethyl ammonium chloride (Praepagen), were investigated as organic modifiers. Increased affinity for organic liquids was observed after organic modification of the MMT. Stable hybrid latices were obtained even though miniemulsion stability was disturbed to some extent by the presence of the OMMTs during the synthesis. Highly intercalated and exfoliated polymer-MMT nanocomposites films were produced with good MMT dispersion throughout the polymeric matrix. Materials containing MMT modified with the 16 carbons alkyl chain salt (CTAC) resulted in the largest increments of storage modulus, indicating that single chain quaternary salts provide higher increments on mechanical properties. Films presenting exfoliated structure resulted in the largest increments in the onset temperature of decomposition. For the range of OMMT loading studied, the nanocomposite structure influenced more significantly the thermal stability properties of the hybrid material than did the OMMT loading. The film containing 3 wt % MMT modified with the two 18 carbons alkyl chains salt (Praepagen) provided the highest increment of onset temperature of decomposition. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3658-3669, 2011

Spectroscopic study of the polymerization of intercalated anilinium ions in different montmorillonite clays

The polymerization of the intercalated aniline ions was studied in three different clays, Swy2-montmorillonite (MMT), synthetic mica-montmorillonite (Synl) and pillarized Swy2-montmorillonite (PILC). PANI is formed between the MMT and Syn1 clay layers, being confirmed by the shift of d(001) peak in the X-ray pattern. X-ray Absorption near to Si K edge (Si K XANES) data show that the structures of clays are preserved after the polymerization process and in addition to the SEM images show that morphologies of the clays are maintained after polymerization, indicating no polymerization in their external surface. UV-vis-NIR and resonance Raman data display that the PANI formed in Syn1 galleries has higher amount of phenazinic rings than observed for PANI intercalated in montmorillonite (MMT) clay. No polymer formation was detected in the PILC. N K XANES and EPR spectroscopies show the presence of azo and radical nitrogen in intercalated PAN! chains. Hence, the results are rationalized considering the structural differences between the clays for understanding the role of the anilinium polymerization within the clays galleries. (C) 2011 Elsevier B.V. All rights reserved.

High Solids Content, Soap-Free, Film-Forming Latexes Stabilized by Laponite Clay Platelets

High solids content film-forming poly[styrene-co-(n-butyl acrylate)] [poly(Sty-co-BuA)] latexes armored with Laponite clay platelets have been synthesized by soap-free emulsion copolymerization of styrene and n-butyl acrylate. The polymerizations were performed in batch in the presence of Laponite and a methyl ether acrylateterminated poly(ethylene glycol) macromonomer in order to promote polymer/clay association. The overall polymerization kinetics showed a pronounced effect of clay on nucleation and stabilization of the latex particles. Cryo-transmission electron microscopy observation confirmed the armored morphology and indicated that the majority of Laponite platelets were located at the particle surface. The resulting nanostructured films displayed enhanced mechanical properties.

Poly(ethylene glycol) decorated poly(methylmethacrylate) nanoparticles for protein adsorption

Poly(ethylene glycol) decorated poly( methyl methacrylate) particles were synthesized by means of emulsion polymerization using poly(ethylene glycol) sorbitan monolaurate (Tween-20) as surfactant. PMMA/PEG particles presented mean diameter (195 +/- 15) nm, indicating narrow size distribution. The adsorption behavior of bovine serum albumin (BSA) and concanavalin A (ConA) onto PMMA/PEG particles was investigated by means of spectrophotometry. Adsorption isotherms obtained for BSA onto PMMA/PEG particles fitted well sigmoidal function, which is typical for multilayer adsorption. Con A adsorbed irreversibly onto PMMA/PEG particles. The efficiency of ConA covered particles to induce dengue virus quick agglutination was evaluated. (C) 2010 Elsevier B.V. All rights reserved.

Development of a Continuous Emulsion Copolymerization Process in a Tubular Reactor

This contribution describes the development of a continuous emulsion copolymerization processs for vinyl acetate and n-butyl acrylate in a tubular reactor. Special features of this reactor include the use of oscillatory (pulsed) flow and internals (sieve plates) to prevent polymer fouling and promote good radial mixing, along with a controlled amount of axial mixing. The copolymer system studied (vinyl acetate and butyl acrylate) is strongly prone to composition drift due to very different reactivity ratios. An axially dispersed plug flow model, based on classical free radical copolymerization kinetics, was developed for this process and used successfully to optimize the lateral feeding profile to reduce compositional drift. An energy balance was included in the model equations to predict the effect of temperature variations on the process. The model predictions were validated with experimental data for monomer conversion, copolymer composition, average particle size, and temperature measured along the reactor length.

Modeling Vinyl Acetate and n-Butyl Acrylate Emulsion Copolymerization Process

This work presents a mathematical model for the vinyl acetate and n-butyl acrylate emulsion copolymerization process in batch reactors. The model is able to explain the effects of simultaneous changes in emulsifier concentration, initiator concentration, monomer-to-water ratio, and monomer feed composition on monomer conversion, copolymer composition and, to lesser extent, average particle size evolution histories. The main features of the system, such as the increase in the rate of polymerization as temperature, emulsifier, and initiator concentrations increase are correctly represented by the model. The model accounts for the basic features of the process and may be useful for practical applications, despite its simplicity and a reduced number of adjustable parameters.

Polymerization shrinkage stress of composites photoactivated by different light sources

The purpose of this study was to compare the polymerization shrinkage stress of composite resins (microfilled, microhybrid and hybrid) photoactivated by quartz-tungsten halogen light (QTH) and light-emitting diode (LED). Glass rods (5.0 mm x 5.0 cm) were fabricated and had one of the surfaces air-abraded with aluminum oxide and coated with a layer of an adhesive system, which was photoactivated with the QTH unit. The glass rods were vertically assembled, in pairs, to a universal testing machine and the composites were applied to the lower rod. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The 20 composites were polymerized by either QTH (n=10) or LED (n=10) curing units. Polymerization was carried out using 2 devices positioned in opposite sides, which were simultaneously activated for 40 s. Shrinkage stress was analyzed twice: shortly after polymerization (t40s) and 10 min later (t10min). Data were analyzed statistically by 2-way ANOVA and Tukey's test (a=5%). The shrinkage stress for all composites was higher at t10min than at t40s, regardless of the activation source. Microfilled composite resins showed lower shrinkage stress values compared to the other composite resins. For the hybrid and microhybrid composite resins, the light source had no influence on the shrinkage stress, except for microfilled composite at t10min. It may be concluded that the composition of composite resins is the factor with the strongest influence on shrinkage stress.

Simultaneous determination of Cr, Fe, Ni and V in crude oil by emulsion sampling graphite furnace atomic absorption spectrometry

In this work a simple and reliable method for the simultaneous determination of Cr, Fe, Ni and V in crude oil, using emulsion sampling graphite furnace atomic absorption spectrometry is proposed. Under the best conditions, sample masses around 50 mg were weighed in polypropylene tubes and emulsified in a mixture of 0.5% (v v(-1)) hexane + 6% (m v(-1)) Triton X-100 (R). Considering the compromised conditions, the pyrolysis an atomization temperatures for the simultaneous determination of Cr, Fe, Ni and V were 1400 degrees C and 2500 degrees C, respectively. Aliquots of 20 mu L of reference solution and sample emulsion were co-injected into the graphite tube with 10 mu L of 1.0 g L(-1) Mg(NO(3))(2) as chemical modifier. The detection limits (n = 10, 3 sigma) and characteristic masses were, respectively: 0.07 mu g g(-1) and 19 pg for Cr; 2.15 mu g g(-1) and 31 pg for Fe; 1.25 mu g g(-1) and 44 pg for Ni; and 1.15 mu g g(-1) and 149 pg for V. The reliability of the proposed method was checked by fuel oil Standard Reference Material (SRMTriton X-100 (R) 1634c - NIST) analysis. The concentrations found presented no statistical differences compared to the certified values at 95% confidence level.

Solution Polymerization of N-vinylcaprolactam in 1,4-dioxane. Kinetic Dependence on Temperature, Monomer, and Initiator Concentrations

The kinetics of the solution free radical polymerization of N-vinylcaprolactam, in 1,4-dioxane and under various polymerization conditions was studied. Azobisisobutyronitrile and 3-mercaptopropionic acid were used as initiator and as chain transfer agent (CTA), respectively. The influence of monomer and initiator concentrations and polymerization temperature on the rate of polymerizations (R(p)) was investigated. In general, high conversions were obtained. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to the monomer was greater than unity. The overall activation energy of 53.6 kJ mol(-1) was obtained in the temperature range 60-80 degrees C. The decreasing of the absolute molecular weights when increasing the CIA concentration was confirmed by GPC/SEC/LALS analyses. It was confirmed by UV-visible analyses the effect of molecular weights on the lower critical solution temperature of the polymers. It was also verified that the addition of the CTA influenced the kinetic of the polymerizations. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 229-240, 2010

Compatible Ternary Blends of Chitosan/poly(vinyl alcohol)/poly(lactic acid) Produced by Oil-in-Water Emulsion Processing

Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends-produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained When PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible; The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend.

The Effect of the Mixtures of Photoinitiators in Polymerization Efficiencies

The photoinitiated polymerization of methyl methacrylate using the mixtures of camphorquinone (CQ) and acylphosphine oxides (monoacylphosphine oxide, MAPO or bisacylphosphine oxide,BAPO) was studied to determine the possible synergistic effects. The addition of the acylphosphines to CQ resulted in an increase of the polymerization rate compared with CQ alone. On the other hand, a significant decrease of the polymerization quantum yield is observed for the mixtures compared with the pure acylphosphines. Therefore, the increase in the polymerization efficiency of the two rnixtures studied, MAPO/CQ and BAPO/CQ (compared with CQ) can be traced to the larger light absorption range, rather than to the onset of new mechanisms. The presence of the coinitiator ethyl 4-dimethylaminobenzoate, EDB, always present in CQ formulations, has no effect at all on the rates of polymerization photoinitiated by the acylphosphine oxides. From the point of view of photopolymerization quantum yields, an antagonistic effect is observed because Of the energy transfer of the M more efficient initiator (MAPO or BAPO) to the less efficient one (CQ). (C) 2008 Wiley Periodicals, Inc. j Appl Polym Sci 112: 129-134, 2009

Comparison of adsorbent films obtained by plasma polymerization of oxygenated organic compounds

Thin films obtained by plasma polymerization of ethyl ether, methyl or ethyl acetate, acetaldehyde, acetone and 2-propanol were compared. Infrared spectroscopy (FFIR), resistance to chemicals, contact angle measurements, X-ray photoelectron spectroscopy (XPS), optical and scanning electron microscopy (SEM), and quartz crystal microbalance (QCM) were carried out. For all films FTIR showed high intensity for polar bonds yet the films are not resistant to polar solvents. Contact angle measurements revealed hydrophilic and organophilic surfaces and XPS pointed out a high proportion of oxygenated bonds. All films showed good step coverage and peeling was significant only with acetone and 2-propanol. All films are adsorbent for organic compounds in a large scale of polarity but acetaldehyde and 2-propanol act like a selective membrane. Also, deposition of these films on hydrophobic substrates leads to island formation. A possible model to explain the results must consider the hydrogen bridge formation on 2-propanol and acetaldehyde films. Ethyl ether, ethyl and methyl acetate showed good characteristics for development of sensor and sample pretreatment using miniaturized devices. (C) 2007 Elsevier B.V. All rights reserved.

Investigation of Cationic Polymerization of beta-Pinene Using Calorimetric Measurements

An experimental investigation of the kinetics of cationic polymerization of beta-pinene was performed using two different initiator systems under two different operating conditions (shot additions of initiator, and continuous feeding of monomer). The experiments were done using calorimetric measurements under isoperibolic conditions. The heat of polymerization of beta-pinene was found to be -30.6 kcal . mol(-1). A simple kinetic model was tentatively proposed, and the model fit reasonably well to the different experimental runs. Different values of the fitting parameters were obtained for runs carried out under different conditions, which can probably be ascribed to the presence of adventitious impurities in the commercial-grade monomer used.