Emulsion Homopolymerization Research Articles

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

AbstractIn 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 multivariate 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. magnified image

Some comparative aspects of particle formation and rate of reaction in emulsion polymerization of vinyl acetate and butyl acrylate

AbstractThe comparative study of monomers, in terms of particle formation and rate of polymerization, facilitates the interpretation of the results from the corresponding copolymerization runs and can be considered as a preliminary step toward formulation of copolymerization reactions. Batch emulsion homopolymerization of vinyl acetate (VA) and butyl acrylate (BA), as model monomers with a wide water solubility disparity, were carried out to investigate the effects of variations in the monomer concentration, electrolyte concentration, reaction volume, and surfactant type on the kinetics of polymerization. With sodium lauryl sulfate as surfactant, VA emulsion polymerization produced more particles than BA at a lower monomer concentration, but fewer particles at a higher monomer concentration. At a lower VA concentration, a depressed growth for newly formed particles during interval III contributed to the formation of a large number of particles. The application of aerosol MA and OT surfactants improved the stability of polyvinyl acetate (PVA) particles so that a larger number of polymer particles was obtained for VA, in comparison with BA. BA emulsion polymerization showed little sensitivity to electrolyte concentrations and reaction volumes within the range studied. The colloidal stability of PVA particles was found to be quite sensitive toward the aforementioned variables. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of Reaction Temperature on the Gel Content of Acrylic Latexes

AbstractThe effect of reaction temperature on the kinetics and the microstructure properties of polyacrylates produced by seeded semicontinuous emulsion homopolymerization of two acrylate monomers (butyl acrylate and 2‐ethylhexyl acrylate) initiated by a thermal initiator was investigated. Contrary to what has been reported at higher temperatures (75–95 °C), increasing reaction temperature (from 60 to 80 °C) led to a decrease of the amount of gel content produced in the semicontinuous polymerizations. These results were analyzed by means of a Monte‐Carlo model of the process.magnified image

Nitroxide-Mediated Controlled/Living Free-Radical Surfactant-Free Emulsion Polymerization of Methyl Methacrylate Using a Poly(methacrylic acid)-Based Macroalkoxyamine Initiator

Water-soluble, SG1 nitroxide-capped poly(methacrylic acid-co-styrene) macroalkoxyamines with ∼10 mol % of styrene subunits were used as initiators in the surfactant-free, ab initio, batch, emulsion homopolymerization of methyl methacrylate and its copolymerization with a low percentage of styrene, in alkaline conditions at temperatures below 90 °C. The polymerizations were well-controlled, with a very high initiating efficiency, due to the high dissociation rate constant of the macroalkoxyamines. It led to the in situ formation of amphiphilic block copolymers that self-assembled into small particles with diameter below 100 nm, according to a polymerization-induced micellization process. The polymerization kinetics, the control over molar mass and molar distribution, and the colloidal characteristics of the so-formed block copolymer micelles were studied in detail. This work represents a breakthrough in controlled/living radical polymerization in aqueous emulsion with the development of new, very efficient macroinitiators used as the sole additive for initiation, stabilization, and chain-growth control. It is also the first development of nitroxide-mediated emulsion polymerization of methyl methacrylate performed at low temperature.

Simultaneous Monitoring of Polymer and Particle Characteristics during Emulsion Polymerization

Emulsion polymerization reactions constitute complex, nonequilibrium systems in which there is strong interaction between polymers, monomers, and the colloidal structures that mediate the reactions. A novel and general method was sought to monitor emulsion polymerization reactions. Instrumentation and methods were hence developed here to achieve, for the first time, simultaneous monitoring of the evolving characteristics of both the organosoluble components (monomer conversion, polymer molar mass, and reduced viscosity) and the colloidal components (particle size of monomer droplets and nucleated polymer particles). No empirical models were required for these determinations. This represents a new capability for the broadening ACOMP platform (automatic continuous online monitoring of polymerization reactions). The method was applied to free radical emulsion homopolymerization of methyl methacrylate and butyl acrylate over a wide monomer concentration range, with and without surfactant stabilization. A succ...

Emulsion Polymerization of Styrene and Vinyl Acetate with Cationic Surfactant

Summary: In this study, the emulsion homopolymerization system containing vinyl acetate and styrene, potassium persulfate, and a new cationic surfactant was studied in the classical glass emulsion polymerization reactor. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate and styrene latex properties were investigated depending on surfactant percentage in homopolymerizations.

Emulsion Polymerization of Styrene and Vinyl Acetate with Cationic Surfactant

AbstractSummary: In this study, the emulsion homopolymerization system containing vinyl acetate and styrene, potassium persulfate, and a new cationic surfactant was studied in the classical glass emulsion polymerization reactor. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate and styrene latex properties were investigated depending on surfactant percentage in homopolymerizations.

Model based operation of emulsion polymerization reactors with evaporative cooling: Application to vinyl acetate homopolymerization

This work aims at maximizing the productivity of emulsion homopolymerization processes. A dynamic model of emulsion polymerization processes is extended by the inclusion of vaporization from the liquid phases in the reactor to the gaseous phase. The multi-component gas–liquid mass transfer phenomenon is described by the Maxwell–Stefan diffusion equations, which are solved by a special algorithm. A novel operation strategy is developed for running a reactor optimally with respect to batch time. This strategy is applied first to an industrial scale reactor, which is run without using evaporative cooling. Then, based on the extended model, controlled vaporization is included by which additional heat is removed from the reaction system. This makes it possible to extend the restrictions imposed by the limited heat removal of the cooling jacket considerably. Simulation results are presented for the homopolymerization of vinyl acetate in an industrial scale reactor operated in semi-batch mode. The results show that a significant amount of heat can be removed by evaporative cooling thus leading to higher productivity.

Fluorinated monomer–styrene copolymer latex particles: I. kinetic studies in a soap-free aqueous medium

Soap-free emulsion copolymerization of 2, 2, 2-trifluoroethyl acrylate (3FEA) with styrene was carried out by using potassium persulfate as an initiator, and the effects of the weight fraction of 3FEA in the monomer feed on the kinetics and the particle size were investigated. Monomer conversions were followed by a gravimetric method, revealing that the overall polymerization rate increased exponentially with an increase in the weight fraction of 3FEA. According to dynamic light scattering measurement, the final particle size was found to decrease with an increase in the weight fraction of 3FEA. The number of particles for 3FEA homopolymerization was roughly twice as large as that at the fraction of 0.9, although both fractions had the almost same polymerization rates. These results indicate that soap-free emulsion homopolymerization of 3FEA would proceed not only inside the polymer particles but also in the aqueous phase throughout the polymerization.

Preparation of a New Polymeric Surfactant for Emulsion Polymerization

AbstractThe stability of polymeric dispersions is a property of practical importance and hence, the search for an optimized strategy to equip polymer dispersions with sufficient stability is a matter of continuous research during the last years. The kernel is to reach a sufficient stability, as it is required during polymerization, conditioning, or storage and to allow coagulation or coalescence of particles when it is needed, such as during separation of polymer from latex or during film formation. In this study, the emulsion homopolymerization system containing vinyl acetate, potassium persulfate, new polymeric surfactant, NaHCO3 and water was studied in the classical glass emulsion polymerization reactor. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate latex properties were investigated depending on vinyl acetate percentage in homopolymerization.

New emulsion polymerization tubular reactor with internal angular baffles: Reaction temperature effect

AbstractDeterministic models of physicochemical, mathematical, and computational sciences were used for modeling and simulation of emulsion homopolymerization process of styrene with baffles into tubular reactor (TR) as static mixer. Modeling and simulation were approximate to steady state, cylindrical one‐dimensional model, fully developed laminar plug flow, and they were solved with finite volume method and programmed with Fortran language. Also, the Smith‐Ewart model was considered to estimate the monomer conversion and Arrhenius chemical kinetics was considered as laminar finite‐rate model to compute chemical source. The experimental‐inductive and mathematical‐deductive methods were applied for obtaining mass balance results and properties characterization. The objective is to model, to simulate, and to analyze the emulsion polymerization reactor performance with internal‐inclined angular baffles, and to compare with continuous TR in variable reaction temperature. The predictions were validated with experimental results for the isothermic and TR, with a good concordance. The results in no isothermal conditions without and with baffles were better than in isothermal conditions without and with baffles in relation to the desired properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2572–2581, 2006

Monitoring emulsion homopolymerization reactions using FT-Raman spectroscopy

The present work describes a methodology for estimation of monomer concentration during homopolymerization reactions by Raman spectroscopy. The estimation is done using linear models based on two different approaches: a univariate approach and a multivariate approach (with principal component regression, PCR, or partial least squares regression, PLS). The linear models are fitted with data from spectra collected from synthetic samples, i.e., samples prepared by dispersing a known concentration of monomer in polymer emulsions. Homopolymerizations of butyl acrylate and of vinyl acetate were monitored by collecting samples from the reactor, and results show that the methodology is efficient for the model fitting and that Raman spectroscopy is a promising technique for on-line monitoring of the emulsion polymerization process.

Modelling and Simulation of Complex Aspects of Multicomponent Emulsion Polymerization

The focus of this work is the refinement of a general mechanistic simulator for multi‐component free radical emulsion polymerization. The effort includes three main areas of simulator development, namely, model development, database development and simulator verification. The model is general and can predict the dynamic evolution of emulsion polymerizations for a variety of monomer systems while giving the user as many “model options” as possible for fine tuning. The model has been extensively tested for several copolymerization systems including combinations of the monomers, styrene, methyl methacrylate, methyl acrylate, butyl acrylate, acrylonitrile, 2‐ehtyl hexyl acrylate and vinyl acetate. The simulator has been developed using a mechanistic framework that is analogous to the multicomponent free radical bulk and solution polymerization model developed in Gao and Penlidis (1996&1998) and is a continuation of Gao and Penlidis ([2002]), which explored emulsion homopolymerization and preliminary copolymer...

Biobjective control of emulsion polymerizations: control of the polymer composition and the concentration of monomer in the polymer particles

A decoupled control law is proposed to control the concentration of monomer in the polymer particles in emulsion homopolymerization, copolymerization and terpolymerization processes and simultaneously to insure the production of a homogeneous polymer composition. Nonlinear geometric controllers are used to calculate the monomer flow rates that accomplish this purpose. The controllers are based on the estimation of the residual number of moles of free monomer that is obtained by calorimetry and using nonlinear high gain observers in this work. The technique is experimentally validated using the butyl acrylate, methyl methacrylate and vinyl acetate monomers.

Development of new concepts for the control of polymerization processes: Multiobjective optimization and decision engineering. I. Application to emulsion homopolymerization of styrene

AbstractThis article deals with the development of a multicriteria analysis, and its application to the optimization of batch emulsion polymerization processes. This new approach in the domain of polymer reaction engineering illustrates how a multiobjective optimization aided by a genetic algorithm and using the Pareto concept of domination is useful. In this process (emulsion homopolymerization of styrene), several objectives were simultaneously required, e.g., a high quality of the resulting products together with a high productivity. The aim of this study was to find the optimal experimental conditions to obtain simultaneously the minimum reaction time and designed values for both average molecular weights and particles size. To do that, an adapted mathematical model, able to describe all the process physicochemical phenomena, was been first elaborated. The multicriteria analysis then gave a set of nondominated points with conflicting criteria. A decision support system was then developed and applied to rank the Pareto solutions set and to propose some good solutions by taking into account the decision maker's preferences. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2383–2396, 2003

Monitoring of Seeded Batch, Semi‐batch, and Second Stage Emulsion Polymerization by Low Resolution Raman Spectroscopy

Low resolution Raman spectroscopy (LRRS) offers a convenient way to monitor many different polymerization processes and reactor environments. LRRS can be used as an additional tool for process control to determine the conversion inside the reactor in real time without disruption to the reaction. Critical to polymerization monitoring, the efficiency of LRRS eliminates the lag between taking samples and calculating conversion. For each system, the phenyl ring of styrene or polystyrene provides an internal reference, which can be used to eliminate fluctuations in laser intensity. This paper demonstrates that the LRRS system can monitor seeded emulsion homopolymerizations in batch and semi‐batch as well as second stage emulsion polymerizations with some acceptable level of confidence.

MATHEMATICAL MODELING OF PARTICLE MORPHOLOGY DEVELOPMENT INDUCED BY RADICAL CONCENTRATION GRADIENTS IN SEEDED STYRENE HOMOPOLYMERIZATION

The development of concentration gradients in the seeded emulsion homopolymerization of styrene has been studied using a mathematical model. Under ideal conditions, emulsion polymer particles are expected to be relatively uniform across their radius. When this is true, kinetic models can be reliably used to predict the reaction rates, molecular weight, and composition (for copolymerizations). However for large particles, large radial gradients in the polymer radical concentration can develop during polymerization. While gradients in the monomer concentration are not observed, the radical concentration gradients result in non-uniform reaction rates across the particle radius, rendering conventional models unreliable. This study examines the effect of seed particle diameter and various kinetic parameters on the development of particle morphology.

Stabilization and kinetics in the emulsion copolymerization of butyl acrylate and methyl methacrylate

AbstractWe carried out emulsion homopolymerizations and copolymerizations of butyl acrylate (BuA) and methyl methacrylate (MMA) with different types and concentrations of surfactants to determine the influence of these parameters on the particle size and particle size distribution and to elucidate the mechanism of particle formation. As expected, the mechanisms of nucleation above and below the critical micelle concentration were very different; however, it was also found that the presence of partially soluble monomers such as MMA in the water phase had a significant influence on the critical micelle concentration of Triton X‐405 (>50%). In addition, the nucleation mechanism during copolymerization seemed to be dominated by BuA, with the number of particles per liter being very similar to the number nucleated during its homopolymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2832–2846, 2001

Effect of Monomer Feed Rate on Chain Transfer to Polymer in Semibatch Emulsion Polymerization of Vinyl Acetate Studied by NMR Spectroscopy

The effect of growth-stage monomer feed rate on the extent of chain transfer to polymer in semibatch emulsion homopolymerizations of vinyl acetate has been studied by using 13C NMR spectroscopy to quantify the mol % branches in the poly(vinyl acetate) formed. Three 37.5% final solids content emulsion homopolymerizations of vinyl acetate were carried out at 70 °C using identical seed stages, but different monomer feed rates of 0.35, 1.39, and 2.08% min-1 in the growth stages. The polymerizations performed using the feed rate of 0.35% min-1 proceeded under monomer-starved conditions throughout, and the mol % branches increased steadily with overall conversion. Use of the higher feed rates led to lower instantaneous conversions from the end of the seed stage (17% overall conversion) to about 40% overall conversion, from which point onward the polymerizations proceeded under monomer-starved conditions. During the period of reduced instantaneous conversion, the frequency of chain transfer to polymer was lower,...

Emulsion (co) polymerization of styrene and butyl acrylate monitored by on-line Raman spectroscopy

The homo- and copolymerizations of styrene and n-butyl acrylate were studied by on-line in-situ Raman spectroscopy.Results from the solution (homo)polymerizations proved to be very useful in the quantification of the Raman data from the emulsion homopolymerization. From the homopolymerization data it was possible to successfully calculate the partial monomer conversions for the emulsion copolymerization of thes monomers.