Kinetics Of Emulsion Polymerization Research Articles

Kinetics of the Emulsion Polymerization of Vinylidene Fluoride and Hexafluoropropylene

The kinetics of emulsion polymerization of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) has been investigated both experimentally and through the development of an appropriate model. Despite the practical relevance of this copolymer, information about the polymerization kinetics in the literature are rather scarce. A reasonable polymerization mechanism involves quite a number of kinetic parameters, which all need to be evaluated independently. This was obtained by running a limited number of polymerization reactions, but performing a rather accurate characterization of the polymer produced, including the polymerization rate, molecular weight, and chain end group distribution. These quantities allow for the reliable estimation of the involved kinetic parameters. The reliability of the developed model has been assessed by comparison with a second independent set of experimental data, where different operating conditions, in terms of pressure, initial concentration of the initiator, and chain-tran...

Emulsion polymerization of styrene using an alkali-soluble random copolymer as polymeric emulsifier

An alkali-soluble random copolymer (ASR), poly(styrene/α-methylstyrene/acrylic acid), was used as a polymeric emulsifier in the emulsion polymerization of styrene. The calorimetric technique was applied to study the kinetics of emulsion polymerization of styrene using ASR and a conventional ionic emulsifier, sodium dodecyl benzenesulfonate (SDBS). ASR could form aggregates like micelles, and the solubilization ability of the aggregates was dependent on the neutralization degree of ASR. The rate of polymerization in the ASR system was lower than that in the SDBS system. This result can be explained by the creation of a hairy ASR layer around the particle surface, which decreases the diffusion rate of free radicals through this region. Although a decrease in particle size was observed, the rate of polymerization decreased with increasing ASR concentration. The higher the concentration of ASR is, the thicker and denser ASR layer may be, and the more difficult it would therefore be for radicals to reach the particle through this layer of ASR. The rate of polymerization decreased with increasing the neutralization degree of ASR. The aggregates with high neutralization of ASR are less efficient in solubilizing the monomer and capturing initiator radicals than that of the lower neutralization degree, which leads to decrease in rate of polymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2865–2872, 1998

Experimental study of emulsion polymerization with crosslinking

Herein is reported the results of an extensive experimental investigation of the kinetics of emulsion polymerization as affected by crosslinking in the polymer particles. The model monomer system, methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA), was chosen for this study due to its earlier comprehensive investigation in bulk polymerization. Standard recipes with sodium dodecylsulfate (SDS) as anionic emulsifier and potassium persulfate (KPS) as initiator were used for the batch emulsion polymerizations. Results, which clearly show the effect of crosslinking on the kinetics, are discussed in detail. These include swellability of polymer particles by monomer; polymer particle nucleation rates, below and above the critical micelle concentration (CMC); average number of radicals per particle; and gel-sol levels. It was found advantageous to use electron spin resonance (ESR) to follow radical concentrations during crosslinking in polymer particles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 935–957, 1997

Inverse emulsion polymerization of acrylamide and salts of acrylic acid

Kinetics of the persulfate-initiated inverse emulsion polymerization of acrylamide and acrylic acid sodium and ammonium salt have been investigated. Rate orders with respect to the initiator, the monomers and the emulsifier were determined for all three monomers. Influences of the change of concentration of the individual components of the polymerization system on molecular weight and particle size of the resulting polymers were described. Overall activation energies of polymerizations were determined. Results of the kinetics measurements for the non-ionic acrylamide and the ionic salt of acrylic acid were compared. Dependence of the polymerization rate R p on the concentration of components in the polymerization system can be expressed for all three mononers by the following equation: R p = [ I] 0.5 [M] 1.5 [E] 0.1. These kinetic data are in good agreement with the supposed mechanism of polymerization. The almost sesquimolecular rate order with respect to the monomer proves to the participation of the monomer on the initiation reaction. This fact also explains the reason of the unusually low polymerization temperature of 40 °C. The persulfate-initiated inverse emulsion polymerization of acrylic monomers takes place as a solution polymerization in microparticles.

Emulsion terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate: Experimental results

A systematic study of the terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate (BA/MMA/VAc) was conducted. In this stage of the study, batch emulsion terpolymerizations were performed in a 5 L stainless steel pilot plant reactor. The experiments were designed using a Bayesian (optimal) technique. The polymers produced were characterized for conversion, composition, molecular weight, and particle size. Conversion, terpolymer composition, number- and weight-average molecular weight, and average particle size results are discussed in light of the influence of seven factors and the interaction of these factors. The factors studied include monomer feed composition, initiator concentration, chain transfer agent concentration, impurity concentration, initiator type, emulsifier concentration, and temperature. A two-stage rate phenomenon, similar to that occurring in bulk co- and terpolymerization and emulsion copolymerization of acrylic/vinyl acetate systems was observed in the conversion, composition and molecular weight data. Furthermore, an interesting yet often ignored effect of impurities on emulsion polymerization kinetics was explained.

Some parameters affecting the emulsifier-free emulsion polymerization of vinyl acetate

The kinetics of emulsifier-free emulsion polymerization of vinyl acetate using the redox initiation system of potassium persulfate-potassium metabisulfite was studied. The effect of the reaction conditions on the rate of polymerization was also investigated. The polymerization proceeded smoothly until high conversion and yielded stable emulsions. The apparent activation energy for the polymerization system was calculated and the effect of some inorganic substances on the rate of polymerization was also revealed. © 1997 John Wiley & Sons, Inc.

Kinetics of emulsifier-free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 106 to 1.2 × 106 g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.

Kinetics of emulsifier‐free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 106 to 1.2 × 106 g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.

Kinetics of the potassium persulfate-initiated inverse emulsion polymerization of sodium acrylate solutions

The kinetics of the K2S2O8-initiated inverse emulsion polymerization of aqueous sodium acrylate solutions in kerosene with Span 80 as the emulsifier has been studied. The conversion-time curves are S-shaped. The following expressions have been obtained for the maximum rate of polymerization and the molecular weight of the polymers under the experimental conditions investigated: Rmax ∞ [K2S2O8]0.78[sodium acrylate]1.5[Span 80]0.1, (OVERLINE)M(/OVERLINE)u ∞ [K2S2O8]−0.37[sodium acrylate]2.9[Span 80]−0.2. The activation energy for the maximum rate of polymerization is 94.8 kJ mol−1. The results suggest a monomer–droplet–nucleation mechanism for the system studied. © 1996 John Wiley & Sons, Inc.

Kinetic aspect of the emulsion polymerization of cyclothexyl methacrylate

AbstractThe emulsion polymerization kinetics of cyclohexyl methacrylate (CHMA) at 50°C using a mixture of anionic and nonionic surfactants was investigated. The product of the propagation rate constant (Kp) and the number of radicals per particle (n̄) increased monotonously with the volume‐average particle diameter (Dv). The value of Kp was estimated to be 260 L/(mol · s). Changing the monomer mass fraction in the recipe (from 0,14 to 0,40), the value of n̄ remained constant and close to 0,5. On the other hand, increasing the initiator concentration ([I]), the value of n̄ increased rapidly and then leveled off.

Monte carlo simulation of emulsion polymerization — linear, branched, and crosslinked polymers

AbstractA new Monte Carlo approach for the kinetics of emulsion polymerization is discussed. The diameters of polymer particles produced in emulsion polymerizations are in the submicrometer range; therefore, it is straightforward to simulate the formation processes of all polymer molecules in each polymer particle by application of the Monte Carlo method with a well‐designed algorithm. In the Monte Carlo technique, virtually any kinetic event, such as the desorption of oligomeric radicals, chain‐length‐dependent reaction kinetics, branching and crosslinking reactions, can be accounted for. In principle, neither idealizations nor approximations, which are usually required in the analytical approaches, are not necessary. As a consequence one can observe the structure of each polymer molecule directly; therefore, very detailed information can be obtained easily, including the full distributions of the dead and live polymer molecular weights, and the spatial distribution of the branched and crosslinked polymer chains in the case of nonlinear polymerizations. Monte Carlo simulations promise to provide greater insight into the complex molecular processes which occur during emulsion polymerizations.

Desorption of free radicals in semibatch emulsion polymerization of methyl acrylate

AbstractDesorption of free radicals from particles can cause an emulsion polymerization system to deviate from Smith–Ewart case II kinetics. A mechanistic model has been developed to predict the effect of desorption of radicals from particles on the kinetics of semibatch emulsion polymerization of methyl acrylate under the monomer‐starved condition. Experimental data available in the literature are used to assess the proposed kinetic model. The model predicts the experimental data reasonably well for a wide range of monomer feed rates. The rate of polymerization increases with an increase in the rate of monomer addition. The kinetic data are also useful in evaluating the desorption rate constant (K′d) for methyl acrylate. The best fitted value of K′d at 50°C is 4 × 10‐12 cm2/s, which is in good agreement with the theoretical values predicted by desorption theory. © 1995 John Wiley & Sons, Inc.

Diffusion‐controlled semibatch emulsion polymerization of styrene

AbstractSemibatch emulsion polymerization of styrene under the monomer‐starved condition is strongly affected by the gel effect. A mechanistic model based on diffusion‐controlled reaction mechanisms is developed to predict the kinetics of semibatch emulsion polymerization. Experimental data available in the literature are employed to assess the proposed model. Reasonable agreement between the model predictions and experimental data is observed. The simulation results suggest that the reaction system approaches Smith–Ewart case II kinetics (n̄ = 0.5) when the concentration of monomer in the particles is close to the saturation value, whereas the reaction system under the monomer‐starved condition is characterized by diffusion‐limited reaction mechanisms (n̄≥0.5). © 1995 John Wiley & Sons, Inc.

Influence of disproportionated rosin acid soap on the emulsion polymerization kinetics of styrene

AbstractThe effect of disproportionated rosin acid soap (DRAS) on the emulsion polymerization kinetics of styrene has been studied. Batch experiments reveal a significant influence of chain transfer and limited particle coagulation on the polymerization process. For the recipes studied, the number of growing chains in the emulsion and consequently the polymerization rate were found to be independent of the particle number during the interval of coagulation. However, for relatively large particles (dp ≈ 100 nm), the polymerization rate was proportional to the particle number, indicating Smith–Ewart case II kinetics. These effects have been shown to be well predicted by model calculations using a radical population balance over the particles. Since DRAS is derived from naturally occurring constituents found in pine trees, its performance, and with that the properties of the product latex, may vary significantly. However, if the performance of DRAS is known, the recipe and process conditions can be optimized. For this reason a procedure has been developed to quantify the performance of DRAS from the simple batch experiments discussed in this paper, the polymerization kinetics, and the information obtained about the coagulation process. © 1995 John Wiley & Sons, Inc.

Simulation model for the molecular weight distribution in emulsion polymerization

AbstractA Monte Carlo simulation model for the kinetics of emulsion polymerization is proposed. In the present model, the formation of each polymer molecule is simulated by the use of only a couple of probability functions; therefore, the calculation can be handled well even on personal computers. It is straightforward to account for virtually any kinetic event, such as the desorption of oligomeric radicals and chain length dependence of kinetic parameters, and as a consequence very detailed information such as the full distributions of the dead polymer molecular weights and the macroradicals among various polymer particles can be obtained. When bimolecular terminations are the dominant chain stoppage mechanism, the instantaneous molecular weight distribution (produced in a very small time interval) becomes broader than that for homogeneous polymerizations due to a higher possibility that short and long polymer radicals react with each other if bimolecular reactions are fast enough. The increase in the polydispersity of the MWD is fairly large, especially when bimolecular termination by disproportionation is significant; however, the gel permeation chromatography (GPC) may not be a suitable analytical technique to detect such broadening since oligomeric peaks may not be observed in the elution curve. The present simulation method provides greater insight into the complicated phenomena of emulsion polymerizations. © 1995 John Wiley & Sons, Inc.

Kinetics of long-chain branching in emulsion polymerization: 1. Chain transfer to polymer

New simulation models to predict the molecular weight distribution in emulsion polymerization that includes chain transfer to polymer are proposed. When the frequency of branching is not very large, the kinetics of emulsion polymerization can be modelled effectively as a large number of semibatch reactors as long as monomer droplets exist and of batch reactors after the disappearance of monomer droplets. In such cases, a simulation method based on the branching density distribution proposed earlier for non-linear polymerizations in homogeneous media shows its versatility to describe the kinetics of non-linear emulsion polymerization. However, the calculated results based on a direct simulation model that simulates all polymer molecules in each polymer particle clearly show that the fact that each polymer particle consists of a limited number of polymer molecules must be accounted for as the branching density increases. In general, such compartmentalization effects are important when one considers the molecular weight distribution development of non-linear polymer chains that are formed in emulsion polymerization.

Monomers in Polymer Dispersions. Part IV: Partition of Acrylonitrile in Rubber Latex as Studied by Raman Spectroscopy

The swelling of polymeric latex particles with monomers and the partition of slightly water soluble monomers between the particle and aqueous phases are of great importance in understanding the kinetics of emulsion polymerization and particle structure formation. The overall rate of polymerization is directly influenced by the monomer concentration at the loci of chain propagation reaction (latex particle, monomer droplet, or aqueous phase). In addition, initiator efficiency, rates of radical transfer, and copolymer or graft composition (in multistage reactions) also depend on monomer concentration and partition.

Emulsion polymerization of vinyl propionate using a newly developed redox pair initiation system

The kinetics of emulsion polymerization of vinyl propionate (VP) using the redox system potassium persulfate (KPS)/acetone-sodium bisulfite (ASBS) as redox pair initiation system is studied at 25°C. The effect of different initiator concentrations on the rate of polymerization and on the number and size of particles of the formed emulsion latices is established. The polymerization proceeded smoothly till high conversion and yielded stable emulsion latices. The rate of polymerization was found to be dependent on the initiator concentration to the 2 5 power.

Kinetics studies of two‐stage soapless emulsion polymerization of butyl acrylate and methyl methacrylate

AbstractIn this work, butyl acrylate (BA) and methyl methacrylate (MMA) were used as monomers and K2S2O8 was used as the initiator to study the kinetics of two‐stage soapless emulsion polymerization. The first stage of the reaction was to synthesize polyBA (PBA) seeds, and the second stage of the reaction was a seeded polymerization of MMA. The results showed that an increase of initiator concentration would increase the rate of polymerization and the number of polymer particles, but would decrease the size of the polymer particles and the weight‐average molecular weight of the polymers. On the other hand, a decrease of the weight ratio of BA/MMA caused a decrease in the reaction rate and the weight‐average molecular weight of the polymers in the second stage of the reaction. The morphology of emulsion particles was observed from transmission election microscopy (TEM). The polymer particles were very uniform in size and showed coreshell morphology with PBA as a core and poly MMA (PMMA) as a shell. © 1994 John Wiley & Sons, Inc.

Tubular reactors for emulsion polymerization: II. Model comparisons with experiments

AbstractA dynamic model for emulsion polymerization in a tubular reactor has been developed and compared with experimental data. The model uses an axial dispersion coefficient to fit experimentally measured residence time distributions and to represent axial mixing during reaction. Very general emulsion polymerization kinetics are assumed so that a wide range of monomers and operating conditions can be handled. Orthogonal collocation on finite elements was chosen as the numerical solution technique. Comparisons show good agreement between model and experiments for two different monomers.