Number Of Polymer Particles Research Articles

Effect of dose rate on emulsion and microemulsion polymerization of styrene

Emulsion and microemulsion polymerization of styrene were initiated with a gamma ray to study the effect of dose rate on polymerization. In both systems, there is an apparent plateau of polymerization rate in the curve of reaction rate vs. conversion. It was shown that emulsion polymerization conformed to the Smith–Ewart theory very well. Changing the dose rate in interval 2 had no great influence on polymerization rate, but it changed the average lifetime of radicals in polymer particles and affected the molecular weight of polymer produced. For microemulsion polymerization it was assumed that in the plateau it is the number of growing polymer particles being kept constant, not the number of polymer particles. When the dose rate was changed while the polymerization came into the constant period, the polymerization rate and the molecular weight of the polymer varied with the dose rate. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 257–262, 1998

Dispersion copolymerization of poly(oxyethylene) macromonomers and styrene

The kinetics of dispersion copolymerization of methacryloyl-terminated poly(oxyethylene) (PEO-MA) and p-vinylbenzyl-terminated (PEO-St) polyoxyethylene macromonomers and styrene (St), initiated by a water- and/or oil-soluble initiator, was investigated using conventional gravimetric and NMR methods at 60°C. The batch copolymerizations in the water/ethanol continuous phase were conducted to high conversion. The rate of polymerization was described by the curve with a maximum at very low conversion. The initial rate of polymerization and the number-average molecular weight were found to decrease with increasing [PEO-MA], and the decrease was more pronounced in the range of a high macromonomer concentration. The rate per particle (at ca. 20% conversion) was found to be proportional to the −1.55th, the particle size to the −0.92nd, and the number of particles (at final conversion) to the 3.2nd power of [PEO-MA], respectively. At the beginning of polymerization the continuous phase is the main reaction locus. As the polymerization advances, the reaction locus is shifted from the continuous phase to the polymer particles. The transform of the reaction loci from the continuous phase to the polymer particles increases the rate of polymerization and the polymer molecular weights. The increase of the weight ratio PEO-MA/St favors the formation of monodisperse polymer particles, the colloidal stability of dispersion, and the formation of a larger number of polymer particles. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3131–3139, 1997

Dispersion copolymerization of poly(oxyethylene) macromonomers and styrene

The kinetics of dispersion copolymerization of methacryloyl-terminated poly(oxyethylene) (PEO-MA) and p-vinylbenzyl-terminated (PEO-St) polyoxyethylene macromonomers and styrene (St), initiated by a water- and/or oil-soluble initiator, was investigated using conventional gravimetric and NMR methods at 60°C. The batch copolymerizations in the water/ethanol continuous phase were conducted to high conversion. The rate of polymerization was described by the curve with a maximum at very low conversion. The initial rate of polymerization and the number-average molecular weight were found to decrease with increasing [PEO-MA], and the decrease was more pronounced in the range of a high macromonomer concentration. The rate per particle (at ca. 20% conversion) was found to be proportional to the −1.55th, the particle size to the −0.92nd, and the number of particles (at final conversion) to the 3.2nd power of [PEO-MA], respectively. At the beginning of polymerization the continuous phase is the main reaction locus. As the polymerization advances, the reaction locus is shifted from the continuous phase to the polymer particles. The transform of the reaction loci from the continuous phase to the polymer particles increases the rate of polymerization and the polymer molecular weights. The increase of the weight ratio PEO-MA/St favors the formation of monodisperse polymer particles, the colloidal stability of dispersion, and the formation of a larger number of polymer particles. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3131–3139, 1997

Preparation and characterization of polystyrene and styrene-butyl acrylate copolymer latices

Emulsion polymerization of styrene (S) and emulsion copolymerization of styrene with butyl acrylate (BuA) using potassium persulfate (KPS)/different aromatic aldehydic sodium bisulfite adducts as developed redox pair initiation systems were investigated at variable initiator, emulsifier concentrations and feed monomer compositions for studying the morphological characteristics of the obtained latices. It was found that the developed redox pair initiation system increased the number of polymer particles per unit volume of water ( Nt) more than the classical system. Also, N t , decreased with increasing initiator concentration, but increased with increasing emulsifier concentration for both the classical and developed ones. The volume-average particle diameter D ̄ v was found to be dependent on the different redox initiators: potassium persulfate/methylbenzaldehyde sodium bisulfite (KPS/MeBSBS), potassium persulfate/chlorobenzaldehyde sodium bisulfite (KPS/CBSBS), potassium persulfate/methoxybenzaldehyde sodium bisulfite (KPS/MBSBS), potassium persulfate/benzaldehyde sodium bisulfite (KPS/BSBS) and potassium persulfate/sodium bisulfite (KPS/SBS) to the powers 0.15, 0.27, 0.30, 1.80 and 0.70, respectively, while N t , is dependent on emulsifier concentration to the powers 0.48, 1.00, 2.08, 3.33 and 4.41 with respect to the different redox systems KPS/SBS, KPS/MBSBS, KPS/CBSBS, KPS/BSBS and KPS/MeSBSB. The polydispersity index ( D w D w ) for the emulsion latices prepared using different emulsifier concentrations was found to be in the range 1.00–1.29, i.e. they are relatively narrow. This means that the emulsion polymerization of styrene was not in the so-called induction period. Increasing BuA ratio in the feed monomer composition of the prepared S/BuA copolymer lattices led to a decrease in N t .

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.

Photopolymerization of Butyl Acrylate Microemulsions 1. Post-polymerization

The oil-in-water-type microemulsion polymerization of butyl acrylate initiated by UV light was investigated. The polymerization showed two nonstationary rate intervals with a short rise to a maximum. The rate of polymerization was found to be proportional to the 0·7th power of the incident light intensity. The number of radicals per particle was found to be much below 0·5. The initiating radicals are supposed to be formed by the decomposition of the excited (SDS/BA)* intermediates (micelles). Desorbed radicals were found to increase the number of new particles after the cessation of illumination. The number of polymer particles increased during the whole polymerization. The micellar mechanism was proved to apply to the present system. The dependence of the molecular weight, or the relative viscosity of the microemulsion versus conversion is described by a curve with a maximum.

Polymerization of Miniemulsions Prepared from Polystyrene in Styrene Solutions. 2. Kinetics and Mechanism

The kinetics and mechanism of polymerization of miniemulsions prepared from 1% polystyrene in styrene solutions were investigated by conducting reactions with a varying potassium persulfate initiator concentration, and the results were compared with those for miniemulsions prepared in the absence of polymer. The addition of the polystyrene to the miniemulsions was shown to greatly increase the number of polymer particles produced and the overall polymerization rate obtained. The final number of polymer particles was determined for both systems and was shown to vary with the 0.31 power of the initiator concentration in the absence of polymer but was independent of the initiator concentration for miniemulsions prepared from 1% polystyrene in styrene solutions. The final particle size distributions also differed when polystyrene was added to the miniemulsions. The miniemulsions prepared in the absence of polymer produced negatively skewed particle size distributions, the particle size decreasing with increasing initiator concentration. The miniemulsions prepared from 1% polystyrene in styrene solutions produced bimodal particle size distributions for all but the highest initiator concentration employed. By treating the system in an analogous fashion to seeded emulsion polymerization, it was demonstrated that the mechanism for polymerization of miniemulsions prepared from 1% polystyrene in styrene solutions proceeds by radical entry into highly monomer-swollen, preformed polymer particles. Calculation of the average number of radicals per particle for this system revealed that Smith-Ewart case 1 and/or case 2 kinetics were obeyed

Polymerization of Miniemulsions Prepared from Polystyrene in Styrene Solutions. 1. Benchmarks and Limits

Recently, experimental results indicating differences between the polymerization kinetics of styrene miniemulsions prepared with and without small amounts of polystyrene added to the oil phase have been reported. The work is expanded here to better define the range of conditions under which this behavior is observed. Styrene miniemulsions and conventional emulsions prepared with and without the addition of a small amount of polystyrene to the oil phase were polymerized at 70 o C in an automated reaction calorimeter. The results show that miniemulsions prepared with as little as 0.05 wt% polymer based on the oil phase exhibit a substantial increase in the polymerization rate and number of polymer particles produced over miniemulsions prepared in the absence of polymer. An increase in the polymerization rate was observed when either cetyl alcohol or hexadecane was used as the cosurfactant; however, the increase was greater for cetyl alcohol. In addition, the homogenization of a polymer solution without a cosurfactant was demonstrated to yield an unstable miniemulsion (i.e., a cosurfactant is required for the formation of a stable miniemulsion). Samples withdrawn before and after the polymerization of a 1% polystyrene in styrene miniemulsion (using cetyl alcohol as the cosurfactant) revealed that the initial number of miniemulsion droplets was nearly the same as the final number of polymer particles. The latter is taken as partial proof that a large fraction (approaching 1) of the initial number of droplets captured aqueous phase free radicals and became polymer particles during this polymerization

Polymerization of Miniemulsions Prepared from Polystyrene in Styrene Solutions. 3. Potential Differences between Miniemulsion Droplets and Polymer Particles

In two previous papers, it was demonstrated that the addition of a small amount of polystyrene to the styrene used in preparing miniemulsions results in a substantial increase in the overall polymerization rate and the number of polymer particles formed. In this paper, this behavior is attributed to a basic difference in the abilities of miniemulsion droplets and polymer particles to capture aqueous phase free radicals. It is hypothesized that miniemulsions prepared from polystyrene in styrene solutions resemble the polymer particles formed in normal (i.e., no polymer) miniemulsion polymerizations at early conversions. This being the case, these polymer-containing droplets are able to effectlively compete with growing polymer particles for free radicals, whereas their counterparts which contain no polymer are not, and as a result a greater fraction of the initial droplets become polymer particles. Based on this mechanism, it is speculated that the presence of the polymer increases the capture efficiency of the droplets by modifying either their interior (i.e., by increasing the interior viscosity, thereby increasing the probability of a radical to propagate rather than exit) or the droplet/water interface (i.e., by disrupting a SLS/CA interfacial barrier to radical entry). Experimental results are reported which support the latter

Start-up procedures in the emulsion copolymerization of vinyl esters in a continuous loop reactor

Different start-up strategies for the 55 wt% solids content redox-initiated emulsion copolymerization of vinyl acetate and Veova 10 in a continuous loop reactor were studied to determine the optimal start-up procedure in terms of smoothness of the operation and minimum out-of-specification product. These strategies included different initial charges and temperature profiles. The evolutions of the monomer conversion, particle size, number of polymer particles and molecular weight distribution during the start-up were analysed and the effect of the start-up procedure on the steady-state values of these variables determined.

Styrene polymerization in ternary microemulsions: effects of water-soluble and oil-soluble initiators

The polymerization of styrene in ternary microemulsions stabilized by the cationic surfactant tetradecyltrimethylammonium bromide was studied as a function of concentrations of water-soluble (potassium persulfate, KPS) and oil-soluble (AIBN) initiators. At a particular molar ratio of the initiators, similar maximum rates of polymerization can be achieved from using both types of the initiators. In addition, both initiated systems produced microlatexes with similar hydrodynamic radius, number of polymer particles, molecular weight of polystyrene and number of polymer chain per latex particle. But the dependencies of these latex parameters on concentrations of KPS and AIBN may not be the same. The polymerization mechanism appears to be similar, irrespective of using KPS or AIBN. It is discussed in terms of “effective radicals” produced for the polymerization. While the different dependencies of some latex parameters on concentrations of the initiators are attributed to the different efficiencies of the initiators in producing “effective radicals”.

High solids content emulsion terpolymerization of vinyl acetate, methyl methacrylate, and butyl acrylate. I. Kinetics

AbstractThe kinetics of the high solids content emulsion terpolymerization of vinyl acetate, methyl methacrylate, and butyl acrylate were investigated. The effect of feed flow rate, total amount of emulsifier, distribution of emulsifier between the initial charge and the feed, concentration of initiator, and solids content on the time evolution of the conversion, terpolymer composition, and total number of polymer particles were investigated. The experimental results were analyzed by means of a mathematical model that incorporated the main features of the system. © 1994 John Wiley & Sons, Inc.

Formation of polystyrene nanoparticles in ternary cationic microemulsions

The polymerization of styrene has been studied in ternary microemulsions which were stabilized by tetradecyltrimethylammonium bromide or octadecyltrimethylammonium chloride. The initiation of polymerization occurred mainly in the styrene-swollen microemulsion droplets, and the polymeric particles grew by recruiting monomer and surfactant from uninitiated droplets. The average hydrodynamic radius ( R b) of swollen particles first increased rapidly to a maximum at ∼4 or 7% conversion, and then decreased slowly to a constant value. The variation in size follows the trend as simulated by a recent thermodynamic model. Due to the continuous nucleation, the number of polymer particles and the polydispersity of particle sizes increased continuously throughout the course of the polymerization process. The low average number of free radicals per particle ( n ̄ <0.5 ) may be responsible for polystyrene with high molecular weights ( M ̄ w =6−11 × 10 6 ).

Kinetics and Mechanisms of Unseeded Emulsion Polymerization of Methyl Methacrylate

Unseeded emulsion polymerization of methyl methacrylate was carried out at 50 °C using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator, respectively, to clarify the effects of emulsifier, initiator and monomer concentrations initially charged on the kinetic features of the polymerization such as the number of polymer particles produced and the course of polymerization. To describe the observed kinetic features, a quantitative kinetic model for particle nucleation and growth is proposed on the basis of the assumption that polymer particles are generated from emulsifier micelles. Furthermore, the rate coefficients for radical termination and propagation in the polymer particles are empirically correlated as a function of the weight fraction of polymer in the polymer particles. It is shown that by using these empirical rate coefficients and the proposed kinetic model, the observed monomer conversion versus time histories can be successfully simulated up to almost the end of polymerization, when the emulsifier concentration is higher than the critical micelle concentration.

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 &amp; Sons, Inc.

Effect of some sodium bisulfite adducts of different chain lengths on the course of the emulsion polymerization of vinyl acetate

AbstractThe emulsion polymerization of vinyl acetate using some bisulfite adducts of different chain lengths with potassium persulfate as the redox initiation system, in the absence of emulsifier, was studied. The effects of such adducts, which contain the same weight equivalent of bisulfite anion, on the rate of polymerization, maximum conversion, and stability of the produced polymer lattices as well as the morphological characteristics including volume‐average diameters and the number of polymer particles per unit volume of water were investigated. The rate of polymerization was found to be dependent on the concentration of benzaldehyde, acetaldehyde, octyl aldehyde, methyl propyl ketone, and acetone sodium bisulfite adducts to the powers 0.54, 0.66, 0.95, 1.0, and 1.1, respectively. Also, it was found that increasing adduct chain lengths decreases the volume‐average diameter, increases the obtained lattice stability, and improves the morphology of the polymeric particles, where a spherical morphology and extra stability were obtained in the presence of the octyl aldehyde adduct. © 1993 John Wiley &amp; Sons, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America.

Kinetics and mechanisms of emulsion polymerization initiated by oil‐soluble initiators. IV. Kinetic modeling of unseeded emulsion polymerization of styrene initiated by 2,2′‐azobisisobutyronitrile

AbstractTo explain the kinetic features of particle formation and growth in unseeded emulsion polymerization initiated by oil‐soluble initiators, a mathematical kinetic model is proposed, based on the assumption that when initiator radicals or monomer radicals in the water phase enter monomer‐solubilized emulsifier micelles, initiate polymerization, and propagate to a chain length which is long enough not to desorb from the micelles, the micelles are regarded to be transformed into polymer particles. It is demonstrated by comparing the experimental results obtained in the emulsion polymerization of styrene initiated by the oil‐soluble initiator, 2,2'‐azobisisobutyronitrile, with sodium lauryl sulfate as emulsifier that the proposed kinetic model satisfactorily explains the kinetic features such as the effects of initial emulsifier, initiator, and monomer concentrations on both the number of polymer particles produced and the monomer conversion versus time histories. © 1993 John Wiley &amp; Sons, Inc.

Particle nucleation in emulsion copolymerization containing multifunctional monomers

AbstractCharacteristic features of particle nucleation and growth in the emulsion copolymerization of styrene and multifunctional monomers such as ethylene glycol dimethacrylate and divinylbenzene were investigated. It was found that in these emulsion copolymerization systems the rate of polymerization per particle decreased drastically with an increase in the content of the multifunctional monomer in the initial monomer feed, and the number of polymer particles produced, on the other hand, increased corresponding to the decrease in the rate of polymerization per particle. The increase in the number of polymer particles produced was explained on the basis of Smith‐Ewart theory, which predicts that the number of polymer particles produced would increase inversely proportional to the 0.4 power of the volumetric growth rate per particle, that is the rate of polymerization per particle during the interval of particle formation (Interval I). It was pointed out that the decrease in the rate of polymerization per particle in Interval I would be due mainly to a decrease in the monomer concentration in the polymer particles which was caused by crosslinking networks of the resultant polymer.

Modeling semicontinuous emulsion terpolymerization

A mathematical model for the emulsion terpolymerization process was developed. The outputs of the model are the time evolution of the number of polymer particles, conversions of the monomers, latex solids content and terpolymer composition. The model was checked during the seeded semicontinuous emulsion terpolymerization of methyl methacrylate, butyl acrylate and vinyl acetate carried out using high solids content latexes. The parameters of the model were estimated using all the experimental results by means of a direct search algorithm. An excellent fitting of the experimental data was achieved.

Semi‐batch Processes for Emulsion Polymerisation

AbstractEssential features and advantages of semi‐batch emulsion polymerisation are described. Variations of polymerisation rate, polymer particle number, particle size, copolymer composition and molecular weight distribution are considered and the use of mathematical models is reviewed. Suggestions for future work, both experimental and modelling, are made.