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.     

Emulsion polymerization of vinyl acetate using a polymerizable surfactant. I. Kinetic studies

A polymerizable surfactant, sodium dodecyl allyl sulfosuccinate (TREM LF-40; Henkel) and its nonpolymerizable counterpart were used in comparative studies of the emulsion polymerization of vinyl acetate. The conversion-time behavior differed for the two surfactants; the TREM LF-40 showed a decrease in the polymerization rate with increasing concentration while its hydrogenated derivative showed the opposite behavior, the rate increasing with increasing surfactant. Particle size analysis revealed a decreasing particle size with increasing surfactant concentration for both series of reactions. An explanation for the seemingly ambiguous results obtained for the polymerizable surfactant was sought by examining the reactivity of its vinyl group in copolymerization with vinyl acetate and its allylic group in a chain transfer reaction. The results suggest that both the copolymerization and chain transfer reactions can lead to the observed reduction in polymerization rate with increasing TREM LF-40 concentration. © 1992 John Wiley & Sons, Inc.     

Mechanism of emulsion polymerization of styrene using a reactive surfactant

The emulsion polymerization of styrene using the reactive surfactant sodium dodecyl allyl sulfosuccinate (TREM LF‐40) was studied. The polymerization kinetics were found to be unusual in that R_p was not directly proportional to N_p (R_p ∝ N_p^0.67). Several reasons are stated to explain the unusual kinetics, including chain transfer to TREM LF‐40, copolymerization of styrene with TREM LF‐40, and the influence of the homopolymer of TREM LF‐40 [poly(TREM)] and/or the copolymer [poly(TREM‐co‐styrene)] on the entry and exit rates of free radicals. The possibility of both chain transfer and copolymerization exists primarily at the oil/water interface, whereas both can also occur in the aqueous and monomer phases. Bulk polymerizations of styrene in the presence of TREM LF‐40 and poly(TREM) were conducted, and the results show that the reaction rate decreased for the styrene/TREM LF‐40 system. Latex characterization by serum replacement and titration measurements provided evidence for the chemical bonding of TREM LF‐40 to the polymer particles. The fraction of chemically bound reactive surfactant decreased with increasing surfactant concentration and increased with increasing initiator concentration. Relatively high contact angles of water on films cast from the latexes showed that TREM LF‐40 did not migrate significantly to the surface of the film, which was consistent with the latex‐surface characterization results. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3093–3105, 2001     

Emulsion copolymerization of styrene with a nonionic styrenic polymerizable surfactant

Among the variety of possible structures for polymerizable surfactants, it seems clear that the most interesting should be those with the reactive group located in the hydrophobic part of the molecule. We report here a study based on such a surfactant. Its general formula is A set of surfactants has been produced with m varying from 23 to 48 and n = 6 or 12. The compounds have been characterised by ¹H-NMR (nuclear magnetic resonance), size exclusion chromatography, surface tension measurements and turbidimetry. These surfactants have been copolymerized with styrene in emulsion polymerization. The coagulum is rather important, except if m is large enough. Although the incorporation of the surfactant in the latex is rather high. Most of the anchored surfactant remains at the surface and is not too buried inside. The particle size decreases with both the amount of surfactant and the length of its hydrophilic part. The use of these polymerizable surfactants leads to an excellent stability of the latex against the addition of electrolytes, and also against freeze-thawing constraints.     

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.     

The emulsion polymerization of vinyl acetate. Factors controlling particle surface area and rate of polymerization

An emulsion polymerization system with uniform continuous addition of vinyl acetate monomer, Pluronic F68 surfactant, and persulfate initiator has been examined with variation of the surfactant concentration over a tenfold range. The particle surface area per unit weight of emulsion was found to vary directly as the surfactant/monomer ratio, as also did the emulsion viscosity. At constant polymer/emulsion weight the number of particles per unit emulsion weight varied directly as the cube of the surfactant concentration. It is shown that these relationships apply also to other monomers, such as styrene and methacrylate esters. The solubility of vinyl acetate in a range of Pluronic F68 aqueous solutions was determined, and it was shown that the rate of polymerization is dependent on the solubility of the monomer in the surfactant solution. It is concluded that when a water-soluble initiator is used, polymerization proceeds in the aqueous phase. The principal factors controlling the rate of polymerization in the emulsion polymerization of vinyl acetate are, consequently, the initiating system and the concentration of monomer in the aqueous phase. Solubilization characteristics indicate that the surfactant concentration will have a much greater effect on the less water-soluble monomers, such as styrene, than on the more soluble ones, such as vinyl acetate.     

Synthesis and emulsion copolymerization of amphiphilic poly(2-oxazoline) macromonomer possessing a vinyl ester group

The present article describes the synthesis and emulsion copolymerization of a block-type amphiphilic poly(2-oxazoline) macromonomer possessing a polymerizable vinyl ester group. The macromonomer was synthesized by one-pot two-stage block copolymerization of 2-oxazolines using vinyl iodoacetate as initiator. 2-Methyl- and 2-n-butyl-2-oxazolines were employed for the construction of hydrophilic and hydrophobic segments, respectively. The surface activities evaluated by the surface tension of the macromonomer in water were fairly good. Emulsion copolymerization of vinyl acetate with the macromonomer was carried out. The macromonomer acted as a polymeric surfactant, as well as a comonomer. The resulting copolymer latex particles were spherical and their diameter was in the sub-micron range. The effects of the composition of the macromonomer on the emulsion copolymerization and the resulting latex particles were examined. © 1993 John Wiley & Sons, Inc.     

Synthesis of a novel series of polymerizable surfactants and application in emulsion polymerization

A series of polymerization surfactants (surfmers) was synthesized, whose structures combined the characteristics of polyoxyethylene as nonionic group and quaternary ammonium a as cationic group. The structures of the product were confirmed by MS, and the content of cationic‐activity matter was determined by two‐phase titration. The surfmers were then used with constant addition profiles in semicontinuous polymerization of vinyl acetate–butyl acrylate–Veova 10–hexafluorobutyl methacrylate, and the polydispersity indexes (PDI) were lower than 0.1. The particle size, amount of coagulum, and stability against electrolyte and freeze/thaw were evaluated. As a reference, an unreactive surfactant cetyl trimethyl ammonium bromide (CTAB) was also used for the polymerization. Compared to CTAB, the surfmers behaved much better. Not only stabilities to electrolyte and water resistance were improved, but also freeze/thaw stability got a superior performance. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and characterization of polysiloxane-poly(butyl acrylate-styrene) composite latices and their film properties

Gamma ray induced seeded emulsion co-polymerization of styrene and butyl acrylate was carried out in the presence of polymerizable polysiloxane seed latex which was obtained by the ring opening co-polymerization of octamethyl cyclotetrasiloxane (D₄) and tetramethyl tetravinyl cyclotetrasiloxane (VD₄) catalyzed by dodecylbenzene sulphonic acid (DBSA). A series of polysiloxane seed latices with different molecular weight, vinyl content, and particle size were used. The conversion-time curve showed that the polymerization rate was accelerated much by the seed latex. The obtained composite latices also showed good storage stability, mechanical stability and high electrolyte resistance ability. The morphology of the composite latex particles was found to be a quite uniform fine structure by transmission electron microscope (TEM). The graft polymerization between polymerizable polysiloxane and butyl acrylate or styrene was confirmed by the Fourier transform infrared spectroscopy (FT-IR) and the graft efficiency was also studied. The influence of seed content, molecular weight, vinyl content of the polysiloxane and seed latex particles size to the mechanical performance, water absorption ratio, surface properties, transparency and UV resistance of the latex films, was also investigated.     

Prediction of polymer composition in batch emulsion copolymerization

Monomer partitioning in emulsion copolymerization plays a key role in determining composition drift and polymerization rates. The combination of recently developed thermodynamically based monomer partitioning relationships with mass balance equations, makes predictions of monomer partitioning in emulsion copolymerizations possible in terms of monomer mole fractions and monomer concentrations in the particle and aqueous phases. Using this approach, the effects of monomer to water ratios and polymer volumes on the monomer mole fraction within the polymer particle phase in a nonpolymerizing system at thermodynamic equilibrium can be determined. Comparison of these monomer partitioning predictions with experiments for the monomer system methyl acrylate—vinyl acetate shows good agreement. Furthermore, composition drift occurring in a polymerizing system as a function of conversion can be predicted if the assumption is made that equilibrium is maintained during reaction. Comparison of predictions with experimental results for emulsion copolymerizations of the monomer systems methyl acrylate—vinyl acetate and methyl acrylate—indene shows good agreement. © 1994 John Wiley & Sons, Inc.     

Particle formation under monomer‐starved conditions in the semibatch emulsion polymerization of styrene. I. Experimental

Particle formation and particle growth compete in the course of an emulsion polymerization reaction. Any variation in the rate of particle growth, therefore, will result in an opposite effect on the rate of particle formation. The particle formation in a semibatch emulsion polymerization of styrene under monomer‐starved conditions was studied. The semibatch emulsion polymerization reactions were started by the monomer being fed at a low rate to a reaction vessel containing deionized water, an emulsifier, and an initiator. The number of polymer particles increased with a decreasing monomer feed rate. A much larger number of particles (within 1–2 orders of magnitude) than that generally expected from a conventional batch emulsion polymerization was obtained. The results showed a higher dependence of the number of polymer particles on the emulsifier and initiator concentrations compared with that for a batch emulsion polymerization. The size distribution of the particles was characterized by a positive skewness due to the declining rate of the growth of particles during the nucleation stage. A routine for monomer partitioning among the polymer phase, the aqueous phase, and micelles was developed. The results showed that particle formation most likely occurred under monomer‐starved conditions. A small average radical number was obtained because of the formation of a large number of polymer particles, so the kinetics of the system could be explained by a zero–one system. The particle size distribution of the latexes broadened with time as a result of stochastic broadening associated with zero–one systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3940–3952, 2001     

Ethylene–vinyl acetate semi-batch emulsion copolymerization: Use of factorial experiments for improved process understanding

A good working knowledge of the mechanism and an appreciation of the effects the process variables have on the properties of interest are required for optimization and control of polymerization processes. Despite the importance of ethylene-vinyl acetate emulsion copolymers, limited kinetic information is available. Results from a series of factorial experiments are presented here which examine the emulsion polymerization of ethylene with vinyl acetate. Copolymers of up to 32 wt % ethylene have been produced at an ethylene pressure of 500 psig and a temperature of 20°C. The effects of the process variables on the rate of polymerization, copolymer composition, particle size and number, molecular weight averages, and gel content are discussed. The kinetic results obtained suggest process improvements for the production of homogeneous copolymer. Mechanistically, the locus of polymerization has been verified as the polymer particles and little water phase polymerization was observed. © 1993 John Wiley & Sons, Inc.     

Phosphate‐Loaded Hydrogel Nanoparticles for Sepsis Prevention Prepared via Inverse Miniemulsion Polymerization

Local depletion of intestinal phosphate triggers changes in bacterial phenotypes that adversely affect the health of the host. This article describes a process for encapsulating phosphates in crosslinked poly(ethylene glycol) diacrylate (PEGDA) nanoparticles using inverse miniemulsion polymerization as a drug delivery approach for sustained release of phosphates to the intestinal epithelium. The effects of crosslinker, PEGDA co‐monomer, N‐vinyl pyrrolidone, (NVP) and surfactant concentrations on the nanoparticle size distribution, swelling ratio and monomer conversion are investigated. Increased surfactant and PEGDA concentrations result in smaller particle size and swelling ratio. A copolymerization model of crosslinking is used to predict conversion and gelation dynamics as a function of polymerization conditions. The model assumes that bulk polymerization can be used to approximate inverse miniemulsion polymerization with an aqueous‐phase initiator. The initiator efficiency is used as an adjustable parameter to simulate the conversion dynamics, thus accounting for radical confinement effects and interaction with emulsifier molecules.     

Suspended Emulsion Copolymerization of Acrylonitrile with Methyl Acrylate: Effects of Reaction Parameters on the Polymerization

Acrylonitrile/methyl acrylate copolymers were synthesized by suspended emulsion polymerization with water as dispersed phase and monomers as continuous phase, potassium peroxydisulphate (KPS) as initiator, Span-80 as emulsifier, and poly(vinyl alcohol) (PVA) as suspending agent. Effects of reaction parameters such as water/monomer mass ratio, concentration of initiator, polymerization temperature and agitation rate on polymerization conversion and the particle size distribution of acrylonitrile/methyl acrylate copolymers were studied. It was found that polymerization conversion increased with an increase of water/monomer mass ratio, concentration of initiator and polymerization temperature, while the agitation rate had no significant effect on the polymerization conversion. Particle size distribution became narrower with an increase of water/monomer mass ratio and agitation rate. Under the same initiator concentration and polymerization temperature, particle size distribution became wider along with polymerization time. The differential scanning calorimetry (DSC) results indicated that the peak temperature of the copolymers decreased with increasing MA content.     

The mechanism of core–shell inversion in two-stage latexes

In two-stage latexes where the first polymer is more hydrophilic than the second, inversion of the core and shell can occur. The mechanism of core–shell inversion during the initial and final intervals of the second-stage polymerization was investigated using model PMMA/PS systems. The phase behavior of polymer solutions intended to model the two-stage system during the initial interval of the second stage polymerization has yielded some insight into the thermodynamics of phase inversion. If the second stage monomer dissolves first stage polymer, the latter will tend to precipitate at the water/monomer interface, particularly in the presence of surfactant. The energy of the oil/water interface is thereby reduced. In the final interval, when much of the second monomer has polymerized, phase mobility is crucial to the inversion process.     

Polymerization of vinyl acetate in aqueous media. Part IV. Influence of preformed (“seed”) latex upon polymerization kinetics and particle size

The polymerization of aqueous solutions of vinyl acetate initiated by K₂S₂O₈, has been studied in the presence of different concentrations of a fine “seed” latex, both in the absence and in the presence of a surfactant (sodium hexadecyl sulfate). Both kinetics and final latex size were measured, the latter showing whether fresh nucleation had occurred or not. The results suggest that surfactant adsorbed on the latex surface greatly influences the capture, by the latex surface, of oligomers formed in the aqueous phase and this, in turn, markedly affects both nucleation and kinetics. The number of free radicals per particle does not appear to be constant even with the finest particles used (ca. 50 mμ).     

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.     

Polymerizable benzophenone derivatives for labeling vinyl acetate‐butylacrylate latex particles

We describe the synthesis and characterization of three new polymerizable benzophenone derivatives [2‐acryloxy‐5‐methyl benzophenone ( 8 ), 4′‐dimethylamino‐2‐acryloxy‐5‐methyl benzophenone ( 9 ), and 4′‐dimethylamino‐2‐(β‐acryloxyethyl)oxy‐5‐methyl benzophenone ( 10 )]. We show that these monomers can successfully be incorporated into vinyl acetate (VAc) copolymer latex particles. These particles were prepared by semicontinuous emulsion polymerization and mini‐emulsion polymerization of VAc with butylacrylate (BA) for VAc/BA = 4/1 by weight. The two monomers 9 and 10 bearing the 4′‐dimethylamino group satisfy the important spectroscopic criteria required of a dye to serve as an acceptor chromophore for nonradiative energy transfer from phenanthrene (Phe) as the donor. Their UV absorption spectra suggest significant overlap with the emission spectrum of Phe, which can be incorporated into P(VAc‐co‐BA) latex through copolymerization with 9‐acryloxymethyl Phe ( 2 ). In addition, these chromophores provide a window in their absorption spectra for excitation of the Phe chromophore at 300 nm. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3001–3011, 2002     

Miniemulsion copolymerization of vinyl acetate and butyl acrylate. I. Differences between the miniemulsion copolymerization and the emulsion copolymerization processes

Differences between the emulsion copolymerization and miniemulsion copolymerization processes, in terms of emulsifier adsorption, emulsion stability, polymerization kinetics, copolymer composition and dynamic mechanical properties were studied for the comonomer mixture of 50:50 molar ratio vinyl acetate (VA+)—butyl acrylate (BuA), using sodium hexadecyl sulfate (SHS) as a surfactant and hexadecane (HD) as a co-surfactant. The use of hexadecane with the appropriate SHS initial concentration led to a higher adsorption of surfactant, smaller droplet size, higher stability of the emulsions, lower polymerization rates, and larger latex particle size. The copolymer composition during the initial 70% conversion was found to be less rich in Vac monomer units for the miniemulsion process. The dynamic mechanical properties of the copolymer films showed less mixing between the BuA-rich core and the VAc-rich shell in the miniemulsion latexes compared to the conventional latex films.     

Synthesis of Bimodal PVC Latexes by Emulsion Polymerization: An Experimental and Modeling Study

The onset and extent of secondary particle formation in the seeded emulsion polymerization of vinyl chloride were investigated by performing a series of seeded polymerizations at different concentrations of seed latex and surfactant. It was found that, in general, both the onset and the extent of secondary particle formation are determined not only by the rate of homogeneous nucleation, but also by the rates of particle coagulation. A comparison of methods to compute the evolution of the particle size distribution in vinyl chloride emulsion polymerization was also carried out. For growth processes, the widely-used pseudo-bulk model gives correct answers. For processes involving particle formation, on the other hand, this model cannot be used because it neglects, among others, the effects of nucleation and coagulation on the radical number distribution. To surmount this problem, we propose to use the zero-one-two model, for which the full population balance equations are given here.