Emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate

The kinetics of the emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate have been examined over a range of comonomer compositions. The rate of polymerization was found to increase dramatically in the presence of small amounts of sodium styrene sulfonate. This increase is attributed to the increased number of particles formed when sodium styrene sulfonate was present and to a gel effect enhanced by ion association. At low concentrations of functional comonomer, where a monodisperse product was obtained, a homogeneous nucleation mechanism of particle generation is proposed. At higher concentrations, broader and then bimodal size distributions were obtained, and this is ascribed to significant aqueous phase polymerization of sodium styrene sulfonate. The water-soluble homopolymer is supposed to act as a locus of polymerization. The occurrence of this aqueous phase side reaction and the generation of secondary particles makes impossible the preparation of highly sulfonated polystyrene latexes by batch or seeded batch emulsion copolymerization.     

Sulfonated polystyrene ionomers prepared by emulsion copolymerization of styrene and sodium styrene sulfonate

Sulfonated polystyrene (S–PS), which is of considerable scientific and technological interest, has been traditionally prepared by the sulfonation of preformed polystyrene. This report describes the preparation and properties of S–PS prepared by emulsion copolymerization of styrene and sodium styrene sulfonate. S–PS prepared by copolymerization gave solubility, solution behavior and thermal characteristics that are consistent with an ionomeric structure. The solubility characteristics indicated some chain-to-chain sulfonate heterogeneity. Thermal analysis studies indicated that the glass transition does not increase with increasing sulfonate content. This is contrary to what has been observed for S–PS prepared by sulfonation and suggests that the S–PS prepared by copolymerization is fundamentally different in structure than S–PS prepared by sulfonation of polystyrene.     

Radiation-initiated emulsion copolymerization of styrene and carboxylic acid monomers

The emulsion Copolymerization of styrene and carboxylic acid monomers such as acrylic, methacrylic, and itaconic acids (AAc, MAAc, IAc) was studied by using ⁶⁰Co γ-rays as initiator and sodium do-decylsulfate as emulsifier. The polymerization behavior of these acid monomers was followed by simultaneous conductometric and potentiometric titrations for a latex sample taken in polymerization. The polymerization rate of these acid monomers increases in the following order of hydrophobicity: IAc < AAc < MAAc; this suggests that their polymerization sites are mainly the surface and/or subsurface regions of latex particles. The copolymerization rate of styrene and acid monomer increases with an increase in the acid monomer content for AAc and MAAc, whereas for IAc the rate decreases. The particle sizes determined by the stopped-flow method reveal that this variation of copolymerization rate cannot be explained by the number of growing particles and should be attributed to another factor; for instance, the transfer rate of styrene molecules from oil droplets to growing particles.     

Modeling of unseeded emulsion copolymerization of styrene and methyl methacrylate

A mathematical model for the unseeded emulsion copolymerization of styrene and methyl methacrylate has been developed. This model, which includes a new rate coefficient for radical desorption, was used to analyze the effect of the styrene/methyl methacrylate molar ratio in the initial charge on the number of particles, overall conversion and copolymer composition. It was found that the number of particles increased with the methyl methacrylate content and that a drift of the copolymer composition resulted during the polymerization of styrene/methyl methacrylate molar ratios other than 50/50. Good agreement between experimental results and model predictions was achieved.     

Emulsion copolymerization of styrene and methyl methacrylate

Chain transfer constants to monomer have been measured by an emulsion copolymerization technique at 44°C. The monomer transfer constant (ratio of transfer to propagation rate constants) is 1.9 × 10^?5 for styrene polymerization and 0.4 × 10^?5 for the methyl methacrylate reaction. Cross-transfer reactions are important in this system; the sum of the cross-transfer constants is 5.8 × 10^?5. Reactivity ratios measured in emulsion were r₁ (styrene) = 0.44, r₂ = 0.46. Those in bulk polymerizations were r₁ = 0.45, r₂ = 0.48. These sets of values are not significantly different. Monomer feed compcsition in the polymerizing particles is the same as in the monomer droplets in emulsion copolymerization, despite the higher water solubility of methyl methacrylate. The equilibrium monomer concentration in the particles in interval-2 emulsion polymerization was constant and independent of monomer feed composition for feeds containing 0.25–1.0 mole fraction styrene. Radical concentration is estimated to go through a minimum with increasing methyl methacrylate content in the feed. Rates of copolymerization can be calculated a priori when the concentrations of monomers in the polymer particles are known.     

Preparation of esters of styrene sulfonic acid and their emulsion copolymerization with isoprene

Sulfonate-containing rubbers were prepared by emulsion copolymerization of isoprene and the secondary butyl ester of styrene sulfonic acid. Substantially gel-free copolymers of relatively high sulfonate content were prepared. It was shown that hydrolysis of the ester copolymers with a suitable base can lead to the formation of ionically crosslinked elastomers.     

Emulsion copolymerization of styrene with monomeric emulsifiers

Monomeric emulsifiers with different copolymerization reactivities were used as stabilizers in emulsion polymerization of styrene initiated by 2,2′ azobisisobutyronitrile (AIBN). A significant change in emulsifier function was observed between equal micellar concentrations of surface-active sodium sulfopropyl alkyl maleates and the corresponding sodium sulfopropyl dodecyl fumarate. In the presence of less reactive maleates, copolymerization mainly occurs in the interface of the monomer swollen particles, while copolymerization with the fumarate in the first period of emulsion polymerization leads to polyelectrolyte formation in the water phase.     

A unique transurf in styrene emulsion polymerization

The surface-active, chain transfer agent (‘transurf’) sodium ω-mercapto-decane sulfonate, SMDSo, was synthesized, purified, and its interfacial properties determined. The compound acted normally in styrene emulsion polymerization to produce extremely stable colloids containing only sulfonate ionic surface functional groups. It was then used to control the surface charge density of a model polystyrene colloid by means of seeded emulsion polymerization. Surface charge could thus be increased 16-fold over that of the seed particles, and was due solely to sulfonate groups introduced by the SMDSo. Unlike most conventional emulsion polymerizations, this technique allows one to control surface chemistry independently of particle size. To cite this article: C.C. Fifield, R.M. Fitch, C. R. Chimie 6 (2003).     

Preparation of highly sulfonated polystyrene model colloids

Previous attempts to prepare monodisperse styrene/sodium styrene sulfonate copolymer latexes by batch, seeded, and semicontinuous emulsion polymerization were unsuccessful at high concentrations of the functional comonomer. Broad, and sometimes bimodal, size distributions, and large amounts of water soluble homopolymer were obtained. After removal of free monomer, solute and adsorbed homopolymer and copolymer, the overall incorporation of the functional comonomer was found to be low. To overcome these problems, a two stage “shot-growth” or in situ seeding technique was developed. A first stage copolymerization was carried out with a low concentration of sodium styrene sulfonate: the purpose of the functional comonomer was to enhance the stability and regulate the size of the seed particles. When this reaction had reached high conversion (> 90%), a second stage monomer mixture was added. The ratio of styrene to sodium styrene sulfonate in this mixture determined the final surface charge density. The mechanism by which the NaSS is incorporated in the polymer particles is considered to be by solution copolymerization with solute styrene monomer to form surface active oligoradicals. These radicals adsorb on the particle surface, initiate polymerization and become inextricably bound, preventing their transfer back to the aqueous phase. By this means, it was possible to vary independently the particle size and surface charge density. High concentrations of functional comonomer could be polymerized without undue wastage (incorporations were only slightly less than 100%) or loss of monodispersity. In extreme cases, the area per functional group fell below the theoretical minimum, indicating considerable hydration of the surface layers.     

Emulsion copolymerization of styrene and methacrylic acid in the presence of a polyethylene oxide based-polymerizable stabilizer with a shorter chain length

The emulsion copolymerization of styrene and methacrylic acid (MAA) was performed in the presence of a relatively new macromonomer, poly(ethylene glycol) ethyl ether methacrylate (PEG-EEM) as a stabilizer. In contrast to similar studies, a macromonomer having relatively shorter polyethylene oxide chain length (i.e., M_n:246, n ≈ 3.0) was selected for this study. Highly uniform and carboxyl functionalized latex particles in the size range of 0.16–0.50 μm were obtained by changing MAA, PEG-EEM, total monomer, and initiator concentrations. The use of PEG-EEM as a stabilizer resulted in larger monodisperse particles relative to those obtained by the emulsifier-free emulsion copolymerization of styrene and MAA. The particle size decreased and the polymerization rate increased with the increasing MAA feed concentration. The application of power law model indicated that MAA concentration was more effective in the presence of PEG-EEM for control of particle size relative to similar systems. The latex particles with higher numbers of surface-carboxyl groups were obtained with the higher MAA feed concentrations. Although the particle size decreased and the polymerization rate increased with the increasing PEG-EEM concentration in the emulsion polymerization of styrene, both of them remained roughly constant with the increasing PEG-EEM concentration in the presence of MAA. Received: 21 December 2000 Accepted: 13 July 2000     

Production of anomalous particles in the process of emulsifier-free emulsion copolymerization of styrene and 2-hydroxyethyl methacrylate

It was found that copolymer particles produced by emulsifier-free emulsion copolymerization of styrene and 2-hydroxyethyl methacrylate had an anomalous shape with uneven surface. The formation mechanism is discussed.     

Coagulum formation and elimination in emulsion copolymerization of tribromostyrene with styrene

Coagulum formation in emulsion polymerization of tribromostyrene and also in its copolymerization with styrene has been shown to be due to thermal polymerization. The latter takes place in the monomer reservoirs, even in the absence of radical generating initiators, converting them into sticky particles which then form the undesired coagulum. The coagulum formation phenomenon can thus be remedied by reducing the thermal initiation level through a semi-batch emulsion polymerization method, by lowering the polymerization temperature, and reduction of the collision frequency of monomer/polymer particles.     

Microemulsion polymerization of styrene

Initiation of polymerization in styrene oil-in-water microemulsions by water-soluble potassium persulfate of oil-soluble 2,2′-azobis-(2-methyl butyronitrile) at 70°C gave stable latexes which were bluish and less translucent than the original microemulsions. The effects of initiator concentration, polymerization temperature, and monomer concentration on the kinetics, particle size distributions, and molecular weight distributions were investigated. The kinetics of polymerization were measured by dilatometry. In all cases, the polymerization rate shows only two intervals, which increased to a maximum and then decreased. There was no apparent constant rate period and no gel effect. A longer nucleation period was found for polymerizations initiated by potassium persulfate as compared to 2,2′-azobis-(2-methyl butyronitrile). The small latex particle size (20–30 nm) and high polymer molecular weight (1–2 × 10⁶) implies that each latex particle consists of two or three polystyrene molecules. The maximum polymerization rate and number of particles varied with the 0.47 and 0.40 powers of potassium persulfate concentration, and the 0.39 and 0.38 powers of 2,2′-azobis-(2-methyl butyronitrile) concentration, respectively. This is consistent with the 0.4 power predicted by Smith–Ewart Case 2 kinetics. Microemulsion polymerizations of styrene–toluene mixtures at the same oil-water phase ratio gave lower polymerization rates and lower molecular weights, but the same latex particle size as with styrene alone. A mechanism is proposed, which comprised initiation and polymerization in the microemulsion droplets, by comparing the kinetics of microemulsion polymerization with conventional emulsion and miniemulsion polymerization systems.     

60Co-initiated copolymerization of styrene with vinyl acetate

The kinetic behavior of the ⁶⁰Co-initiated copolymerization at 25°C of styrene with vinyl acetate at 1100 and 2000 rad/hr was studied. As in the case of thermal and photochemical copolymerizations of these monomers, the growing chains are particularly rich in styrene units, and the overall rate is affected by a diluent effect due to the vinyl acetate monomer. However, in the case of the radiation copolymerization, this effect is partially counterbalanced by an increase of the initiation rate with the vinyl acetate concentration; the polymerization rate curve shows a maximum at a vinyl acetate molar fraction of 0.25. This effect is due to the very different free radical yields of these two monomers. The experimental results may be understood on the basis of a kinetic scheme which involves an energy transfer process from the excited vinyl acetate molecules to the styrene monomer and a termination reaction of the growing chains by very short styrene radicals when the mixture is rich in vinyl acetate.     

Emulsifier-free emulsion polymerization of the comonomer system styrene/tetrahydrofurfuryl metacrylate

 The emulsifier-free emulsion copolymerization of styrene and tetrahydrofurfuryl methacrylate (TMA) in aqueous phase is described. Monodisperse latex particles with diameters from about 280 to 620 nm are obtained consisting of a hydro-phobic polystyrene core and a hydrophilic poly-TMA shell. The influence of a variation of TMA, styrene and initiator (potassium persulfate) concentration in the original emulsion on particle size, molecular weight and composition of the copolymer is described. The concentration of TMA and initiator affects the number of primary particles but not the size of the final particles, whereas the styrene concentration strongly influences the particle diameter, a large size being favored by a high styrene concentration. The molecular weights of the polymers are between 6.2×10⁴ and 7.0×10⁵ g/mole. Size exclusion chromatography of polymer solutions in tetra-hydrofuran shows that high molecular weights are especially found in large particles, which are preferentially formed in emulsions with a high concentration of styrene. ¹H-NMR spectroscopy of the polymer shows that only about 50% of the initial TMA concentration are polymerized in the particles. Thus the copolymers prepared at increasing styrene concentration and constant initiator concentration of the emulsion show an increasing polystyrene content and are formed in particles of increasing size. Received: 4 June 1997 Accepted: 19 August 1997     

Effect of the number of seed polymer particles on the kinetic behavior of the seeded emulsion copolymerization of styrene and acrylamide

The seeded emulsion copolymerizations of styrene and acrylamide were carried out at 50°C using polystyrene latex particles as the seed and potassium persulfate as the initiator, respectively. It was found that the change in the number of seed particles initially charged causes a drastic change in the kinetic behavior of this seeded emulsion copolymerization system: when the number of seed particles initially charged was less than a certain critical value, both styrene and acrylamide started polymerization from the beginning of the reaction. However, when the number of seed particles was higher than this critical value, an apparent induction period suddenly emerged only for acrylamide polymerization, that is, acrylamide did not start polymerization until the styrene conversion exceeded around 75%, while the styrene polymerization started and continued very smoothly from the beginning of the reaction. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2689–2695, 1997     

Investigation of cationic copolymerization of styrene with p-benzoquinone

The kinetics of copolymerization of styrene with p-benzoquinone in the presence of BF₃OEt₂ is investigated. The rate constants and activation energy of the copolymerization process are determined. The reaction orders for monomer and catalyst are estimated. It is found that the rate of styrene and quinone copolymerization increase and the induction period decreases owing to addition of the latter. It is shown that the copolymerization rate achieves its maximum at an equimolal ratio of monomers. This phenomenon is explained by formation of active molecular complex between styrene and p-benzoquinone. On the basis of obtained data the course of copolymerization is interpreted and the cationic mechanism of copolymerization process is proposed.     

One-step synthesis of poly(methacrylic acid) macromonomers and application to soap-free emulsion copolymerization with styrene

Allylic sulfides such as α-(tert-butylthiomethyl)styrene and α-(2-hydroxyethylthiomethyl)styrene worked as effective chain transfer agents in the radical polymerization of methacrylic acid, to afford a one-step synthesis of water-soluble macromonomers with the 2-phenylallyl end groups. The macromonomers were found to be effective, particularly in the partially neutralized form, in emulsion copolymerization with styrene in water, to give stable emulsions with nearly monodisperse, submicron-sized particles. The microspheres thus obtained are considered to have carboxyl groups densely bound on the surface as a result of an organized copolymerization.     

The role of chain transfer agents in the emulsion polymerization of styrene

The effect of chain transfer agents on the nucleation and growth of polymer particles in the emulsion polymerization of styrene were examined extensively. The chain transfer agents used are carbon tetrachloride, carbon tetrabromide, and four primary mercaptans (C₂, n-C₄, n-C₇, and n-C₁₂). It is shown that with an increase in the amount of chain transfer agents charged the rate of polymerization per particle decreases progressively. The number of polymer particles formed, on the other hand, increases initially then decreases. These effects can be enhanced by using a chain transfer agent with higher values of chain transfer constant and solubility in water. It is also demonstrated that with increasing radical desorption from the particles, aided by chain transfer agents, the emulsifier dependence exponent for the number of polymer particles formed increases from 0.6 to 1.0 and the initiator dependence exponent decreases from 0.4 to 0. The effect of chain transfer agents on the nucleation and growth of polymer particles in the emulsion polymerization of styrene can be explained in terms of desorption of chain-transfered radicals from the polymer particles.     

Terpolymerization of acrylonitrile,styrene, and 2,3-dibromopropyl acrylate

The terpolymerization of acrylonitrile with styrene and 2,3-dibromopropyl acrylate in emulsion and dimethyl formamide solution was investigated. Polymerizations, when stopped at low conversions, yielded terpolymers that showed good agreement between experimental and theoretical copolymerization composition data, calculated from the Alfrey-Goldfinger equation. The relationship between monomer feed and terpolymer compositions is displayed on triangular coordinate graphs proposed by Slocombe. By using a computer program the lines of unique composition and binary azeotropic composition for both systems were established. In the case of emulsion polymerization the azeotropic ternary point was determined at a molar ratio for acrylonitrile/styrene/2,3-dibromopropyl acrylate of 0.27/0.61/0.12. The experimental results of emulsion terpolymerization fit the calculated curves satisfactorily over a wide range of monomer compositions up to high conversions. The influence of 2,3-dibromopropyl acrylate on the thermal and flammability characteristics of the terpolymers is described.