On the emulsion polymerization of styrene in the presence of a nonionic emulsifier

The batch emulsion polymerization kinetics of styrene (St) initiated by a water-soluble peroxodisulfate in the presence of a nonionic emulsifier was investigated. The polymerization rate versus the conversion curves showed two nonstationary rate intervals, two rate maxima, and Smith–Ewart Interval 2 (nondistinct). The rate of polymerization and number of nucleated polymer particles were proportional to the 1.4th and 2.4th powers, respectively, of the emulsifier concentration. Deviation from the micellar nucleation model was attributed to the low water solubility of the emulsifier, the low level of the micellar emulsifier, and the mixed modes of particle nucleation. In emulsion polymerizations with a low emulsifier concentration, the number of radicals per particle and particle size increased with increasing conversion, and the increase was more pronounced at a low conversion. By contrast, in emulsion polymerizations with a high emulsifier concentration, the number of radicals per particle decreased with increasing conversion. This is discussed in terms of the mixed models of particle nucleation, the gel effect, and the pseudobulk kinetics. The formation of monodisperse latex particles was attributed to coagulative nucleation and droplet nucleation for the polymerizations with low and high emulsifier concentrations, respectively. The effects of the continuous release of the emulsifier from nonmicellar aggregates and monomer droplets, the close-packing structure of the droplet surface, and the hydrophobic nature of the emulsifier on the emulsion polymerization of St are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4422–4431, 1999     

Microemulsion polymerization of styrene using a polymerizable nonionic surfactant and a cationic surfactant

High polymer/surfactant weight ratios (up to about 15:1) of polystyrene microlatexes have been successfully produced by microemulsion polymerization using a small amount of polymerizable surfactant, ω-methoxypoly(ethylene oxide)₄₀ undecyl α-methacrylate macromonomer (PEO-R-MA-40), and cetyltrimethylammonium bromide (CTAB). After generating “seeding particles” in a ternary microemulsion containing only 0.2 wt% CTAB and 0.1 wt% styrene, the additional styrene containing less than 1 wt% PEO-R-MA-40 was added dropwise to the polymerized microemulsion for a period of about 4 h at room temperature. PEO-R-MA-40 copolymerized readily with styrene. The stable microlatexes were bluish-transparent at a lower polymer content and became bluish-opaque at a higher polymer content. Nearly monodisperse latex particles with diameters ranging from 50 to 80 nm and their molar masses ranging from 0.6 to 1.6 × 10⁶ g/mol could be obtained by varying the polymerization conditions. The dependence of the number of particles per milliliter of microlatex, the latex particle size and the copolymer molar mass on the polymerization time is discussed in conjunction with the effect of the macromonomer concentration. Received: 25 October/2000 Accepted: 2 February 2001     

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.     

Electroinitiated cationic polymerization of styrene in the presence of ferric chloride

The electroinitiated polymerization of styrene has been studied in acetone with ferric chloride as the electrolyte. At a fixed monomer concentration, the polymer yield depends on the current strength as well as the concentration of ferric chloride. The molecular weight of the polymer lies in the range of 1000–3000. Addition of zinc chloride to the system or replacement of the solvent by DMF (partly or fully) or methanol retards the polymerization. The current exponent of polymerization is unity with a reaction rate constant of 4.416 × 10^?2 reaction percent per hour. The locus of polymerization is the anode compartment. A cationic mechanism has been proposed for the polymerization, the initiating step consisting of an electron transfer from an adsorbed charge transfer complex of styrene and ferric chloride.     

The effect of pH on emulsion polymerization of styrene in the presence of an amphoteric emulsifier

An emulsion polymerization of styrene in the presence of an amphoteric emulsifier of the betaine type; N,N-dimethyl-n-laurylbetaine (LNB), has been studied at various pH values. The relationships between the physicochemical properties of LNB aqueous solutions, the emulsion polymerization process and the characteristics of the synthesized latex particles were studied under various pH conditions. The polymerization rate and the particle number concentration decreased with increasing pH of LNB aqueous solution and changed in shape at both ca. pH 4 and pH 8–10. The properties of LNB aqueous solution also changed with the pH and changed in shape at the same pH as that of the emulsion polymerization. These pH values were in good agreement with the pH at which the LNB molecule changed its ionic form. The number of synthesized latex particles was proportional to the number of LNB micelles in the solution, below pH 10. The particle size of the synthesized latex particles and the molecular weight of the latex polymers also changed with the properties of LNB aqueous solutions, accompanying the change of the ionic form of LNB molecules.     

Electroinitiated cationic polymerization of styrene

A constant controlled current was passed through a solution of styrene in methylene chloride containing a tetraalkylammonium salt as supporting electrolyte. Reproducible rates of polymerization were initiated by the electrochemical techniques employed and the kinetics of the reaction were investigated. Sigmoidal curves of conversion versus time were observed. A kinetic relationship of the form In ([M₀]/[M]) = ½ Kt² was derived on the basis of simple assumptions regarding the mechanism and fitted the data accurately. The rate constants obtained were compared to others reported, and the influences of ion association on the values of the rate constants obtained are discussed. The reactions were decreased in rate by a reversal of polarity of the electrodes. However, the stoichiometry of the production of active centers and of their destruction was not ideal, in that each electron did not result in the initiation of a polymer chain.     

Emulsion polymerization of styrene: Nucleation studies with nonionic emulsifier

The nucleation mechanism of styrene emulsion polymerization in the presence of the nonionic surfactant Emulphogene BC-840 was investigated. It was found that the conversion-time curves of this system show two rate regions. The change in rate occurs at ca. 40% conversion. Second-stage nucleation leads to a faster rate and consequently to a bimodally dispersed latex. The particle size distribution is relatively narrow before 40% conversion. The bimodally dispersed latex shows a bimodal molecular weight distribution in gel permeation chromatography and the results from fractional “creaming” of the latex indicate that the small-size particles contain the higher-molecular-weight polymer.     

Effect of formaldehyde on the cationic polymerization of styrene

Polymerization of styrene has been carried out in the presence of formaldehyde at 30°C in benzene solution by using boron trifluoride etherate as a catalyst. The rate of polymerization in the initial stage was accelerated with addition of formaldehyde, while the steady-state rate of polymerization was retarded in the presence of formaldehyde. The acceleration for the rate of polymerization was found only in a short time from the beginning. The steady-state rate of polymerization followed the equation: where [C]₀ and [F]₀ are initial concentrations of catalyst and formaldehyde, [M] is the monomer concentration, and k₁, k₂, and k₃ are constants. It has been assumed that the chain-transfer reaction does not involve formaldehyde itself but rather the reaction products of formaldehyde, such as polystyrene having ethoxy or hydroxymethyl ends. The apparent chain-transfer constant for the added formaldehyde has been determined to be 1.63.     

Microemulsion polymerization of butyl acrylate. IV. Effect of emulsifier concentration

The oil/water microemulsion polymerizations of butyl acrylate initiated by a water (ammonium peroxodisulfate, APS) or oil (dibenzoyl peroxide, DBP) soluble radical initiator at different emulsifier concentrations were investigated. The rate of polymerization vs. conversion curve shows two intervals. The rate of polymerization is found to decrease with the emulsifier concentration. This finding was discussed in terms of the decrease of both radical and monomer concentration, the chain transfer to emulsifier, desorption of chaintransferred radicals, and the contribution of solution polymerization. The polymerization is faster with APS. In the APS system the rate per particle or the number of radicals per particle increases exponentially with increasing particle size. The particle size and number increase during the whole polymerization. This behavior was discussed in terms of the nucleation of monomer-containing micelles and agglomeration of primary particles during the whole polymerization. © 1995 John Wiley & Sons, Inc.     

Anionic polymerization of styrene in the presence of pyridine

An interesting effect of pyridine on the anionic polymerization of styrene in THF is described. Pyridine forms a complex with living polystyrene and greatly slows the polymerization rate without changing the degree of polymerization. From kinetic and spectroscopic studies, it was clear that there exist two active species in this system and the complex between living polystyrene and pyridine was of the 1:1 type, which itself had a weak ability to grow. The formation constant of the complex K was found to be about 4 × 10⁵ l./mole. The effect of substituted pyridine was also studied and the nature of the complex was discussed.     

Nanopore microspheres prepared by a cationic surfmer in the miniemulsion polymerization of styrene

A polymerizable cationic quaternary ammonium surfactant (CQAS) based on 2‐(dimethylamino)ethyl methacrylate (DMAEMA) was successfully synthesized via quaternization reaction. The product was characterized by FTIR and ¹H NMR spectroscopy, and its critical micelle concentration (CMC) was obtained by surface tension measurement. The surfmer acted well as comonomer and surfactant to stabilize monomer droplets during miniemulsion polymerization. To identify whether this system undergoes miniemulsion nucleation mechanism, surface tension, particle size, and N_droplet/N_particle of the system were also measured. The effect of concentration and counter‐ion of the surfmer, and pH value of the system were systematically investigated by kinetic analysis and dynamic light scattering (DLS). The resulting nanopore microspheres were observed by transmission electron micrograph (TEM) and field emission scanning electron micrograph (FESEM) and showed the nanopore morphology with reasonable stability. Another cationic surfactant cetyltrimethylammonium bromide (CTAB) was used for comparative studies. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5800–5810, 2007     

Effects of triphenylsulfonium hexafluorophosphate in the radiation-induced cationic polymerization of styrene

Radiation-induced cationic polymerization of styrene was studied in methylene chloride in the presence of triphenylsulfonium hexafluorophosphate. Acceleration in polymerization and an increase in molecular weight at a low temperature (?78°C) were observed in the presence of triphenylsulfonium salt. A study of pulse radiolysis revealed that both effects are due mainly to PF^?6, which forms ion pairs with the cationic species involved in the polymerization.     

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     

Radiation-induced polymerization of styrene in the presence of n-dibutyl disulfide

The γ-radiation-induced polymerization of pure styrene and styrene-n-dibutyl disulfide mixtures has been studied at a number of temperatures and dose rates. Up to 0.04 Mrad/hr the rates were proportional to the square root of the dose rate. By measuring the rates at a number of disulfide concentrations and at three different dose rates, the relative rates of radical formation were determined by kinetic analysis. Considerable energy transfer from the styrene to the disulfide was found. The relative contributions of energy transfer and radical formation were separated by using the kinetic scheme of Nikitina and Bagdasaryan. Values of 8.5 and 3.1 were found for the relative rates of radical production and energy transfer, respectively. This leads to a G (radical) value of 3.1 for n-dibutyl disulfide. With azobisisobutyronitrile as the initiator, the chain transfer constant to the disulfide was determined at 55°C. Finally, the sulfur content of a number of the polymers were determined, an average of two sulfur atoms per polymer chain was found. In general, the rate of polymerization was found to increase in the presence of dibutyl disulfide.