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     

Role of the nonionic surfactant Triton X-405 in emulsion polymerization. I. Homopolymerization of styrene

The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separate nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of the surfactant between the phases was found to play the major role in determining the nucleation mechanism(s) in these polymerizations. Although the total concentration of the emulsifier was always added at a level above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant initially present in the aqueous phase was below its CMC due to the partitioning. This CMC was also found to increase with increasing total surfactant because the distribution of the surfactant (varying ethylene oxide chain length) depended on the partitioning between the phases. Under these conditions, the first of the two nucleation periods was attributed to homogeneous nucleation, while the second was attributed to micellar nucleation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3813–3825, 1997     

Effect of temperature on styrene emulsion polymerization in the presence of sodium dodecyl sulfate. II

The batch emulsion polymerization kinetics of styrene initiated by a water‐soluble peroxodisulfate at different temperatures in the presence of sodium dodecyl sulfate was investigated. The curves of the polymerization rate versus conversion show two distinct nonstationary‐rate intervals and a shoulder occurring at a high conversion, whereas the stationary‐rate interval is very short. The nonstationary‐state polymerization is discussed in terms of the long‐term particle‐nucleation period, the additional formation of radicals by thermal initiation, the depressed monomer‐droplet degradation, the elimination of charged radicals through aqueous‐phase termination, the relatively narrow particle‐size distribution and constant polydispersity index throughout the reaction, and a mixed mode of continuous particle nucleation. The maximum rate of polymerization (or the number of polymer particles nucleated) is proportional to the rate of initiation to the 0.27 power, which indicates lower nucleation efficiency as compared to classical emulsion polymerization. The low activation energy of polymerization is attributed to the small barrier for the entering radicals. The overall activation energy was controlled by the initiation and propagation steps. The high ratio of the absorption rate of radicals by latex particles to the formation rate of radicals in water can be attributed to the efficient entry of uncharged radicals and the additional formation of radicals by thermally induced initiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1477–1486, 2000     

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     

Electrosteric stability of styrene/acrylic acid copolymer latices under emulsion polymerization reaction conditions

Acrylic acid (AA) is used in many emulsion polymerization formulations to improve the colloidal stability during and after the production of latex products. Theoretically, the improved stability originates from electrostatic repulsion complemented with steric repulsion. The objective of this work was to study the contribution of AA to the colloidal stability of polystyrene and styrene/AA copolymer latices under simulated reaction conditions. The strength of electrostatic and steric repulsion forces as a function of the electrolyte concentration, pH, and temperature was investigated via coagulation experiments with monomer‐swollen latices in stirred tank reactors. Transmission electron microscopy pictures and dynamic light scattering measurements provided an understanding of the conditions and mechanisms leading to coagulation. The experiments demonstrated that the presence of surface‐bound carboxylic groups only improved the colloidal stability if the carboxylic groups were charged, that is, at a high pH. At a low pH, the copolymer latices were even less stable than the homopolymer latex, and this indicated that the addition of AA did not improve the colloidal stability of a growing polystyrene latex. With respect to emulsion polymerization process operations, insufficient mixing and a highly concentrated electrolyte feed were found to be sources of fouling and enhanced macroscopic coagulation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 726–732, 2005     

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     

Poly(propene-co-maleic acid) with lateral perester groups as initiator in the emulsion polymerization of styrene

The influence of the initiator structure on the reaction process was investigated. In addition to the initiator concentration, its molar mass and the content of perester groups in the single molecule are determining factors that influence the course of reaction. Quantitative relationships are shown. The initiator is bonded by grafting reactions on the surface of the latex particles. The grafted moiety is dependent on the initiator structure and reaction temperature. Latices with polydispersities lower than 1.1 are obtained. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2045–2054, 1999     

Analysis of mass transport limitation during emulsion polymerization using reaction calorimetry and conductivity measurement

The seeded emulsion polymerization of styrene was investigated by reaction calorimetry in combination with conductivity measurements using the RC1e calorimeter (Mettler Toledo). Varying the stirrer speed showed the existence of mass transport limitation in the lower speed range. For the case of using the autoclave HP60 with an anchor stirrer a minimum stirrer speed of 400 rpm is required to be sure of adequate mixing in the reactor.     

On the kinetics of styrene emulsion polymerization above CMC. I. A mathematical model

A detailed mathematical model of the kinetics of styrene emulsion polymerization has been proposed. Its main features/assumptions are compartmentalization, micellar and homogeneous nucleation, particle formation by both initiator‐derived and desorbed radicals, dependence on the particle size of the rate coefficients, thermodynamic considerations, and aqueous phase kinetics. The model predicts that micellar nucleation dominates over homogeneous nucleation and that the evolution of the nucleation rate reaches a maximum, where desorbed radicals have an important contribution. Initiator‐derived radicals with only one monomeric unit have also a significant contribution on the rate of capture in particles. The results suggest that the correctness of the instantaneous termination approach depends not only on the size of the particle, but also on the type of entering radical (initiator‐derived or monomeric). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2201–2218, 2000     

An experimental investigation on the evolution of the molecular weight distribution in styrene emulsion polymerization

Styrene ab initio emulsion polymerizations were conducted at 70°C in an automated reaction calorimeter. Two polymerizations were performed, one above and the other below the critical micelle concentration (CMC) of the surfactant, thus ensuring differing polymerization kinetics between the two: the system below the CMC gave large particles that were expected to follow pseudobulk kinetics, while that above the CMC gave small particles that were expected to follow zero-one kinetics. The evolutions of the molecular weight distributions (MWDs) were characterized by removing samples periodically during the course of the reactions and analyzing with gel permeation chromatography. Interpretation of the data used average molecular weights, the GPC MWDs, and the number MWDs, as functions of conversion. It was found that all of the number MWDs (plotted as ln (number of polymer chains) vs. molecular weight of polymer chains) were concave-up at low molecular weights and become nearly linear at molecular weights (≥3−4 × 10⁶); this linearity is expected from theory. The slope of the high molecular weight region was consistent with theory for the dominant mode for chain stoppage: termination and transfer for the pseudobulk system and (predominantly) chain transfer to monomer for the zero-one system. The most likely explanation for the concavity of the number MWDs is a heterogeneity of radicals: some surface anchored with sulfate end groups and others (with hydrogen end groups arising from transfer to monomer and/or reentry) being more mobile. Thus, two types of termination are proposed: slow reaction-diffusion for the less mobile surface anchored chains, and rapid short-long (center of mass) termination for the more mobile hydrogen-terminated chains. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 989–1006, 1997     

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     

Transition from microemulsion to emulsion polymerization: Mechanism and final properties

Microemulsion and emulsion polymerization can have some similarities in starting conditions and polymerization mechanisms, but the resulting latices are unalike in particle size and molecular weight. Here we show that polymerizations can be formulated that display the characteristics often separately associated with microemulsion or emulsion polymerization. Kinetic modeling and particle size measurements show that emulsion polymerizations with initial concentrations close to the microemulsion–emulsion phase boundary demonstrate relatively fast consumption of monomer droplets and produce smaller particles. Because of their high surfactant concentrations, none of the emulsion polymerizations examined demonstrate the classical Smith–Ewart kinetics usually associated with emulsion polymerization. Instead these emulsion polymerizations have a long period of particle nucleation that subsides only after the disappearance of monomer droplets. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5253–5261, 2004     

苯丙乳液合成反应条件优化

以苯乙烯、丙烯酸、丙烯酸丁酯、甲基丙烯酸甲酯等为单体,采用乳液聚合制备了苯丙乳液,研究了合成温度、引发剂用量、乳化剂用量、功能性单体丙烯酸用量等反应条件对苯丙乳液性能的影响,并探讨了丙烯酸单体对乳液耐酸碱稳定性的影响,确定了合成反应条件.结果表明,随着合成温度的提高,混合单体的转化率迅速增加,78℃时转化率最大(达到97.1%),而后随温度继续提高基本保持不变.混合单体转化率随过硫酸钾引发剂用量的增加呈现先增加后逐渐降低的趋势,当过硫酸钾与混合单体质量比为0.010时转化率最大,此时单体转化完全.此外,随着乳化剂用量增加,乳液的外观、钙离子稳定性、凝胶等性能都有所提高,但吸水率也相应增加.最佳合成反应条件为:合成温度为78℃,混合单体组成为15g苯乙烯、2g丙烯酸、18g丙烯酸丁酯、8g甲基丙烯酸甲酯,引发剂和乳化剂与单体质量比分别为0.010和0.035.得到的苯丙乳液在酸性条件下具有良好的稳定性.     

Pickering emulsion polymerization kinetics of styrene: Comparison of bare and surface modified SiO2 nanoparticles

A step towards the understanding of some mechanistic events occurring in the styrene Pickering emulsions, using a SiO₂ dispersion, is presented. Polymerizations at 80°C with different levels of a water soluble initiator were performed. The emulsion polymer content was ca. 15% with conversions close to 90%. With conversion and particle size measurements, the particle density was estimated for bare and surface modified SiO₂ particles. Then, the average number of radicals per particle was inferred, yielding a pseudo-bulk type polymerization. It was found that bare SiO₂ nanoparticles do not participate in the nucleation mechanism; however, they, along with the initiator, promote an enhanced oligomer coagulation. On the other hand, the hexadecyltrimethylammonium bromide modified SiO₂ nanoparticles do participate in the nucleation and coagulation mechanisms, yielding more stable and smaller poorly-covered polymer particles. This approach allowed untangling some events such as: particle nucleation, radical entry to particles, particle density, coagulation and vitreous and Trommsdorff effects.     

A kinetic investigation of surfactant‐free emulsion polymerization of styrene using laponite clay platelets as stabilizers

We report the kinetics and mechanism of soap‐free emulsion polymerization of styrene using laponite platelets as stabilizers. The polymerization was initiated by potassium persulfate and the latex particles were stabilized by laponite platelets dispersed in water. Laponite adsorption on the polymer particles was enhanced by the addition of poly(ethylene glycol) monomethylether methacrylate (PEGMA). Particle nucleation can be described using the classical homogeneous nucleation mechanism followed by coagulation of unstable precursors. Oligomeric radicals formed in the water phase become insoluble and precipitate on the laponite surface leading to primary precursor particles composed of a few polymer chains and one or several clay platelets. Mature latex particles are then generated by coagulation and growth of the previously formed precursor particles. Both the nucleation and initial aggregation rates increased in the presence of PEGMA. Calorimetric monitoring of the polymerization allowed estimating the heat produced by the reaction and the monomer conversion. Hence, using the monomer material balance, the number of radicals in the polymer particles could be estimated precisely. The average number of radicals per particle, $ \bar n $ , was found to be high in the range 3–6. This result was attributed to strong attractive interactions between the growing radicals and the clay surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Kinetics of styrene emulsion polymerization in the presence of montmorillonite

The effect of the pristine sodium montmorillonite (Na⁺-MMT) on the styrene emulsion polymerizations with different concentrations of SDS ([SDS]) was investigated. At constant [SDS], the polymerization rate is faster for the run with 1 wt.% Na⁺-MMT compared to the counterpart without Na⁺-MMT. Micelle nucleation predominates in the polymerizations with [SDS] ≧ 13 mM. On the other hand, the contribution of the polymerization associated with the Na⁺-MMT platelets increases significantly when [SDS] decreases from 13 to 9 mM. At [SDS] (e.g., 2 mM) < CMC, homogeneous nucleation controls the particle formation process and polymerization kinetics. Moreover, the contribution of the Na⁺-MMT platelets that act as extra reaction loci to the polymerization kinetics is even comparable to the run in the absence of Na⁺-MMT. The resultant polymer particle size, polymer molecular weight and zeta potential were characterized and a preliminary model was developed to qualitatively study the differences between the polymerizations in the presence and absence of 1 wt.% Na⁺-MMT.     

Living radical emulsion polymerization using the nanoprecipitation technique: An extension to atom transfer radical polymerization

Living radical polymerizations of styrene were performed under emulsion atom transfer radical polymerization conditions with latexes prepared by a nanoprecipitation technique recently developed for the stable free‐radical polymerization process. Latexes were prepared by the precipitation of a solution of low‐molecular‐weight polystyrene in acetone into a solution of a surfactant in water. The resulting particles were swollen with styrene and then heated. The effects of various surfactants and hydrophobic ligands, the reaction temperature, and the ligand/copper(I) bromide ratio were studied. The best results were obtained with the nonionic surfactant Brij 98 in combination with the hydrophobic ligand N,N‐bis(2‐pyridylmethyl)octadecylamine and a ligand/copper(I) bromide ratio of 1.5 at a reaction temperature of 85–90 °C. Under these conditions, latexes with good colloidal stability with average particle diameters of 200 nm were obtained. The molecular weight distributions of the polystyrenes were narrow, although the experimental molecular weights were slightly larger than the theoretical ones because not all the macroinitiator appeared to reinitiate. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4027–4038, 2006     

Characterization of water-soluble oligomers formed during the emulsion polymerization of styrene by means of isotachophoresis

The concentrations and probable nature of charged oligomers formed by aqueous-phase termination in the persulfate-initiated emulsion polymerization of styrene were measured by isotachophoresis. Isotachophoresis has some advantages over other techniques (e.g., GPC, UV spectroscopy) in that it separates species according to their molecular weight, geometry, and charge. The charged water-soluble oligomeric species were detected in experiments in which particles were nucleated in a surfactant-free environment. Identification of the moieties present was made by comparison with model compounds. Evidence was found for bimolecular combination as a major mechanism of termination in the aqueous phase, although the possibility of disproportionation could not be ruled out. The species formed in the aqueous phase under saturated monomer conditions were found to be subject to further reaction towards the end of polymerization. The surface adsorption characteristics of the compounds formed were compared with those of known surfactants and showed good agreement with the assumptions in the model of Maxwell et. al. [Macromolecules, 24 , 1629 (1991)] for initiator efficiencies in emulsion polymerization. The relatively large concentrations of nonradical aqueous–soluble oligomeric compounds demonstrate conclusively that initiator efficiencies are not 100%, as is often assumed in such systems. © 1993 John Wiley & Sons, Inc.     

Kinetics and mechanism of emulsifier-free emulsion polymerization. III. Particle growth mechanism of seeded styrene/potassium persulfate system

For seeded emulsifier-free emulsion polymerizations of styrene/potassium persulfate (KPS)/water system using the three sizes of seeds: 1020, 1620, and 1923 Å, analysis on the data of conversion and MWD suggests a shell region polymerization mechanism for the particle growth period as the particle diameter is larger than about 1500–2000 Å. The shell region has thickness of about 100 Å. The occurrence of shell region polymerization is attributed to the higher average number of radicals per particle (n ? 2?7) for the large particle, causing the polymer radicals (with the sulfate ends anchoring on the particle surface) to be terminated by combination at lower MW. Thus, the radical ends have no chance to arrive at the core of the particles. As the smallest seed is used, the rate of polymerization is of zero order, the same as in the conventional emulsion polymerization. MW of the polymer produced in the cases, in which the shell region polymerization occurs, increases with conversion in the entire process, different from the conventional case in which the MW increases first up to about 60% conversion and then decreases. © 1992 John Wiley & Sons, Inc.