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     

Generalizing the polymerization conditions for the production of monodisperse polymeric particles via dispersion polymerization

In this study, the preparation of various methacrylic particles with monodisperse size via dispersion polymerization in polar media was discussed. The effect of various polymerization conditions such as polarity of the medium, monomer, stabilizer, and initiator concentration, polymerization temperature, and initiator type on the size and size distribution of these particles was evaluated. The experimental results showed that, with a decrease in the difference between medium solubility parameter (MSP) and polymer solubility parameter (PSP), stabilizer concentration and with an increase in monomer content size of the particles increased and size distribution of them became broader. The obtained results showed that the particle size and size distribution of various polymers were different functions of initiator concentration. It means that, for the production of monodisperse particles, specific amount of initiator is needed for each type of the polymers. Moreover, it was observed that the size and size distribution of the particles with higher polarity were more sensitive to changing the polarity of the medium, and the size distribution of the particles with lower glass transition temperature (T _g) is more sensitive to changing the stabilizer concentration which is because of less stability of them. Furthermore, to our surprise, the obtained results showed that, in MSP-PSP of 18.5 MPa^0.5, size and size distribution of all types of the particles became equivalent.     

Comparison of oil-soluble and water-soluble initiation of styrene polymerization in a three-component microemulsion

The polymerization of styrene in three-component oil-in-water microemulsions made with the cationic surfactant dodecyltrimethylammonium bromide is studied by dilatometry and quasielastic light scattering as a function of type and concentration of initiator. Fast polymerization rates, high conversions, and high molecular weight polymers are achieved with both oil-soluble (AIBN) and water-soluble (potassium persulfate) initiators. The rate of polymerization shows initiation and termination intervals, but no constant-rate interval is observed. Stable monodisperse microlatexes are obtained with both types of initiators. For both AIBN and potassium persulfate, polystyrene molecular weight is proportional to initiator concentration [I]^–0.4 and particle radii decrease as [I]^–0.2. Polymerization initiation occurs in or at the microemulsion droplets, and polymer particles grow by recruiting monomer and surfactant from uninitiated swollen micelles.     

苯乙烯/二乙烯基苯在乙醇/乙二醇单甲醚中分散共聚合速率及粒子大小的研究

以乙醇 乙二醇单甲醚 (EOH EGME)为介质 ,羟丙基纤维素 (HPC)为稳定剂 ,偶氮二异丁腈 (AIBN)为引发剂进行了苯乙烯和二乙烯基苯的分散共聚合研究 .制得粒径在 6～ 10 μm范围内的单分散交联聚苯乙烯微球 (CPS) .探讨了不同介质配比 ,以及苯乙烯、二乙烯基苯、引发剂的浓度对微球大小、粒径分布、聚合速率及稳定性的影响 .当苯乙烯和AIBN浓度增加时 ,聚合速率和平均粒子尺寸增加 ,而粒子分布变宽 ,粒子数先增加 ,而后降低 .随着EOH EGME比例的增加 ,平均粒子尺寸增加 ,而分布指数降低 ,稳定剂增加 ,粒子尺寸降低和粒子数增加 ,但对聚合速率及粒子分布影响不太明显 .另外还探讨了单体和交联剂的后滴加法对微球大小、粒径分布的影响     

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.     

Stepwise dansyl grafting on the kaolinite interlayer surface

A block copolymer (PS-b-poly(l-Glu)) composed of polystyrene and poly(l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene. When dispersion polymerization of styrene was conducted at 70 °C in 80% dimethylformamide-water with 0.5 wt% PS-b-poly(l-Glu), spherical polystyrene particles with D_n = 0.72 μm and narrow size distribution were obtained. Whereas AIBN concentration did not have any effects on particle size, molecular weight of the polystyrene particles was strongly dependent on the initiator concentration. As concentration of the PS-b-poly(l-Glu) increased from 0.2 to 1.0 wt%, particle size decreased from D_n = 0.91 to 0.69 μm with keeping surface area occupied by one poly(l-glutamic acid) chain about S = 50 nm². On the other hand, an increase in initial concentration of styrene from 2 to 20 wt% caused an increase in particle size from D_n = 0.48 to 1.36 μm and a decrease in surface area per poly(l-glutamic acid) block from S = 91 to 45 nm². Colloidal stability of the polystyrene particles in aqueous solution was responsive to pH due to the surface-grafted poly(l-glutamic acid). For dispersion polymerization of styrene, the PS-b-poly(l-Glu) functions as both a stabilizer and a surface modifier.     

An experimental study on the kinetics and mechanisms of styrene polymerization in oil‐in‐water microemulsion initiated by oil‐soluble initiators

In order to clarify the kinetic role of oil‐soluble initiators in microemulsion polymerization, the oil‐in‐water (O/W) microemulsion polymerizations of styrene are carried out using four kinds of azo‐type oil‐soluble initiators with widely different water‐solubility. The results are compared with those observed when a water‐soluble initiator, potassium persulfate (KPS) is used. For all the oil‐soluble initiators used, the molecular weight of polymers and the average size of polymer particles do not change with the monomer conversion and the initial initiator concentration. The monomer conversion is expressed as a function of r_i^0.5t, where r_i is the rate of radical generation in the whole reaction system and t is the reaction time. These characteristics are quite the same as those observed when KPS is used as an initiator. When the polymerizations are carried out with the rate of radical generation in the whole reaction system fixed at the same value, the rates of polymerization are almost the same for all the oil‐soluble initiators employed, irrespective of their water‐solubility, but are significantly lower (ca. 1/3) than that with KPS. Then, the following conclusions are given: (1) The radicals generated not only in the aqueous phase, but also in the micelle and polymer particle phase are almost equally effective for the polymerization. However, (2) only a small portion (ca. 1/9) of the radicals generated in both phases participate in the polymerization. (3) Bimolecular termination of a growing radical in the polymer particle with an entering radical and with a pair of radicals generated in the polymer particles is negligible, and hence, the molecular weight of polymers is determined only by chain transfer to monomer.     

Effect of reaction parameters on the dispersion polymerization of 1‐vinyl‐2‐pyrrolidone

Nonporous hydrogel microspheres 0.1–1.3 μm in diameter were prepared by the dispersion copolymerization of 1‐vinyl‐2‐pyrrolidone and ethylene dimethacrylate as a crosslinking agent. The crosslinking was evidenced by solid state ¹³C NMR and elemental analysis. The effect of various parameters including selection of solvent (cyclohexane, butyl acetate), initiator (4,4′‐azobis(4‐cyanopentanoic acid), 2,2′‐azobisisobutyronitrile, dibenzoyl peroxide) and stabilizer on the properties of resulting microspheres has been studied. Dynamic light scattering and photographic examination were used for determination of the diameter and polydispersity of microspheres. Increasing concentration of steric stabilizer in the initial polymerization mixture decreased the particle size. The particle size depended on the molecular weight of polystyrene‐block‐hydrogenated polyisoprene stabilizer, but not on the number of PS and polybutadiene blocks in the styrene–butadiene block copolymer stabilizers. Dibenzoyl peroxide used as an initiator resulted in agglomeration of particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 653–663, 2000     

Effect of monomer water solubility on cationic microemulsion polymerization of three components (water,surfactant, and monomer)

Here, we present the oil/water (O/W) microemulsion polymerization in three‐component microemulsions of n‐butyl acrylate, ethyl acrylate, and methyl acrylate, monomers with similar chemical structures but different water solubilities using the cationic surfactant dodecyl trimethyl ammonium bromide. The effects of monomer water solubility, initiator type and initial monomer concentration on the polymerization kinetics were studied. Reaction rates were high with final conversions between 70 and 98% depending on the monomer and reaction conditions. The final latexes were bluish, with a particle size ranging between 20 and 50 nm and polymer with molar masses in the order of 10⁶ g mol^?1. Increasing monomer water solubility resulted in a slower reaction rate, larger particles and a lower number density of particles. A higher reaction rate, larger average particle size and higher particle number density were obtained by increasing the monomer concentration. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Nonaqueous polystyrene dispersions: Radical dispersion polymerization in the presence of ab block copolymers of polystyrene and poly(dimethyl siloxane)

Well defined AB block copolymers of polystyrene and poly(dimethyl siloxane) have been used as stabilizers in the dispersion polymerisation of styrene in n-alkanes. The dependences of the particle size and particle size distribution on the relative block lengths in the copolymer have been studied. From phase separation studies of polystyrene in n-alkanes, both in the presence and absence of AB block copolymer, the threshold molecular weight for precipitation has been determined. An understanding of the dispersion polymerization kinetics and the broad particle size distribution follows from the relatively high solubility of low molecular weight polystyrene in n-alkanes.     

Reversible Addition Fragmentation Chain Transfer Mediated Dispersion Polymerization of Styrene

Polystyrene microspheres have been synthesized by the reversible addition-fragmentation chain transfer (RAFT) mediated dispersion polymerization in an alcoholic media in the presence of poly(N-vinylpyrrolidone) as stabilizer and 2,2′-azobisisobutyronitrile as a conventional radical initiator. In order to obtain monodisperse polystyrene particles with controlled architecture, the post–addition of RAFT agent was employed to replace the weak point from the pre-addition of RAFT. The feature of preaddition and postaddition of RAFT agent was studied on the polymerization kinetics, particle size and its distribution and on the particle stability. The living polymerization behavior as well as the particle stability was observed only in the postaddition of RAFT. The effects of different concentration on the postaddition of RAFT agent were investigated in terms of molecular weight, molecular weight distribution, particle size and its distribution. The final polydispersity index (PDI) value, particle size and the stability of the dispersion system were found to be greatly influenced by the RAFT agent. This result showed that the postaddition of RAFT agent in the dispersion polymerization not only controls the molecular weight and PDI but also produces stable monodisperse polymer particles.     

Emulsion polymerization of styrene. I. Review of experimental data and digital simulation

Isothermal emulsion polymerization at 60°C of styrene in a batch reactor were studied by using sodium lauryl sulfate as surfactant and potassium persulfate as initiator source. The concentrations of surfactant and initiator were varied during the runs. The polymerization evolution was followed as samples were taken at regular intervals. These emulsion samples were analyzed for monomer conversion, rate of polymerization, as well as for the size and the size distribution of the particles. The molecular weight and molecular weight distribution were obtained by gel permeation chromatography. Our study showed that fresh nucleation takes place even at high conversion, causing a continuous shifting toward broadening of particle size distribution. Contrary to the theory of Smith and Ewart, which assumes a constant number of particles during interval II of the polymerization reaction, our digital simulation of the reaction presents better experimental results with a variable number of particles, and indicates that the Hui–Hamielec model for termination constant k_t as function of conversion is not applicable under our working conditions.     

Mechanism of graft copolymerization of styrene onto deproteinized natural rubber

High conversion and high grafting efficiency attained by graft copolymerization of styrene onto deproteinized natural rubber (DPNR) was investigated with respect to the molecular weight of grafted polystyrene. The graft copolymerization was performed with tert-butyl hydroperoxide/tetraethylenepentamine as an initiator after deproteinization of natural rubber with urea. Grafted polystyrene was isolated from the resulting graft copolymer by ozonolysis reaction. After the ozonolysis of the graft copolymer of DPNR and polystyrene (DPNR-g-PS), the molecular weight of grafted polystyrene was determined by size exclusion chromatography. Effects of initiator and monomer concentrations were investigated with respect to the molecular weight of the grafted polystyrene, which was found to depend on not only the number of active site generated on the rubber particle but also the feed of styrene. Deactivation and chain transfer of the active sites were attributed to effective amount of styrene used for the graft copolymerization.     

Modified structural model for predicting particle size in the microemulsion and emulsion polymerization of styrene under microwave irradiation

In this study, the microemulsion and emulsion polymerization of styrene at 70 degrees C in the presence of sodium dodecyl sulfate (SDS, surfactant) and potassium persulfate (KPS, initiator) was conducted under microwave radiation. Laser light scattering was used to characterize the resultant polystyrene latex particles formed at different polymerization stages. The influence of the initial emulsion composition, that is, the SDS, KPS, and styrene concentrations, on the final particle size led us to a simple modified structural model in which we considered the stabilization effects of both the surfactant and the ionic end groups generated from the initiator. This model extended the application of the previous Wu plot from microemulsion polymerization to emulsion polymerization. Using this model, we were not only able to control the particle size but were also able to predict the monomer concentration dependence of the number of the resultant latex particles and the effect of diluting the reaction mixture on the resultant particle size.     

Dispersion copolymerization of styrene and glycidyl methacrylate in polar solvents

Monodispersed copolymer microspheres consisting of styrene and glycidyl methacrylate have been prepared by dispersion polymerization. The effects of various polymerization parameters on the particle size and size distribution were systematically investigated. The initial solubility parameter of the system had a significant effect on the final particle size and size distribution. With decreasing initial solubility parameter, the particle size increased and the size distribution broadened. The particle size decreased with increasing stabilizer concentration, the amount of styrene in the monomer mixture, and decreasing initiator concentration. Received: 30 September 1998 Accepted in revised form: 10 December 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     

Anionic dispersion polymerization of styrene. I. Investigation of parameters for preparation of uniform micron-size polystyrene particles with narrow molecular weight distribution

Anionic dispersion polymerization in a hexane medium has been applied to the synthesis of monodisperse polystyrene particles in the size range of 1.41–6.16 μm, and having narrow molecular weight distributions M_w/M_n of 1.02–1.28. sec-Butyllithium was used as the initiator. Polystyrene-block-polybutadiene diblock copolymer containing 23% polystyrene block, (i.e., Stereon 730A) with a molecular weight of 147,000 g/mol and a polydispersity of 1.05, was found to be a suitable steric stabilizer for the preparation of micron-size polystyrene particles with narrow size distribution. Tetrahydrofuran (THF) was used as a promoter for obtaining narrow molecular weight distributions. However, this study revealed that the addition of small amounts of THF as promoter broadened the particle size distribution. High solids content polystyrene dispersions were also prepared without using any promoter by both batch and/or multi-addition monomer processes. © 1996 John Wiley & Sons, Inc.     

Size control of polystyrene nodules formed on silica particles in soap-free emulsion polymerization with amphoteric initiator

An amphoteric initiator of 2,2′-azobis[N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was applied to fabrication of raspberry-shaped composite particles in soap-free emulsion polymerization of styrene in the presence of silica particles surface-modified with 3-methacryoxypropyltrimethoxysilane. In the polymerizations, pH of the solution was ranged from 7.9 to 9.9 to alter dissociation degree of ionizable groups in the initiator. Raspberry-shaped particles were obtained in a pH range of 8.0 to 9.3 followed by a tendency in which average size of polystyrene (PSt) nodules adsorbed onto the silica particles decreased with pH. This tendency was similar to that of polymer particles formed in conventional soap-free emulsion polymerization in the absence of the silica particles. An increase in silica particle concentration led to a decrease in the final size in PSt nodules. The decrease was caused by the stabilization of polymer particles fixed to the silica surface against polymer particle aggregation in water phase.     

Microemulsion Polymerization: An Undergraduate Experiment in the Synthesis of Nanosized Polystyrene Particles

The synthesis of polystyrene nanoparticles through microemulsion polymerization is presented as an undergraduate advanced organic laboratory exercise. The resultant polymers molecular weight and particle size are studied as a function of monomer and initiator concentration. A comparison of cationic vs. anionic surfactants, and their effects on the polymer produced through microemulsion polymerization are also investigated. A direct relationship is observed between molecular weight and monomer concentration. A direct relationship is also found for the particle size of the latex produced. An inverse relationship is observed for molecular weight and particle size as the initiator concentration was raised. Comparison of molecular weight and latex size for cationic and anionic surfactants demonstrates that the anionic surfactant produces both a higher molecular weight and a larger latex size over the entire monomer and initiator concentration ranges.     

Synthesis of monodisperse anionic submicron polystyrene particles by stabilizer-free dispersion polymerization in alcoholic media

In this work, monodisperse polystyrene (PS) particles were synthesized in ethanol/water medium using sodium salt of styrene sulfonic acid and 2,2′-azobis(isobutyronitrile) as ionic comonomer and nonionic initiator, respectively. The polymerization was carried out at low agitation speed, and no stabilizer (or surfactant) was added to the polymerization medium. This polymerization system (stabilizer-free dispersion polymerization) was initiated as a homogeneous solution of monomer, comonomer, medium, and initiator. With the production of free radicals, polymerization developed into a heterogeneous system. The effect of various polymerization conditions on the size and size distribution of the obtained particles was evaluated. The experimental results showed that with an increase in ethanol content, the size of the particles increased while no significant change was observed in particle size distribution. Furthermore, with increasing ionic comonomer content, the size of the particles decreased and their size distribution became broader. Moreover, it was observed that addition of an electrolyte to the polymerization medium also increased the particles’ size and broadened their size distribution. It is noteworthy to point out that the coagulation occurred in higher amounts of electrolyte. Finally, it is concluded that the polar component of Hansen solubility parameter of the polymerization medium affects the particle size and particle size distribution greatly.