Toughened polystyrene composites by the concentrated emulsion pathway

Rubber–styrene solutions of various compositions and containing a suitable initiator have been polymerized starting from concentrated emulsions in which the above solutions constitute the dispersed phase and solutions of sodium dodecylsulfate in water the continuous phase. Latexes of rubber-modified polystyrene composites have been thus obtained. Solutions of rubber–styrene have been also polymerized by bulk polymerization for comparison purposes. The molecular weights have been determined from intrinsic viscosity measurements, and the mechanical properties of the composites have been studied via tensile testings. Because of the lower mobility of the high-molecular radicals in the concentrated emulsions, higher molecular weights have been obtained by the concentrated emulsion polymerization than by the bulk polymerization method. The tensile properties and toughness of the composites have been determined. While the two polymerization methods provide high, comparable toughness, the concentrated emulsion method generates latexes that can be easily processed in any desirable shape. © 1994 John Wiley & Sons, Inc.     

Semiinterpenetrating polymer network latexes via concentrated emulsion polymerization

Latexes of semiinterpenetrating polymer networks (SIPN) of polyurethane (PU) and poly(methyl methacrylate) (PMMA) were prepared via the concentrated emulsion polymerization. In this procedure, a partially cross-linked PU was first prepared in a low polarity solvent from the appropriate precursors. Subsequently, MMA and an initiator were introduced into the solution, and the solution was used as the dispersed phase of a concentrated emulsion in water. Finally, SIPN latexes were obtained via the polymerization of the concentrated emulsion. For comparison purposes, SIPN materials have been also prepared via bulk polymerization. The studies with differential scanning calorimetry and transmission electronic microscopy showed that partial interpenetration was achieved in the SIPN latexes. The tensile behavior and particle morphology of the SIPN materials were investigated by changing the proportion of PU, the molar ratio of NCO/OH, the theoretical cross-link density, and the concentration of the initiator. The SIPN latexes prepared possess a high toughness. © 1995 John Wiley & Sons, Inc.     

A new concentrated emulsion polymerization pathway

To ensure the stability of the concentrated emulsions that are employed as precursors for polymerization, a two-step concentrated emulsion polymerization pathway is described. In the first step, the monomer is partially polymerized by heating at 50°C until a certain conversion is reached. Subsequently, the partially polymerized monomer is used as the dispersed phase to prepare a concentrated emulsion in which water constitutes the continuous phase. The concentrated emulsion has a large volume fraction of the dispersed phase (0.74–0.99) and the appearance of a gel. Several typical monomers are employed to correlate the stability of the concentrated emulsion and the extent of partial polymerization of the dispersed phase. It was found that monomers, which cannot lead to stable concentrated emulsions, can generate them after partial polymerization. Subsequent polymerization of the concentrated emulsion leads to latex particles. Copolymers and polymer composites were also prepared by the two-step procedure. In the latter case, water was replaced with a solution of a hydrophilic monomer in water as the continuous phase. © 1992 John Wiley & Sons, Inc.     

Preparation of flexible polyhedral particles via concentrated emulsion templating polymerization

This paper presents recent efforts on the preparation of flexible polyhedral particles via concentrated emulsion templating polymerization in which the hydrophilic monomer (acrylamide) and hydrophobic monomer (butyl acrylate) are polymerized simultaneously in the continuous and dispersed phase, respectively. Such templating polymerization has been enhanced in our systems owing to the introduction of acrylamide monomer and their higher polymerization rate in continuous phase as compared with butyl acrylate in dispersed phase. Diffusion between the different phases was also inhibited. Furthermore, the stability of the concentrated emulsion and the molecular weight of the produced poly(butyl acrylate) were found to be significantly affected by the amount of redox initiator. The morphology of the particles could be controlled by varying the volume fraction of the dispersed phase and the polyhedral particles were achieved at higher volume fraction. Copyright © 2005 Society of Chemical Industry     

Rigid rod polyamides based on 2,2′,6,6′-tetrasubstituted biphenyls: Synthesis,characterization, and structures

Solutions of rubber in mixtures of styrene, methacrylate, and/or butyl methacrylate containing proper amounts of initiator have been polymerized to produce novel polymer composites—MBBS. In these composites, it is expected that tri-component and bi-component copolymers as well as homopolymers coexist. The tensile behavior of composites of various compositions was investigated. At certain weight ratio of monomers, excellent combinations of tensile strength, elongation, and toughness were obtained, which are better than those of most commercial engineering plastics. There is an optimum amount of butyl methacrylate, which is dependent upon the contents of the other monomers, for which the toughness acquires a maximum value. The concentrated emulsion polymerization was employed to prepare the MBBS composite latexes and the products were compared with those prepared via bulk polymerization. While the two polymerization methods provide high, comparable tensile properties and toughness, the concentrated emulsion method generates latexes which can be more easily processed in any desirable shape. © 1994 John Wiley & Sons, Inc.     

Preparation of latex carriers for controlled release by concentrated emulsion polymerization

Spherical latexes of submicron diameter containing a model hydrophobic herbicide, namely, 2-(2,4-dichlorophenoxy)-propionic acid, were prepared by the concentrated emulsion polymerization method. A mixture of styrene, herbicide, and initiator was dispersed into a small amount of water (6% by volume based on the entire emulsion) containing surfactant, at room temperature. The heating at 40°C of the foam like gel thus obtained led to the formation of latexes containing the herbicide. It was found that the model herbicide dispersed in the polymer latex was released to water over a period of serveral weeks and that the amount released was strongly dependent upon temperature and latex concentration in water.     

Self-compatibilization of polymer blends via concentrated emulsions

Summary A novel approach to the formation and compatibilization of polymeric blends is suggested, namely the self-compatibilization via concentrated emulsions. In this method, two concentrated emulsions are prepared from different monomers and subjected to partial polymerization; at least one concentrated emulsion contains also some di-vinyl-terminated macro-monomers. A blend is formed by mixing the partially polymerized latexes and subjecting the mixture to complete polymerization. Some AB networks, with the macro-monomers as chains A and the homo- and co-polymers generated from the other monomers as chains B, are formed, which ensure the self-compatibilization of the resulting blend. Blends of styrene-co-methyl methacrylate and poly (vinyl acetate) were prepared and investigated as a model system.     

Concentrated emulsions pathways to polymer blending

A new method of preparation of polymer composites involving the concentrated emulsion polymerization is described. In this kind of emulsion, the volume fraction of the dispersed phase is very large (as large as 0.99), while the volume fraction of the continuous phase is very small. In the present case, a monomer containing an appropriate initiator constitutes the dispersed phase and a dilute solution of surfactant in water constitutes the continuous phase. In a first step, two such concentrated emulsions containing different monomers were prepared and each of them was subjected to heating at 40°C for partial polymerization. Subsequently, the two partially polymerized systems were mechanically mixed, and the mixture was subjected to additional polymerization, drying, and sintering by heating at various temperatures for various time intervals. Partially polymerized concentrated emulsions of polystyrene, poly(buthyl methacrylate), poly(buthyl acrylate), and cross linked polystyrene, whose conversions were less than 5%, were employed. Conversions higher than 5% led to large increases in the viscosity of the concentrated emulsions, making their mixing difficult. N.m.r. spectroscopy was used to obtain information about the extent of copolymerization between the two monomers. Electron microscopy examination of the surfaces obtained by the fracture of the composites revealed that the latex particles aggregated with relatively slight changes in size and shape.     

Acrylonitrile-co-vinyl acetate with uniform composition via adiabatic, self-heating copolymerization in a concentrated emulsion

A copolymer of acrylonitrile and vinyl acetate was prepared via the room temperature-initiated, self-heating polymerization of a concentrated emulsion. A mixture of the monomers containing an oxidant was first dispersed in an aqueous solution of surfactants to generate a concentrated emulsion with a volume fraction of 0.8 of the dispersed phase. An aqueous solution of reductants was subsequently introduced into the concentrated emulsion to initiate polymerization together with the oxidant. Since the container was properly insulated, the system self-heated because of the energy released from polymerization, and achieved a high conversion in 30 min. The molecular weight distribution was determined using the gel permeation chromatography (GPC), and the composition of the product was determined via elemental analysis. The GPC traces indicated that the molecular weight was a function of time. The longer the polymerization time, the greater the molecular weight. During polymerization, the composition remained almost unchanged. These two results differ from those of the traditional radical polymerization.     

Compatibilization of polystyrene/poly(butyl methacrylate)/poly[(ethylene glycol) dimethacrylate] blends via concentrated emulsion polymerization

Two concentrated emulsions in water containing styrene and butyl methacrylate (BMA) as dispersed phases were prepared. Each of them contained a small amount of an amphiphilic macromonomer, poly[(ethylene glycol) dimethacrylate] (PEGD), in the continuous phase. The two concentrated emulsions were partially polymerized at 50 °C until conversions of about 22.5 % were reached. They were then mixed mechanically and the mixture was subjected to complete polymerization. During the latter polymerization, homopolymers of styrene and BMA and copolymers of the two were generated. The copolymers, particularly the crosslinked structures, which were formed through copolymerization of PEGD with styrene and BMA at the interface of the latexes, provided compatibilizers for the homopolymers. This blend of homopolymers, copolymers and crosslinked structures possessed excellent toughness and processability. The blends were characterized by their gel content, and by X‐ray photoelectron spectroscopy, rheometric testing, dynamic mechanical thermal analysis, transmission electron microscopy and impact strength measurements. Copyright © 2005 Society of Chemical Industry     

Amphiphilic particles with hydrophilic core/hydrophobic shell prepared via inverted emulsions

An aqueous solution of acrylamide, its crosslinker (N,N'-methylenebisacrylamide), and an oxidant (ammonium persulfate) was first used to prepare an inverted concentrated emulsion in hexane. Span 80, which is soluble in hexane, was employed as a dispersant. The polymerization of acrylamide in the concentrated emulsion was greatly accelerated by introducing an aqueous solution of a reductant (sodium metabisulfite); it started at room temperature and was completed in a few seconds, resulting in a pastelike product. The system thus obtained was subsequently diluted with hexane containing a hydrophobic monomer. When styrene was used as the hydrophobic monomer, cumene hydroperoxide (which, together with sodium metabisulfite present in the dispersed phase, constitutes the initiator for the polymerization of styrene) was dissolved in the continuous phase. When vinylidene chloride was employed as the hydrophobic monomer, no additional initiator besides sodium metabisulfite and ammonium persulfate already present in the hydrophilic phase had to be employed. The use of initiators which are present only in the hydrophilic phase, and hence also at the interface between this phase and hexane, ensured the polymerization of the hydrophobic monomer as shells that encapsulate the polyacrylamide latexes. Under the proper conditions, a porous outer shell can be generated, which makes the hydrophilic chains present inside accessible. Such hydrophilic core/hydrophobic porous shell particles can be dispersed in water, where they remain stable for a long time, and in hydrophobic liquids, where they remain stable for at least 24 h. For this reason, we call these kinds of particles amphiphilic particles. © 1996 John Wiley & Sons, Inc.     

High-rate polymerization of acrylonitrile and butyl acrylate based on a concentrated emulsion

A mixture of acrylonitrile and butyl acrylate was polymerized starting from a concentrated emulsion in water. The polymerization was initiated at room temperature by a redox system, consisting of reductants dissolved in the water phase and an oxidant dissolved in the dispersed phase. The initial polymerization was carried out adiabatically with self-heating until a temperature of about 70 °C was reached; this was followed by additional heating in a water bath at a higher temperature, up to a total polymerization time of 30 min. The conversion thus achieved was higher than that obtained via the adiabatic process alone. An optimum temperature during the additional heating was observed. Because of the gel effect, the molecular weight of the product increased with time and the reaction rate became affected by diffusion. The additional heating enhanced the mobility of the species in the system, thus ensuring a final product with a composition near that of the feed.     

Entry in emulsion polymerization using a mixture of sodium polystyrene sulfonate and sodium dodecyl sulfate as the surfactant

A mixture of sodium polystyrene sulfonate (NaPSS) and anionic surfactant, sodium dodecyl sulfate (SDS), was used as the emulsifier in the emulsion polymerization of styrene at 60 °C. The latexes prepared were stable, bearing the better resistance to the addition of electrolyte, and have the larger values in particle size and the higher polymerization rates than those counterparts prepared using SDS only. The NaPSS was prepared by a series of process: a concentrated cyclohexane solution of an anionically polymerized polystyrene (PS) was sulfonated with sulfuric acid at 80 °C, and then neutralized and purified through dialysis. The data of average polymer number per particle (n_p) were found useful in investigating the surfactant content effect on the entry of radicals into particles, where the latex particle size plays an important role.     

Room temperature-initiated and self-heating copolymerization of acrylonitrile with vinyl acetate

A novel polymerization method [Ruckenstein and Li, Polymer Bull., 37, 43 (1996)]—room temperature-initiated, self-heating polymerization—was applied to both bulk and concentrated emulsion copolymerization of acrylonitrile (AN) with vinyl acetate (VAc). A redox system was employed as an initiator, with the oxidant dissolved in the monomers and the reductants (two reductants were employed) in the aqueous phase. In the bulk polymerization, the oxidant (cumene hydroperoxide) was dissolved in the mixture of monomers, and the two reductants (sodium metabisulfite and ferrous sulfate) were introduced as an aqueous solution. In the concentrated emulsion polymerization, a mixture of the monomers containing dissolved oxidant was first used as the dispersed phase of a concentrated emulsion in water, and the aqueous solution of reductants was subsequently added to the concentrated emulsion. In both cases, the polymerization started at room temperature, just after the reductants were introduced. Because the reactor was insulated, the heat generated by the reaction was mostly used to accelerate the polymerization, which reached a high conversion in 30 min. The effects of various parameters on the polymerization were investigated. Optimum values were found for the volume fraction of the dispersed phase, for the wt ratios of the two reductants and of the oxidant to reductants, and for the surfactant and reductant concentrations. One concludes that the concentrated emulsion polymerization method is particularly suitable for the room temperature-initiated, self-heating polymerization. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 999–1011, 1998     

Preparation of high molecular weight monodisperse polystyrene latexes by concentrated emulsion polymerization

The preparation of high molecular weight monodisperse polystyrene (PS) latexes by the concentrated emulsion polymerization is investigated. The PS latexes thus obtained have diameters in the range of 0.1–0.3 μm. The average size and the dispersity of the latexes are dependent on the concentration of surfactant (SDS), the monomer volume fraction, and the amount of monpolymerizable additive (decane). The ionic strength does not seem to affect the size but affect the dispersity of the latexes. Under proper conditions, monodisperse particles can be prepared with a quite small standard deviation. © 1993 John Wiley & Sons, Inc.     

Room temperature initiated and self-heating polymerization via concentrated emulsions: application to acrylonitrile based polymers

Summary A novel concentrated emulsion polymerization procedure, in which the polymerization is initiated at room temperature and the heat generated by the reaction accelerates the process, is proposed. The polymerization of acrylonitrile (AN) and its copolymerization with vinylidene chloride (VDC) are used as examples. AN (alone or with a comonomer) containing an oxidant was first dispersed in water to generate a concentrated emulsion. The polymerization of the monomers was initiated at room temperature by introducing an aqueous solution containing a mixture of reductants (ferrous sulfate and sodium metabisulfite) into the concentrated emulsion. The heat generated in the system increased its temperature and accelerated the polymerization. The polymerization was completed in one hour with conversions higher than 90%. The small volume of the continuous phase in a concentrated emulsion constitutes an advantage of the procedure, since only a small amount of the produced heat is used for its heating. In addition, because the reductant, which is present in the water phase, together with the oxidant, which is present in the oil phase, constitute the initiator, the large oil-water interfacial area of the concentrated emulsion constitutes an additional advantage.     

Polystyrene latex particles bearing primary amine groups via soap‐free emulsion polymerization

Polystyrene latexes were prepared in the presence of an amino‐containing functional comonomer, N‐(3‐aminopropyl)methacrylamide hydrochloride (APMH), via soap‐free batch emulsion polymerization initiated by the cationic initiator 2,2′‐azobis(2‐amidinopropane) dihydrochloride. These latexes were characterized by studying the influence of the ionic comonomers on the polymerization kinetics, particle size, surface charge density and colloidal properties. The synthesized latexes were monodisperse with a final size between 100 and 600 nm depending on the APMH concentration. The initial polymerization rate and the particle number increased in accordance with the Smith–Ewart theory for soap‐free styrene emulsion polymerization with a hydrophilic functional comonomer. The final functionalization rate of the particles has been particularly studied with the intention of fitting the prepared latexes to be used in the immobilization of biological molecules for biological sample preparation and diagnostic applications. © 2020 Society of Chemical Industry     

Phase distribution and separation in poly(2-acetoxyethyl methacrylate)/polystyrene latex interpenetrating polymer networks

A series of latex interpenetrating polymer networks (LIPNs) were prepared via two-stage soap-free emulsion polymerization of styrene on cross-linked poly(2-acetoxyethyl methacrylate) (PAEMA) seed latexes, using potassium persulfate as initiator. It was found that a compositional gradient was present when PAEMA seeds cross-linked either lightly or highly were used. The polystyrene (PS) phase is localized near the particle center in the former case, while it is segregated near the surface in the latter case. A uniform distribution of PS phase in LIPN was formed, if moderately cross-linked PAEMA seed was used. All the LIPNs appeared to be microphase-separated, and increase of cross-linking degree in seed latexes decreased the PS-rich domain size. The results were explained by the particle growth mechanism that involved the formation of surface-active oligomeric radicals in water phase, adsorption of the radicals onto monomer-swollen particle/water interface, and chain propagation in the interface with subsequent phase migration dominated by the competitive effects of thermodynamics and kinetics.     

Polymerization of acrylamide in single-phase in-verse dispersion systems at high volume fractions of dispersed phase

The preparation of single-phase inverse microemulsions of toluene/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water/acrylamide (AAm) is described and their properties prior to polymerization (macro and microviscosity as a function of volume fraction Φ_aw of the dispersed aqueous (water + acrylamide) phase, of the [to-luene]/[AOT] molar ratio and of the acrylamide/water mass ratio) were studied. The polymerization of acrylamide in dispersion systems was initiated by the oilsoluble initiator dibenzoyl peroxide at 60°C. The polymerization rate of acrylamide for a given [toluene]/[AOT] molar ratio and AAm/water mass ratio monotonically decreases beyond a Φ_aw value of 20%. The polymer particle size in polymerized systems as well as the molecular mass of polymer in the polymer particles increase on increasing the acrylamide concentration in the aqueous phase and/or the Φ_aw values of the dispersion system. On increasing the surfactant AOT concentration both polymer particle size and polymer molecular mass decrease for a given set of other relevant parameters of the dispersion system (i.e. [toluene]/[AOT] and AAm/water ratios). The polymerized inverse dispersion system can be converted to an oil-in-water dispersion by addition of water.     

Preparation and Characterization of magnetic latexes using Styrene monomer

Summary Preparation of magnetic latexes using styrene as monomer was carried out via miniemulsion polymerization. Magnetite (Fe₃O₄), with an average size of 12nm was used as magnetic particles. An organic phase is prepared dispersing the magnetite in styrene where bis(2-ethyl, hexyl) sulphosuccinate (AOT) is used as dispersant of the particles. The dispersion is miniemulsified in water using Cethyltrimethylammonium bromide (CTAB) as second emulsifier forming a stable emulsion. The miniemulsion polymerization was carried out at 60° C and was initiated with 2,2 Azo-bis-iso-butyronitrile (AIBN). The latexes obtained were characterized by X-ray diffraction, Magnetometry and Transmission Electronic Microscopy.