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.     

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.     

The concentrated emulsion approach to toughened polymer composites: A review

A series of tough polymers were prepared by combining flexible with rigid chains, using the method of concentrated emulsion polymerization. The tough materials obtained can be classified into four types: [a] those prepared via the polymerization of a monomer containing a dissolved elastomer, starting from its concentrated emulsion in water; [b] those prepared via heterogeneous (interfacial) crosslinking of two partially polymerized concentrated emulsion in water containing incipient latexes; [c] those prepared as semi-interpenetrating or AB network latexes, starting from a concentrated emulsion in water and [d] those prepared by mixing two partially polymerized concentrated emulsions and completing the polymerization. A concentrated emulsion differs from the conventional emulsion in that the volume fraction of the dispersed phase is higher than that of the most compact arrangement of monosize spheres (0.74) and can be as high as 0.99. The cells of a highly concentrated emulsion are no longer spherical, but polyhedral in shape, compactly packed and separated by thin films of continuous phase. As a result of such structure, a high polymerization rate and a high molecular weight can be achieved, the size (in the colloidal range) of the flexible phase can be controlled and the latter phase can be uniformly dispersed in the rigid one. Consequently, the concentrated emulsion method constitutes a suitable pathway to toughened composites. Owing to the compact packing of cells, the concentrated emulsion polymerization method is particularly suitable for cases in which reactions occur at the cell interface. For the materials of type [d], these reactions generate quasi-block copolymers, which compatibilize (via “auto-compatibilization”) the components of blends.     

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     

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.     

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.     

Preparation of a water-permselective composite membrane by the concentrated emulsion method: Its swelling and permselectivity characteristics

A water-permselective composite membrane was prepared by the concentrated emulsion polymerization method. A large volume fraction of an aqueous sodium acrylate solution was dispersed in a small amount of divinyl benzene. Each of the two phases contained a suitable initiator and the continuous phase contained an appropriate surfactant. The concentrated emulsion thus obtained has the appearance and behavior of a gel. The gel was sandwiched between tow glass plates and subjected to polymerization via heating at 45°C for 24 h. The resulting membrane was dried and further employed in several kinds of experiments. The swelling of the membrane in water depends on the pH of water and can be as large as 86. At low pH values, the swelling was very small. The permeation rate of a water-ethanol mixture was in the range of 96–560 g/m² h and decreased with increasing alcohol concentration and increasing poly(sodium acrylate) fraction in the membrane. The permselectivity varied between 32 and 235, increasing with increasing poly(sodium acrylate) fraction in the membrane and with increasing or decreasing ethanol concentration (depending upon the composition of the membrane). The activation energy for pervaporation varied between 6.58 and 8.14 kcal/mol, depending upon the composition of the feed. The permselectivity decreased slightly with increasing temperature.     

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     

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     

Facile fabrication of polystyrene/halloysite nanotube microspheres with core–shell structure via Pickering suspension polymerization

In this article, a facile method for fabrication of core–shell nanocomposite microspheres with polystyrene (PS) as the core and halloysite nanotubes (HNTs) as the shell via Pickering suspension polymerization was introduced. Stable Pickering emulsions of styrene in water were prepared using HNTs without any modification as a particulate emulsifier. The size of the Pickering emulsions varied from 195.7 to 26.7?μm with the water phase volume fraction increasing from 33.3 to 90.9?%. The resulting Pickering emulsions with the water phase volume fraction of above 66.7?% were easily polymerized in situ at 70?°C without stirring. HNTs played an important role during polymerization and effectively acted as building blocks for creating organic–inorganic nanocomposite microspheres after polymerization. The sizes of PS/HNTs microspheres were roughly in accord with that of the corresponding emulsion droplets before polymerization. The effect of the water phase volume fraction on the stability of Pickering emulsions and the morphologies of nanocomposite microspheres was investigated by optical microscopy, confocal laser scanning microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and so on.     

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.     

Influence of microstructure on dynamic mechanical behaviour of polymeric composites with complex inclusions

The dynamic mechanical properties of polymeric composites composed of crosslinked poly(n-butyl methacrylate) continuous-phase and crosslinked polystyrene dispersed phase with poly(n-butyl methacrylate) occlusion have been examined. The composite samples were prepared by mixing and swelling of the crosslinked polystyrene particles obtained by emulsifier-free emulsion polymerization, with n-butyl methacrylate and crosslinker, then photopolymerizing at the desired temperature. The composite microstructure was varied by either changing the crosslink density of polystyrene, and temperature of swelling and polymerization, or using different sizes and contents of polystyrene particles. The tan δ peak positions of composite samples are found to be dependent on morphological characteristics as well as the properties of the dispersed phase while the peak height seems to be dependent on the effective volume of dispersed phase composed of polystyrene and poly(n-butyl methacrylate) occlusions. Special attention has been paid to the comparison among composite, homonetworks, and bulk IPN samples that are expected to have the identical structure with the complex dispersed phase of the composite samples. © 1993 John Wiley & Sons, Inc.     

Effect of a surface active pyrrole on the conductivity of polypyrrole composites

A surface active pyrrole, which has a long hydrophobic chain attached to the 3 position of the pyrrole ring, is used to modify the surface properties of the pores of a porous, crosslinked polystyrene. The latter is prepared starting from a concentrated emulsion (an emulsion with a large volume fraction of the dispersed phase, here 0.81) of water dispersed in a continuous medium composed of styrene, divinyl benzene, a suitable surfactant, an initiator, and the surface active pyrrole. This modified crosslinked porous medium is emplyed as the host for a polypyrrole composite that is prepared first by imbibing the host with a solution of pyrrole and subsequently with an oxidant solution. The latter plays the role of catalyst for polymerization as well as the role of dopant. The presence of the head groups of 3-alkyl pyrrole molecules on the surface of the pores of the host polymer increases the affinity of the surface for pyrrole. The improved wetting thus achieved for the pyrrole solution ensures a higher connectivity among the pyrrole films present on the internal surface of the host polymer and increases the conductivity of the polypyrrole composites by a factor of 2 to 14, depending upon the solvents employed for pyrrole and oxidant.     

Self-Compatibilization of poly(butyl methacrylate)/acrylonitrile-co-styrene blends via concentrated emulsion polymerization

Two concentrated emulsions in water were prepared: one from weakly polymerized butyl methacrylate (BMA) and the other one from a weakly polymerized mixture of acrylonitrile (AN) and styrene (St). Each of the concentrated emulsions also contained a small amount of a vinyl-terminated macromonomer (VTM). After the concentrated emulsions were partially polymerized, they were mixed and subjected to complete polymerization. This generated a blend of poly(butyl methacrylate) (PBMA), binary copolymer AN-co-ST (AN—St), and networks containing chains of VTM and those formed from different monomers. The networks constitute compatibilizers between the PBMA and AN—St. Such a preparation method, in which the components and compatibilizer are generated simultaneously, was called self-compatibilization. The blend possesses excellent tensile properties and toughness compared with the ternary copolymer AN—St—BMA and with the solution blends of PBMA/AN—St. The generation of the compatibilizers and the compatibilization mechanism were investigated via kinetic studies. The effects of the VTM, polymerization conditions, and the weight ratio of AN/St were also examined. © 1996 John Wiley & Sons, Inc.     

超浓乳液稳定性的研究

本文简单介绍了超浓乳液的基本概念及用途,并以苯乙烯为分散相,水为连续相,对超浓乳液稳定性进行了详细的研究。研究结果表明,超浓乳液的稳定性与表面活性剂的种类我党有度,分散相性质,分散相的体积分数,电解质浓度,连续相粘度等因素有关。     

核壳型复合聚合物乳液合成工艺研究

以乳化单体加料的种子聚合技术,合成了聚丙烯酸乙酯/聚苯乙烯核壳型复合聚合物乳液.确定了种子聚合过程中乳化剂补加量与聚合单体量之间的定量关系和合理的单体加料速率.该体系所得聚台物乳液的乳胶粒是“翻转型”的核壳结构.     

Oil-in-oil emulsions: a unique tool for the formation of polymer nanoparticles

Polymer latex particles are nanofunctional materials with widespread applications including electronics, pharmaceuticals, photonics, cosmetics, and coatings. These materials are typically prepared using waterborne heterogeneous systems such as emulsion, miniemulsion, and suspension polymerization. However, all of these processes are limited to water-stable catalysts and monomers mainly polymerizable via radical polymerization. In this Account, we describe a method to overcome this limitation: nonaqueous emulsions can serve as a versatile tool for the synthesis of new types of polymer nanoparticles. To form these emulsions, we first needed to find two nonmiscible nonpolar/polar aprotic organic solvents. We used solvent mixtures of either DMF or acetonitrile in alkanes and carefully designed amphiphilic block and statistical copolymers, such as polyisoprene- b-poly(methyl methacrylate) (PI- b-PMMA), as additives to stabilize these emulsions. Unlike aqueous emulsions, these new emulsion systems allowed the use of water-sensitive monomers and catalysts. Although polyaddition and polycondensation reactions usually lead to a large number of side products and only to oligomers in the aqueous phase, these new conditions resulted in high-molecular-weight, defect-free polymers. Furthermore, conducting nanoparticles were produced by the iron(III)-induced synthesis of poly(ethylenedioxythiophene) (PEDOT) in an emulsion of acetonitrile in cyclohexane. Because metallocenes are sensitive to nitrile and carbonyl groups, the acetonitrile and DMF emulsions were not suitable for carrying out metallocene-catalyzed olefin polymerization. Instead, we developed a second system, which consists of alkanes dispersed in perfluoroalkanes. In this case, we designed a new amphipolar polymeric emulsifier with fluorous and aliphatic side chains to stabilize the emulsions. Such heterogeneous mixtures facilitated the catalytic polymerization of ethylene or propylene to give spherical nanoparticles of high molecular weight polyolefins. These nonaqueous systems also allow for the combination of different polymerization techniques to obtain complex architectures such as core-shell structures. Previously, such structures primarily used vinylic monomers, which greatly limited the number of polymer combinations. We have demonstrated how nonaqueous emulsions allow the use of a broad variety of hydrolyzable monomers and sensitive catalysts to yield polyester, polyurethane, polyamide, conducting polymers, and polyolefin latex particles in one step under ambient reaction conditions. This nonpolar emulsion strategy dramatically increases the chemical palette of polymers that can form nanoparticles via emulsion polymerization.     

Templating synthesis of non‐spherical polymer particles and their effect on the fracture toughness of an epoxy‐amine network

Flexible non‐spherical polymer particles were successfully produced via concentrated emulsion polymerization. LUDOX TM‐50 (colloidal silica, 50 wt% suspension in water) was introduced into the continuous phase to strengthen the template and inhibit monomer diffusion between the continuous and dispersed phases. The extent of non‐spherical shape was identified by the roundness value. Transmission electron micrographs showed that the higher the volume fraction of the dispersed phase became, the more non‐spherical were the poly(butyl acrylate) (PBA) particles. As an application, the effect of the non‐spherical particles on the fracture toughness of a modified epoxy‐amine network was studied. Scanning electron micrographs showed that the introduction of the non‐spherical PBA particles improved efficiently the impact strength of the cured epoxy resin. Copyright © 2006 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 and characterization of polyacrylate/polymerized rosin composite emulsions by seeded semicontinuous emulsion polymerization

Polyacrylate/polymerized rosin composite emulsions were prepared by seeded semicontinuous emulsion polymerization of acrylate monomers in which polymerized rosin was dissolved. The effects of polymerized rosin content on the polymerization stability, monomer conversion, polymer structure, and adhesive properties were studied. Polyacrylate/polymerized rosin composites were characterized by gel permeation chromatograph (GPC), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogracvimetry (TG). The results showed that with an increase of polymerized rosin content from 0 to 6 wt %, gel fraction and sol molecular weight decreased obviously but monomer conversion was basically unchanged. In contrast, with a further increase of polymerized rosin content, the decreasing rates of gel fraction, and sol molecular weight were slowed down. Meanwhile, monomer conversion decreased remarkably. Moreover, interface failure changed into cohesive failure after the addition of polymerized rosin, and the peel adhesion and shear resistance of composite latex films declined with the increase of polymerized rosin content. Thermal analysis showed that polymerized rosin and polyacrylate were compatible and the composite latex films had good thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011