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.     

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     

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.     

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.     

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     

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.     

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     

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     

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 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.     

外墙涂料用新型核-壳丙烯酸酯乳液的合成研究

采用半连续种子乳液聚合技术、改进单体加料方式,制备出高弹性、高耐水性、高稳定性的核-壳丙烯酸乳液。讨论了软硬单体的比例、乳化剂、功能性单体、耐水性单体等对乳液胶膜吸水率及延伸率的影响,并对合成的乳液进行了表征。结果表明合成的核-壳乳液有更好的拉伸性能和耐水性。     

交联型丙烯酸酯核壳纳米复合涂料的制备

详细研究了核壳乳液的聚合机理、聚合工艺和软硬单体的比例、单体的滴加速度、交联单体甲基丙烯酸等对乳液性能的影响.在MMA/BA/DMMA/MAA聚合体系中,用半连续法制备出性能优越的核壳乳液,核壳乳液的性能在一定范围内随着交联单体甲基丙烯酸和DMMA的用量的增加提高,甲基丙烯酸最佳用量为单体的4%～6%,DMMA的最佳用量为2.0%.乳液中加入2%纳米二氧化硅对乳液进行改性得到纳米复合涂料.加入的纳米SiO2分散好,不产生团聚,并能显著改善复合涂料的力学性能和耐水性.     

Removal of Residual Monomers from Polymer Emulsions by Steam Stripping

Abstract

Removal rates of residual monomers from polymer emulsions by batch steam stripping were modeled. Model parameters were emulsion batch charge, steam sparge rate, emulsion solids content, and phase—equilibrium relationships for systems containing monomer, polymer, and water. Experiments in which steam was sparged into a column partially filled with emulsion were performed to verify the model. The model and data showed good agreement. Theory and experiments demonstrated that monomer desorption was dependent upon steam sparge rate and solids content, whereas temperatures had little effect on monomer removal.     

Submicron polymer powder in electrodeless radio frequency-induced plasma-initiated polymerization

Of the 30 monomers and monomer combinations investigated, 11 were polymerized into essentially all powder, 17 into predominantly a film, and two could not be polymerized in an electrodeless rf plasma-initiated gas phase polymerization. Efficient powder formation was mainly determined by the type of the monomer, the monomer partial pressure, the type of inert gas used, and the design of the polymerization chamber. The powders examined consisted of spherical particles of submicron size and were almost completely or partially soluble; and in the case of polystyrene, the powders possesses a very narrow particle-size distribution. In all cases, the soluble material was of a very low molecular weight. The best conversion to powder achieved was 18%.     

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     

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.     

In situ surfactant generation as a means of miniemulsification?

In situ emulsification, where the surfactant is synthesized spontaneously at the oil/water interface, has been put forth as a simpler method for the preparation of miniemulsions‐like systems. Miniemulsions are relatively stable oil‐(e.g., monomer)‐in‐water emulsions having droplet sizes anywhere in the range of 50–500 nm, and are typically created with high shear and stabilized by the combination a surfactant and a costabilizer. Using the in situ method of preparation, emulsion stability and droplet and particle sizes were monitored and compared with conventional emulsions and miniemulsions. Styrene emulsions prepared by the in situ method do not demonstrate the stability of a comparable miniemulsion. Upon polymerization, the final particle size generated from the in situ emulsion did not differ significantly from the comparable conventional emulsion polymerization; the reaction mechanism for in situ emulsions is more like conventional emulsion polymerization rather than miniemulsion polymerization. Similar results were found when the in situ method was applied to controlled free radical polymerizations (CFRP), which have been advanced as a potential application of the method. Molecular weight control was found to be achieved via diffusion of the CFRP agents through the aqueous phase owing to limited water solubilities. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fixation of cationic P (st‐BA‐AA‐GMA) emulsion on pigment particles in dyeing of cotton fabrics

Cationic copolymer emulsions of St, BA, AA, and GMA were successfully synthesized via semi‐continuous emulsion polymerization. The properties of synthesized cationic emulsions were characterized by monomer conversion and solid content, differential scanning calorimeter, particle size and distribution, zeta potential, and centrifugal stability. The film performance of the cationic emulsions formed on cotton fiber surface was observed by scanning electricity microscopy. The influence of cationic emulsions on the color data, K/S values and rubbing fastness of dyed cotton fabrics was also investigated. The results show that P (St‐BA‐AA‐GMA) emulsion had larger particle size and higher zeta potential than P (St‐BA‐AA) emulsion. When the films were formed at room temperature, P (St‐BA‐AA‐GMA) emulsion film had better performance than P (St‐BA‐AA) emulsion film. The addition of GMA monomers improved the film performance. P (St‐BA‐AA‐GMA) emulsion films formed at 120 °C after acetic acid solution treatment had the best water resistance. Dyed cotton fabrics pretreated with P (St‐BA‐AA‐GMA) emulsion had better pigment dyeing performance than those pretreated with P (St‐BA‐AA) emulsion. It demonstrates that the addition of GMA monomers further improved the effect of pigment dyeing for cotton fabrics with cationic emulsions as binders. With the increase of P (St‐BA‐AA‐GMA) concentration, the color performance of dye fabrics improved while the rubbing fastness decreased a little. But, the handle and fastness still meets the use standards for consumers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44987.     

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.