Reactive surfactants in heterophase polymerization for high performance polymers

 A variety of nonionic reactive surfactants have been prepared from block copolymer precursors. These precursors are formed from a commercially available polyoxyethylene glycol monomethylether as the hydrophilic sequence of the surfactant; this product is used as initiator of ring opening anionic polymerization of butylene oxide. Finally the reactive surfactants are obtained after proper functionalization of the precursor. The reactive surfactants are an inisurf with an asymmetric azo compound, a transurf with a thiol group, and a few surfmers with acrylic, methacrylic, styrenic and α-methyl styrenic reactive groups. These compounds have been engaged in styrene emulsion or dispersion polymerization. Several of them have been found to be useful for preparing stable latices. Received: 22 July 1997 Accepted: 11 December 1997     

Thermally cleavable surfactants based on furan-maleimide Diels-Alder adducts

Two new surfactant molecules are reported that contain thermally labile Diels-Alder adducts connecting the hydrophilic and hydrophobic sections of each molecule. The two surfactants possess identical hydrophobic dodecyl tail segments but have phenol and carboxylic acid hydrophilic headgroups, respectively. Deprotonation with potassium hydroxide affords the formation of water-soluble surfactants. Room temperature aqueous solutions of both surfactants exhibit classical surface-active agent behavior similar to common analagous alkylaryl surfactant molecules. Critical micelle concentrations have been determined for each surfactant through dynamic surface tension and dye solubilization techniques. Small-angle neutron scattering measurements of the aqueous surfactant solutions indicate the presence of spherical micelles with radii of 16.5 angstroms for the carboxylate and 18.8 angstroms for the phenolate. When these surfactants are exposed to elevated temperatures (>50 degrees C), the retro Diels-Alder reaction occurs, yielding hydrophilic and hydrophobic fragments. Aqueous solutions of each surfactant subsequently exhibit a loss of all surface-active behavior and the micellar aggregates are no longer detectable.     

EFFECTS OF ω-ACRYLOYL POLY (ETHYLENE OXIDE) MACROMONOMER ON EMULSIFIER-FREE EMULSI0N COPOLYMERIZATION OF METHYL METHACRYLATE AND n-BUTYL ACRYLATE*

Well-defined nonionic hydrophilic ω-acryloyl poly(ethylene oxide) macro-monomer (PEO-A) has been prepared by living anionic polymerization of ethylene oxidewith diphenyl methyl potassium as the initiator and acryloyl chloride as the reaction termi-nating agent. The polymer was characterized by FTIR and SEC. The emulsifier-free emul-sion polymerization of methyl methacrylate (MMA) and n-butyl acrylate (BA) containingvarious concentrations of PEO-A was studied. In all cases stable emulsion coplymerizationsof MMA and BA were obtained. The stabilizing effect was found to be dependent on themolecular weight and the feed amount of the macromonomer.     

Surfactant characteristics of polystyrene/poly(ethylene oxide) macromonomers in aqueous solution and on polystyrene latex particles: Two‐step emulsion polymerizations

Macromonomers were synthesized by anionic “living” polymerization. They comprised a poly(ethylene oxide) hydrophilic block and a hydrophobic block or sequence terminated with an unsaturation. The surface activity properties of these materials (critical micelle concentration and parking area) were determined, and the values were compared and discussed in terms of the molecular structure of these new surfactants. Some of the macromonomers were employed as emulsifiers in two‐step emulsion polymerizations. The data obtained were discussed while taking into account the different chemical structures of the macromonomers and the efficiency of these species as emulsifiers in the polymerization recipes. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2767–2776, 2001     

Crosslinking‐induced morphology change of latex nanoparticles: A study of RAFT‐mediated polymerization in aqueous dispersed media using amphiphilic double‐brush copolymers as reactive surfactants

Amphiphilic double‐brush copolymers (DBCs) with each graft site quantitatively carrying both a hydrophilic poly(ethylene oxide) (PEO) graft and a hydrophobic polystyrene (PSt) graft are synthesized by sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization and ring‐opening metathesis polymerization (ROMP). These DBCs are used as both surfactants and polyfunctional RAFT agents in the radical polymerization of St in aqueous dispersed media. Miniemulsions with narrowly dispersed St‐based nanodroplets are readily obtained after ultrasonication of the reaction mixtures. Without the presence of crosslinker, chain‐extension polymerization of St from the DBCs yields well‐defined polymeric latexes with narrow size distributions. However, with the presence of divinylbenzene (DVB) as the crosslinker, vesicular polymeric nanoparticles are formed as the major product. Such crosslinking‐induced change in morphology of the resulting latex nanomaterials may be ascribed to the increase of interfacial curvature in the heterophase systems during crosslinking polymerization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3250–3259     

Synthesis and dilute aqueous solution properties of ester functionalized cationic gemini surfactants having different ethylene oxide units as spacer

New series of ester functionalized quaternary ammonium gemini surfactants having different ethylene oxide units as spacer have been synthesized and investigated for their aggregation behavior and thermodynamic properties of micellization by surface tension, conductivity, and fluorescence methods. The critical micelle concentration (cmc) of these gemini surfactants increases with the increase in the length of polar hydrophilic ethylene oxide spacer. The micellization process has been found to be entropy-driven and dependent on both the tendency of the hydrophobic group of the surfactants to transfer from aqueous environment to interior of micelle as well as the rearrangement of flexible ester-linked ethylene oxide units (hydrophilic spacer) into aqueous phase. The polar ester functional groups and pairs of nonbonding electrons on oxygen atom of ethylene oxide spacer form hydrogen bonding with water molecules enhancing their solubility in aqueous system.     

Removal of aromatic compounds in the aqueous solution via micellar enhanced ultrafiltration: Part 1. Behavior of nonionic surfactants

The effects of nonionic surfactants having different hydrophilicity and membranes having different hydrophobicity and molecular weight cut-off on the performance of micellar-enhanced ultrafiltration (MEUF) process were examined. A homologous series of polyethyleneglycol (PEG) alkylether having different numbers of methylene groups and ethylene oxide groups was used for nonionic surfactants. Polysulfone membranes and cellulose acetate membranes having different molecular cut-off were used for hydrophobic membranes and hydrophilic membranes, respectively. The concentration of surfactant added to pure water was fixed at the value of 100 times of critical micelle concentration (CMC). The flux through polysulfone membranes decreased remarkably due to adsorption mainly caused by hydrophobic interactions between surfactant and membrane material. The decline of solution flux for cellulose acetate membranes was not as serious as that for polysulfone membranes because of hydrophilic properties of cellulose acetate membranes. The surfactant rejections for the cellulose acetate membranes increased with decreasing membrane pore size and with increasing the hydrophobicity of surfactant. On the other hand the surfactant rejections for polysulfone membranes showed totally different rejection trends with those for cellulose acetate membranes. The surfactant rejections for the polysulfone membranes depend on the strength of hydrophobic interactions between surfactant and membrane material and molecular weight of surfactants.     

Characterization of the micellar ring opening metathesis polymerization in water of a norbornene derivative initiated by Hoveyda‐Grubbs' catalyst

Solubilization of the hydrophobic Hoveyda‐Grubbs' catalyst in micellar aqueous phase has been achieved using dodecyl and cetyl ammonium chloride as surfactants. The domain of solubilization has been estimated before carrying out ring‐opening metathesis polymerization in these micellar solutions with a hydrophilic monomer. Kinetics orders have been determined relative to monomer, initiator, and surfactant. A good control of the molecular weight has been obtained for ratios [micelles]/[initiator] over 1. The better control of the polymerization obtained in micellar solution has been explained by a difference of reactivity leading to a more efficient initiation step in the presence of the micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2833–2844, 2008     

Interaction of amphiphilic block copolymer micelles with surfactants

An out line and summary of literature studies on interactions between different types of amphiphilic copolymer micelles with surfactants has been given. This field of research is still emerging and it is difficult presently to make generalisations on the effects of surfactants on the copolymer association. The effects are found to be varied depending upon the nature and type of hydrophobic (hp) core and molecular architecture of the copolymers and the hydrocarbon chain length and head group of surfactants. The information available on limited studies shows that both anionic and cationic surfactants (in micellar or molecular form) equally interact strongly with the associated and unassociated forms of copolymers. The beginning of the interaction is typically displayed as critical aggregation concentration (CAC), which lies always below the critical micelle concentration of the respective surfactant. The surfactants first bind to the hydrophobic core of the copolymer micelles followed by their interaction with the hydrophilic (hl) corona parts. The extent of binding highly depends upon the nature, hydropobicity of the copolymer molecules, length of the hydrocarbon tail and nature of the head group of the surfactant. The micellization of poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–poly(ethylene oxide) was found to be suppressed by the added surfactants and at higher surfactant concentrations, the block copolymer micelles get completely demicellized. This effect was manifested itself in the melting of liquid crystalline phases in the high copolymer concentrations. However, no such destabilization was found for the micelles of polystyrene (PS)–poly(ethylene oxide) copolymers in water. On the contrary, the presence of micellar bound surfactant associates resulted in to large super micellar aggregates through induced intra micellar interactions. But with the change in the hydrophobic part from polystyrene to poly(butadiene) (PB) in the copolymer, the added surfactants not only reduced the micellar size but also transformed cylindrical micelles to spherical ones. The mixtures in general exhibited synergistic effects. So varied association responses were noted in the mixed solutions of surfactants and copolymers.     

The Effects of Salts and Ionic Surfactants on the Micellar Structure of Tri‐Block Copolymer PEO‐PPO‐PEO in Aqueous Solution

The micelles of two poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) block copolymers, P123 and F127 (same mol wt of PPO but different % PEO) in aqueous solution in the absence and presence of salts as well as ionic surfactants were mainly examined by dynamic light scattering (DLS). The study is further supported by cloud point and viscosity measurements. The change in cloud point (CP), as well as the size of micelles in aqueous solution in presence of salts obeys the Hofmeister lyotropic series. Addition of both cationic cetylpyridinium chloride (CPC) and anionic sodium dodecylsulfate (SDS) surfactants in the aqueous solution of P123 show initial decrease of micellar size from 20 nm to nearly 7 nm and then increasing with a double relaxation mode, further in the presence of NaCl this double relaxation mode vanishes. The effect of surfactant on F127, which has much bigger hydrophilic part is different than P123 and have no double relaxation. The relaxation time distributions is obtained using the Laplace inversion routine REPES. Two relaxation modes for P123 are explained on the bases of Pluronic rich mixed micelles containing ionic surfactants and the other smaller, predominantly surfactant rich micelles domains.     

Electrochemical masking for removal of the titanium matrix effect in DPASV determination of thallium

The possibilities for eliminating the matrix effect caused by large concentrations of titanium in an EDTA-based electrolyte have been examined. In these solutions titanium gives a DPASV peak, the height of which decreases with increase in preconcentration time. This effect depends on the pH and is probably caused by impurities in the EDTA. Complete damping of the titanium peak by means of this effect is not possible. The influence of the following surfactants on the DPASV peak for titanium in 0.2M EDTA at pH 4.5 was investigated: polyoxyethylated alkylphenols having an average of 3 and 9.5 ethylene oxide sub-units; polyoxyethylene alcohols having an average of 5 and 20 ethylene oxide sub-units; polyoxyethylene (glycerol mono-oleate) ether having an average of 20 ethylene oxide sub-units; polyoxyethylene (sorbitol mono-oleate) ether having an average of 20 ethylene oxide sub-units; poly(ethylene oxide) having M.W. 5.0 x 10(6); poly(ethylene oxide)poly(propylene oxide) block copolymer having M.W. 1.625 x 10(4); N,N,N,N',N',N'-hexamethylhexamethylenediammonium bromide (HMB); benzyl(diisobutylphenoxyethoxy) dimethylammonium chloride; hexadecyltrimethylammonium bromide; tetrabutylammonium chloride (TBAC); hexadecyldimethylbenzylammonium chloride, hexadecyltributylphosphonium bromide; tetraphenylphosphonium bromide; sodium dodecylsulphate; sodium stearate; sodium dodecylbenzenesulphonate; sodium octadecyloxyethylene ether sulphate; sodium octadecyloxyethylene ether malonate (Malester). Except for TBAC and HMB all the surfactants investigated decreased the titanium peak, although to different degrees. Generally the effect increased in the sequence cationic surfactants < non-ionic surfactants < anionic surfactants. The more hydrophobic non-ionic surfactants decreased the titanium peak more strongly than did the less hydrophobic ones. Malester was found the best of the investigated surfactants for this purpose. Sodium dodecylbenzenesulphonate also gave good results, although in this case an additional peak appeared. In the presence of these last two surfactants iron(III) does not substantially disturb the base-line current.     

Interpenetrating polymer networks templated on bicontinuous microemulsions containing silicone oil, methacrylic acid, and hydroxyethyl methacrylate

Polydimethylsiloxane-poly(methacrylic acid—hydroxyethyl methacrylate) interpenetrating polymer networks (PDMS-P(MAA–HEMA) IPN) were formulated and polymerized simultaneously from bicontinuous microemulsion templates. Microemulsions containing reactive silicone oils and MAA/HEMA in aqueous solution were stabilized with silicone surfactants, and were then reacted at 50 °C for 3 h under an N₂ atmosphere. The formation of bicontinuous morphology was confirmed by laser scanning confocal microscopy, reversible swelling behavior, differential scanning calorimetry, texture analysis, and permeability to vitamin B₁₂ in aqueous solution. Incorporating polymerizable surfactants into the microemulsion aided in stabilizing the initial microemulsion structure during polymerization, yielding a more uniform IPN morphology with domain sizes of <200 nm at equilibrium swelling. The process developed here demonstrates a simple, single-step polymerization approach to forming IPNs from low viscosity microemulsion templates, and could potentially be extended to a variety of hydrophilic and hydrophobic monomers.     

Amphiphilic polylactide-poly(ethylene oxide)-poly(propylene oxide) block copolymers: Self-assembly behavior and cell affinity

Polylactide (PLA) is a biodegradable polyester recognized for its potential use as a biomedical material. Poly(ethylene oxide) (PEO) and copolymers based on PEO and poly(propylene oxide) (PPO) are biocompatible polyethers widely applied in the biomedical field, particularly as macromolecular nonionic surfactants. In this work, PLA blocks were attached to the PEO and to the PEO and PPO-based triblock copolymer PEO–PPO–PEO, through ring-opening polymerization of racemic lactide (rac-LA) to obtain the amphiphilic triblock PLA–PEO–PLA and pentablock PLA–PEO–PPO–PEO–PLA copolymers containing hydrophilic/hydrophobic blocks with variable block mass ratios. The copolymers were evaluated for chemical composition, molar mass, and thermal properties, and they were used to prepare self-assemble aggregates in water from tetrahydrofuran polymer solutions. The combination of scattering light experiments and microscopy techniques revealed the spherical morphology of the aggregates with diameters around 180–200 nm, which comprises a hydrophobic PLA core and a hydrophilic polyether shell. The aggregates are nontoxic to human cervical cancer cell line — HeLa cells, as determined by MTS assay, and the aggregates are potential candidates to be applied in the encapsulation of hydrophobic compounds. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2203–2213     

Non-surface activity and micellization of ionic amphiphilic diblock copolymers in water. Hydrophobic chain length dependence and salt effect on surface activity and the critical micelle concentration

We reported previously (Macromolecules 2003, 36, 5321; Langmuir, 2004, 20, 7412) that amphiphilic diblock copolymers having polyelectrolytes as a hydrophilic segment show almost no surface activity but form micelles in water. In this study, to further investigate this curious and novel phenomenon in surface and interface science, we synthesized another water-soluble ionic amphiphilic diblock copolymer poly(hydrogenated isoprene)-b-sodium poly(styrenesulfonate) PIp-h2-b-PSSNa by living anionic polymerization. Several diblock copolymers with different hydrophobic chain lengths were synthesized and the adsorption behavior at the air/water interface was investigated using surface tension measurement and X-ray reflectivity. A dye-solubilization experiment was carried out to detect the micelle formation. We found that the polymers used in this study also formed micelles above a certain polymer concentration (cmc) without adsorption at the air-water interface under a no-salt condition. Hence, we further confirmed that this phenomenon is universal for amphiphilic ionic block copolymer although it is hard to believe from current surface and interface science. For polymers with long hydrophobic chains (more than three times in length to hydrophilic chain), and at a high salt concentration, a slight adsorption of polymer was observed at the air-water interface. Long hydrophobic chain polymers showed behavior "normal" for low molecular weight ionic surfactants with increasing salt concentration. Hence, the origin of this curious phenomenon might be the macroionic nature of the hydrophilic part. Dynamic light scattering analysis revealed that the hydrodynamic radius of the block copolymer micelle was not largely affected by the addition of salt. The hydrophobic chain length-cmc relationship was found to be unusual; some kind of transition point was found. Furthermore, very interestingly, the cmc of the block copolymer did not decrease with the increase in salt concentration, which is in clear contrast to the fact that cmc of usual ionic small surfactants decreases with increasing salt concentration (Corrin-Harkins law). These behaviors are thought to be the special, but universal, characteristics of ionic amphiphilic diblock copolymers, and the key factor is thought to be a balance between the repulsive force from the water surface by the image charge effect and the hydrophobic adsorption.     

Poly(dimethylamino)ethyl methacrylate for use as a surfactant in the miniemulsion polymerization of styrene

A novel Y-shaped macromonomer based on poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) with a narrow molecular weight distribution was synthesized via oxyanion-initiated polymerization in which a potassium alcoholate of trimethylol propane allyl ether (2K-TMPAE) was used as a difunctional initiator. For the miniemulsion polymerization of styrene, this macromonomer acted well both as a comonomer carrying a reactive C=C double bond in its central section and as a pH-responsive polycationic surfactant in media with different pH values. The resulting microspheres composed of a hydrophobic polystyrene core and a hydrophilic PDMAEMA-protonated corona have shown spherical morphology and are quite stable. The nature of the reactive group, the amount of polymeric surfactant, and pH values in the aqueous medium have been systematically investigated during the miniemulsion polymerization by analyzing the evolution of the monomer conversions. The results of FTIR and (1)H NMR spectra demonstrated the generation of the functional particles. The analyses of TEM micrographs and dynamic light scattering (DLS) confirmed that the latices had a relatively narrow particle size distribution. The measurement of the zeta potential gave further evidence of the "hairy" particle structure. Because the reactive group is located in the central section of the macromonomer, the stabilization mechanism of the polymeric surfactant can be ascribed to (1) the absorption of two polycationic and hydrophilic tails that have electrostatic and steric stabilization to decrease the interface tension and (2) the copolymerization with the styrene monomer.     

聚苯乙烯磺酸钠与阳离子表面活性剂的相互作用和纳米聚集体的生成

在聚苯乙烯磺酸钠(PSS)的水溶液中,引入阳离子表面活性剂(CTAB或DDAB)使与PSS通过静电相互作用实现聚苯乙烯磺酸盐不同程度的中性化,并进而对PSS/表面活性剂复合物在水中的行为特征、特别是PSS因疏水化而产生的聚集行为以及临界聚集浓度等采用多种方法如溶液的透光率;荧光光谱;荧光探针以及扫描电镜观察等进行了研究,得到一些颇为有趣的结果.结果表明PSS-CTAB或DDAB加成物可自发的形成约70 nm的纳米粒子。而中性化程度则对加成物的构型以及体系的透光率等有较大影响。结果还表明所得具有亲水外壳和疏松的疏水内核的聚集体能容易的使疏水分子进入其中。     

Synergistic improvement of foam stability with SiO2 nanoparticles (SiO2-NPs) and different surfactants

Foam fluids are widely used in petroleum engineering, but long-standing foam stability problems have limited the effectiveness of their use. The study explores the synergistic effects and influencing factors of SiO₂ nanoparticles (SiO₂-NPs) with different wettability properties and three different surfactants. The paper investigates the foaming performance of different types of surfactants and analyzes and compares the stability of foam after adding hydrophilic and hydrophobic SiO₂-NPs from macroscopic as well as microscopic perspectives, and the effects of temperature and inorganic salts on the stability of mixed solutions. The experimental results show that: 1) hydrophilic nanoparticles can significantly enhance the foam stability of amphoteric surfactants, with a small increase in the foam stability of anionic and cationic surfactants; 2) The concentration of nanoparticles did not have a significant effect on the stability of the cationic surfactants and this conclusion was verified in the experimental results of the surface tension measured below;3) The cationic surfactants showed better temperature resistance at temperatures of 50–90 °C. Both amphoteric surfactant solutions with the addition of hydrophilic SiO₂-NPs or hydrophobic SiO₂-NPs significantly improved the temperature resistance of the foam at high temperatures. The anionic surfactant solution with hydrophobic SiO₂-NPs did not enhance the solution temperature resistance; 4) The surface tension of the surfactant solution gradually increases with increasing concentration of hydrophilic or hydrophobic SiO₂-NPs and then levels off; 5) the hydrophilic SiO₂-NPs had a significant effect on the salt tolerance of the anionic and amphoteric surfactant solutions. The salt tolerance of cationic surfactant solutions with hydrophobic SiO₂-NPs was better than that of surfactants with hydrophilic SiO₂-NPs.     

Hydrocarbon chain packing in the micellar core of surfactants studied by 1H NMR relaxation

 ¹H NMR spin–lattice and spin–spin relaxation of different types (cationic cetyltrimethyl ammonium bromide, anionic sodium dodecyl sulfonate and nonionic Triton X-100) of surfactants in water solution were studied. Simulation of the decay curves of proton relaxation shows that the spin lattice relaxation of all the samples exhibits exponentially, while the spin–spin relaxation for several protons on the hydrophobic chains forming the micellar core is bi-exponential. The fast relaxing component is attributed to the part of the segments of the hydrophobic chain, situated near or on the surface of the micellar core, while the slower relaxing component is attributed to the rest part staying in the interior. The latter exchanges with the former in equilibrium. Thus, a part of each certain segment of the hydrophobic chain has an opportunity to stay in the surface layer of the micellar core and spend some time on the interface experiencing hydrophilic environment. Generally, the protons on the methylene carbon of the hydrophobic chain nearest to the polar head have more chance to spend time in the hydrophilic environment. However, it seems to be dependent on the chemical structure of the surfactant molecule. Large size of the polar group of CTAB shows steric hindrance on the packing of the hydrophobic chain. Quantitative results are given. The fact, that the fraction of slow relaxing protons on the hydrophilic ethylene oxide long chain of Triton X-100 dominates over that of fast relaxing protons, and that their T ₂ values are larger than those of the protons on the hydrocarbon chain in the interior of the micellar core, suggests that the ethylene oxide chain does not participate in the formation of the micellar core. Received: 10 March 1998 Accepted: 19 June 1998     

新型聚乙烯接枝共聚物的制备与表征

以聚氧乙烯和全氟辛基聚氧乙烯醚(FPEOE)为起始原料, 合成了一系列的特种氟表面活性剂及其丙烯酸酯, 用FTIR和1H NMR对其结构进行了表征, 用最大气泡法测定了其表面张力. 以其作为接枝单体, 利用反应挤出接枝的方法制备了系列功能化聚乙烯, 用FTIR确定了接枝共聚物的结构和接枝率; 用DSC、接触角测量仪和XPS对接枝共聚物的热性能、结晶行为和表面性能进行了测试分析. 结果表明, 随着聚氧乙烯分子量的增加, 氟表面活性剂的表面活性降低; 聚乙烯接枝共聚物的结晶温度高于线形低密度聚乙烯, 且具有较好的亲水性.     

Hydrophilic magnetic polymer latexes. 2. Encapsulation of adsorbed iron oxide nanoparticles

The encapsulation of seed polymer particles coated by anionic iron oxide nanoparticles has been investigated using N-isopropylacrylamide as a main monomer, N,N-methylene bisacrylamide as a crosslinking agent, itaconic acid as a functional monomer and potassium persulfate as an anionic initiator. The magnetic latexes obtained have been characterized with regard to particle size, iron oxide content and electrophoretic mobility. All these properties have been examined by varying several polymerization parameters: reaction medium, monomer(s) and crosslinking agent concentrations, nature of seed latexes and type of polymerization (batch versus shot process). The magnetic content in the polymer microspheres strongly depends on the polymerization procedure (i.e., encapsulation process) and varies between 6 and 23 wt%, and monodisperse magnetic polymer particles were obtained. Received: 28 December 1999 Accepted in revised form: 15 June 1999