Polymerization and characterization of high conductivity and good adhension polypyrrole films for electromagnetic interference shielding

<正>Polypyrrole(PPy) shows a favorable application in the electromagnetic interference(EMI) shielding due to its good electrical conductivity and outstanding air stability.Conducting PPy films with high conductivity and good adhesion were successfully polymerized on the surface of insulating epoxy resin substrates using chemical polymerization.The factors affecting the properties of PPy films,such as the surface morphology,adhesion between PPy film and substrate,electrical conductivity,EMI shielding effectiveness(SE),were investigated.The adhesion was improved significantly through a three-step surface pretreatment of epoxy resin substrates including removing impurities,roughening,and surface modification with silane coupling agent.An enhancement in the conductivity of PPy films of about one order of magnitude was achieved by adding dopant in FeCl_3 solution.The higher the conductivity,the better the shielding effectiveness.Taking sodium p-toluenesulfonate doped PPy film as example,EMI SE was in the practically useful range of about 30 dB over a wide frequency range from 30 MHz to 1500 MHz.The PPy film samples were characterized by scanning electron microscopy (SEM),infrared spectra(IR),X-ray photoelectron spectroscopy(XPS) and the flange coaxial transmission device.The fourpoint probe method was used to measure conductivity of PPy films.     

Surface reactivity of polypyrrole/iron-oxide nanoparticles: electrochemical and CS-AFM investigations

Composite materials based on iron-oxide nanoparticles (magnetite, hematite, and maghemite) and tetraoxalate-doped polypyrrole (PPy) were electrochemically generated from aqueous solutions. Their composition was determined using electrochemical quartz crystal microbalance experiments. The oxide percentage in mass was found to vary from 17 to 27% depending on the oxide identity. They were all shown to be fascinating candidates as protective materials against corrosion of iron and carbon steel materials although maghemite-nanoparticle-loaded polypyrrole films offer the best performances. An anionic surfactant (sodium dodecylsulfate) was added to the electrodeposition solution to avoid the formation of clusters. These anions were also shown to improve the conductivity of the resulting PPy films, while the presence of oxide nanoparticles tends to decrease this same surface conductivity. On the other hand, the correlation between the morphology and the local conductivity appears to be more obvious in the absence of anionic surfactants than in their presence. This aspect is discussed although it still needs further investigation. Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006.     

Preparation of Polypyrrole/Poly(methyl methacrylate) Core-Shell Nanoparticles in Four-Component Microemulsion Media

Electrically conductive polypyrrole (PPy)/poly(methyl methacrylate) (PMMA) core-shell nanoparticles were synthesized by two-step microemulsion polymerization. PPy core particles were prepared in a four-component microemulsion system, which was formed with surfactant cetyltrimethyl ammonium bromide (CTAB), cosurfactant n-pentanol, water, and pyrrole. Ferric chloride and iodine was added as the oxidant and the dopant, respectively. Then the PPy nanoparticles were coated with PMMA to prepare PPy/PMMA core-shell nanoparticles. The morphology of PPy/PMMA core-shell nanoparticles was characterized with transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy was used to characterize the structure of the samples. The electrical conductivities of samples were studied by a Hall effect testing instrument. Despite being coated with a layer of insulation, the conductivity of the composite PPy/PMMA core-shell nanoparticles could still reached to 7.856 × 10^?1 S/cm.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Characteristics of polypyrrole electrodeposited onto roughened substrates composed of gold–silver bimetallic nanoparticles

In this work, the characteristics of polypyrrole (PPy) films electrodeposited onto an electrochemically roughened gold substrate with bimetallic silver and gold nanoparticles were first investigated. First, a silver substrate was roughened by a triangular‐wave oxidation–reduction cycle (ORC) in an aqueous solution containing 0.1 M HCl. Subsequently, a gold substrate was roughened by a similar ORC treatment in this used solution. The results revealed that the surface of the roughened gold substrate demonstrated two different kinds of deposition domains because of the modification of silver nanoparticles. Encouragingly, some novel characteristics of PPy deposited onto this substrate were observed, in comparison with those on the roughened gold substrate without the modification of silver nanoparticles. They included a denser and more compact surface morphology, higher oxidation degree, increased conductivity, and improved surface‐enhanced Raman scattering. Furthermore, the nucleation and growth mechanism for PPy electropolymerization on this silver‐modified roughened gold substrate was distinguishable from that on the unmodified one. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2724–2731, 2006     

Synthesis and Characterization of Conductive Polypyrrole/Montmorillonite Nanocomposites via One-pot Emulsion Polymerization

A series of electrically conductive polypyrrole/clay nanocomposites were synthesized in this work by using one-pot emulsion oxidative polymerization of pyrrole in the presence of unmodified clay and using DBSNa as the surfactant. The effect of surfactant on the morphological and electrical properties of PPy also were investigated and discussed in some extent. Electrical conductivity of the samples was measured by using samples in which the conductive materials was sandwiched between two Ni electrodes at room temperature. PPy/MMT nanocomposites were characterized by using XRD, TEM, TGA and DSC means of investigation. Intercalated structures were determined for the nanocomposites as confirmed by XRD and TEM studies. Electrical conductivity of the nanocomposites was measured to be dependent to the clay content, and the methods of preparation. Measurement also showed that polymerization of pyrrole monomers pre-intercalated between the clay gallery spaces of the clay led to higher conductivity for the nanocomposite in the same level of clay content. Thermal property measurements showed a lower thermal decomposition rate for the PPy/MMT nanocomposites with respect to the PPy.     

Highly transparent and conductive thin films fabricated with nano-silver/double-walled carbon nanotube composites

This study develops a technique for enhancing the electrical conductivity and optical transmittance of transparent double-walled carbon nanotube (DWNT) film. Silver nanoparticles were modified with a NH(2)(CH(2))(2)SH self-assembled monolayer terminated by amino groups and subsequent surface condensation that reacted with functionalized DWNTs. Ag nanoparticles were grafted on the surface of the DWNTs. The low sheet resistance of the resulting thin conductive film on a polyethylene terephthalate (PET) substrate was due to the increased contact areas between DWNTs and work function by grafting Ag nanoparticles on the DWNT surfaces. Increasing the contact area between DWNTs and work function improved the conductivity of the DWNT-Ag thin films. The prepared DWNT-Ag thin films had a sheet resistance of 53.4 Ω/sq with 90.5% optical transmittance at a 550 nm wavelength. After treatment with HNO(3) and annealing at 150 °C for 30 min, a lower sheet resistance of 45.8 Ω/sq and a higher transmittance of 90.4% could be attained. The value of the DC conductivity to optical conductivity (σ(DC)/σ(OP)) ratio is 121.3.     

The importance of the film structure during self-powered ibuprofen salicylate drug release from polypyrrole electrodeposited on AZ31 Mg

Therapeutic drugs uploaded into conjugated conductive polymer matrices deposited on active magnesium alloys serve as controlled-dose, self-powered drug-delivery systems. Preferentially, drugs are added into polymer films in the largest amount possible, mostly to prevent long-term treatments. However, added drugs can interact with the polymer matrix affecting either the structure or the final mechanical properties of the polymer film. In this work, polypyrrole films (PPy) electrodeposited on an AZ31 Mg alloy in ibuprofen and salicylate-containing solutions are investigated in terms of their uploading capacity, surface morphology and mechanical properties. The techniques used to investigate the uploaded PPy films include cyclic voltammetry (CV), scanning electron microscopy (SEM), EDS, and depth-sensing indentation (DSI). A maximum ibuprofen concentration of 440 ± 40 μg cm^?2 was obtained in PPy films in the presence of sodium salicylate. The release fraction of ibuprofen as a function of time is fitted to Avrami’s equation. The hardness and reduced modulus decreased by 54 and 40 %, respectively, when the PPy films are prepared in the presence of sodium ibuprofen compared with those prepared in sodium salicylate only, indicating a more plastic film with ibuprofen.     

Highly conductive free standing polypyrrole films prepared by freezing interfacial polymerization

Highly conductive free standing polypyrrole (PPy) films were prepared by a novel freezing interfacial polymerization method. The films exhibit metallic luster and electrical conductivity up to 2000 S cm(-1). By characterizing with SEM, FTIR, Raman and XRD, the high conductivity is attributed to the smooth surface, higher conjugation length and more ordered molecular structure of PPy.     

Carboxy-endcapped conductive polypyrrole: biomimetic conducting polymer for cell scaffolds and electrodes

Numerous regenerating tissues respond favorably to electrical stimulation, creating a need for a bioactive conducting platform for tissue engineering applications. The drive for biosensors and electrode coatings further requires control of the surface properties of promising conductive materials such as polypyrrole. Here we present carboxy-endcapped polypyrrole (PPy-alpha-COOH), a unique bioactive conducting polymer with a carboxylic acid layer, composed of a polypyrrole (PPy) surface modified with pyrrole-alpha-carboxylic acid (Py-alpha-COOH). This unique structure is simple to produce, provides a stable bioactive surface via covalent bonds, and preserves bulk properties such as electrical conductivity and mechanical integrity. The chemical structure of this polymer composite was characterized by angle-resolved X-ray photoelectron spectroscopy (XPS), which demonstrated the presence of carboxylic acid functionality on the top surface of conductive PPy. A four-point probe test was used to verify the similar conductivity of PPy-alpha-COOH compared to that of standard PPy. To demonstrate the potential to influence cellular activity, the carboxylic acid monolayer surface was grafted with the cell-adhesive Arg-Gly-Asp (RGD) motif. Human umbilical vein endothelial cells (HUVECs) cultured on RGD-modified PPy-alpha-COOH demonstrated significantly higher adhesion and spreading than on the negative controls PPy-alpha-COOH and unmodified PPy.     

In Situ Synthesis of Robust Conductive Cellulose/Polypyrrole Composite Aerogels and Their Potential Application in Nerve Regeneration

Nanostructured conductive polymers can offer analogous environments for extracellular matrix and induce cellular responses by electric stimulation, however, such materials often lack mechanical strength and tend to collapse under small stresses. We prepared electrically conductive nanoporous materials by coating nanoporous cellulose gels (NCG) with polypyrrole (PPy) nanoparticles, which were synthesized in situ from pyrrole monomers supplied as vapor. The resulting NCG/PPy composite hydrogels were converted to aerogels by drying with supercritical CO₂, giving a density of 0.41–0.53 g cm^?3, nitrogen adsorption surface areas of 264–303 m² g^?1, and high mechanical strength. The NCG/PPy composite hydrogels exhibited an electrical conductivity of up to 0.08 S cm^?1. In vitro studies showed that the incorporation of PPy into an NCG enhances the adhesion and proliferation of PC12 cells. Electrical stimulation demonstrated that PC12 cells attached and extended longer neurites when cultured on NCG/PPy composite gels with DBSA dopant. These materials are promising candidates for applications in nerve regeneration, carbon capture, catalyst supports, and many others.     

New biocompatible polypyrrole-based films with good blood compatibility and high electrical conductivity

A novel O-butyryl chitosan (OBCS)-grafted polypyrrole (PPy) film was described. The immobilization was accomplished by photocrosslinking the OBCS onto PPy films under ultraviolet light irradiation. The surfaces of OBCS-grafted PPy film were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). The blood compatibility of the OBCS-grafted PPy film was evaluated by platelet-rich plasma (PRP) contacting experiments and protein adsorption experiments in vitro. These results have demonstrated that the surface with immobilized OBCS shows much less platelet adhesive and fibrinogen adsorption compared to the control surface. The bulk conductivity values of PPy films were measured by a modified four-probe method. The composite films have both good blood compatibility and high electrical conductivity that make them suitable for using as potential biomaterials, such as electrically conducting blood vessel and functionally haemocompatible substrate of biosensor used directly in whole blood.     

Electrochemistry of conductive polymers 37. Nanoscale monitoring of electrical properties during electrochemical growth of polypyrrole and its aging

Electrical and morphological properties of polypyrrole (PPy) films were studied during and after their electrochemical growth under various experimental conditions on a nanometer scale using a current-sensing atomic force microscope (CS-AFM). Of acetonitrile (ACN) solutions containing various amounts of water, one that contained 1.0% water produced the best quality films in their electrical and morphological properties in terms of homogeneities. The degree of doping, as well as time evolution of the film structure and its conductivity, of the PPy films was investigated during their growth in water and ACN with 1.0% water by obtaining the current images at a few designated growing stages, and the results were compared. Well-doped, conductive films were obtained from the very early stage during the electrodeposition of PPy in the ACN solution, while the films were poorly doped in water. As the film deposition progressed further in both aqueous and nonaqueous media, the doped areas spread over the whole surface leading to a more homogeneously conducting film. The current-voltage traces were obtained at each growing stage, which showed that the conductivity increases in both media as the PPy grows; the conductivity of the film grown in ACN is much higher than that of the film grown in water at all growing stages. The electrical properties of the PPy film deteriorated gradually upon exposure to air.     

Preparation and characterization of polypyrrole/magnetite nanocomposites synthesized by in situ chemical oxidative polymerization

This work describes the preparation and characterization of polypyrrole (PPy)/iron oxide nanocomposites fabricated from monodispersed iron oxide nanoparticles in the crystalline form of magnetite (Fe₃O₄) and PPy by in situ chemical oxidative polymerization. Two spherical nanoparticles of magnetite, such as 4 and 8 nm, served as cores were first dispersed in an aqueous solution with anionic surfactant sodium bis(2‐ethylhexyl) sulfosuccinate to form micelle/magnetite spherical templates that avoid the aggregation of magnetite nanoparticles during the further preparation of nanocomposites. The PPy/magnetite nanocomposites were then synthesized on the surface of the spherical templates. Structural and morphological analysis showed that the fabricated PPy/magnetite nanocomposites are core (magnetite)‐shell (PPy) structures. Morphology of the PPy/magnetite nanocomposites containing monodispersed 4‐nm magnetite nanoparticles shows a remarkable change from spherical to tube‐like structures as the content of nanoparticles increases from 12 to 24 wt %. Conductivities of these PPy/magnetite nanocomposites show significant enhancements when compared with those of PPy without magnetite nanoparticles, in particular the conductivities of 36 wt % PPy/magnetite nanocomposites with 4‐nm magnetite nanoparticles are about six times in magnitude higher than those of PPy without magnetite nanocomposites. These results suggest that the tube‐like structures of 36 wt % PPy/magnetite nanocomposites may be served as conducting network to enhance the conductivity of nanocomposites. The magnetic properties of 24 and 36 wt % PPy/magnetitenanocomposites show ferromagnetic behavior and supermagnetism, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1291–1300, 2008     

Low-temperature preparation of highly conductive thin films from acrylic acid-stabilized silver nanoparticles prepared through ligand exchange

The preparation of AcA-stabilized Ag nanoparticles and its application to make highly conductive thin films are reported. The AcA-stabilized Ag nanoparticles were prepared through a ligand exchange of original oleylamine (OLA)-coated Ag nanoparticles with acrylic acid (AcA), which acted as both an antisolvent and a modifying ligand during the ligand exchange process. Efficiencies of the ligand exchange as well as the properties of Ag nanoparticles were analyzed using various techniques including TEM, FT-IR, XPS, TGA, and UV-vis methods. The thin films were fabricated by annealing spin-coated AcA-stabilized Ag nanoparticles. Further, the effects of annealing temperature, time, and film thickness on both the film morphology and electrical conductivity have been investigated. In this work, due to the low boiling temperature of stabilizer (AcA) and adjustment of annealing conditions, high electrical conductivity was obtained for the Ag thin films. For example, when annealing at 175 °C for 30 min, a 70 nm thick film showed a maximum electrical conductivity of 1.12 × 10(5) S cm(-1). A conductive layer on a flexible polymer substrate (e.g., PET) sheet has been successfully prepared by annealing a spin-coated film at 140 °C for 30 min. The combined advantages of long-term stability of the AcA-stabilized Ag nanoparticles, low annealing temperature, and high conductivity of the prepared thin films make this relatively simple method attractive for applications in flexible electronics.     

Flexible NH3 sensors fabricated by in situ self-assembly of polypyrrole

Novel flexible NH₃ gas sensors were formed by the in situ self-assembly of polypyrrole (PPy) on plastic substrates. A negatively charged substrate was prepared by the formation of an organic monolayer (3-mercapto-1-propanesulfonic acid sodium salt—MPS) on a polyester (PET) substrate using a pair of comb-like Au electrodes. Two-cycle poly(4-styrenesulfonic acid) sodium salt/poly(allylamine hydrochloride) (PSS/PAH) bilayers (precursor layer) were then layer-by-layer (LBL) deposited on an MPS-modified substrate. Finally, a monolayer of PPy self-assembled in situ and PPy multilayer thin films self-assembled LBL in situ on a (PSS/PAH)₂/MPS/Au/Cr/PET substrate. The thin films were analyzed by atomic force microscopy (AFM). The effects of the precursor layer (PSS), the deposition time of the monolayer of PPy and the number of PPy multilayers on the gas sensing properties (response) and the flexibility of the sensors were investigated to optimize the fabrication of the film. Additionally, other sensing properties such as sensing linearity, reproducibility, response and recovery times, as well as cross-sensitivity effects were studied. The flexible NH₃ gas sensor exhibited a strong response that was comparable to or even greater than that of sensors that were fabricated on rigid substrate at room temperature.     

Polyamide grafted with polypyrrole: formation, properties, and stability

Conducting textiles of polyamide (PA) fabrics and polypyrrole (PPy) were prepared by in situ oxidative chemical polymerisation of pyrrole (Py) on the surface of PA textiles using FeCl₃ as oxidant. The anionic surfactant, dodecylbenzenesulphonic acid, was used as co-dopant during Py polymerisation on the textile surface. The influence of the monomer amount and polymerisation conditions on formation of the conducting PPy layer, conductivity, morphology, and stability of the prepared PA/PPy was studied. The conductivity of modified textiles decreased rapidly after the washing process, so a special Py-functionalised silane (1-(3-(triethoxysilyl)propylamino)-3-(1-H-pyrrole-1-yl)propan-2-ol; SP) was synthesised and applied to the PA surface prior to PPy formation. The presence of SP on the PA surface after completion of the sol-gel process was verified by Fourier transform infrared spectroscopy with an attenuated total reflectance. Pyrrole polymerisation was subsequently applied to the SP pre-treated textile surface. The influence of SP concentration on both the fastness of the conducting layer after the washing process and stability of the electrical conductivity of the prepared PA/PPy samples was investigated. Surface conductivity of the samples treated and untreated by the sol-gel process of SP was measured both prior to and after washing of the prepared textiles. It was found that an application of 0.6 mass % of SP significantly improved the fastness of the PPy layers. Examination of the modified PA surface using scanning electron microscopy disclosed the differences in the formation of PPy on PA textiles when using SP and also showed differences on the PPy modified textile surface prior to and after washing. The method of X-ray photoelectron spectroscopy was used for a detailed study of the surface composition. It was confirmed that the pre-treatment with Py-functionalised triethoxysilane significantly influenced the chemical composition of the PA surface modified with PPy.     

Polypyrrole (PPy) chemical synthesis with xylan in aqueous medium and production of highly conducting PPy/nanofibrillated cellulose films and coatings

Polypyrrole was chemically synthesised by using, for the first time, Birchwood xylan as additive, and ammonium peroxydisulfate (APS) as oxidant. The impact of additive concentration, polymerisation time and reagents concentration on PPy conductivity was studied. It was shown that, once fixed the pyrrole (Py)/APS and Py/xylan optimal ratios, the best conductivities (26 S/cm) were obtained for short polymerisation times (30 min) and increased reactants concentration. Morphological analysis of PPy particles, Py depletion kinetics and oxido-reduction potential measurements of the solutions provided interpretation elements on the impact of the polymerisation time on PPy pellet conductivity. Furthermore, optimised PPy particles obtained with xylan (PPy_x) were mixed with nanofibrillated cellulose (NFC) in order to obtain freestanding films. Their electrical and handling performances were evaluated at increasing PPy weight fraction in the samples. The conductivity mechanism of the most conductive sample (in comparison with a low performing sample) was investigated by measuring the conductivity as a function of temperature (4–350 K) and two transport regimes were identified. Selected formulations were finally used to produce conducting PPy/NFC coatings on non-absorbent (glass) and absorbent (copy paper) substrates. The impact of NFC in the percolation of PPy particles, then in the coating conductivity, was investigated.     

Organic–inorganic polypyrrole‐surface modified SiO2 hybrid nanocomposites: a facile and green synthetic approach

Organic–inorganic hybrid nanocomposites composed of conductive polypyrrole (PPy) and surface modified silica (SiO₂) were successfully prepared through an in situ chemical oxidative polymerization in supercritical carbon dioxide (scCO₂). SiO₂ nanoparticles were surface modified using 3‐methacryloxypropyltrimethoxysilane (MPTMS) in order to disperse well in the medium. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that the SiO₂ nanoparticles were encapsulated into the polymer. UV‐visible spectra of the diluted colloidal dispersions of PPy/SiO₂ hybrid nanocomposites were similar to those of PPy system. Fourier transform infrared spectroscopy (FT‐IR) suggested the strong interaction between PPy and SiO₂. Surface characterizations of nanocomposites were described by X‐ray photoelectron spectroscopy (XPS). The nanocomposites synthesized in scCO₂ have been shown to possess higher electrical conductivity and thermal stability. Copyright © 2009 John Wiley & Sons, Ltd.     

Polypyrrole thin films formed by admicellar polymerization support the osteogenic differentiation of mesenchymal stem cells

The objective of this study was to evaluate the attachment, proliferation, and differentiation of rat mesenchymal stem cells (MSC) toward the osteoblastic phenotype seeded on polypyrrole (PPy) thin films made by admicellar polymerization. Three different concentrations of pyrrole (Py) monomer (20, 35, and 50 x 10(-3) M) were used with the PPy films deposited on tissue culture polystyrene dishes (TCP). Regular TCP dishes and PPy polymerized on TCP by chemical polymerization without surfactant using 5 x 10(-3) M Py, were used as controls. Rat MSC were seeded on these surfaces and cultured for up to 20 d in osteogenic media. Surface topography was characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and static contact angle. Cell attachment, proliferation, alkaline phosphatase (ALP) activity, and calcium content were measured to evaluate the ability of MSC to adhere and differentiate on PPy-coated TCP. Increased monomer concentrations resulted in PPy films of increased thickness and surface roughness. PPy films generated by different monomer concentrations induced drastically different cellular events. A wide spectrum of cell attachment characteristics (from excellent cell attachment to the complete inability to adhere) were obtained by varying the monomer concentration from 20 m to 50 x 10(-3) M. In particular the 20 x 10(-3) M PPy thin films demonstrated superior induction of MSC osteogenicity, which was comparable to standard TCP dishes, unlike PPy films of similar thickness prepared by chemical polymerization without surfactant. Adhesion of mesenchymal stem cells on tissue culture plates (TCP) coated with polypyrrole thin films made by admicellar polymerization.