Reactive Steric Stabilizer Research Articles

Synthesis and Nano-object Assembly of Biomimetic Block Copolymers for Catalytic Silver Nanoparticles

Biomimetic ABC triblock copolymers of poly[2-(methacryloyloxy)ethyl phosphorylcholine]- b-poly[2-(dimethylamino)ethyl methacrylate]- b-poly(2-hydroxypropyl methacrylate) (PMPC- b-PDMA- b-PHPMA) were synthesized by RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) in the presence of a PMPC- b-PDMA macromolecular chain transfer agent (macro-CTA). This ABC triblock copolymer deploys well-known biocompatible PMPC and PDMA for the coordination of Ag+ ions to form silver nanoparticles in situ on reduction, and PHPMA for assembling (core) in water. The synthesis of PMPC- b-PDMA- b-PHPMA starts when both the reactive steric stabilizer of PMPC25- b-PDMA4 macro-CTA and HPMA monomer are dissolved in water. The growing PHPMA is not soluble in water and begins to assemble based on three-layer onion micelles, in which the outer and inner shells are PMPC and PDMA, respectively. In the synthesis of PMPC25- b-PDMA4- b-PHPMA z at a constant 25% (w/w) solids concentration, the resultant assemblies change from spheres to worms to jellyfishes to vesicles when the targeted PHPMA chain length increases from 100mer to 400mer at full monomer conversion. Furthermore, in the synthesis of identical PMPC25- b-PDMA4- b-PHPMA400 copolymers, the assembly morphology can be controlled from vesicles to spheres through worms by varying the solids concentration in the polymerization mixture, decreasing from 25% (w/w) to 15% (w/w) at full monomer conversion. Thus, the final morphology can be tuned by the degree of polymerization of HPMA and the solids concentration in the polymerization mixture. Using the resultant three PMPC25- b-PDMA4- b-PHPMA400 assemblies as scaffolds, Ag(0) nanoparticles (Ag-NPs) are obtained through in situ reduction of AgNO3 facilitated by electrostatic interactions between the Ag+ ions and PDMA moieties. The resultant Ag-NPs loaded in the assemblies exhibit excellent stability, dispersibility, and activity of catalyst for the reduction of p-nitrophenol. The order of rate constants for the reduction using Ag-NPs loaded in the assemblies is worms > vesicles > spheres, which corresponds to the order of the surface areas of the assemblies of PMPC25- b-PDMA4- b-PHPMA400. These results can be achieved thanks to the kinetically frozen PMPC25- b-PDMA4- b-PHPMA400 assemblies with identical compositions.

Zwitterionic poly(2-(methacryloyloxy) ethyl phosphorylcholine) coated mesoporous silica particles and doping with magnetic nanoparticles

Poly(2(methacryloyloxy) ethyl phosphorylcholine) (PMPC) a zwitterionic biopolymer has been used to prepare hybrid inorganic/organic/inorganic tri-layered magnetic composite particles. Mesoporous SiO2 particles of average diameter 284.8 nm are first prepared by sol-gel technique in presence of cetyltrimethylammonium bromride (CTAB) as template to generate porosity. The surface of mesoporous SiO2 particles is then functionalized to introduce vinyl functionality using silane coupling agent, 3-(trimethoxysilyl) propyl methacrylate (MPS). Finally grafting of MPC is carried out on the surface of mesoporous SiO2 particles by carrying out seeded copolymerization in presence of monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA) as a reactive steric stabilizer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. The prepared composite polymer particles named as SiO2/P(MPC-PEGMA-EGDMA) are finally doped with magnetic iron oxide nanoparticles (Fe3O4) via simultaneous in situ precipitation of Fe2+ and Fe3+ from alkali solution. The final composite particles possessed moderate paramagnetic property having magnetic susceptibility (2.22 × 10−5) which is just one order less than that of reference Fe3O4 nanoparticles (1.00 × 10-4). A comparative adsorption behaviour of biomolecules suggested that surface of SiO2/P(MPC-PEGMA-EGDMA) composite particles resist protein adhesion whereas after doping with Fe3O4 nanoparticles the surface has tendency to adsorb proteins.

In situ nano-objects via RAFT aqueous dispersion polymerization of 2-methoxyethyl acrylate using poly(ethylene oxide) macromolecular chain transfer agent as steric stabilizer

Poly(ethylene oxide)-poly(2-methoxyethyl acrylate) diblock copolymers (PEO-b-PMEA) are synthesized by RAFT aqueous dispersion polymerization of MEA using poly(ethylene oxide) macromolecular chain transfer agent as a reactive steric stabilizer. Both segments are well-known to be bio- and blood-compatible polymers. This formulation enables the production of various particle morphologies such as spheres, worms, and vesicles from the same block copolymer in water. The synthesis starts when both the reactive steric stabilizer and MEA monomer are dissolved in water; however, the growing polymer is not water-soluble and begins to form nano-objects. In the case of the synthesis of PEO113-b-MEA300 diblock copolymers, the nano-objects change from spheres into larger aggregates of worms when the solids concentration in the polymerization increases from 5 to 15 wt% at full monomer conversion. The morphology finally turns into vesicles as the solids concentration increases to 20 wt%. The final block copolymer morphology at full monomer conversion is dictated by not only degree of polymerization of MEA but also the solids concentration in the polymerization mixture.

Synthesis of PMMA Microparticles with a Narrow Size Distribution by Photoinitiated RAFT Dispersion Polymerization with a Macromonomer as the Stabilizer

Macromonomers can serve as efficient and effective stabilizers for dispersion polymerization of monomers such as styrene and methyl methacrylate, but the size distributions of the polymer microparticles obtained tend to be broad. We are interested in functional microbeads which can be used for immunoassays, where the size distribution has to be very narrow. We report a photoinitiated RAFT dispersion polymerization of methyl methacrylate (MMA) in ethanol–water mixtures, with methoxy-poly(ethylene glycol) methacrylate (Mn = 2000 g/mol, EO45) as the reactive steric stabilizer. We identify reaction conditions where one can obtain PMMA microspheres with coefficient of variation in the particle diameter (CVd) less than 3%. Carboxy-functional PMMA microspheres were obtained by a two-stage (seeded) polymerization with methacrylic acid (MAA) added as a comonomer in the second stage. We show that the functional microspheres prepared in this way are effective substrates for the covalent attachment of proteins such as BSA and IgG immunoglobulins. In one set of experiments with a dye-labeled secondary antibody, we found that we could detect 104 IgGs per PMMA microbead.

Synthesis and Characterization of Novel Polyacid-Stabilized Latexes

A series of novel polyacid macromonomers based on 2-hydroxypropyl methacrylate (HPMA) were prepared by atom transfer radical polymerization (ATRP) via a two-step route. First, a range of well-defined PHPMA homopolymer precursors were synthesized by ATRP using a tertiary amine-functionalized initiator, 2-(dimethylamino)ethyl-2-bromoisobutyrylamide, and a CuCl/2, 2'-bipyridine (bpy) catalyst in alcoholic media at 50 °C. ATRP polymerizations were relatively slow and poorly controlled in pure isopropanol (IPA), especially when targeting higher degrees of polymerization (DP > 30). Improved control was achieved by addition of water: low polydispersity (M(w)/M(n) < 1.25) PHPMA homopolymers of DP = 30, 40, 50, 60, or 70 were successfully prepared using a 9:1 w/w % IPA/water mixture at 50 °C. These PHPMA homopolymer precursors were then derivatized to produce the corresponding poly(2-(succinyloxy)propyl methacrylate) (PSPMA) macromonomers by quaternizing the tertiary amine end-group with excess 4-vinylbenzyl chloride, followed by esterification of the pendent hydroxyl groups using excess succinic anhydride at 20 °C. These polyacid macromonomers were evaluated as reactive steric stabilizers for polystyrene latex synthesis under either aqueous emulsion polymerization or alcoholic dispersion polymerization conditions. Near-monodisperse polystyrene latexes were obtained via aqueous emulsion polymerization using 10 wt % PSPMA macromonomer (with respect to styrene monomer) with various initiators as evidenced by scanning electron microscopy, disk centrifuge photosedimentometry and light scattering studies. PSPMA macromomer concentrations as low as 1.0 wt % also produced near-monodisperse latexes, suggesting that these PSPMA macromonomers are highly effective stabilizers. Alcoholic dispersion polymerization of styrene conducted in various ethanol/water mixtures with 10 wt % PSPMA(50) macromonomer produced relatively large near-monodisperse latexes. Increasing the water content in such formulations led to smaller latexes, as expected. Control experiments conducted with 10 wt % PSPMA(50) homopolymer produced relatively large polydisperse latexes via emulsion polymerization and only macroscopic precipitates via alcoholic dispersion polymerization. Thus the terminal styrene group on the macromonomer chains is essential for the formation of well-defined latexes. FT-IR spectroscopy indicated that these latexes contained PSPMA macromonomer, whereas (1)H NMR spectroscopy studies of dissolved latexes allowed stabilizer contents to be determined. Aqueous electrophoresis and X-ray photoelectron spectroscopy studies confirmed that the PSPMA macromonomer chains were located at the latex surface, as expected. Finally, these polyacid-stabilized polystyrene latexes exhibited excellent freeze-thaw stability and remained colloidally stable in the presence of electrolyte.

Near-Monodisperse Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-Based Macromonomers Prepared by Atom Transfer Radical Polymerization and Thiol–Ene Click Chemistry: Novel Reactive Steric Stabilizers for Aqueous Emulsion Polymerization

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepared by the atom transfer radical polymerization (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addition, which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aqueous emulsion polymerization of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diameter. As a comparison, the disulfide-containing PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepared using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw experiments and the addition of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepared in the absence of any steric stabilizer and a PS latex prepared in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addition of an electrolyte, as expected.

Synthesis of Sterically-Stabilized Polystyrene Latexes Using Well-Defined Thermoresponsive Poly(N-isopropylacrylamide) Macromonomers

A series of well-defined thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) macromonomers was prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization followed by aminolysis and nucleophilic Michael addition. 2-(Dodecylthiocarbonothioylthio)-2-methylpropanoic-2-phenoxyethyl ester (CTA) was used as the RAFT chain transfer agent to prepare six PNIPAM-CTA precursors with target degrees of polymerization of 20, 30, 40, 50, 60, and 75. These NIPAM polymerizations were conducted in 1,4-dioxane and proceeded with good control and low polydispersities (Mw/Mn < 1.10) up to more than 90% conversion. The PNIPAM trithiocarbonate end-groups were then converted to methacrylate end-groups by combining (i) aminolysis and (ii) nucleophilic Michael addition using the bifunctional reagent, 3-(acryloyloxy)-2-hydroxypropyl methacrylate (AHPMA), in a one-pot reaction. The resulting PNIPAM macromonomers were evaluated as reactive steric stabilizers for latex syntheses. Near-monodisperse submicrometer-sized latexes were obtained by alcoholic dispersion polymerization of styrene in methanol, as judged by scanning electron microscopy (SEM) and dynamic light scattering (DLS). In contrast, a latex synthesized in the presence of a PNIPAM-CTA had a bimodal size distribution, while thiol-capped PNIPAM chains produced ill-defined nonspherical particles and styrene polymerization conducted in the absence of any stabilizer led to macroscopic precipitation. These control experiments confirm that using the methacrylate-capped macromonomers is essential for successful latex syntheses. 1H NMR analysis confirm the presence of PNIPAM chains in the latex particles and XPS measurements indicate that the stabilizer is located on the particle surface, as expected. The well-known thermo-responsive nature of the stabilizer was successfully transferred to these latexes, which exhibit reversible flocculation upon heating above the LCST of the PNIPAM chains.

Synthesis of Sterically-Stabilized Latexes Using Well-Defined Poly(glycerol monomethacrylate) Macromonomers

A range of well-defined methacrylic macromonomers based on glycerol monomethacrylate (GMA) has been synthesized by atom transfer radical polymerization (ATRP) in alcoholic media using an N-(dimethylamino)ethyl-2-bromoisobutyrylamide initiator. This tertiary amine-functionalized initiator was used to produce six homopolymer precursors with target degrees of polymerization of 20, 30, 40, 50, 60, and 70 via ATRP. These polymerizations proceeded to very high conversions (>95%) and afforded relatively low polydispersities (Mw/Mn ≤ 1.33). The tertiary amine end groups were then quaternized using 4-vinylbenzyl chloride (4-VBC) to afford the corresponding near-monodisperse styrene-functionalized PGMA macromonomers. These PGMA macromonomers were evaluated as reactive steric stabilizers for latex syntheses. Near-monodisperse submicrometer-sized and micrometer-sized polystyrene latexes were obtained by aqueous emulsion and alcoholic dispersion polymerization, respectively, as judged by scanning electron microscopy and dynamic light scattering studies. Attempted latex syntheses conducted in the absence of any macromonomer invariably resulted in macroscopic precipitation under dispersion polymerization conditions, with no evidence of latex formation. Higher molecular weight macromonomers (DP = 40 or 50) generally gave smaller, more monodisperse particles compared with the lower molecular weight macromonomers (DP = 20 or 30). Latex syntheses conducted in the presence of the PGMA50 homopolymer precursor produced particles with significantly larger diameters than those prepared with the corresponding styrene-functionalized PGMA50 macromonomer. Such control experiments confirmed the importance of having terminal styrene groups on the macromonomer chains for successful latex formation. FT-IR spectroscopy indicated the presence of the PGMA50 macromonomer within the polystyrene latex and XPS studies indicated that these stabilizer chains are located at (or very near) the latex surface, as expected. Finally, approximately micrometer-sized latexes can be produced by aqueous dispersion polymerization of 2-hydroxypropyl methacrylate in the presence of the PGMA50 macromonomer.

Preparation of Biocompatible Sterically Stabilized Latexes Using Well-Defined Poly(2-(methacryloyloxy)ethyl phosphorylcholine) Macromonomers

A range of well-defined methacrylic macromonomers based on the biomimetic monomer 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) were synthesized by atom-transfer radical polymerization (ATRP) in alcoholic media using 2-(dimethylamino)ethyl-2-bromoisobutyrylamide. This tertiary amine-functionalized initiator was used to produce homopolymer precursors of various chain lengths via ATRP. These polymerizations were relatively well controlled (M(w)/M(n) < or = 1.30), provided that the target degree of polymerization (DP) did not exceed 30. For higher target DPs, polymerization was only poorly controlled and characterized by broad molecular weight distributions (M(w)/M(n) = 1.50-2.31). The tertiary amine end-group of each nearly monodisperse homopolymer precursor was then quaternized using 4-vinylbenzyl chloride (4-VBC) to afford the corresponding styrene-functionalized macromonomers. PMPC(30) macromonomer proved to be an effective reactive steric stabilizer for the formation of polystyrene latexes when employed at 10 w/w % on the basis of the styrene monomer. Nearly monodisperse submicrometer-sized and micrometer-sized latexes were prepared by aqueous emulsion and alcoholic dispersion polymerization, respectively, as judged by scanning electron microscopy and dynamic light scattering studies. In contrast, attempted alcoholic dispersion polymerization conducted either in the presence of the PMPC(30) homopolymer precursor or in the absence of any macromonomer always resulted in macroscopic precipitation. Such control experiments confirmed the importance of the terminal styrene groups on the macromonomer chains for successful latex formation. FTIR spectroscopy indicated the presence of the PMPC(30) macromonomer within the polystyrene latex, and XPS studies indicated that these stabilizer chains are located at (or very near) the latex surface, as expected. Using PMPC(20) and PMPC(10) macromonomers for the alcoholic dispersion polymerization of styrene led to latexes with substantially broader size distributions compared to those produced using the PMPC(30) macromonomer under the same conditions. Finally, these new sterically stabilized latexes exhibit excellent freeze-thaw stability and salt tolerance.

Ab initio dispersion polymerization of styrene in the presence of the poly(methacrylic acid) macro-RAFT agent

Stable, spherical, polystyrene particles were synthesized in ab initio dispersion polymerization by using the poly(methacrylic acid)[PMAA] macro-RAFT agent. The presence of the PMAA macro-RAFT agent on the polystyrene (PS) particles was confirmed by NMR and FTIR spectroscopy. The PS particle size was influenced by the concentration of the RAFT agent and monomer due to the initial nucleation. When the concentration of the PMAA macro-RAFT agent was increased from 2 to 10 wt% relative to the monomer, the average particle size decreased from 2.31 to 1.36 μm, the conversion decreased from 93.3 to 88.9%, the weight-average molecular weight increased from 46,300 to 150,200 g mol−1 and the PDI decreased from 2.79 to 1.94, respectively. In particular, the incorporation of 10 wt% of PMAA macro-RAFT agent produced monodisperse PS spheres of 1.36 μm with a coefficient of variation (CV) of 6.44%. Thus, the PMAA macro-RAFT agent worked as a reactive steric stabilizer providing monodisperse, micron-sized, PS particles.

Stimulus-Responsive Liquid Marbles

Millimeter-sized "liquid marbles" are usually prepared using highly hydrophobic particles such as fluorosilane-treated lycopodium powder or alkylated silica sols. In the present work it is shown that "liquid marbles" can be prepared using sterically stabilized polystyrene latex; remarkably, such latex particles can be readily prepared by aqueous emulsion polymerization using a well-defined styrene-functionalized poly(2-(diethylamino)ethyl methacrylate) macromonomer as a reactive steric stabilizer. The macromonomer stabilizer chains are water-soluble when partially protonated below their pK(a) of approximately 7.0 but become sufficiently hydrophobic in their deprotonated form to allow formation of robust "liquid marbles" that remain stable when placed at the air/water interface. Moreover, the stabilizer chains confer pH-responsive behavior on the "liquid marbles"; addition of acid to the aqueous subphase causes immediate destruction of the "liquid marble".

Preparation of stable foams using sterically stabilized pH-responsive latexes synthesized by emulsion polymerization

Three near-monodisperse poly(2-vinylpyridine) (P2VP) latexes of 380 nm, 640 nm and 820 nm diameter were prepared in turn by emulsion copolymerization of 2-vinylpyridine and divinylbenzene using a monomethoxy-capped poly(ethylene glycol) monomethacrylate (PEGMA) macromonomer as a reactive steric stabilizer. Each of these latexes proved to be effective particulate stabilizers for the production of long-lived foams by either hand-shaking or using foam columns. Scanning electron microscopy studies confirmed that the dried foams contained well-defined latex bilayers in each case, suggesting that the original air bubbles were stabilized with latex monolayers. Dried foams prepared using the smallest latex exhibited interesting optical effects when viewed in reflectance mode. This is most likely due to light diffraction by the latex bilayers, since the mean latex diameter of 380 nm is approximately half that of visible light. These PEGMA–P2VP particles undergo a latex-to-microgel transition at low pH. Such swelling causes catastrophic instability within the wet foams, presumably due to microgel desorption from the air–water interface. Thus these latex foams exhibit pH-responsive behavior.

How Does the Nature of the Steric Stabilizer Affect the Pickering Emulsifier Performance of Lightly Cross-Linked, Acid-Swellable Poly(2-vinylpyridine) Latexes?

A near-monodisperse styrene-functionalized poly[2-(dimethylamino)ethyl methacrylate] (PDMA) macromonomer was evaluated as a reactive steric stabilizer for the preparation of poly(2-vinylpyridine (P2VP) latexes via emulsion polymerization. The solution pH was shown to be a critical parameter for successful syntheses: stable latexes with minimal coagulum were only obtained at (or above) neutral pH. The presence of the grafted PDMA stabilizer in a near-monodisperse P2VP latex of 280 nm diameter was indicated by FT-IR spectroscopy and quantified at 6.0 wt % using 1H NMR spectroscopy. XPS studies confirmed that this stabilizer was located at the latex surface, as expected. Combined DLS and electrophoretic data indicated that these PDMA-P2VP particles exist in three states depending on the solution pH: swollen cationic microgels were obtained below pH 4.1, nonsolvated latex particles with a cationic stabilizer layer were obtained at intermediate pH, and flocculated latex particles with neutral PDMA stabilizer chains were obtained at around pH 8.5. Finally, this PDMA-P2VP latex was shown to be a superior Pickering emulsifier for stabilizing water-in-1-undecanol emulsions than either a poly(ethylene glycol)-stabilized P2VP latex or a charge-stabilized P2VP latex. This serves to illustrate the important role played by the steric stabilizer in determining particle wettability.

Hydroxy and Di‐Hydroxy End‐Capped Polybutadiene as Reactive Steric Stabilizers for the Synthesis of Polyurethane Particles in Organic Dispersant Media

AbstractSummary: The synthesis of polyurethane particles by polyaddition of ethylene glycol (EG) and tolylene‐2,4‐diisocyanate (TDI) in cyclohexane at 60 °C was investigated in the presence of ω‐hydroxy and ω,ω′‐dihydroxy polybutadiene, used as reactive steric stabilizers. The effect of the functionality and concentration of the reactive polybutadiene, as well as the monomer addition procedure, onto the polyurethane particle formation was studied. Calibrated PUR particles with an average diameter in the range 1–2 µm could be readily obtained.

Polyaddition reaction in a dispersed medium: elaboration of new core‐shell polyurethane particles

AbstractThe elaboration in a dispersed organic medium of calibrated polyurethane particles with a core‐shell structure is presented in this paper. The objective could be achieved by using a series of reactive steric stabilizers of the type ω‐(OH)x‐poly(n‐butyl acrylate), ‐polystyrene, ‐polysiloxane or ‐polybutadiene (x=1 or 2) that play the role of surfmers during the polyaddition reaction between ethylene glycol and tolylene‐2,4‐diisocyanate, in cyclohexane as a dispersant medium. The final size of the polyurethane particles (0,5‐10 μm) was found to be a function of the steric stabilizer characteristics (nature, molar mass and concentration) and of the addition procedure of the different reactants. These novel particles constituted of a polyurethane core and various shells depending on the stabilizer used exhibit specific and original properties.

Synthesis, polymerization, and dispersion copolymerization of poly(ethylene oxide) macromonomers carrying methacryloyloxyalkyl end groups

Poly(ethylene oxide) macromonomers carrying methoxy group on the one (α-) end and methacryloyloxyhexyl or methacry-loyloxydecyl group on the other (ω-) end were prepared, homopolymerized in water, and dispersion-copolymer-ized with styrene or methyl methacrylate in a methanol-water mixture. They were found to polymerize more rapidly and to produce stable polystyrene dispersions more effectively, as compared to the corresponding macromonomers carrying either α-methoxy and or α-dodecyloxy and ω-methacryloyloxy end groups. Thus, the amphiphilic constitution of the macromonomers such that favors the polymerizing methacrylate end groups to locally concentrate into the micelle core or to the particle surface while the poly(ethylene oxide) chains extending to the medium appears to be most important in enhancing their polymerizability and effectiveness as reactive steric stabilizers. On the other hand, stable poly(methyl methacrylate) particles with a number of craters or pleats on the surface were produced with a PEO macromono-mer with α-methoxy and co-methacryloyloxy end groups.

NEW REACTIVE POLYELECTROLYTE STABILIZERS FOR POLYANILINE COLLOIDS

We describe the preparation and characterization of polyaniline colloids using two new reactive steric stabilizers based on anionic poly(sodium styrene sulfonate) and cationic poly(2-(dimethylamino)ethyl methacrylate) copolymers. Both these polyelectrolyte stabilizers contain reactive comonomers (either N-phenylmaleimide or 4-aminostyrene), which promote chemical grafting of the stabilizer onto the surface of the polyaniline particles. These polyaniline colloids have been characterized in terms of their chemical composition, particle size, morphology and conductivity by various techniques, including elemental microanalyses, IR spectroscopy, visible absorption spectroscopy, disc centrifuge photosedimentometry, transmission electron microscopy and d.c. conductivity. © 1997 Elsevier Science Ltd. All rights reserved

Effect of poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group as a steric stabilizer on dispersion polymerization of styrene

In dispersion polymerization of styrene in ethanol, effects of a reactive steric stabilizer, poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group (P(VAc/VA)-SH), were investigated. In the absence of the thiol end group, the dispersion coagulated at the middle stage of the polymerization, while in the presence of the thiol end group, the polymerization proceeded successfully to result in close to monodisperse particles. The reactive thiol group acts as a site of formation of the block copolymer, that is, polystyrene-b-P(VAc/VA), which is utilized as an effective dispersant. From the measurement on molecular weights during the course of polymerization, two polymerization loci were realized. Addition of butyl methacrylate to styrene affected markedly not only rate of polymerization but also particle size. © 1996 John Wiley & Sons, Inc.

Surface characterization of colloidal polypyrrole particles synthesized with reactive steric stabilizers using X-ray photoelectron spectroscopy

Abstract X-ray photoelectron spectroscopy has been used to characterize the surfaces of polypyrrole colloids synthesized using reactive steric stabilizers based on statistical copolymers of 2-(dimethylamino)ethyl methacrylate. Three different copolymer stabilizers, containing 2-vinylpyrrole, 3-vinylthiophene and 2,2′-bithiophene-5-methyl methacrylate graft sites respectively, were examined. In each case, the grafted copolymer stabilizer was detected at the surface of the polypyrrole particles, which is consistent with the accepted steric stabilization mechanism of colloid stability. With the bithiophene-based copolymer stabilizer, the sulfur atoms in the bithiophene groups acted as unique elemental markers, and thus aided the detection and quantification of the stabilizer component. The atomic ratio of nitrogen to sulfur as determined by X.p.s. for this polypyrrole colloid was significantly higher than that observed for the corresponding copolymer stabilizer. This excess surface nitrogen was attributed to the polypyrrole component and is consistent with the relatively high solid-state conductivity (ca. 10−1 to 100 S cm−1) measured on compressed pellets of this dried colloid. The presence of the other two copolymer stabilizers at the surface of the polypyrrole particles is less obvious but can be verified from close inspection and comparison of the C1s and N1s core-line spectra of the two polypyrrole colloids, their corresponding copolymer stabilizers and a polypyrrole ‘bulk powder’ control sample respectively.