Milena Špírková

Polyaniline dispersions 8. The control of particle morphology

Abstract Polyaniline dispersions are obtained when aniline is oxidized in an acidic aqueous medium with ammonium peroxodisulfate in the presence of hydroxypropylcellulose. The progress of aniline polymerization has been monitored by the acidity changes and the formation of colloidal particles by dynamic light scattering. Submicrometre spherical polyaniline particles of good uniformity in size are produced at 0°C, while at 40°C the resulting objects have coral-like cylindrical morphology. A similar change of particle shape has been achieved at 0°C by the acceleration of polyaniline formation by addition of a mediator, p -phenylenediamine. The concept of the formation of spherical and non-spherical morphologies and the role of the autoacceleration effect in the dispersion polymerization of aniline are proposed. Polymerization in the frozen reaction mixture at −25°C yielded a macroporous composite.

Novel pH-Responsive Nanoparticles

In this work we report a new type of pH-responsive micelle-like nanoparticle. Reversible nanoscale structures are formed in solutions of a pH-sensitive hydrophobic polyelectrolyte, poly( N-methacryloyl- l-valine) or poly( N-methacryloyl- l-phenylalanine), and nonionic surfactant (Brij 98) in the presence of hydrochloric acid. The influence of composition and pH on particles size and shape was investigated by a variety of methods. An entitys size and polydispersity could be varied in a broad range making them a perspective candidate as a drug carrier. Unlike the case of typical micelles, our results indicate the presence of cavities in the formed particles. A hypothetical model of a nanoparticle and mechanism of formation are proposed.

Effect of hydrophobic interactions on properties and stability of DNA-polyelectrolyte complexes.

Polyplexes are polyelectrolyte complexes of DNA and polycations, designed for potential gene delivery. We investigated the properties of new polyplexes formed from cholesterol-modified polycations and DNA. Three complexes were tested; their cholesterol contents were 1.4, 6.3, and 8.7 mol %. UV spectroscopy and fluorescence assay using ethidium bromide proved the formation of polyplexes. The kinetics of turbidity of polyplexes solutions in physiological solution showed that the colloid stability of polyplexes increases with increasing content of cholesterol in polycations. Dynamic, static, and electrophoretic light scattering, small-angle X-ray scattering, and atomic force microscopy were used for characterization of polyplexes. The observed hydrodynamic radii of polyplexes were in the range of 30-60 nm; they were related to the polycation/DNA ratio and hydrophobicity of the used polycations (the cholesterol content). The properties of polyplex particles depend, in addition to polycation structure, on the rate of polycation addition to DNA solutions.

Structural and Surface Properties of Novel Polyurethane Films

In this work, novel polycarbonatediol- and polybutadienediol-based polyurethanes (PU) with promising properties were prepared and compared with an analogous polypropyleneglycol-based product. Hexamethylenediisocyanate was used as isocyanate (NCO) component. All three PU systems were subsequently modified by the incorporation of two different nanofillers (Montmorillonite clays): “Cloisite 15A” and “Bentonite for organic systems.” The PUs were prepared in form of film coatings and characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), and wide angle X-ray scattering (WAXS). Their chemical microstructure was checked by 13C-NMR spectroscopy.

pH-dependent self-assembly of polystyrene-block-poly((sulfamate-carboxylate)isoprene) copolymer in aqueous media.

The amphiphilic polystyrene- block-poly((sulfamate-carboxylate)isoprene) (PS-PISC) diblock copolymer was synthesized from the precursor diblock copolymer polystyrene- block-isoprene by reaction with chlorosulfonyl isocyanate. The structure and behavior of self-assembled PS-PISC nanoparticles was studied in alkaline and acidic aqueous solutions by a combination of static and dynamic light scattering, analytical ultracentrifugation, atomic force and cryogenic transmission electron microscopies, NMR spectroscopy, potentiometric titration, and fluorometry using pyrene as a polarity-sensitive fluorescent probe. It was found that PS-PISC exists in aqueous solutions in the form of micellar aggregates. The aggregation tendency increases with decreasing effective charge density in the shell, that is, with decreasing pH of the solution, and aggregates found in alkaline aqueous media have much smaller molar masses than those formed in acidic media. The latter are dense, collapsed structures with immobile PISC domains in which most of the COOH and NH 2 (+)SO 3 (-) groups are buried inside of the nanoparticles. The swelling of PISC domains and disentanglement of PISC chains after addition of a base are slow processes occurring on the time scale of days.

Preparation and characterisation of hybrid organic/inorganic coatings and films

SummariesHybrid organic/inorganic coatings and free-standing films made from GTMS [3-glycidyloxy)propyl]trimethoxysilane, GMDES [3-(glycidyloxy)propyl]methyldiethoxysilane, poly(oxypropylene) of different molecular weights end-capped by amino groups (Jeffamine D-230, D-400 and T-403), and in some cases, colloidal silica, were prepared and characterised. Hydrochloric acid as a catalyst for the sol-gel process and water/propan-2-ol mixture as a solvent were chosen. The structure, morphology and mechanical properties of these scratch-resistant systems were studied by static and dynamic mechanical analysis, small-angle x-ray scattering, NMR spectroscopy and atomic force microscopy. The coatings were fully transparent and colourless with a smooth surface and showed suitable mechanical properties.RésuméDes films indépendants [freestanding] et des revêtements hybrides organiques/inorganiques, préparés à partir du GTMS [3-(glycidyloxy)propyl]triméthoxysilane, GMDES [3-(glycidyloxy)propyl] méthyldiéthoxysilane, poly(oxypropylène) de poids moléculaires variés et dont les extrémités se terminent par des groupes amino (Jeffamine D-230, D-400 et T-403) et dans quelques cas par la silice colloïdal, ont été préparés et caractérisés. On a choisi l’acide chlorhydrique en tant que catalyseur pour le procédé sol-gel et une mélange eau/propan-2-ol comme solvant La structure, la morphologie, et les propriétés mécaniques de ces systèmes qui résistent aux eraflures ont été étudiées par le moyen d’analyses mécaniques statiques et dynamiques, de la diffusion x aux petits angles, de la spectroscopie NMR et de la microscopie force atomique. Les revêtements étaient tout à fait transparents et incolores, ayant la surface lisse. Ils ont manifesté des propriétés mécaniques pertinentes.ZusammenfassungHybrid organische/anorganische Beschichtungen und freistehende Films aus GTMS [3-(Glycidyloxy)propyl]trimethoxysilan, GMDES [3-(Glycidyloxy)propyl]methyldiethoxysilan, Poly(oxypropylen) von verschiedenem Molekulargewicht, die mit Aminogruppen wie Jeffamine D-230. D-400 and T-403 endverkappt sind, und in einigen Fällen aus kolloiden Silikaten, wurden hergestellt und characterisiert. Wir verwendeted Salzsäure als Katalyst für den Sol-Gel Prozess und eine Mischung aus Wasser und Propan-2-ol als Lösungsmittel. Wir studierten die Struktur. Morphologie und mechanischen Eigenschaften dieser kratzfesten Systeme durch statische und dynamische mechanische Analyse, Kleinwinkel-Röntgenverteilung, NMR Spektroskopie und Atomkraftmikroskopie. Die Beschichtungen waren völlig transparent und farblos mit einer glatten Oberfläche, und zeigten geeignete mechanische Eigenschaften.

Electrically anisotropic polyaniline-polyurethane composites

Abstract Electrically conducting polyaniline particles were organized by electric field in a liquid medium, and subsequently polymerized into a Polyurethane network. The chains of PANI particles oriented in the field became fixed in the network. In this way, electrically anisotropic materials were prepared: the conductivity in the direction parallel to the orientation was several times higher than that in the perpendicular one. The conductivity increases and electrical anisotropy reversibly decreases with growing temperature.

Comparison of Environmentally Friendly, Selective Polyurethane Catalysts

Selected commercially available amines, including N-substituted morpholines, were evaluated as single catalysts and as catalyst mixtures for polyurethane foam preparation. The motivation was the search for economically and environmentally attractive replacements of “classical” catalysts, like diazabicyclooctane, dibutyltindilaurate, and N,N-bis(2-dimethylaminoethyl)methylamine. Especially interesting was replacing dibutyltindilaurate, and also the possibility of using reactive catalyst derivatives that would be incorporated into polyurethanes, thus reducing the content of volatile organic compounds in the polymer. The catalysts were tested on a α,ω-polybutadienediol + toluenediisocyanate-based system. In some experiments, toluenediisocyanate was replaced by the more reactive and environmentally friendly 4,4′-Methylenebis(phenylisocyanate) and polybutadienediol by polypropyleneglycol.

Electrically anisotropic materials: polyaniline particles organized in a polyurethane network†

Electrically conducting polyaniline particles were organized by an electric field in a liquid medium, which was subsequently polymerized to produce a polyurethane network. The changes in electrical conductivity during polymerization were recorded. The chains of conducting polyaniline particles oriented in the direction of the electric field became fixed in the polymer network. In this way, electrically anisotropic materials were produced. The conductivity in the direction parallel to the orientation was several times higher than that in the perpendicular one. The conductivity of these composite materials increases with temperature, while the electrical anisotropy decreases. The effect of electrical anisotropy is explained by simple geometric considerations.

Extent of side reactions and gelation of polyether polyurethanes

SummaryGelation and gel build-up due to a side reaction in poly-(oxypropylene) diol — 4,4′-diisocyanatodiphenylmethane systems, catalyzed by dibutyltin dilaurate and containing excess NCO groups was studied at 60 to 140°C. Formation of allophanate groups from urethane and urea and biuret from traces of water were the main side reactions. The extent of these reactions was monitored by the determination of isocyanate reacted in excess to that consumed for the formation of urethane and urea groups. Two gel point were observed: one corresponding to the sol→gel transition at a low excess of NCO groups and the other one corresponding to the gel→sol transition at a high excess of NCO groups. The width of the gel and the maximum amount of gel decrease with increasing temperature.