Abstract: Artificial neural networks as a semi-empirical modelling tool for physical property predictions in polymer science new generation high performance polymers by displacement polymerization acrylamide polymers transparent polyolefins the polyolefins stabilizers with intramolecular synergism high-temperature stabilization of polyolefins poly(malic acid) from natural sources stabilization of polyolefins gamma radiation induced preparation of polyelectrolytes and its use for treatment of waste water polyvinylchloride (PVC)/thermoplastic polyurethane (TPU) polymeric blends mechanical properties of ionomers and ionomer blends metallocene based polyolefins - product characteristics preparations and properties of porous poly(vinyl alcohol)-poly(vinyl acetate) composites hydrophobization of polyanionic polymers to achieve higher biological activity uniform latex particles reaction mechanism of vinyl polymerization with amine in redox and photo-induced charge-transfer initiation systems photoinitiation of free-radical polymerization by organometallic compounds chemical modification of polystyrenes in the presence of cationic catalysis and their industrial applications performance of polyethylenes in relation to their molecular structure the crystallization of polyethylene under high pressure structure, stability, and degradation of PVC solution state of metal complex calixarenes and polymetric calixarenes thermodynamic opportunity of degradation reaction initiation polymerization by ylides. (Part contents).

Abstract: pH-responsive gels of hydrophobically modified (HM) weak polyacid were prepared from acrylic acid and n-alkyl acrylates (n = 8, 12, 18). The HM gels obtained bear up to 20 mol % of n-alkyl acrylate units randomly distributed along the network chains. The pH-driven swelling of these gels upon ionization in an aqueous medium was studied. The effect of the fraction and of the side chain length of n-alkyl acrylate groups on the equilibrium degree of swelling was examined. It was shown that the swelling transition shifts to alkaline pH with increasing hydrophobicity of the gel. This was explained by the stabilization of the collapsed state of the gel by hydrophobic aggregation of n-alkyl side chains. The formation of such aggregates, which break down in the course of gel ionization, was confirmed by the fluorescent probe method with pyrene as a probe and by NMR spectroscopy. Potentiometric titration data of HM poly(acrylic acid) (PAA) gels and of the corresponding linear copolymers evidence that the introducti...

Abstract: Polyelectrolyte complex formation between components with strong ionic groups and high molecular weights were studied by static light scattering as a function of the mixing ratio and the ionic strength of the medium. Sodium poly(styrenesulfonate) and sodium poly(methacrylate) were used as polyanions and poly(diallyldimethylammonium chloride) and its copolymer with acrylamide were used as polycations. Very small amounts of sodium chloride lead to a drastic decrease of the level of aggregation, while higher ionic strength results in macroscopic flocculation.

Abstract: Polyelectrolyte multilayers containing electrochemically active viologen units have been constructed using the layer-by-layer deposition technique with poly(styrenesulfonate) and poly(butanylviologen) as polyanion and polycation, respectively. All redox active material is electrochemically addressable in multilayers made from these polymers. Cyclic voltammetry, ellipsometry, and UV−vis spectroscopy indicate a systematic dependence of the amount of material contained in these ultrathin films on the number of deposition cycles, although initial layers are significantly thinner. When the distance between a redox active layer and the electrode was varied by interposing non-electrochemically active layer pairs, it was determined that the material within the redox active layer was distributed over a distance of at least 2.5 layer pairs away from the nominal location of the redox active layer. This evidence for extensive interpenetration between layers was confirmed using variable-angle XPS, which revealed a 1:1...

Abstract: A self-consistent field analytical theory is developed to analyze the equilibrium structure of weakly charged polyelectrolyte brushes in salt-free solutions. In contrast to previous studies based on the local electroneutrality approximation valid for sufficiently strongly charged or densely grafted (“osmotic”) brushes, we consider a general case comprising both limits of weakly and strongly charged systems without any a priori assumptions about the distribution of counterions. The analytical expressions for various structural properties of free and confined polyelectrolyte brushes are obtained and compared to existing scaling predictions. The elastic response and structural rearrangement in the polyelectrolyte brush under compression are analyzed.

Abstract: Near-monodisperse, micrometre-sized poly(N-vinylpyrrolidone)-stabilized polystyrene latexes have been coated with polypyrrole by in situ deposition of the conducting polymer from aqueous solution. If the conducting polymer overlayer is sufficiently thin, it lies inside the steric stabilizer layer and the coated latexes retain reasonable colloid stability. The polypyrrole loading on the latex particles was systemically varied over a wide range (1–50 mass%) simply by changing the initial latex concentration. Pressed pellet conductivity measurements on the dried composites indicated an anomalously low percolation threshold of 1–2 vol. %, which is consistent with the conducting polymer component lying on the surface of (rather than within the interior of) the latex particles. IR spectroscopy studies of the composites confirmed the presence of several strong absorption bands due to the polypyrrole component. However, scanning electron microscopy (SEM) studies showed no evidence for the polypyrrole overlayer, which suggests that it must be very smooth and uniform. Disk centrifuge photosedimentometry (DCP) studies on the coated latexes revealed the presence of doublets and higher aggregates which indicates that these dispersions are weakly flocculated. However, if the polypyrrole overlayer is very thin (<10 nm) the coated particles exist in solution mainly as singlets with relatively few doublets or larger floccs. Polystyrene latex can also be coated with other conducting polymers such as polyaniline and poly(3,4-ethylenedioxythiophene). Finally, both polyelectrolytes and physically adsorbed poly(N-vinylpyrrolidone) can provide an effective steric barrier to allow controlled deposition of the conducting polymer overlayer.

Abstract: The behavior of clays in soils, groundwater aquifers, and aquatic environments is controlled to a large extent by flocculation and dispersion phenomena. Dispersed clay particles can become mobile and facilitate the translocation of strongly sorbed pollutants in the environment. In this study, the adsorption of a soil humic acid to Na-kaolinite and the resulting effect on surface charge and colloidal stability of kaolinite were investigated in dilute aqueous suspensions. The pH dependence (pH 3-11) of humic acid adsorption to kaolinite in a NaClO 4 background electrolyte was studied with batch experiments at three different ionic strengths (0.001, 0.01, and 0.1 M). Sorption of humic acid increased with decreasing pH or increasing ionic strength, a behavior that is typical for anionic polyelectrolytes with carboxylic junctional groups. Electrophoretic mobility measurements showed that pure kaolinite had positive net total particle surface charge at low pH and negative surface charge at high pH, with an isoelectric point at pH 4.8 (in 0.01 M NaClO 4 ,). With increasing amounts of humic acid sorbed to the kaolinite surface, the electrophoretic mobility was continuously shifted to more negative values. At low pH, this resulted in charge reversal from positive to negative net total particle surface charge. Additions of small amounts of humic acid to the kaolinite suspensions resulted in large increases in colloidal stability. At low pH, this was probably due to reversal of edge charge from positive to negative preventing edge-to-face flocculation. In additlon, a general increase in negative surface charge density and steric stabilization effects may contribute to the influence of adsorbed humic acid on the colloidal stability of kaolinite.

Abstract: Introduction polymeric catalysts photoresponsive polymers electrically conducting polymers and their applications as functional materials magnetic polymers oxygen-carrying and oxygen-permeating polymers polymeric inclusion complexes hydrophobic modification of poly(MA-CDA) to enhance biological activity a Novel biomaterial - aramid-silicone resin polymeric materials for second-order nonlinear optical applications ion-conducting polymers chitin heparinoids - their preparation and specificities unimer micelles of functionalized amphiphilic polyelectrolytes polymer gels.

Abstract: A new method for the patterning of ionic layer-by-layer assembled films with micron-sized features is presented. Self-assembled monolayers (SAMs) were used as templates to direct the deposition of sulfonated polystyrene (SPS) and poly(diallyldimethylammonium chloride) (PDAC) multilayers onto a surface. Both polyelectrolytes were assembled electrostatically from dilute solutions (10 and 20 mM on a repeat unit basis) with varying amounts of sodium chloride. The ionic content was varied from 0 to 4 M NaCl. The optimal conditions for templating were found at moderate salt contents. At high salt contents (≥1 M NaCl) the templating behavior of the chemically patterned SAM surface completely reversed due to electrostatic screening and dehydration of an oligo(ethylene glycol)surface, indicating that ionic strength can be used to dramatically alter polyion deposition behavior on the functionalized surface.

Abstract: Spontaneous sequential adsorption of poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) (layer-by-layer deposition) onto surface-oxidized poly(4-methyl-1-pentene) film was studied with the objective of creating an asymmetric gas separation membrane consisting of a thin multilayer barrier layer on a more permeable polymer film. Poly(4-methyl-1-pentene) film was first surface-oxidized with chromic acid solution to introduce carboxylic acid functionality to the surface for depositing the first layer. By alternating the poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) depositions, multilayered structures were prepared with the total number of layers up to 104. Gas permeabilities of composite membranes prepared by this layer-by-layer deposition technique were determined for hydrogen, oxygen, and nitrogen. The depressed gas permeabilities of the composite membranes are explained by dense and rigid packing of the polyelectrolytes in stratified layers. The multilayered poly(allylam...

Abstract: Chitosan, a cationic polysaccharide, was heterogeneously deacetylated with a 47% sodium hydroxide solution and followed by a homogeneous reacetylation with acetic anhydrides to control the N-acetyl content of the chitosan having a similar molecular weight. The chitosans having different degrees of N-acetylation were complexed with sodium alginate, an anionic polysaccharide, and the formation behavior of polyelectrolyte complexes (PECs) was examined by the viscometry in various pH ranges. The maximum mixing ratio (Rmax) increased with a decrease in the degree of N-acetylation of the chitosan at the same pH, and with a decrease in pH at the same degree of N-acetylation. Similarly, N-acylated chitosans were also prepared. The N-acyl chitosans scarcely affected the formation behavior of PECs with sodium alginates. For the application of the PECs produced, the microencapsulation of a drug was performed and the release property of drug was tested. The microcapsules were prepared in one step by the extrusion of a solution of guaifenesin and sodium alginate into a solution containing calcium chloride and chitosan through interpolymeric ionic interactions. The drug release during the drug-loaded microcapsules storage in saline was found to depend on the pH where the microcapsules were formed and the kind of N-acyl groups introduced to the chitosan. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 425–432, 1997

Abstract: The consecutive layer-by-layer adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) on colloidal charged latex particles is investigated by measuring the electrophoretic mobility as a function of pH and ionic strength over a broad range (electrophoretic fingerprinting) Meaningful interpretation of the data required the development of a nonlinear approach to hairy particle electrophoresis including dissociation, adsorption, and association Steric and electrostatic exclusion of mobile ions from the hairy layer has been considered Also, the surface conductivity correction is extended to the case of charged hairy layer particles We deposited up to three polyelectrolyte layers The following were found: (i) Each layer deposition is accompanied by charge overcompensation and (ii) Not only the top layer but also the underneath layers and the naked latex particle surface contribute to the particle mobility This can be interpreted as an incomplete coverage or a polyelectrolyte

Abstract: A novel semi-interpenetrating polymer network (semi-IPN) membrane composed of crosslinked chitosan(cr-CS) and poly(acrylic acid) (PAA) was prepared. Evidence from infrared spectra proved the formation of polyelectrolyte complex through electrostatic interaction between groups from CS and COO− groups from PAA. The semi-IPN membrane swelled at high pH and at low pH exhibited a typical pH-sensitivity. Its swelling degrees in different salt solutions with the same ionic valence and equal ionic strength were on similar levels. Under certain ionic strength (I = 1.5 mol/L), the degree of swelling increased with increased metal ionic valence. Furthermore, the elongation of the semi-IPN membrane could vary reversibly by immersion into CaCl2 solution and KCl solution alternately. Reasons for the chemomechanical behavior are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1445–1450, 1997

Abstract: The complexation of a charged micelle and an oppositely charged polyelectrolyte was studied by the use of a simple model system. The size of the micelle was varied to correspond to the change in su...

Abstract: In this report, we describe novel polymeric composite films formed from multilayers of amine-terminated dendrimers and poly(maleic anhydride)-c-(methyl vinyl ether) (Gantrez) grafted onto Au-coated Si wafers. These composite membranes exhibit fully reversible, pH-switchable permselectivity for both cationic and anionic redox-active probe molecules. The pH-dependent change in charge of the dendrimer amine groups and the carboxylic groups derived from the random coil polyanhydride chains serve as independent ion gates. These gates pass cations only at high pH, anions only at low pH, and both cations and anions at intermediate pH (Figure 1). Polymeric materials demonstrating this switchable permselective function have not previously been reported. Dispersions of cationic and anionic polyelectrolytes usually result in spontaneous flocculation and precipitation due to strong electrostatic interactions,1 but the layer-by-layer synthetic approach used here avoids this problem. Responsive or “smart” membrane systems have been studied previously. Such materials have applications in controlled release, selective filtration, electronic devices, and chemical sensors and biosensors.2-9 Anionic or cationic polymeric membranes that have permselectivity toward electroactive counterions due to the membrane charge have also been studied.10-12 For example, Anson et al. have studied membrane systems derived from polyelectrolytes such as the polysulfonated fluoropolymer Nafion, poly(acrylic acid), and poly(4-vinylpyridine) that show electrostatic binding of electroactive counterions.10 These materials are related to those described here, but they are not pH switchable between cationic and anionic forms. Moreover, previous work has typically involved much thicker cast films. Recently, Martin and co-workers developed an electronically switchable, ion-exchange membrane system consisting of cylindrical nanoscopic metal tubules whose surface potential can be electronically manipulated to either pass or exclude anions and cations.13 Our new work uses a nanocomposite polymeric ultrathin film that relies on homogeneously dispersed pH-responsive amine and carboxyl groups to induce fully reversible permselectivity into an electrode-supported membrane. The highly functionalized composite thin films were synthesized in a covalent, layer-by-layer fashion by using a general method recently developed in our laboratories.14 First, a selfassembled monolayer (SAM) of dendrimers on a Au-coated Si wafer was prepared by immersion of the substrate in a methanol solution containing a fourth generation, amine-terminated Starburst (PAMAM) dendrimer.15 The resulting dendrimer SAM, denoted as layer D0, was then allowed to react with Gantrez, to afford a first layer of Gantrez (Gz1) covalently linked to D0 Via amic acid bonds. Repetitive sequential deposition leads to additional covalently linked layers of the G4 PAMAM dendrimer and Gantrez: D1, Gz2, D2, and so on. Although the topmost layer is chemically distinct from those underlying it, we believe that the film interior is more or less homogeneous, as shown in Figure 1. These composite films consist of dendritic units having amphoteric internal and peripheral amine groups mixed with the Gantrez network containing amphoteric carboxyls. This structure constitutes the basis for the permselective, pH-responsive supramolecular gate. The extent of ionic permeability of the D2 films was investigated under different pH conditions by using anionic Fe(CN)6 and cationic Ru(NH3)6 as redox probe molecules. Figure 2 shows cyclic voltammograms of electrodes modified with the D2 films in an aqueous solution containing 5 mM of either Fe(CN)6 or Ru(NH3)6 buffered at pH 3.0, 7.0, and 11.0. The shape and magnitude of these voltammograms are significantly affected by pH. For example, the peak current density resulting from Fe(CN)6 reduction is about 750 μA/ cm2 at pH 3.0 while there is essentially no reduction current at pH 11.0. The voltammetric results clearly indicate that the D2 films are open (“On”) to the negatively charged probe, Fe(CN)6, at pH 3.0, but impermeable (“Off”) to the probe at pH 11.0. This responsive behavior is fully reversible to repetitive switching of the pH for up to at least 10 cycles. * Authors to whom correspondence should be addressed. † Phone: (409) 845-3437. Fax: (409) 845-2964. E-mail: Bergbreiter@ chemvx.tamu.edu. ‡ Phone: (409)-845-5629. Fax: (409) 845-1399. E-mail: Crooks@ chemvx.tamu.edu. (1) Kotz, J. Polymeric Materials Encyclopedia; Salamone, J. C., Ed., CRC Press: Boca Raton, FL, 1996; Vol. 8, pp 5762-5771. (2) Odashima, K.; Koga, K. ComprehensiVe Supramolecular Chemistry; Vogtle, F., Ed.; Elsevier Science Inc.: New York, 1996; Vol. 2, pp 143194. (3) Riggs, J. A.; Smith, B. D. J. Am. Chem. Soc. 1997, 119, 27652766. (4) Fyles, T. M.; James, T. D.; Kaye, K. C. J. Am. Chem. Soc. 1993, 115, 12315-12321. (5) Ito, Y.; Park, Y. S.; Imanishi, Y. J. Am. Chem. Soc. 1997, 119, 27392740. (6) Kent, M. S.; Factor, M. S.; Satija, S.; Gallagher, P.; Smith, G. S. Macromolecules 1996, 29, 2843-2849. (7) Yoshida, R.; Uchida, K.; Kaneko, Y.; Sakai, K.; Kikuchi, A.; Sakurai, Y.; Okano, T. Nature 1995, 374, 240-242. (8) Thomas, J. L.; You, H.; Tirrell, D. A. J. Am. Chem. Soc. 1995, 117, 2949-2950. (9) Barbucci, R.; Casolaro, M.; Magnani, A. J. Controlled Release 1991, 17, 79-84. (10) (a) Yoshikawa, M.; Anson, F. C. J. Phys. Chem. 1996, 100, 41994204. (b) Redepenning, J.; Anson, F. C. J. Phys. Chem. 1987, 91, 45494553. (11) (a) Ewing, A. G.; Feldman, B. J.; Murray, R. W. J. Phys. Chem. 1985, 89, 1263-1269. (b) Burgmayer, P.; Murray, R. W. J. Phys. Chem. 1984, 88, 2515-2521. (12) Oh, S.-M.; Faulkner, L. R. J. Am. Chem. Soc. 1989, 111, 56135618. (13) Nishizawa, M.; Menon, V. P.; Martin, C. R. Science 1995, 268, 700-702. (14) Liu, Y.; Bruening, M. L.; Bergbreiter, D. E.; Crooks, R. M. Angew. Chem., Int. Ed. Engl. In press. (15) Tokuhisa, H.; Zhao, M.; Baker, L. A.; Phan, V. T.; Dermody, D. L.; Garcia, M. E.; Peez, R.; Crooks, R. M. In preparation. Figure 1. Schematic illustration of the pH-switchable “On/Off” function of the composite film. The polyamine dendrimer units are covalently attached to the Gantrez polymer network. At high pH the film has a net negative charge that excludes anions but passes cations; at low pH it is positively charged and excludes cations but passes anions; and at intermediate pH, it passes both cations and anions. 8720 J. Am. Chem. Soc. 1997, 119, 8720-8721

Abstract: Rheological and photophysical data are presented for a hydrophobically modified alkali-soluble copolymer, of a constitution similar to materials currently employed as rheology modifiers in water-borne coatings. The copolymer comprises a polyelectrolyte backbone bearing ethoxylate side chains capped with complex alkylaryl groups of a high molar volume. In aqueous alkaline media, the hydrophobes associate dynamically, the topology of the network so formed being dependent on the polymer concentration. Photophysical studies, employing pyrene as a hydrophobic fluorescent probe, indicate the presence of hydrophobic associations. At concentrations below the coil overlap concentration, c*, these associations are predominantly intramolecular. At higher polymer concentrations, intermolecular interactions become more probable. This change in network topology is in qualitative agreement with previous theoretical considerations of associative polymer systems and is reflected in an unusually high concentration dependen...

Abstract: Water-soluble sodium poly(2-(3-thienyloxy)ethanesulfonate) and sodium poly(2-(4-methyl-3-thienyloxy)ethanesulfonate) have been synthesized. The sulfonic acid form of these new polymers has revealed a self-acid-doping reaction that leads to stable, highly conducting (0.5−5 S/cm) materials together with low absorption in the visible range. This process is reversible, and upon deprotonation, the insulating and dark polymers are recovered. The high doping and conductivity levels seem to be related to the relatively low oxidation potentials (0.44−0.50 V vs Ag/AgCl) of these polymers, which allows an almost complete (reversible) oxidation reaction in air (oxygen), catalyzed by the presence of the sulfonic acid moiety.

Abstract: The preparation of aqueous α-Al 2 O 3 , α-SiO 2 and α-SiC suspensions with polyelectrolytes, i.e. the NH 4 + salt of polymethacrylic acid (PMA-NH 4 + ) and the acidic form of polyethylene imine (PEI-H + ), is investigated. It is based on the adsorption of these polyelectrolytes which in turn depends mainly on the nature of the polyelectrolyte, and the charge density that develops on the powder surface in water. The efficiency of these dispersants is primarily attributed to the electrostatic interaction between -COO − groups of PMA-NH 4 + and positive sites on the alumina surface at pH 8–9 as well as between -NH 2 + -groups of PEI-H + and negative sites of the silica surface or of the oxidized surface of silicon carbide in acidic media. Good dispersion and stability of dispersions are then obtained through electrostatic and steric stabilization. As an application, the preparation of an Al 2 O 3 -SiC aqueous mixed slurry was investigated as a preliminary step in the processing of Al 2 O 3 /SiC nanocomposites.

Abstract: In the present study, the extension and contraction of the polymer chains in `polyelectrolyte brushes` grafted on a nanoporous polymeric membrane were visualized using atomic force microscopy, which enables direct microscopic observation in water. Pore size was estimated by measuring the rate of water permeation through the membrane. The rate of water permeation through an ungrafted membrane was independent of pH. The rate of permeation through the grafted membrane was found to be less than that of the ungrafted membrane, but was dependent upon pH. The rate was high at low pH, but was nearly zero at neutral pH. These changes in permeation were repeatedly carried out by pH changes, because the polyelectrolyte brush was covalently grafted on the membrane. 19 refs., 1 fig.

Abstract: Derivatives of poly(sodium acrylate) bearing a few mole percent of perfluoroalkyl side chains were synthesized Their solution properties were investigated by rheology and compared to those of their hydrogenated analogues As the hydrogenated modified polymers, these new materials display an associating behavior In semidilute solution the modified polymer exhibits viscosities of several orders of magnitude higher than the unmodified poly(sodium acrylate) However, this viscosifying effect is more pronounced for the perfluorinated derivatives By comparing the rheological behaviors we find that a polymer bearing C7F15CH2 side groups is as associative as a polymer containing the same fraction of C13H27 chains This is in agreement with Ravey and Stebe's1 conclusions concerning surfactant association that a CF2 is equivalent to 17CH2 as regards its hydrophobicity Mixtures of the perfluorinated polymers with their hydrogenated analogues or with hydrogenated surfactants were successively studied For low mo

Abstract: Recent literature is reviewed concerning the influence of suspension pH and ion concentrations on the zeta-potential of near-stoichiometric BaTiO3 powders. New work is reported concerning the surface chemistry and rheology of BaTiO3 powder in aqueous phase suspensions prepared without the use of surfactants or polyelectrolytes.