Showing papers on "Polymer published in 1996"

Polymer Layered Silicate Nanocomposites

Abstract: Polymer nanocomposites with layered silicates as the inorganic phase (reinforcement) are discussed. The materials design and synthesis rely on the ability of layered silicates to intercalate in the galleries between their layers a wide range of monomers and polymers. Special emphasis is placed on a new, versatile and environmentally benign synthesis approach by polymer melt intercalation. In contrast to in-situ polymerization and solution intercalation, melt intercalation involves mixing the layered silicate with the polymer and heating the mixture above the softening point of the polymer. Compatibility with various polymers is accomplished by derivatizing the silicates with alkyl ammonium cations via an ion exchange reaction. By fine-tuning the surface characteristics nanodispersion (i. e. intercalation or delamination) can be accomplished. The resulting polymer layered silicate (PLS) nanocomposites exhibit properties dramatically different from their more conventional counterparts. For example, PLS nanocomposites can attain a particular degree of stiffness, strength and barrier properties with far less inorganic content than comparable glass- or mineral reinforced polymers and, therefore, they are far lighter in weight. In addition, PLS nanocomposites exhibit significant increase in thermal stability as well as self-extinguishing characteristics. The combination of improved properties, convenient processing and low cost has already led to a few commercial applications with more currently under development.

Nanometre diameter fibres of polymer, produced by electrospinning

Abstract: Electrospinning uses electrical forces to produce polymer fibres with nanometre-scale diameters. Electrospinning occurs when the electrical forces at the surface of a polymer solution or melt overcome the surface tension and cause an electrically charged jet to be ejected. When the jet dries or solidifies, an electrically charged fibre remains. This charged fibre can be directed or accelerated by electrical forces and then collected in sheets or other useful geometrical forms. More than 20 polymers, including polyethylene oxide, nylon, polyimide, DNA, polyaramid, and polyaniline, have been electrospun in our laboratory. Most were spun from solution, although spinning from the melt in vacuum and air was also demonstrated. Electrospinning from polymer melts in a vacuum is advantageous because higher fields and higher temperatures can be used than in air.

Polymeric Materials Encyclopedia, Twelve Volume Set

Abstract: Additives Biodegradable Polymers Biomaterials for the Body Biomimetic Materials Biosensors Blends Block Copolymers Block Copolymer Micelles Comb-like Polymers Commercial Resins, Plastics, Elastomers Composites Compatibilizers Conducting Polymers Contact Lens Materials Controlled Release Dendrictic Polymers Dendrimers Dental Polymers Immobilized Enzymes Electrorheological Fluids Engineering Plastics Ferroelectric Polymers Ferromagnetic Polymers Fillers Flame-Resistant Material Flocculants Fluorine-containing Polymers Functional Polymers Gas Barrier Polymers Gas Separation Membranes Gelling Agents Group Transfer Polymerization Cyclopolymerization Hair and Skin Care Polymers Hairy Rod-Like Polymers High Solids Coatings Host-Guest Chemistry Hydrophilic Polymers Hydrophilic Surfaces Hydrogels Hyper-Branched Polymers Immortal Polymerization Inclusion Polymerization Inorganic/Organic Hybrids Interpenetrating Polymer Networks Ionomers Ladder Polymers Liquid Crystalline Polymers Living Polymers (Radical, Cation, Anion, and Coordination) Macrocyclic Polymers Macromonomers Membranes Metallocene Catalysis Metal Complexation Polymers Microbial Polymers Microencapsulated particles Microspheres Molecular Assemblies Molecular Complexes Molecular Composites Molecular Recognition Monodisperse Particles Monodisperse Polymers Network Polymers New Catalysts Systems New Fabrics New Initiating Systems New Living Polymer Systems New Polymerization Methods New Resins Nonlinear Optical Materials Nonthrombogenic Polymers Nucleic Acid Analogs Olefin-Carbon Monoxide Copolymers Optically Active Polymers Organometallic Polymers Pervaporation Membranes Phase Transfer Catalysts Phosphorous-Containing Polymers Photochromic Polymers Photoinitiators New Polymer Systems Poly (Ether Ketone) Poly (Ether Sulfone) Polyelectrolytes Polyelectrolyte Complexes Polyesters Polyimides Polymers from Natural Resources Polysilanes Preceramic Polymers Recycling Ring-Opening Polymerization Smart Materials Star Polymers Supramolecular Assembly Surface Modification Polymeric Surfactants Suture Materials Thermoplastic Composites Thermoreversible Gels Water-Borne Coatings Ziegler-Natta Catalysts Zwitterionic Polymerization

Structure and Dynamics of Polymer-Layered Silicate Nanocomposites

Abstract: The static and dynamic properties of polymer-layered silicate nanocomposites are discussed in the context of polymers in confined media. Despite the topological constraints imposed by the host lattice, mass transport of the polymer into the silicate layers (at least in the case of essentially non-polar polystyrene) appears to be unhindered and exhibits mobility similar to that of the pure polymer. However, both the local and global dynamics of the polymer in the hybrids are dramatically different from those in the bulk. On a local scale, intercalated polymer chains exhibit higher flexibility along their backbone along with a marked suppression (or even absence) of cooperative dynamics typically associated with the glass transition. On a global scale, relaxation of polymer chains either tethered to or in close proximity (<1 nm as in intercalated hybrids) to the host surface are dramatically altered and parallel those of other intrinsically anisotropic materials such as block copolymers and liquid crystals.

Specific Intermolecular Interaction of Carbon Dioxide with Polymers

Abstract: Fourier transform IR spectroscopy has been used to investigate the interaction of carbon dioxide with polymers. IR transmission and attenuated total reflectance spectra were obtained for CO2 impregnated into polymer films. It has been shown that the polymers possessing electron-donating functional groups (e.g., carbonyl groups) exhibit specific interactions with CO2, most probably of Lewis acid−base nature. An unusual aspect is the use of the bending mode (ν2) of CO2 to probe polymer−CO2 interactions. The evidence of the interaction is the observation of the splitting of the band corresponding to the CO2 ν2 mode. This splitting indicates that the double degeneracy of the ν2 mode is removed due to the interaction of electron lone pairs of the carbonyl oxygen with the carbon atom of the CO2 molecule. This splitting has not been observed for polymers lacking electron-donating functional groups (e.g., poly(ethylene)). In contrast, the ν3 mode shows little if any sensitivity to this interaction, which is in ac...

Crosslinked polymer compositions and methods for their use

Abstract: Crosslinked polymer compositions comprise a first synthetic polymer containing multiple nucleophilic groups covalently bound to a second synthetic polymer containing multiple electrophilic groups. The first synthetic polymer is preferably a synthetic polypeptide or a polyethylene glycol that has been modified to contain multiple nucleophilic groups, such as primary amino (-NH2) or thiol (-SH) groups. The second synthetic polymer may be a hydrophilic or hydrophobic synthetic polymer which contains, or has been derivatized to contain, two or more electrophilic groups, such as succinimidyl groups. The compositions may further comprise other components, such as naturally occurring polysaccharides or proteins (such as glycosaminoglycans or collagen) and/or biologically active agents. Also disclosed are methods for using the crosslinked polymer compositions to effect adhesion between a first surface and a second surface; to effect tissue augmentation; to prevent the formation of surgical adhesions; and to coat a surface of a synthetic implant.

Synthesis of long prebiotic oligomers on mineral surfaces

Abstract: Most theories of the origin of biological organization assume that polymers with lengths in the range of 30-60 monomers are needed to make a genetic system viable. But it has not proved possible to synthesize plausibly prebiotic polymers this long by condensation in aqueous solution, because hydrolysis competes with polymerization. The potential of mineral surfaces to facilitate prebiotic polymerization was pointed out long ago. Here we describe a system that models prebiotic polymerization by the oligomerization of activated monomers -both nucleotides and amino acids. We find that whereas the reactions in solution produce only short oligomers (the longest typically being a 10-mer), the presence of mineral surfaces (montmorillonite for nucleotides, illite and hydroxylapatite for amino adds) induces the formation of oligomers up to 55 monomers long. These are formed by successive "feedings" with the monomers; polymerization takes place on the mineral surfaces in a manner akin to solid-phase synthesis of biopolymers.

Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a Light-Emitting p-n Junction.

Abstract: Solid-state polymer light-emitting electrochemical cells have been fabricated using thin films of blends of poly(1,4-phenylenevinylene) and poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate. The cells contain three layers: the polymer film (as the emissive layer) and indium-tin oxide and aluminum films as the two contact electrodes. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a light-emitting p-n junction is formed in between. The admixed polymer electrolyte provides the counterions and the ionic conductivity necessary for doping. The p-n junction is dynamic and reversible, with an internal built-in potential close to the band gap of the redox-active conjugated polymer (2.4 eV for PPV). Green light emitted from the p-n junction was observed with a turn-on voltage of about 2.4 V. The devices reached 8 cd/m(2) at 3 V and 100 cd/m(2) at 4 V, with an external quantum efficiency of 0.3-0.4% photons/electron. The response speed of these cells was around 1 s, depending on the diffusion of ions. Once the light-emitting junction had been formed, the subsequent operation had fast response (microsecond scale or faster) and was no longer diffusion-controlled.

New polymers by metallocene catalysis

Abstract: Work in the field of application of metallocene-based catalysis in olefin, diolefin and styrene polymerization has become a research topic of growing interest in recent years. A great number of symmetric and chiral zirconocenes have been synthesized, that give tailored polymers of totally different structures. Single site catalysts have the capability of permitting the user to control polymer tacticity, molecular weight and molecular weight distribution more efficiently. Beside the homopolymers of polyethylene and poly(propylene), new kinds of copolymers and elastomers can be synthesized.

Surface Treatments of Polymers for Biocompatibility

Abstract: Biological recognition mediates cell and tissue interactions with biomaterials, be the materials employed in a biotechnical environment in vitro or a biomedical environment in vivo. These interactions are typically mediated by proteins that have adsorbed to the biomaterial surface. The principles of protein adsorption and biological recognition are described. Polymer surface modifications to reduce protein adsorption upon biomaterial surfaces are summarized, as are modifications to enhance the irreversible adsorption of proteins. Using these approaches, it may be possible to reduce the extent to which the biomaterial surface and the protein-biomaterial surface are recognized by cells and tissues. Polymer surface modifications to incorporate oligopeptide-, saccharide-, and oligosaccharide-based receptor-binding sequences are described to enable direct binding of cells with the polymer surface. With use of these approaches, it is possible to endow an entirely synthetic material with the biological recognition characteristics of biological macromolecules.

Design of Narrow-Bandgap Polymers. Syntheses and Properties of Monomers and Polymers Containing Aromatic-Donor and o-Quinoid-Acceptor Units

Abstract: A series of novel monomers and polymers containing aromatic-donor and o-quinoid-acceptor units was prepared, and the relationship between their spectral and electrochemical properties and their structures was investigated. X-ray structure analyses of the monomers possessing thiophene units revealed coplanar conformations, whereas calculations of the monomers containing N-methylpyrrole showed torsional conformations. Cyclic voltammetry showed amphoteric properties for all the monomers and p- and n-doping processes for most of the polymers. The reduction potentials were primarily dependent on the electron-accepting character of the o-quinoid-acceptor units. The electrochemical behavior of the polymers was characterized by cyclic voltammetry and suggested narrow-bandgap systems. The bandgaps determined from optical absorption spectra range from 0.5 to 1.4 eV. The polymer composed of thiophenes and benzo[1,2-c;3,4-c‘]bis[1,2,5]thiadiazole exhibited the narrowest bandgap.

Polymers and the Periodic Table: Recent Developments in Inorganic Polymer Science†

Abstract: Polysiloxanes [R2SiO]n, polyphosphazenes [R2PN]n, and polysilanes [R2Si]n illustrate that the incorporation of inorganic elements into a polymer main chain can lead to useful properties. These include low temperature flexibility, high thermal and oxidative stability, flame retardancy, novel forms of chemical reactivity, and intriguing electrical and optical characteristics arising from unusual electronic effects such as the delocalization of σ electrons. However, until recently, the development of inorganic polymer science has been held back by the synthetic problem of finding ways to join atoms of inorganic elements together into long chains. This review surveys many of the exciting advances in the field of inorganic polymers over the past decade and focuses mainly on the new inorganic polymer systems that have been prepared during this period. These include random-network polysilynes, poly(carbophosphazene)s, sulfur–nitrogen–phosphorus polymers, poly(organooxothiazene)s, and, very recently, the first examples of polystannanes that possess a main chain of tin atoms. Transition metal based polymer science has also experienced a number of synthetic break-throughs and new materials include high molecular weight metallocene-based polymers, polymetallaynes incorporating elements such as iron, nickel, and rhodium, liquid crystalline organocobalt and organochromium polymers, and lanthanide-based polymers.

Preparation and Characterization of PMMA-Clay Hybrid Composite by Emulsion Polymerization

Abstract: Nanocomposites are prepared by a simple technique of emulsion polymerization using MMA monomer and Na+-montmorillonite. The products are purified by hot toluene extraction and characterized by FT-IR, X-ray diffraction, TGA, DSC, and tensile testing. The structural investigation confirms that the products are intercalated with PMMA chain molecules oriented parallel to the direction of lamellar layers whose separation is consequently more enlarged than in the polymer-free clay. DSC traces also corroborate the confinement of the polymer in the inorganic layer by exhibiting no observable transition in the thermogram. Both the thermal stability and tensile properties of the products appear to be substantially enhanced. The ion-dipole bonding is believed to be the driving force for the introduction and fixation of the organic polymer to the interfaces of montmorillonite. © 1996 John Wiley & Sons, Inc.

Structure in Thin and Ultrathin Spin-Cast Polymer Films

Abstract: The molecular organization in ultrathin polymer films (thicknesses less than 1000 angstroms) and thin polymer films (thicknesses between 1000 and 10,000 angstroms) may differ substantially from that of bulk polymers, which can lead to important differences in resulting thermophysical properties. Such constrained geometry films have been fabricated from amorphous poly(3-methyl-4-hydroxy styrene) (PMHS) and semicrystalline poly(di-n-hexyl silane) (PD6S) by means of spin-casting. The residual solvent content is substantially greater in ultrathin PMHS films, which suggests a higher glass transition temperature that results from a stronger hydrogen-bonded network as compared with that in thicker films. Crystallization of PD6S is substantially hindered in ultrathin films, in which a critical thickness of 150 angstroms is needed for crystalline morphology to exist and in which the rate of crystallization is initially slow but increases rapidly as the film approaches 500 angstroms in thickness.

Molecularly imprinted polymer beads : Suspension polymerization using a liquid perfluorocarbon as the dispersing phase

Abstract: A suspension polymerization technique suitable for molecular imprinting is described, based on the use of a liquid perfluorocarbon as the dispersing phase. This dispersant does not interfere with the interactions between functional monomers and print molecules required for the recognition process during molecular imprinting. The method produces polymer beads, with almost quantitative yield, which can be used after only a simple washing step. An acrylate polymer with perfluorocarbon and poly(oxyethylene) ester groups was used to stabilize an emulsion of functional monomer, cross-linker, print molecule, initiator, and porogenic solvent in perfluoro(methylcyclohexane). Initiation of polymerization by UV irradiation resulted in polymer beads. The average bead size could be controlled between about 50 and 5 μm by varying the amount of stabilizing polymer. SEM of the beads indicated spherical particles with morphology typical of beads made by suspension polymerization. The technique was applicable to a range of...

Monolithic, “Molded”, Porous Materials with High Flow Characteristics for Separations, Catalysis, or Solid-Phase Chemistry: Control of Porous Properties during Polymerization

Abstract: The porosity and flow characteristics of macroporous polymer monoliths that may be used to prepare separation media, flow-through reactors, catalysts, or supports for solid-phase chemistry can be controlled easily during their preparation. Key variables such as temperature, composition of the pore-forming solvent mixture, and content of cross-linking divinyl monomer allow the tuning of average pore size within a broad range spanning 2 orders of magnitude. The polymerization temperature, through its effects on the kinetics of polymerization, is a particularly effective means of control, allowing the preparation of macroporous polymers with different pore size distributions from a single composition of the polymerization mixture. The choice of pore-forming solvent is also important, larger pores being obtained in a poor solvent due to an earlier onset of phase separation. Increasing the proportion of the cross-linking agent present in the monomer mixture not only affects the composition of the final monolit...

Humidity sensors based on polymer thin films

Abstract: Studies on humidity sensors fabricated with organic polymers for the last 10 years are reviewed. Several useful methods for improving the characteristics of humidity sensors based on polymers are proposed. In the case of a resistive-type sensor, cross-linking of hydrophilic polymers or formation of interpenetrated polymer networks with a hydrophobic polymer makes the hydrophilic polymers durable at high humidities. Graft polymerization is another method of preparing water-resistive humidity sensors. In the case of capacitive-type sensors, cross-linking is also useful to modify the hydrophobic polymer to produce a sensor with small hysteresis, high selectivity and high sensitivity.

Mitigation of CO2 by Chemical Conversion: Plausible Chemical Reactions and Promising Products

Abstract: A critical literature analysis was conducted on the viable usage of CO2 in the framework of the attempts to reduce the emissions of CO2 into the atmosphere from various processes or the rate of increase of the concentration of CO2 in the atmosphere. Applications based on the physical properties of CO2 are summarized first. Major examples are applications in supercritical extraction, enhanced oil recovery, and use as inert gas in fire extinguishing and safety application in industry. The various possibilities of use in chemical applications are systematically discussed. CO2 can react with several hydrocarbons and nitrogen-containing compounds (NH3, amines, imines). It can be used as a weak acid or as an oxidizing agent. It can be reduced electrochemically, photochemically, or chemically or by a syngas route. A variety of products can be manufactured from CO2, e.g., acids, alcohols, esters, lactones, carbamates, urethanes, urea derivatives, various copolymers, and polymers. In particular, polycarbonates are...

Effect of strongly favorable substrate interactions on the thermal properties of ultrathin polymer films.

Abstract: The thermal behavior of ultrathin films of poly-(2)-vinylpyridine spin-cast on acid-cleaned silicon oxide substrates is considered. The interaction between the polymer and the substrate is polar in nature and very favorable. As a means of examining the thermal properties of the films, x-ray reflectivity is used to measure the temperature dependence of the film thickness. This experimentally measured thickness-temperature data is used to determine transition temperatures and thermal expansivities. Significantly increased transition temperatures (20-50 \ifmmode^\circ\else\textdegree\fi{}C above the measured bulk glass transition temperature) are observed in ultrathin polymer films. The transition temperature increases with decreasing film thickness, while the degree of thermal expansion below the transition temperature decreases with decreasing film thickness. If one assumes that a region of reduced chain mobility exists near the solid substrate-polymer interface, an analysis of the measured thermal expansion behavior below the transition temperature indicates that the length scale of substrate interactions is on the order of the macromolecular size.

2,7-aryl-9-substituted fluorenes and 9-substituted fluorene oligomers and polymers

Abstract: The invention relates to 2,7-substituted-9-substituted fluorenes and 9-substituted fluorene oligomers and polymers. The fluorenes, oligomers and polymers are substituted at the 9-position with two hydrocarbyl moieties which may optionally contain one or more of sulfur, nitrogen, oxygen, phosphorous or silicon heteroatoms; a C5-20 ring structure formed with the 9-carbon on the fluorene ring or a C4-20 ring structure formed with the 9-carbon containing one or more heteroatoms of sulfur, nitrogen or oxygen; or a hydrocarbylidene moiety. In one embodiment, the fluorenes are substituted at the 2- and 7-positions with aryl moieties which may further be substituted with moieties which are capable of cross-linking or chain extension or a trialkylsiloxy moiety. The fluorene polymers and oligomers may be substituted at the 2- and 7'-positions. The monomer units of the fluorene oligomers and polymers are bound to one another at the 2- and 7'-positions. The 2,7'-aryl-9-substituted fluorene oligomers and polymers may be further reacted with one another to form higher molecular weight polymers by causing the optional moieties on the terminal 2,7'-aryl moieties, which are capable of cross-linking or chain extension, to undergo chain extension or cross-linking. Also disclosed are processes for preparing the disclosed compounds.

Characterization of Vectors for Gene Therapy Formed by Self-Assembly of DNA with Synthetic Block Co-Polymers

Abstract: Cationic polymers can self-assemble with DNA to form polyelectrolyte complexes capable of gene delivery, although biocompatibility of the complexes is generally limited. Here we have used A-B type cationic-hydrophilic block co-polymers to introduce a protective surface hydrophilic shielding following oriented self-assembly with DNA. Block co-polymers of poly(ethylene glycol)–poly-l-lysine (pEG-pLL) and poly-N-(2-hydroxypropyl)methacrylamide–poly(trimethylammonioethyl methacrylate chloride) (pHPMA–pTMAEM) both show spontaneous formation of complexes with DNA. Surface charge measured by zeta potential is decreased compared with equivalent polycation–DNA complexes in each case. Atomic force microscopy shows that pHPMA–pTMAEM/DNA complexes are discrete spheres similar to those formed between DNA and simple polycations, whereas pEG–pLL/DNA complexes adopt an extended structure. Biological properties depend on the charge ratio of formation. At optimal charge ratio, pEG–pLL/DNA complexes show efficient ...

Classification of homogeneous ethylene‐octene copolymers based on comonomer content

Abstract: Ethylene-octene copolymers prepared by Dow's INSITE™ constrained geometry catalyst technology present a broad range of solid-state structures from highly crystalline, lamellar morphologies to the granular morphology of low crystallinity copolymers. As the comonomer content increases, the accompanying tensile behavior changes from necking and cold drawing typical of a semicrystalline thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Although changes in morphological features and tensile properties occur gradually with increasing comonomer content, the combined body of observations from melting behavior, morphology, dynamic mechanical response, yielding, and large-scale deformation suggest a classification scheme with four distinct categories. Materials with densities higher than 0.93 g/cc, type IV, exhibit a lamellar morphology with well-developed spherulitic superstructure. Type III polymers with densities between 0.93 and 0.91 g/cc have thinner lamellae and smaller spherulites. Type II materials with densities between 0.91 and 0.89 g/cc have a mixed morphology of small lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities less than 0.89 g/cc have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting temperature, and the granular, nonlamellar morphology. © 1996 John Wiley & Sons, Inc.