Showing papers on "Polymer published in 2004"

Inkjet Printing of Polymers: State of the Art and Future Developments

Abstract: Inkjet printing is considered to be a key technology in the field of defined polymer deposition. This article provides an introduction to inkjet printing technology and a short overview of the available instrumentation. Examples of polymer inkjet printing are given, including the manufacturing of multicolor polymer light-emitting diode displays, polymer electronics, three-dimensional printing, and oral dosage forms for controlled drug release. Special emphasis is placed upon the utilized polymers and conditions, such as polymer structure, molar mass, solvents, and concentration. Studies on viscoelastic fluid jets and the formation of viscoelastic droplets under gravity indicate that strain hardening is the key parameter that determines the inkjet printability of polymer solutions.

Multifunctional Carbon Nanotube Yarns by Downsizing an Ancient Technology

Abstract: By introducing twist during spinning of multiwalled carbon nanotubes from nanotube forests to make multi-ply, torque-stabilized yarns, we achieve yarn strengths greater than 460 megapascals. These yarns deform hysteretically over large strain ranges, reversibly providing up to 48% energy damping, and are nearly as tough as fibers used for bulletproof vests. Unlike ordinary fibers and yarns, these nanotube yarns are not degraded in strength by overhand knotting. They also retain their strength and flexibility after heating in air at 450°C for an hour or when immersed in liquid nitrogen. High creep resistance and high electrical conductivity are observed and are retained after polymer infiltration, which substantially increases yarn strength.

Aligned multiwalled carbon nanotube membranes.

Abstract: An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure Data on Ru(NH3)6(3+) transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH3)6(3+) flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing

Polymer brushes via surface-initiated polymerizations

Abstract: Polymer brushes produced by controlled surface-initiated polymerization provide a route to surfaces coated with well-defined thin polymer films that are covalently bound to the substrate. All of the major controlled polymerization techniques have been applied to the synthesis of polymer brushes and examples of each are presented here. Many examples of brush synthesis in the literature have used the living atom transfer radical polymerization (ATRP) system, and in this tutorial review a particular focus is given to examples of this technique.

Chitin and chitosan: Chemistry, properties and applications

Abstract: Chitin and chitosan are considerably versatile and promising biomaterials. The deacetylated chitin derivative, chitosan is more useful and interesting bioactive polymer. Despite its biodegradability, it has many reactive amino side groups, which offer possibilities of chemical modifications, formation of a large variety of useful derivatives that are commercially available or can be made available via graft reactions and ionic interactions. This study looks at the contemporary research in chitin and chitosan towards applications in various industrial and biomedical fields.

Spinning Continuous Fibers for Nanotechnology

Abstract: Carbon nanotubes are attracting a lot of attention as the building blocks of nanotechnology. But nanotubes are difficult to align and process into useful materials. In his Perspective, Dzenis discusses the process of nanofiber electrospinning, in which continuous threads of polymers or ceramic precursors are emitted from a liquid surface as thin jets. These continuous nanofibers may offer an alternative for new nanotechnology applications.

Remotely actuated polymer nanocomposites--stress-recovery of carbon-nanotube-filled thermoplastic elastomers.

Abstract: Stimuli-responsive (active) materials undergo large-scale shape or property changes in response to an external stimulus such as stress, temperature, light or pH1,2. Technological uses range from durable, shape-recovery eye-glass frames, to temperature-sensitive switches, to the generation of stress to induce mechanical motion3,4,5,6,7,8,9. Here, we demonstrate that the uniform dispersion of 1–5 vol.% of carbon nanotubes in a thermoplastic elastomer yields nanocomposites that can store and subsequently release, through remote means, up to 50% more recovery stress than the pristine resin. The anisotropic nanotubes increase the rubbery modulus by a factor of 2 to 5 (for 1–5 vol.%) and improve shape fixity by enhancing strain-induced crystallization. Non-radiative decay of infrared photons absorbed by the nanotubes raises the internal temperature, melting strain-induced polymer crystallites (which act as physical crosslinks that secure the deformed shape) and remotely trigger the release of the stored strain energy. Comparable effects occur for electrically induced actuation associated with Joule heating of the matrix when a current is passed through the conductive percolative network of the nanotubes within the resin. This unique combination of properties, directly arising from the nanocomposite morphology, demonstrates new opportunities for the design and fabrication of stimuli-responsive polymers, which are otherwise not available in one material system.

Identification of polymers as major components of atmospheric organic aerosols.

Abstract: Results from photooxidation of aromatic compounds in a reaction chamber show that a substantial fraction of the organic aerosol mass is composed of polymers. This polymerization results from reactions of carbonyls and their hydrates. After aging for more than 20 hours, about 50% of the particle mass consists of polymers with a molecular mass up to 1000 daltons. This results in a lower volatility of this secondary organic aerosol and a higher aerosol yield than a model using vapor pressures of individual organic species would predict.

Electrospinning Nanofibers as Uniaxially Aligned Arrays and Layer‐by‐Layer Stacked Films

Abstract: The conventional procedure for electrospinning has been modified to generate nanofibers as uniaxially aligned arrays over large areas. The key to the success of this method was the use of a collector composed of two conductive strips separated by an insulating gap of variable width. Directed by electrostatic interactions, the charged nanofibers were stretched to span across the gap and became uniaxially aligned arrays. Two types of gaps have been demonstrated: void gaps and gaps made of a highly insulating material. When a void gap was used, the nanofibers could readily be transferred onto the surfaces of other substrates for various applications. When an insulating substrate was involved, the electrodes could be patterned in various designs on the solid insulator. In both cases, the nanofibers could be conveniently stacked into multi-layered architectures with controllable hierarchical structures. This new version of electrospinning has already been successfully applied to a range of different materials that include organic polymers, carbon, ceramics, and composites.

Rodlike Cellulose Microcrystals: Structure, Properties, and Applications

Abstract: Summary: In this article we present some interesting properties of rodlike cellulose microcrystals (so-called “whiskers”). These microcrystals can be obtained from different cellulose sources such as wood, cotton, or animal origin. When submitted to acid hydrolysis, the cellulose fibers yield stable aqueous suspensions because of the presence of negative charges on the surface of the microcrystallites during the hydrolysis process. The obtained microcrystals are rod-shaped particles, the dimensions of which depend on the cellulose origin. For instance, the cotton whiskers have typical dimensions varying from 100 to 300 nm in length, L, and 8 to 10 nm in diameter, d, while those of the tunicate whiskers range from 100 nm to few micrometers in length and 10 to 20 nm in diameter. At very low concentrations, these whiskers are randomly suspended in water and form an isotropic phase. When the concentration reaches a critical value, the whiskers spontaneously display ordered phases showing interesting liquid crystal properties (nematic and chiral nematic). The chiral nematic orders can be retained after evaporation of the solvent (generally water), leaving iridescent films. The reflected color can be controlled by changing either the ionic strength or by applying an electric field. These colloidal particles have been investigated using several techniques including small-angle neutron scattering (SANS), small angle X-ray scattering, rheology, and more recently dynamic and static light scattering techniques (DLS and SLS) to highlight their static and dynamic behavior. Because of their geometry, important axis ratio (L/d), and high crystallinity, these rods have been also extensively used to process nanocomposites based on polymer matrices, to reinforce their mechanical properties. All these properties are discussed in this contribution. Rodlike nanocrystals in aqueous suspension (left, Tunicate, 1 wt.-%) and film (right), observed between cross-polarizers.

Compositions that can produce polymers

Abstract: This invention provides a compositions that are useful for polymerizing at least one monomer into at least one polymer.

Multicolored Electrochromism in Polymers: Structures and Devices

Abstract: A review of electrochromic (EC) polymers and their applications in absorption/transmission, reflective, and patterned electrochromic devices (ECDs) is presented. Fundamental properties of EC materials such as optical contrast, coloration efficiency, switching speed, and stability are described along with the commonly used characterization methods. The origin of electrochromism in conjugated polymers is explained in terms of the electronic structure changes in the backbone upon doping/dedoping. The ability to tailor the EC properties of conjugated polymers and tune their color states via modification of the polymer structure is demonstrated. Multicolor electrochromic materials can be obtained by substitution of a parent polymer and controlled polymerization of comonomers and with blends and laminates of homopolymers. Absorption/transmission-type ECDs from complementarily colored polymers and reflective-type ECDs on metalized substrates are illustrated with several examples from the literature. Finally, sev...

Large-scale fabrication of wafer-size colloidal crystals, macroporous polymers and nanocomposites by spin-coating.

Abstract: This paper reports a simple spin-coating technique for rapidly fabricating three types of technologically important materials--colloidal crystal, macroporous polymer, and polymeric nanocomposite, each with high crystalline qualities and wafer-scale sizes. Dispersion of monodisperse silica colloids in triacrylate monomers is spin-coated onto a variety of substrates. Shear-induced ordering and subsequent polymerization lead to the formation of three-dimensionally (3D) ordered colloidal crystals trapped inside a polymer matrix. The thickness of as-synthesized colloidal crystal-polymer nanocomposite is highly uniform and can be controlled simply by changing the spin speed and time. Selective removal of the polymer matrix and silica spheres lead to the formation of large-area colloidal crystals and macroporous polymers, respectively. The wafer-scale process is compatible with standard semiconductor microfabrication, as multiple micrometer-sized patterns can be created simultaneously for potential device applications. Normal-incidence transmission spectra in the visible and near-infrared regions show distinct peaks due to Bragg diffraction from 3D ordered structures. The spin-coating process opens a new route to the fundamental studies of shear-induced crystallization, melting and relaxation.

Controlled functionalization of multiwalled carbon nanotubes by in situ atom transfer radical polymerization.

Abstract: The in situ ATRP (atom transfer radical polymerization) “grafting from” approach was successfully applied to graft poly(methyl methacrylate) (PMMA) onto the convex surfaces of multiwalled carbon nanotubes (MWNT). The thickness of the coated polymer layers can be conveniently controlled by the feed ratio of MMA to preliminarily functionalized MWNT (MWNT-Br). The resulting MWNT-based polymer brushes were characterized and confirmed with FTIR, 1H NMR, SEM, TEM, and TGA. Moreover, the approach has been extended to the copolymerization system, affording novel hybrid core−shell nanoobjects with MWNT as the core and amphiphilic poly(methyl methacrylate)-block-poly(hydroxyethyl methacrylate) (PMMA-b-PHEMA) as the shell. The approach presented here may open an avenue for exploring and preparing novel carbon nanotubes-based nanomaterials and molecular devices with tailor-made structure, architecture, and properties.

Recent Advances for Intumescent Polymers

Abstract: Summary: This paper reviews recent approaches for making intumescent systems The mechanisms of action involving intumescence are described and commented on Synergistic aspects using zeolites and organoclays are also considered and discussed New strategies are examined on the basis of the mechanism of intumescence The approach of using char forming polymers as additives (blend technology) is also fully discussed This consists of substituting classical polyols (char forming agents) with char forming polymers (polyamides and thermoplastic polyurethane) It will be shown that the advantages of this concept are to obtain flame-retarded (FR) polymer blends with improved mechanical properties in comparison with polymers loaded with classical formulations, and the avoidance of problems due to the water solubility of the polyols and their migration The “nanocomposite approach” enhances the performance of intumescent systems by using a nanostructured char forming polymer It will be shown that this combination of intumescence via the blending approach and nanocomposites enhances both flame retardancy and mechanical properties, and allows many specifications to be produced (for example, the design of EVA-based materials for flame retarded low voltage cables and wire) This appears to be one of the most promising ways for designing new efficient intumescent materials Intumescent residue after LOI test of an intumescent poly(propylene)

Compliant osteosynthesis fixation plate

Abstract: A bendable polymer tissue fixation device suitable to be implanted into a living body, consisting of a highly porous body, made from a polymer, the porous body having a plurality of pores, such that the device is capable of being smoothly bent, wherein the bending collapses a portion of the pores to form a radius curve, and the polymer fixation device is rigid enough to protect a tissue from shifting. Preferably, the polymer fixation device may be capable of being gradually resorbed by said living body. In one embodiment, the polymer fixation device consists of a plurality of layers distinguishable by various characteristics, such as structural or chemical properties. In another embodiment, the polymer fixation device may feature additional materials which serve to reinforce or otherwise alter the structure or physical characteristics of the device, or alternatively the additional materials serve to deliver therapies to the living being.

Reinforcing Epoxy Polymer Composites Through Covalent Integration of Functionalized Nanotubes

Abstract: Strong interfacial bonding and homogenous dispersion have been found to be necessary conditions to take full advantage of the extraordinary properties of nanotubes for reinforcement of composites. We have developed a fully integrated nanotube composite material through the use of functionalized single-walled carbon nanotubes (SWNTs). The functionalization was performed via the reaction of terminal diamines with alkylcarboxyl groups attached to the SWNTs in the course of a dicarboxylic acid acyl peroxide treatment. Nanotube-reinforced epoxy polymer composites were prepared by dissolving the functionalized SWNTs in organic solvent followed by mixing with epoxy resin and curing agent. In this hybrid material system, nanotubes are covalently integrated into the epoxy matrix and become part of the crosslinked structure rather than just a separate component. Results demonstrated dramatic enhancement in the mechanical properties of an epoxy polymer material, for example, 30–70 % increase in ultimate strength and modulus with the addition of only small quantities (1–4 wt.-%) of functionalized SWNTs. The nanotube-reinforced epoxy composites also exhibited an increased strain to failure, which suggests higher toughness.

Recent Catalytic Advances in the Chemistry of Substituted Furans from Carbohydrates and in the Ensuing Polymers

Abstract: In this review, an overview is given on the last development of catalytic methods for the preparation of substituted furans from carbohydrates and ensuing polymers. The review starts with the recent aspects in the synthesis of some key furan monomers in the presence of solid catalysts. In the second part, selected examples are given of polymerization systems leading to furan-based materials with promising properties, thus constituting a serious alternative to petroleum-based counterparts. Finally, a short examination is given on what could be the future of furan chemistry with the recent development of ionic liquids as solvents.

Control of encapsulation efficiency and initial burst in polymeric microparticle systems

Abstract: Initial burst is one of the major challenges in protein-encapsulated microparticle systems. Since protein release during the initial stage depends mostly on the diffusional escape of the protein, major approaches to prevent the initial burst have focused on efficient encapsulation of the protein within the microparticles. For this reason, control of encapsulation efficiency and the extent of initial burst are based on common formulation parameters. The present article provides a literature review of the formulation parameters that are known to influence the two properties in the emulsion-solvent evaporation/extraction method. Physical and chemical properties of encapsulating polymers, solvent systems, polymer-drug interactions, and properties of the continuous phase are some of the influential variables. Most parameters affect encapsulation efficiency and initial burst by modifying solidification rate of the dispersed phase. In order to prevent many unfavorable events such as pore formation, drug loss, and drug migration that occur while the dispersed phase is in the semi-solid state, it is important to understand and optimize these variables.

Aqueous RAFT polymerization: recent developments in synthesis of functional water-soluble (co)polymers with controlled structures.

Abstract: Reversible addition−fragmentation chain transfer (RAFT) polymerization has been the focus of intensive research over the past few years since this methodology allows the synthetic tailoring of macromolecules with complex architectures including block, graft, comb, and star structures with predetermined molecular weight, terminal functionality, and narrow molecular weight distribution. In this paper we recount significant milestones in achieving controlled free radical homopolymerization and block copolymerization of water-soluble and amphiphilic monomers including nonionic, cationic, anionic, and zwitterionic species. It is shown that under aqueous conditions, control of homopolymerization and further blocking to extend the molecular weight or to produce precisely structured block copolymers require not only careful selection of reagents (initiator, chain transfer agent, and monomer) but also regulation or elimination of hydrolysis of the ω-terminal thiocarbonylthio functionality. The technological potent...

Detection and Amplification of Chirality by Helical Polymers

Abstract: A unique feature of synthetic helical polymers for the detection and amplification of chirality is briefly described in this article. In sharp contrast to host-guest and supramolecular systems that use small synthetic receptor molecules, chirality can be significantly amplified in a helical polymer, such as poly(phenylacetylene)s with functional pendants, which enable the detection of a tiny imbalance in biologically important chiral molecules through a noncovalent bonding interaction with high cooperativity. The rational design of polymeric receptors can be possible by using chromophoric helical polymers combined with functional groups as the pendants, which target particular chiral guest molecules for developing a highly efficient chirality-sensing system. The chirality sensing of other small molecular and supramolecular systems is also briefly described for comparison.

DNA-templated organic synthesis: nature's strategy for controlling chemical reactivity applied to synthetic molecules.

Abstract: In contrast to the approach commonly taken by chemists, nature controls chemical reactivity by modulating the effective molarity of highly dilute reactants through macromolecule-templated synthesis. Nature's approach enables complex mixtures in a single solution to react with efficiencies and selectivities that cannot be achieved in conventional laboratory synthesis. DNA-templated organic synthesis (DTS) is emerging as a surprisingly general way to control the reactivity of synthetic molecules by using nature's effective-molarity-based approach. Recent developments have expanded the scope and capabilities of DTS from its origins as a model of prebiotic nucleic acid replication to its current ability to translate DNA sequences into complex small-molecule and polymer products of multistep organic synthesis. An understanding of fundamental principles underlying DTS has played an important role in these developments. Early applications of DTS include nucleic acid sensing, small-molecule discovery, and reaction discovery with the help of translation, selection, and amplification methods previously available only to biological molecules.

Optical sensors based on hybrid aptamer/conjugated polymer complexes

Abstract: An optical sensor for detecting a target comprising a singlestranded aptamer complementary to said target, and a water-soluble cationic polythiophene derivative of the following formula: wherein “n” is an integer ranging from 6 to 100, is disclosed The optical sensor allows for the detection of targets selected from the group consisting of potassium ions, small organic molecules, amino acids, proteins, whole cells and nucleotides The detection is based on the formation of hybrid anionic aptamer/cationic poly-thiophene complexes

Inkjet printing of well-defined polymer dots and arrays.

Abstract: Inkjet printing represents a highly promising polymer deposition method, which is used for, for example, the fabrication of multicolor polyLED displays and polymer-based electronics parts. The challenge is to print well-defined polymer structures from dilute solution. We have eliminated the formation of ring stains by printing nonvolatile acetophenone-based inks on a perfluorinated substrate using different polymers. (De)pinning of the contact line of the printed droplet, as related to the choice of solvent, is identified as the key factor that determines the shape of the deposit, whereas the choice of polymer is of minor importance. Adding 10 wt % or more of acetophenone to a volatile solvent (ethyl acetate)-based polymer solution changes the shape of the deposit from ring-like to dot-like, which may be due to the establishment of a solvent composition gradient. Arrays of closely spaced dots have also been printed. The size of the dots is considerably smaller than the nozzle diameter. This may prove a potential strategy for the inkjet printing of submicrometer structures.