Showing papers on "Polymer published in 1992"

Elastic substantially linear olefin polymers

Abstract: Elastic substantially linear olefin polymers are disclosed which have processability similar to highly branched low density polyethylene (LDPE), but the strength and toughness of linear low density polyethylene (LLDPE). The polymers have processing indices (PI's) less than or equal to 70 percent of those of a comparative linear olefin polymer and a critical shear rate at onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a traditional linear olefin polymer at about the same I2 and Mw?Mn. The novel polymers can also have from 0.01 to 3 long chain branches/1000 carbons along the polymer backbone and have higher low/zero shear viscosity and lower high shear viscosity than comparative linear olefin polymers. The novel polymers can also be characterized as having a melt flow ratio, I10/I2, » 5.63, a molecular weight distribution, Mw/Mn, defined by the equation: Mw/Mn « (I10/I2) - 4.63, and a critical shear stress at onset of gross melt fracture greater than 4 x 10?6? dyne/cm2.

Absorbable surgical repair devices

Abstract: A load-bearing, bioabsorbable surgical repair device manufactured from a copolymer having a plurality of first linkages of lactide or lactide/glycolide, and a plurality of second linkages of a polymer having a glass transition temperature below ambient temperature. The second linkages preferably are selected from: 1,3-dioxan-2-one; 1,4-dioxan-2-one; and e-caprolactone.

Synthesis of Fluoropolymers in Supercritical Carbon Dioxide

Abstract: Fluoropolymers are used in many technologically demanding applications because of their balance of high-performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids. The homogeneous solution polymerization of highly fluorinated acrylic monomers can be achieved in supercritical carbon dioxide by using free radical methods. In addition, detailed decomposition rates and efficiency factors were measured for azobisisobutyronitrile in supercritical carbon dioxide and were compared to those obtained with conventional liquid solvents.

Chemical tuning of electroluminescent copolymers to improve emission efficiencies and allow patterning

Abstract: ONE advantage of using conjugated polymers in semiconductor applications is that they can be processed using techniques well established for conventional polymers. We reported recently that poly(p-phenylenevinylene) could be used as the active layer in a light-emitting diode1, producing yellow/green emission. We have now found that related copolymers, comprising a combination of different arylene units, can be chemically tuned to provide a range of materials with considerably improved properties for this and other applications. By incorporating two different leaving groups into a precursor copolymer, we can selectively eliminate one of these, to give a conjugated/non-conjugated copolymer, or both, to give a fully conjugated copolymer. This allows us to induce local variations in the Π-Π* electronic energy gap at both the molecular and supramolecular level. Variations at the molecular level can act to trap excitons, hindering their migration to quenching sites, and we find that these materials give strongly enhanced quantum yields for electroluminescence (by a factor of up to 30). They also allow control of the colour of emission. Variations at the supramolecular level, by patterning the films to control the progress of conversion, allow the production of structures suitable for multicolour displays. The ability to pattern the film also allows for fabrication of optical waveguides, as regions with different energy gaps have different refractive indices.

X-ray structural studies of poly(3-alkylthiophenes): an example of an inverse comb

Abstract: X-ray diffraction studies of oriented poly(3-n-alkylthiophene) (P3AT's) solution-cast films show that these samples are characterized by well-organized lamellar structures whereby stacks of planar thiophene main chains are uniformly spaced by the allyl side chains. In spite of considerable hydrocarbon chemical bonding and conformational disorder, a high degree of structural regularity is observed with appreciable three-dimensional ordering of the polymer chains. Analysis of the results leads to suggestive models in which an open packing of the alkyl chains is maintained with considerable side-chain disorder and side-chain mobility

Viscoelastic properties of physically crosslinked networks. 1. Transient network theory

Abstract: A simple model is introduced to describe the dynamics of physically cross-linked networks in which junctions are sufficiently weak to break and recombine in thermal fluctuations. The time-evolution equation under arbitrary macrodeformation is derived for the creation and annihilation of the junctions-and hence for the number of elastically effective polymer chains with a fixed end-to-end vector. We focus our attention specifically on the unentangled networks in which the molecular weight M, between neighboring junctions is smaller than the entanglement molecular weight Me, so that each chain obeys Rouse dynamics modified by sticky trapping centers rather than reptation. Stress-strain relation under shear and elonga- tional deformation is detailed for a model network which is made up of polymers of uniform length with associating functional groups at their chain ends. On longer time scales than the junction breakage time, the total number of effective chains decreases with time-resulting in an intranetwork flow. In most polymer blends or solutions of practical interest, polymer chains carry specific groups interacting with each other by associative forces capable of forming bonds, and hence a description in terms of van der Waals type interaction-or x parameter in lattice-theoretical termi- nology-is insufficient. These forces include hydrogen bonding, ionic association, stereocomplex formation, cross- linking by the crystalline segments, and solvent complex- ation. In most common cases the bonding energy is comparable to the thermal energy, so that the bond formation is reversible by the change in temperature or concentration. Thermodynamics of network formation and multiphase competition were studied by the present authors1t2 to describe phase behavior peculiar to the polymer fluids interacting via specific associating forces. The present paper concerns dynamic properties of the thermoreversible networks (or physical gels) to study enhanced viscoelasticity due to the presence of the temporal junctions. There has been an accumulation of evidences that networks with reversible junctions exhibit highly enhanced viscoelastic properties which are quite different from ordinary polymer melts. Typical examples of the exper- imental studies can be taken from biological macro- molecule~~-~ in which networks are formed by hydrogen bonding. It turned out that a mechanical spectrum of dynamical moduli does not show any softening in low frequencies but is rather insensitive over a wide range of frequencies covering from to lo2 rad/s and also that relaxation of stress does not seem to obey a simple exponential decay but is rather well described by a power law.4 It was also found that the complex viscosity is in most cases larger than the stationary viscosity when compared at the frequency which is the same as the stationary shear rate, thus suggesting a failure of the Cox- Merz rule. Another example in current research is that of ther- moplastic elastmers6s7 in which synthetic polymers are cross-linked by specific associating groups. These include, in addition to the hydrogen bonding, charge (electron) transfer, ion pairing, acid-base interaction, dipole-

Enhanced electrical conductivity in regioselectively synthesized poly(3-alkylthiophenes)

Abstract: A regioselective synthetic method to poly(3-alkylthiophenes) provides structurally homogeneous poly(3-dodecylthiophene), which upon oxidation with I2 leads to polymers with average conductivities of 600 cm–1 and maximum conductivities of 1000 S cm–1.

DNA electrophoresis in microlithographic arrays

Abstract: We have used optical microlithography to fabricate capped quasi-two-dimensional obstacle courses in SiO2. We report here observations using epifluorescence microscopy of the electrophoresis and length fractionation of large DNA molecules confined in arrays. Simple reptation theory, based on the work of deGennes, predicts that at low electric fields the electrophoretic mobility of a polymer of length L much greater than the persistence length p scales inversely with L (ref. 2). But elongation of the coil in the matrix at sufficiently strong electric fields results in a length-independent electrophoretic mobility. The application of suitably timed pulsed electric fields restores the fractionating power of gels for long molecules but the protocols of pulsed-field electrophoresis are semi-empirical because the complex and ill-understood gel matrix plays a critical role in fractionation. Microlithographically constructed obstacle arrays, with their low dimensionality, small volume and extremely reproducible topography, will make it possible to understand the motion and fractionation of large polymer molecules in complex but well characterized topologies.

The first regioregular head-to-tail poly(3-hexylthiophene-2,5-diyl) and a regiorandom isopolymer: nickel versus palladium catalysis of 2(5)-bromo-5(2)-(bromozincio)-3-hexylthiophene polymerization

Abstract: Recent research on poly(alkylthiophenes) (PAT) has concentrated on the regularity and structure of the polymer chain of PAT. The 3-alkyl substituent in a thiophene ring can be incorporated into a polymer chain with two different regioregularities: head-to-tail (HT) and head-to-head (HH). Head-to-head linkages can cause defects in the polymer chain. The highest regioregularity reported to date for HT-PAT is 91% (usually 50-60% HT regioregularity). The authors report herein a new and facile synthesis which leads to the first completely head-to-tail regioregular poly(3-hexylthiophene 2,5-diyl) (HT-PHT) and an alternative synthesis which yields an unusual regiorandom PHT with almost equal distribution of different linkages in the polymer chain. Both polymers have been characterized by NMR, IR, elemental analysis, GPC (gel-permeation chromatography), and UV-vis. 11 refs., 2 figs., 1 tab.

High Performance Catalyzed Membranes of Ultra‐low Pt Loadings for Polymer Electrolyte Fuel Cells

Abstract: This paper reports on polymer electrolyte membranes that are catalyzed by the direct application of thin film catalyst layers cast from solutions of suspended Pt/C catalyst and solubilized Nafion ionomer. Both the ionomeric membrane and the solubilized ionmer are in the Na{sup +} form during casting to enable higher curing temperatures, which results in more robust catalyst layers. In addition to simplifying the fabrication process, the direct application apparently provides enhanced bonding at the interface between the membrane and the catalyst layer. Consequently, the performances of fuel cells utilizing these catalyzed membranes with ultra-low platinum loading are superior to those achieved with other approaches to polymer electrolyte membranes of low Pt loading.

Spectroscopy of polymers

Abstract: Theory of polymer characterization vibrational spectroscopy of polymers experimental IR spectroscopy of Polymers applications of IR spectroscopy to polymers Raman spectroscopy of polymers high-resolution NMR spectroscopy of polymers in solution special editing techniques for high-resolution NMR spectroscopy of polymers high-resolution NMR spectroscopy of solid polymers applications of high-resolution solid-state NMR spectroscopy of polymers NMR relaxation spectroscopy of polymers NMR imaging of polymeric materials.

A superabsorbent polymer having improved absorbency properties

Abstract: Super-absorbent polymers having superior dryness properties when incorporated into absorbent articles are made from acrylic acid and crosslinking agent polymerized under controlled conditions.

Cholesteric liquid crystal/polymer dispersion for haze‐free light shutters

Abstract: A new dispersion involving a polymer in low concentration with a cholesteric liquid crystal is reported. Two types of light modulators from these materials are described as a normal mode shutter which is opaque (light scattering) in the field‐OFF state and transparent in the field‐ON state and a reverse‐mode shutter with the opposite field conditions. The transparent state of both cells is haze‐free for all viewing angles making the material attractive for window applications and direct view displays.

Structural modification of polymer films by ion irradiation

Abstract: The atomic and electronic structure of polymer films undergoes deep modifications during high energy (keV-MeV) ion irradiation, from molecular solid to amorphous material. At low energy density (10 22 –10 24 eV cm 3 ) typical effects include chain scissions, crosslinks, molecular emission and double bonds formation. In hydrocarbon polymer (polystyrene, polyethylene) the main effect of irradiation is the formation of new bonds as detected by molecular weight distribution, solubility and optical measurements. Moreover the concentration of trigonal carbon (sp 2 ) in the polymer changes with ion fluence (10 11 –10 14 ions cm 2 ) and stabilizes to a value of 20% independently on the initial chemical structure of the irradiated sample. Photoemission spectroscopy shows an evolution of valence band states from localized to extended states. At high energy density (10 24 –10 26 eV cm 3 ) the irradiated polymer continues to evolve showing spectroscopic characteristics close to those of hydrogenated amorphous carbon. Trigonal carbon concentration changes with ion fluence (10 14 –10 16 ions cm 2 ) reaching the steady state value of 60% and the hydrogen concentration decreases to 20%. Moreover the values of the optical gap (2.5–0.5 eV) suggest the presence of medium range order in the obtained hydrogenated amorphous carbon. These values are consistent with the formation of graphitic clusters, whose size goes from 5 A to 20 A by changing the ion fluence (or energy density).

Development of polymer blend morphology during compounding in a twin-screw extruder. Part I: Droplet dispersion and coalescence—a review

Abstract: The theoretical and experimental data on the breakup of droplets are reviewed. Several factors influence development of droplets: flow type and its intensity, viscosity ratio, elasticity of polymers, composition, thermodynamic interactions, time, etc. For Newtonian systems undergoing small, linear deformation, both the viscosity ratio and the capillary number control deformability of drops. On the other hand, the breakup process can be described by the dimensionless breakup time and the critical capillary number. Drops are more efficiently broken in elongational flow than in shear, especially when the viscosity ratio λ≥3

Thermoreversible gelation of polymers and biopolymers

Abstract: Part 1: gel formation thermal behaviour and phase diagrams. Part 2: gel morphology and molecular structure gelation mechanisms. Part 3: mechanical properties.

Anti-infective and anti-inflammatory releasing systems for medical devices

Abstract: Devices are provided having a polymer coating incorporating compounds inhibiting inflammation and infection, along with subsequent tissue growth onto and around the device. Preferred embodiments include catheters, tubes, and implants that abut tissue following implantation into the body, especially for use in the naso-oto-pharyngeal areas of the body, where localized chronic infection/inflammation of the tissues surrounding the implant may be decreased by sustained release of antibiotics, antifungals, antivirals, anti-inflammatories, and other compounds, such as anticoagulants and anesthetics. Preferred polymeric coatings are thin, well adhered to the underlying device, and formed of a biocompatible, non-bioerodible polymer such as polyurethane or ethylene vinyl acetate. The drug is incorporated either by solvent casting or by absorption into the solidified polymer. The drug incorporated polymer can also be used to form devices, or portions of devices, for implantation.

Polymeric compositions useful as controlled release implants

Abstract: The invention is directed to an improved system for controlled release of biologically active materials and to a liquid composition for its formation. The liquid composition is composed of a thermoplastic polymer, rate modifying agent, bioactive material and organic solvent. The liquid composition is capable of forming a biodegradable and/or bioerodible microporous, solid polymer matrix. The matrix is useful as an implant in patients (humans and animals) for delivery of biologically active substances to tissues or organs.

Changes in Esterification of the Uronic Acid Groups of Cell Wall Polysaccharides during Elongation of Maize Coleoptiles

Abstract: Cell walls of grasses have two major polysaccharides that contain uronic acids, the hemicellulosic glucuronoarabinoxylans and the galactosyluronic acid-rich pectins. A technique whereby esterified uronic acid carboxyl groups are reduced selectively to yield their respective 6,6-dideuterio neutral sugars was used to determine the extent of esterification and changes in esterification of these two uronic acids during elongation of maize (Zea mays L.) coleoptiles. The glucosyluronic acids of glucuronoarabinoxylans did not appear to be esterified at any time during coleoptile elongation. The galactosyluronic acids of embryonal coleoptiles were about 65% esterified, but this proportion increased to nearly 80% during the rapid elongation phase before returning to about 60% at the end of elongation. Methyl esters accounted for about two-thirds of the total esterified galacturonic acid in cell walls of unexpanded coleoptiles. The proportion of methyl esters decreased throughout elongation and did not account for the increase in the proportion of esterified galactosyluronic acid units during growth. The results indicate that the galactosyluronic acid units of grass pectic polysaccharides may be converted to other kinds of esters or form ester-like chemical interactions during expansion of the cell wall. Accumulation of novel esters or ester-like interactions is coincident with covalent attachment of polymers containing galactosyluronic acid units to the cell wall.

Process for the preparation of an olefin polymer

Abstract: The present invention relates to zwitterionic neutral transition metal compounds. The compounds are suitable as catalyst components for the polymerization of olefins.

Primary and secondary oxygen-induced C1s binding energy shifts in X-ray photoelectron spectroscopy of polymers

Abstract: A total of 43 polymers containing only C, H, and O have been studied using an X-ray photoelectron spectroscopy instrument capable of the highest energy resolution avallable to date. The primary alm was to reinvestigate the C1s binding energy shifts for oxygen functionalltles and to systematically investigate secondary (β) shifts for the first time. In addition, this large data set has revealed the effects of vibrational fine structure on C1s component line width/shape and the effects of shake-up/shake-off (in photoemission from C=O groups) on nonstoichoimetry of C1s component intensities

Double percolation effect on the electrical conductivity of conductive particles filled polymer blends

Abstract: Electrical conductivity of carbon black (CB) filled polymer blends which are incompatible with each other was studied as a function of the polymer's blend ratio Transmission electron microscope (TEM) analysis shows that CB distributes unevenly in each component of a polymer blend TEM photographs of phase structure of solvent extracted HDPE/PMMA blend and solvent extraction experiments of PMMA/PP blend detect the blend ratio at which the structural continuity of filler rich phase is formed The electrical conductivity of polymer blends is found to be determined by two factors One is the concentration of CB in the filler rich phase and the other is the structural continuity of this phase This double percolation affects the conductivity of conductive particle filled polymer blends

Delamination R-curve phenomena due to damage

Abstract: Resistance to delamination in composites can be enhanced by a variety of bridging mechanisms. The bridging zone size is usually several times the lamina thickness, so it is questionable to think of delamination resistance as a material property independent of specimen size and geometry. When measured with slender beams, the plateau resistance is found to be independent of the beam thickness. However, the steady-state bridging zone size increases with the beam thickness. Further implications of the large-scale bridging are studied using a family of steady-state, mixed-mode delamination beams, in conjunction with an idealized damage response. The complete solution is obtained for the model, which allows the R-curves to be constructed for given model parameters. The significance of the steady-state cracking, which is crucial in understanding delamination R-curves, is elucidated by contrasting double-cantilever beams loaded by moments and by wedge forces. As an inverse process, it is recommended that R-curves be used as an experimental probe to study localized damage response, such as polymer craze and interface separation.

Optically induced and erased birefringence and dichroism in azoaromatic polymers

Abstract: Dichroism and birefringence are shown to be optically induced and erased in high‐glass‐transition azoaromatic polymers. The resulting polarization information is easily detected and exhibits long‐term stability. This optically induced reorientation of the azoaromatic molecules will have wide applications in image recording and in electro‐optical devices.

Use of intermolecular hydrogen bonding for the induction of liquid crystallinity in the side chain of polysiloxanes

Abstract: A new type of liquid crystalline side chain polysiloxane has been built through self-assembly via intermolecular hydrogen bonding between H-bond donor and acceptor moieties. Poly(methylsiloxanes) and poly(methyl-co-dimethylsiloxanes) with side chains containing 4-alkoxybenzoic acid pendant groups attached through aliphatic spacers were synthesized for use as H-bond donor polymers. trans-4[(4-Methoxybenzoyl)oxy]-4'-stilbazole and trans-4-ethoxy-4'-stilbazole were prepared as representative mesogenic or nonmesogenic H-bond acceptors, respectively

Continuous process for manufacture of lactide polymers with controlled optical purity

Abstract: A process for the continuous production of polylactide polymers from lactic acid which incorporates removal of water or a solvent carrier to concentrate the lactic acid feed followed by polymerization to a low-molecular-weight prepolymer. This prepolymer is fed to a reactor in which a catalyst is added to facilitate generation of lactide, the depolymerization product of polylactic acid. The lactide generated is continuously fed to a distillation system as a liquid or vapor wherein water and other impurities are removed. The resultant purified liquid lactide is fed directly to a polymerization process.

Heat sealable polyolefin films containing very low density ethylene copolymers.

Abstract: The invention provides laminar polyolefin film materials having a base film layer comprising a blend of an olefin polymer and up to about 30% by weight of at least one very low density copolymer of ethylene and a C 3 to C 20 alpha olefin comonomer copolymerizable with ethylene, said base layer having a heat sealable film layer present on one or both surfaces thereof comprising a very low density copolymer of ethylene and a copolymerizable C 5 to C 12 alpha olefin comonomer. The ethylene copolymer constituents of the film are characterized as having a density in the range of about 0.88 g/cm 3 to abut 0.915 g/cm 3 , a melt index in the range of about 0.5 dg/min to about 7.5 dg/min, a molecular weight distribution (M w /M n ) of about 1.5 to about 3.5 and an essentially single melting point in the range of about 60° C. to about 115° C., measured as a DSC peak T m . Films of this invention exhibit extremely good hot tack seal strength at temperatures in the range of from about 200° to 290° F. thereby rendering them extremely useful as packaging materials in high speed packaging operations.