scispace - formally typeset
Search or ask a question

Showing papers on "Polymer published in 1991"


Journal ArticleDOI
TL;DR: In this article, the authors studied the electrical conductivity of carbon black (CB) filled polymer blends and found that CB distribution is unevenly distributed in each component of the polymer blend, and that the filler distribution concentrates at interface of two polymers.
Abstract: Dispersion state of carbon black(CB) was studied in polymer blends which are incompatible with each other. It was found that CB distributes unevenly in each component of the polymer blend. There are two types of distribution. (1) One is almost predominantly distributed in one phase of the blend matrix, and in this phase fillers are relatively homogeneously distributed in the same manner as a single polymer composite. (2) In the second, the filler distribution concentrates at interface of two polymers. As long as the viscosities of two polymers are comparable, interfacial energy is the main factor determining uneven distribution of fillers in polymer blend matrices. This heterogeneous dispersion of conductive fillers has much effect on the electrical conductivity of CB filled polymer blends. The electrical conductivity of CB filled polymer blends is determined by two factors. One is concentration of CB in the filler rich phase and the other is phase continuity of this phase. These double percolations affect conductivity of conductive particle filled polymer blends.

921 citations


Journal ArticleDOI
TL;DR: The physico-mechanical properties of degradable polymers used for medical applications have been characterized and flexural storage modulus as a function of temperature was determined by dynamic mechanical analysis.

736 citations


Journal ArticleDOI
Owen W. Webster1
22 Feb 1991-Science
TL;DR: Living polymerization techniques can be used to achieve a high degree of control over polymer chain architecture, which results in polymers with widely diverse physical properties, even though they are made from readily available low-cost monomers.
Abstract: Living polymerization techniques can be used to achieve a high degree of control over polymer chain architecture. Examples of the type of polymers that can be synthesized include block copolymers, comb-shaped polymers, multiarmed polymers, ladder polymers, and cyclic polymers. This control of structure, in turn, results in polymers with widely diverse physical properties, even though they are made from readily available low-cost monomers.

698 citations


Journal ArticleDOI
01 Aug 1991-Nature
TL;DR: In this article, a thin, single-crystal-like film of poly(tetrafluoroethylene) (PTFE) is deposited mechanically on a smooth substrate such as glass.
Abstract: THE formation of highly oriented structures such as single crystals, single-domain liquid crystals and systems comprising uniaxially oriented crystallites is important in many applications of thin films and interfaces, ranging from materials reinforcement to molecular electronics. Of the methods that exist for forming such oriented structures, however, few have sufficient generality to make them applicable to materials of differing chemical composition or physical properties. Here we present a simple and surprisingly versatile method1 for orienting a wide variety of crystalline and liquid-crystalline materials, including polymers, monomers and small organic and inorganic molecules. In our technique, a thin, single-crystal-like film of poly(tetrafluoroethylene) (PTFE) is deposited mechanically on a smooth substrate such as glass. Materials grown on this coated surface from solution, melt or vapour phases show a remarkable degree of alignment.

540 citations


Journal ArticleDOI
01 Jan 1991-Nature
TL;DR: Inomata et al. as discussed by the authors reported a phase transition in an interpenetrating polymer network of poly(acrylamide) and poly (acrylic acid) that is controlled by cooperative 'zipping' interactions between the molecules which result from hydrogen bonding.
Abstract: INTERACTIONS between macromolecules fall into four categories: ionic, hydrophobic, van der Waals and hydrogen bonding. Phase transitions in polymer gels provide a means of studying these interactions. Many gels will undergo reversible, discontinuous volume changes in response to changes in, for example, temperature, gel composition or light irradiation1–5. These transitions result from the competition between repulsive intermolecular forces, usually electrostatic in nature, that act to expand the polymer network, and an attractive force that acts to shrink it. Volume transitions in gels have been observed that are driven by all of the above-mentioned forces except hydrogen bonding (ref 6–10; T.T. et al, unpublished data; H. Inomata et al., personal communication). Here we report on a phase transition in an interpenetrating polymer network of poly(acrylamide) and poly(acrylic acid) that completes this picture—it is controlled by cooperative 'zipping' interactions between the molecules which result from hydrogen bonding. Cooperativity is an essential feature of the interactions, in that independent hydrogen bonds would not provide a sufficient driving force for the transition. A further novel characteristic of this phase transition is that the swelling (in water) is induced by an increase rather than a decrease in temperature.

463 citations


Journal ArticleDOI
07 Jun 1991-Science
TL;DR: The permanent morphological changes induced in this conjugated polymer system and others indicate the potential for development of universal membranes for gas separations.
Abstract: Permeabilities for a series of gases through free-standing films of the conjugated polymer polyaniline are reported. A remarkable selectivity has been achieved for important gas pairs incuding hydrogen-nitrogen, oxygen-nitrogen, and carbon dioxide-methane. The selectivity values of 3590 for H(2)/N(2), 30 for O(2)/N(2), and 336 for CO(2)/CH(4) surpass the highest previously reported values of 313, 16, and 60 for the nonconjugated polymers poly(trifluorochloroethylene), cellulose nitrate, and a fluorinated polyimide, respectively. The process for tailoring gas selectivity of a polyaniline membrane involves first enhancing the permeabilities of gases with small diameters [ 3.5 A diameter) through controlled redoping of the polymer. The permanent morphological changes induced in this conjugated polymer system and others indicate the potential for development of universal membranes for gas separations.

399 citations


Journal ArticleDOI
TL;DR: In this article, phase separation in parallel to the hydrolysis and gelation of alkoxysilane solution containing poly(sodium styrenesulfonate) (NaPSS) has been investigated.
Abstract: Phase separation which occurs in parallel to the hydrolysis and gelation of alkoxysilane solution containing poly(sodium styrenesulfonate) (NaPSS) has been investigated. Depending on the reaction conditions, gel morphologies such as isolated pores, particle aggregates, and interconnected continuous pores from 0.1 to 100 μm long have been observed. Time-resolved light scattering of gelling solution suggested the occurrence of spinodal phase separation through the polymerization of silica and the subsequent freezing of the developing structure by sol-gel transition. The effects of reaction parameters on the periodic size are explained mainly in terms of their influence on the “chemical cooling” rate which is determined by the polymerizatica rate of silica and the solubility of NaPSS in the reacting solution.

371 citations


Patent
30 Sep 1991
TL;DR: In this paper, an apparatus and method for producing ethylene polymer are provided which employ a conduit in the form of a closed loop (i.e., loop reactor) for receiving a flow of a monomer which includes ethylene, a polymerization catalyst and a diluent therethrough for the polymerization of the monomer to ethylene.
Abstract: An apparatus and method for producing ethylene polymer are provided which employ a conduit in the form of a closed loop (i.e. loop reactor) for receiving a flow of a monomer which includes ethylene, a polymerization catalyst and a diluent therethrough for the polymerization of the monomer to ethylene polymer. The conduit comprises at least one pipe constructed of rolled plate around which coolant fluid passes in heat exchange relationship.

332 citations


Journal ArticleDOI
F. Jonas1, L Schrader1
TL;DR: The use of modern organic conductors (as opposed to the more traditional carbon black or salts) as fillers for the production of antistatic polymers is advantageous, especially for the formation of films.

330 citations


Patent
05 Jul 1991
TL;DR: In this paper, a new series of degradable polymeric matrices were prepared by blending polymers that degrade by hydrolysis such as poly(L-lactic acid)(PLA), and nonionic Pluronic™ surfactants, block copolymers of polyethyleneoxide (PEO) and polypropyleneoxide (PPO).
Abstract: A new series of degradable polymeric matrices were prepared by blending polymers that degrade by hydrolysis such as poly(L-lactic acid)(PLA), and nonionic Pluronic™ surfactants, block copolymers of polyethyleneoxide (PEO) and polypropyleneoxide (PPO). The water content of the polymer blend films was controlled by mixing different types of block copolymers and by adjusting their amount. In aqueous solution, the blends revealed the typical liquid-crystalline phase transition of Pluronic™ polymers, suggesting the formation of a gel-like structure within the polymer skeleton. Poly(lactic acid) degradation rates were not affected by the blending procedure, although the hydration degree in these matrices was higher. When used as drug-releasing matrices, these blends extended protein release and minimized the initial protein burst, as compared to the pure polymer.

304 citations


Journal ArticleDOI
TL;DR: It was concluded that PEO 18,500 had a chain length that was optimal, using this technique for surface incorporation, to reduce protein adsorption and hence prevent protein-mediated biological interactions.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the thermo-oxidative and thermodynamic stability of polypropylene and high density polyethylene (Cr-catalyst technology) using multiple extrusions.

Patent
22 Nov 1991
TL;DR: In this paper, a method for cyclization and reversal of the polarity of polymers on a substrate was proposed, which finds particular application in the formation of peptides and oligonucleotides.
Abstract: A method for cyclization and reversal of the polarity of polymers on a substrate. The method provides for the formation of a polymer on a substrate (2) with a tether molecule (4). Through unmasking of a protective group (PG2) a cyclic polymer (6) is formed. Through cleavage of an appropriate bond, a polarity reversed polymer (8) is formed. The method finds particular application in the formation of, for example, peptides and oligonucleotides.

Journal ArticleDOI
TL;DR: In this article, conditions for the synthesis of polymers with respect to reaction time and yield were studied with a number of monomers at different concentrations and in solvents with different buffers with pH range of 5.0-7.5.
Abstract: Polymers were synthesized from substituted phenolic and aromatic amine compounds with hydrogen peroxide as the source of an oxidizing agent and horseradish peroxidase enzyme as the catalyst. The polymerization reaction was carried out in a monophasic organic solvent with small amounts of water at room temperature. Conditions for the synthesis of polymers with respect to reaction time and yield were studied with a number of monomers at different concentrations and in solvents with different buffers with pH range of 5.0–7.5. Physical and chemical properties of these homo-and copolymers were determined with respect to melting point, solubility, elemental analysis, molecular weight distribution, infrared absorption (including FTIR), solid-state 13C nuclear magnetic resonance, thermal gravimetric analysis, and differential scanning calorimetry. The enzyme catalyzed reactions produced polymers of molecular weight greater than 400,000 which were further fractionated by differential solubility in solvent mixtures and the molecular weight distribution of the polymer fractions were determined. In general, the polymers synthesized have low solubilities, high melting points, and some degree of branching.


Journal ArticleDOI
TL;DR: Silicon polymers were pyrolyzed to form silicon oxycarbides that contained only silicon, oxygen, and carbon, and NMR showed that the polymers had a silicon-oxygen backbone with branching and ring units as discussed by the authors.
Abstract: Silicone polymers were pyrolyzed to form silicon oxycarbides that contained only silicon, oxygen, and carbon. The starting polymers were mainly methyl trichlorosilane with a small amount of dimethyl dichlorosilane. NMR showed that the polymers had a silicon-oxygen backbone with branching and ring units. When the polymer was heated in hydrogen, toluene and isopropyl alcohol, used in production of the polymer, were given off in the temperature range 150 °C to 500 °C. Substantial decomposition of the polymer itself began only above about 700°by evolution of methane. The network of silicon-oxygen bonds and silicon-carbon bonds did not react and was preserved; the silicon-carbon bonds were linked into the silicon-oxygen network. The silicon oxycarbide was stable above 1000 °C, showing no dimensional changes above this temperature. The interior of the silicon oxycarbide was at very low effective oxygen pressure because oxygen diffused slowly in it. There was also a protective layer of silicon dioxide on the surface of the silicon oxycarbide.

Journal ArticleDOI
TL;DR: In this paper, the authors used very small samples (0.02 cm 3 ) to obtain phase diagrams for different molecular weights of polystyrene in cyclohexane, methylacetate, ethylacetate and tert-butyl-acetate.
Abstract: Thermooptical analysis (TOA) provides a simple, rapid, and reliable experimental method to determine cloud-point curves of binary polymer/solvent systems. Phase diagrams have been obtained for different molecular weights of polystyrene in cyclohexane, methylacetate, ethylacetate, and tert-butylacetate and for poly(ethylene glycol) in water. Polystyrene solutions exhibit both upper and lower critical solution temperatures, while aqueous poly(ethylen glycol) solutions give closed-loop phase diagrams. The TOA apparatus described here uses very small samples (0.02 cm 3 )

Journal ArticleDOI
TL;DR: A simple equation to model the dependence of the glass transition temperature (T g ) on the extent of reaction in highly cross-linked thermosetting polymers has been derived in this article, assuming that the increase in T g is caused by decrease in chain-end concentration, formation of effective cross-links, and further decrease in the configurational entropy due to departure from Gaussian behavior at high cross-link densities.
Abstract: A simple equation to model the dependence of the glass transition temperature (T g ) on the extent of reaction in highly cross-linked thermosetting polymers has been derived. The model assumes that the increase in T g is caused by (a) decrease in chain-end concentration, (b) formation of effective cross-links, and (c) further decrease in the configurational entropy due to departure from Gaussian behavior at high cross-link densities


Book
01 Jan 1991
TL;DR: Conventional and Environmentally-Sensitive Hydrogels for Medical and Industrial Uses, and Thermo-Responsive Polymeric hydrogels and Their Application to Pulsatile Drug Release.
Abstract: Fundamentals.- Characterization of Gel Structure by Means of SAXS and SANS.- Physical Gelation of Synthetic and Biological Macromolecules.- Effects of Shear Modulus of Polymer Gels.- Interaction between Solvent Molecules and Networks in Biogels -Viscoelasticity, Strength.- Synthesis and Properties of Inorganic/Organic Hybrid Gels by the Sol-Gel Process.- Biologicals.- Excitation Process and Swelling of Nerve Fibers.- Cytoskeletons Are Functionally Differentiated in the Squid Giant Axon.- Synthetic Vitreous Body of PVA Hydrogel.- Immobilization of Bioactive Substances with PVA Supports.- Electric Modulation of Polymer Gel Contraction and Animal Cell Proliferation.- Separation.- Separation of Organic Solvent/Water Mixtures by Acrylamide Gel Membrane Supported by Silica-Alumina Porous Membrane.- Permeation Mechanism for a Thermo-Sensitive Switching-Functional Composite Membrane of Porous Glass and Hydrogel.- Gel Dewatering Process for Biological Slurry.- Sensors and Actuators.- A Polymer Composite Showing Electrocontractile Response.- Conversion of Chemical into Mechanical Energy by Synthetic Polymer Gels (Chemomechanical System).- Amphoteric Polyvinyl Alcohol Hydrogel and Electrohydrodynamic Control Method for Artificial Muscles.- Deformation Behaviors of Polymer Gels in Electric Field.- Thermoresponsive Polymer Hydrogel.- Contraction Behavior of Poly(acrylonitrile) Gel Fibers.- Measuring Contact Stress with 19F-NMR Spectroscopy.- Drug Delivery System.- Conventional and Environmentally-Sensitive Hydrogels for Medical and Industrial Uses.- Thermo-Responsive Polymeric Hydrogels and Their Application to Pulsatile Drug Release.- Hydrophobic Weak Polybasic Gels: Factors Controling Swelling Equilibria.- Diffusion-Reaction through Coated Gel Containing Enzyme Effects of Asymmetry and Sol-Gel Transition.

MonographDOI
13 May 1991
TL;DR: Polymers as Rheology modifiers: An Overview Rheological Measurements Extensional Viscometry of Polymer Solutions Preparation, Characterization, and Rheologological behavior of Water-Swellable Polymer Networks Chemical Grafting of Poly(ethylene oxide) onto Polystyrene Latex: Synthesis, characterisation and rheology Electrosteric Stabilization of Oil-in-Water Emulsions by Hydrophobically Modified Poly(acrylic acid) Thickeners Effects of Process Variables on the Emulsion and Solution Properties
Abstract: Polymers as Rheology Modifiers: An Overview Rheological Measurements Extensional Viscometry of Polymer Solutions Preparation, Characterization, and Rheological Behavior of Water-Swellable Polymer Networks Chemical Grafting of Poly(ethylene oxide) onto Polystyrene Latex: Synthesis, Characterization and Rheology Electrosteric Stabilization of Oil-in-Water Emulsions by Hydrophobically Modified Poly(acrylic Acid) Thickeners Effects of Process Variables on the Emulsion and Solution Properties of Hydrophobically Modified Alkali-Swellable Emulsion Thickeners Rheological Behavior of Liquid-Crystalline Polymer-Polymer Blends Shear-Thickening Behavior of Ionomers and Their Complexes Hydrocarbon-Soluable Associating Polymers as Antimisting and Drag-Reducing Agents Association of Acrylamide-Dodecylmethacrylate Copolymers in Aqueous Solution Systems Approach to Rheology Control Steady-Shear and Linear-Viscoelastic Material Properties of Model Associative Polymer Solutions Surfactant Influences on Hydrophobically Modified Thickener Rheology Polymers as Lubricating-Oil Viscosity Modifiers Solution Rheology of Ethylene-Propylene Copolymers in Hydrocarbon Solvents Rheological Properties of High-Molecular-Weight Poly[(methyl methacrylate)-co-butylacrylate] Solutions: Influence of Polymer-Solvent Interactions Thermal Characteristics of Waxy, High-Pour-Point Crudes That Respond to Rheology Modifiers Melt Rheology and Strain-Induced Crystallization of Polypropylene and Its High-Density Polyethylene Blends Dynamic Uniaxial Extensional Viscosity: Response in Spray Applications

Patent
29 Mar 1991
TL;DR: In this paper, an electrode for a biosensor (eg, a glucose biosensor) has a layer of an electrically insulating polymer formed in situ on its operating surface by electropolymerization, which is sufficiently porous to permit smaller electroactive molecules (e.g., hydrogen peroxide) generated through contact of the enzyme with the analyte molecules to diffuse through to the electrode surface.
Abstract: An electrode for a biosensor (eg, a glucose biosensor) has a layer of an electrically insulating polymer formed in situ on its operating surface by electropolymerization For example, a diaminobenzene and a dihydroxybenzene (eg, 1,3-diaminobenzene and resorcinol) are copolymerized on the electrode's surface by immersing the electrode in a circulating dilute solution of the monomers in deaerated phosphate buffer, and applying a small, continuously cycling voltage between that electrode and another electrode (eg, from 000 V to 080 V) until current flow between the electrodes decreases to a minimum Because the polymer is electrically insulating, polymerization ceases while the polymer layer is still very thin (eg, 10 nm) An analyte sensing agent, eg, an enzyme such as immobilized glucose oxidase, is imbedded in the polymer, but with a number of its analyte recognition sites unblocked The polymer layer shields the electrode surface from interferrents and fouling agents such as uric acid and proteins, but it is sufficiently porous to permit smaller electroactive molecules (eg, hydrogen peroxide) generated through contact of the enzyme with the analyte molecules to diffuse through to the electrode surface Preferably a ferrocene compound (eg, alpha-hydroxy-ethylferrocene or 1,1'-dimethylferrocene), which functions as an electron mediator, is applied to the polymer film, and held there by adsorption

Journal Article
TL;DR: In this paper, a microporous gel of N-isopropylacrylamide was synthesized by increasing the solution temperature above the lower critical solution temperature of the polymer during the copolymerization/crosslinking reaction.
Abstract: A microporous gel of N-isopropylacrylamide was synthesized by increasing the solution temperature above the lower critical solution temperature of the polymer during the copolymerization/crosslinking reaction. In response to changes in temperature this gel expands 120 times faster and contrasts 3000 times faster than comparable homogeneous gels

Journal ArticleDOI
TL;DR: In this paper, polyhype polymers with completely interconnected cellular structures of overall very low density are prepared by polymerization of the styrene-divinylbenzene continuous oil phase of a number of high internal phase emulsions (HIPE).
Abstract: Polyhype polymers with completely interconnected cellular structures of overall very low density are prepared by polymerization of the styrene-divinylbenzene continuous oil phase of a number of high internal phase emulsions (HIPE). By adjustment of the level of crosslinker and by use of eitheir a precipitating porogen or a solvating porogen in the comonomer oil phase, a secondary pore structure is generated within the cell «walls» of the polymers. Their surface area and their pore volume are determined

Book
30 Sep 1991
TL;DR: In this paper, the authors discuss the application of organic photochromic polymer systems, including the use of spiroxazines and their use in photo-chromic lenses for optical applications.
Abstract: Optical applications of organic photochromic polymer systems, C.B.McArdle spiroxazines and their use in photochromic lenses, J.C.Crano, W.S.Kwak and C.N.Welch fulgicides and fulgimides - a promising class of photochromics for application, J.Whittal monochromic liquid crystal polymers, V.Krongauz photoresponsive polymers - reversible control of polymer conformation in solution and gel phases, M.Irie high and low molecular weight photochromic viologen-based systems, H.Kamogawa.

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this paper, a mixture of nylon 6 with various ABS materials including styrene/acrylonitrile, SAN, matrix component were examined for rheological behaviour, mechanical properties, and phase morphology.

Patent
20 May 1991
TL;DR: In this paper, a supported olefin polymerization catalyst composition comprising a precursor and a catalyst activator was proposed, which is used in the presence of small amounts of hydrogen to produce polymers having multimodal molecular weight distribution in a single reactor.
Abstract: There is disclosed a supported olefin polymerization catalyst composition comprising a precursor and a catalyst activator. The precursor comprises a magnesium compound, e.g., dibutylmagnesium, a cyclopentadienyl group - containing zirconium compound, and a titanium and/or a vanadium compound, e.g., TiCl₄, and an organic compound, e.g., an alcohol. The catalyst activator is a mixture of a conventional Ziegler/Natta co-catalyst and a zirconium sites activator, e.g., methylaluminumoxane. The catalyst is used in the presence of small amounts of hydrogen to produce polymers having multimodal molecular weight distribution in a single reactor.

Journal ArticleDOI
TL;DR: The dependence of the intrinsic viscosity and the radius of gyration upon molecular weight M w (40000-220000) for poly(3-hexylthiophene) in THF dilute solution was found to be characteristic of a moderately good solvent as discussed by the authors.
Abstract: The dependence of the intrinsic viscosity and the radius of gyration upon molecular weight M w (40000-220000) for poly(3-hexylthiophene) in THF dilute solution was found to be characteristic of a moderately good solvent. Similar solution characteristics were observed in CHCl 3 . Macromolecular dimensions determined by different techniques indicate that this polymer exist as isolated flexible-coil chains in dilute THF solution with a persistance length of 2.4±0.3 nm.


Journal ArticleDOI
Kenneth R. Shull1
TL;DR: In this article, a detailed self-consistent field theory is used to calculate the properties of end-adsorbed polymer chains, or polymer ‘brushes,’ in equilibrium with a blend of adsorbing B polymer and nonadsorbing A polymer.
Abstract: A detailed self‐consistent field theory is used to calculate the properties of end‐adsorbed polymer chains, or polymer ‘‘brushes,’’ in equilibrium with a blend of adsorbing B polymer and nonadsorbing A polymer. The brush properties depend on χab, Na/Nb and β, where χab is the Flory interaction parameter characterizing the thermodynamic interaction between the A and B polymers, Na and Nb are the respective degrees of polymerization of the A and B polymers and kBTβ is the net attractive interaction between the adsorbing chain end and the surface. For χab=0, β≫1 and Na/Nb≫1 an asymptotic limit is reached where the brush properties are completely specified by z*/Rbg, where z* is the integrated surface excess of the adsorbing polymer and Rbg is its unperturbed radius of gyration. In this strong adsorption, dry brush regime the volume fraction of adsorbing polymer at the surface increases rapidly from 0.0 to 0.96 as z*/Rbg increases from 0.0 to 1.6. For z*/Rbg>1.6 the surface volume fraction of the adsorbing po...