Showing papers on "Polymer published in 1972"

Artificial skin I. Preparation and properties of Pluronic F-127 gels for treatment of burns

Abstract: The preparation of block polymer surface-active agents derived solely from propylene oxide and ethylene oxide is described. The physical properties of a nonionic surfactant of 12,500 molecular weight, Pluronic F-127, are presented. The toxicity data of the polymeric series is reviewed. The preparation of cold aqueous solutions of the F-127 solution, to which silver salts and other medicaments are then added, is described. By raising the temperature, these fluid liquids are then converted to strong “ringing” gels or viscous ointments which are suitable for application to a burn wound or abraded skin area. The factors involved in altering the yield strength of the gel are presented.

The Vibrational Properties of Disordered Systems: Numerical Studies

Abstract: A review is presented of the direct numerical approach to the study of the atomic vibrational properties of disordered systems. The basis and details of the numerical methods employed are first described. This is followed by a review of applications of the approach to two-component disordered lattices, glasses, mixed-crystal systems, orientationally disordered crystals, and random polymers.

Friction and molecular structure: the behaviour of some thermoplastics

Abstract: This paper describes an experimental study of the friction and transfer of some thermoplastic polymers sliding over clean surfaces. With PTFE and high density polyethylene sliding at low speeds on smooth surfaces of glass or polished metals there is a marked difference between static and kinetic friction. The static friction is of the order of $\mu =0.2$ and is accompanied by transfer of lumps of polymer several hundred angstroms thick. This frictional behaviour is 'normal' and may be explained in terms of the bulk properties of the polymers. However, once sliding has commenced and the slider acquires a preferred orientation the friction falls to a much lower value $(\mu <0.1)$ and the transfer is either in the form of an extremely thin film (PTFE) or discrete streaks less than 10 nm thick (PE). This behaviour does not depend on the degree of crystallinity or on the crystalline texture of the polymer. If the molecular structure is changed by introducing an appreciable number of bulky side groups (e.g. TFE-HFP copolymers, PCTFE or low density PE) the kinetic friction remains the same as the static value. The friction and transfer are those of 'normal' polymers and resemble polypropylene and amorphous polymers such as PMMA and PVC in their behaviour. The results suggest that the low friction and light transfer of PTFE and high density PE during sliding are essentially due to their smooth molecular profiles.

On the Mathematical Modeling of Polymerization Reactors

Abstract: As commercially produced polymers become more of a commodity product, rather than a specialty product, there is a growing need for a more detailed understanding of the phenomena taking place in the polymer reactor. One quantitative form of this process understanding is the mathematical model, which can represent the detailed behavior of a polymer reactor. The mathematical model is an invaluable tool for developing the optimal design and optimal control system for these reactors.

Lactone Polymerization and Polymer Properties

Abstract: The polymerization of lactones provides a facile route to polyesters that is unimpeded by the long reaction cycles and elevated temperatures inherent in the condensation of hydroxyl and acid functional groups. Depending on the structure of the lactone monomer, catalyst/initiator systems are known which allow preparation of extremely high molecular weight polyesters of low polydispersity. In addition to obtaining high molecular weight polyesters in relatively short reaction cycles and at moderate temperature, lactone polymerization allows careful control of polymer end groups through proper selection of the initiating species. The type of end group plays an important role in both the thermal stability and hydrolytic stability of the resulting polyester. This study reviews and updates the field of lactone polymerization with specific emphasis on the chemistry and Theological

Chromocene catalysts for ethylene polymerization: Scope of the polymerization

Abstract: Chromocene deposited on silica supports of high surface area forms a highly active catalyst for polymerization of ethylene. Polymerization is believed to occur by a coordinated anionic mechanism previously outlined. The catalyst formation step liberates cyclopentadiene and leads to a new divalent chromium species containing a cyclopentadienyl ligand. The catalyst has a very high chain-transfer response to hydrogen which permits facile preparation of a full range of molecular weights. Catalyst activity increases with an increase in silica dehydration temperature, chromium content on silica, and ethylene reaction pressure. The temperature-activity profile is characterized by a maximum near 60°C, presumably caused by a deactivation mechanism involving silica hydroxyl groups. A value of 72 was estimated for the ethylene–propylene reactivity ratio (r1). Linear, highly saturated polymers are normally prepared below 100°C. By contrast with other commercial polyethylenes, the chromocene catalyst produces polyethylenes of relatively narrow molecular weight distribution. Above 100°C, unsaturated, branched polymers or oligomers are formed by a simultaneous polymerization–isomerization process.

Hair treating cosmetic compositions containing piperazine based cationic polymer

Abstract: Piperazine-based low molecular weight film-forming cationic polymer is employed in a cosmetic hair-conditioner composition comprising a solution of the polymer in amounts of about 0.1-5 weight percent of the composition in a solvent such as water, acidified water, or aqueous alcohol solution.

Solid-state polymerization of diacetylenes.

Abstract: Differences in the solid‐state reactivity of two substituted diacetylenes with identical lattice symmetry (P21/c) are described in terms of the molecular rotational and translational motion necessary for 1,4‐addition polymerization. The structural relationship between monomer and polymer has been investigated in detail for the solid‐state polymerization of 2,4‐hexadiynediol. For the thermal, uv, or γ‐ray‐induced polymerization of this monomer the same crystallographic relationship was found between the polymer chain direction and the monomer lattice. Mutually reacting monomer molecules are related by a unit‐cell translation along the a/c diagonal, which is perpendicular to the unique axis of this monoclinic crystal. X‐ray diffraction determination of unit‐cell parameters for γ‐ray‐irradiated samples of differing conversion have confirmed that the polymer enters the monomer lattice as a solid solution and verify the mentioned polymerization mechanism. When these irradiated samples were thermally annealed, ...

Crystallization and fusion of self-seeded polymers: II. Growth rate, morphology and isothermal thickening of single crystals of low molecular weight poly(ethylene-oxide) fractions

Abstract: SummarySingle crystals of five low molecular weight and one high m. w. fractions of Poly(ethylene-oxide) were grown isothermally from the supercooled melt using the self seeding procedure. Growth was arrested by rapid quenching of the specimens, which gives rise to highly contrasted outgrowths decorating all the nucleating sites of the crystals, whereas the homogeneously nucleated melt remains optically transparent. This self-decorating procedure delineates the crystal edges and outlines the surface roughness of the lamellae. The surface decoration contrast allows to distinguish between lamellae constituted by folded and fully extended chains.For the five low m. w. fractions the temperature coefficient of the growth rate,G, undergoes at least one sharp transition which can be interpreted by the stepwise variation of the thickness of growing lamellae with crystallization temperature,Tc. For each fraction the transition from extended chain to folded chain crystal growth is extremely sharp and it is accompanied by a radical change in the crystal habit and the surface texture of the lamellae.Chain folded lamellae thicken isothermally during their growth, provided they are surrounded by molten polymer. This isothermal extension of chains can be detected morphologically. It involves two different molecular mechanisms: a nucleation process characterized by incubation periodτ and a growth process characterized by a rateGΦ. Both of these parameters depend strongly onTc and molecular weight. All these features are discussed and tentatively interpreted in terms of kinetic theories of polymer crystal growth.ZusammenfassungEinkristalle von 5 niedermolekularen und einer hochmolekularen Fraktion von Polyäthylenoxyd wurden isotherm aus unterkühlter Schmelze unter Anwendung des self-seeding-Verfahrens kristallisiert. Das Wachstum der Kristallite wurde durch rasche Kühlung der Proben abgebrochen, was Anlaß zu hochkontrastierten Aufwachsungen führt, die die Kristallite umgeben, während die homogene Schmelze optisch transparent bleibt.Diese „Selbstdekorationsprozedur“ erfolgt an den Kanten und Außenlinien der Oberflächenrauhigkeiten der Lamelle. Das Verfahren erlaubt, zwischen Lamellen aus gefalteten Ketten und denen aus gestreckten zu unterscheiden.Für 5 niedermolekulare Fraktionen durchläuft der Temperaturkoeffizient der WachstumsgeschwindigkeitG mindestens einen scharfen Übergang, der durch die schrittweise Variation der Dicke der Lamellen mit der KristallisationstemperaturTc erklärt werden kann. Für jede Fraktion ist der Übergang von gestrecktkettigen zu gefaltetem Kristallwachstum extrem scharf und von einer radikalen Änderung im Habitus der Kristalle und der Oberflächentextur der Lamellen begleitet.Kettengefaltete Lamellen verdicken sich isotherm während ihres Wachsens, vorausgesetzt daß sie von geschmolzenen Polymeren umgeben sind. Diese isotherme Streckung der Ketten kann morphologisch beobachtet werden. Es spielen zwei verschiedene molekulare Mechanismen mit: Ein Keimbildungsprozess, charakterisiert durch eine Inkubationsperiodeτ und ein Wachstumsprozeß, charakterisiert durch seine GeschwindigkeitGΦ.Beide Parameter hängen stark vonTc und dem Molekulargewicht ab. Alle diese Wesenzüge werden diskutiert und interpretiert in Termen der kinetischen Theorien des Polymerwachstums.RésuméEn utilisant le procédé d'autoensemencement on a fait croître des monocristaux de divers Polyoxyéthylènes (cinq fractions de bas poids moléculaire et une de poids moléculaire élevé) à partir du polymère surfondu. Une trempe permet d'arrêter la croissance des cristaux et donne lieu à une décoration contrastée de tous les sites des cristaux susceptibles d'initier une croissance, alors que le liquide surfondue résiduel cristallise par germination homogène et reste transparent. Cette «autodécoration» délimite les bords du cristal et met en évidence la rugosité éventuelle de la surface des lamelles. La décoration superficielle permet de distinguer entre les lamelles formées de chaînes repliées et étendues.Pour les cinq fractions de bas poids moléculaire, la variation thermique de la vitesse de croissance,G, présente au moins une transition nette qui peut être interprétée par la variation discontinue de l'épaisseur des lamelles avec la température de cristallisationTc. Pour chaque fraction, la transition de la croissance en chaîne étirée à celle en chaîne repliée est très nette, et s'accompagne d'une modification importante de la forme des cristaux et de leur état de surface.Les lamelles formées de chaînes repliées s'épaississent d'une mainière isotherme pendant leur croissance si elles sont entourées par du polymère fondu. Cette extension isotherme des chaînes peut être observée morphologiquement. Elle implique deux mécanismes moléculaires différents: en processus de germination, caractérisé par un temps d'incubationτ, et un processus de croissance, caractérisé par une vitesse,GΦ. Ces deux paramètres dépendent fortement de la masse moléculaire et deTc. L'ensemble de ces phénomènes est analysé sur la base des théories cinétiques de la croissance des cristaux de polymères.

Lithographic printing plates and photoresists comprising a photosensitive polymer

Abstract: Photosensitive coating materials comprising polymers containing o-nitrocarbinol ester groups, particularly of polymers and copolymers of o-nitrocarbinol esters of ethylenically unsaturated carboxylic acids, which as a result of exposure become soluble in an alkaline solvent used as developer in which they were not soluble prior to exposure. Such materials are used in particular for coating lithographic printing plates and as photoresists.

Molecular weight and shape of humic acid from sedimentation and diffusion measurements on fractionated extracts

Abstract: Summary Whole humic acid extracts are usually too polydisperse for reliable molecular-weight measurement to be made in the ultracentrifuge by the sedimentation velocity technique. Consequently, the humic acid used in this study was fractionated with respect to molecular weight into fractions of low polydispersity by extensive use of gel-permeation chromatography and other fractionation techniques. The sedimentation and diffusion coefficients of the fractions were determined and molecular-weight values calculated. These values ranged approximately from 2 × 103 to 1.5 × 106, the higher figure not necessarily representing the upper limit for these substances. On the basis of the frictional parameters calculated from the experimental data, it is proposed that the molecule adopts the solution conformation of a randomly coiled polymer in which branching may be significant, particularly at higher molecular weights.

Mechanical Properties of Polymers: The Influence of Molecular Weight and Molecular Weight Distribution

Abstract: The molecular weight and molecular weight distribution of a polymer can markedly affect its mechanical properties. While this has been recognized for a long time, quantitative studies have been relatively difficult to perform for a number of reasons. A major problem has been the characterization of the complete molecular weight distribution curve by fractionation methods because fraction collection and the determination of the various molecular weight averages of polymers is time consuming. Additionally, measurement of the number-average molecular weight, [Mbar]n, by classical osmometry procedure is often unreliable.

Ultrasonic hysteresis absorption in polymers

Abstract: Ultrasonic absorption measurements were made in polymethylmethacrylate, polyethylene, and polyethylene oxide as functions of frequency, temperature, and strain At room temperature, all three polymers show a hysteresis‐type absorption that extends at least over the frequency range from 1 to 107 Hz, as shown by using literature values for results at 1 Hz There is no strain dependence to the absorption in any of the polymers in the strain range from 10−9 to 10−6 The mechanism responsible for the hysteresis absorption is postulated to be the trapping of the polymer in one of its many local metastable potential‐energy minima This mechanism leads to the prediction that the hysteresis absorption should be a linearly decreasing function of volume and this prediction is in reasonable agreement with the experimental data

Interaction of poly(styrene sulfonate) with polycations carrying charges in the chain backbone

Abstract: The interaction between sodium poly(styrene sulfonate) (NaSS) and side-chain charged polycation polymer (pendent type) or main-chain charged polycation polymer (integral type) has been studied. It was found that the polyion complex (the reaction product of these polyelectrolytes) of pendent–pendent type has an equimolar composition at any mixing ratio of two component polymers. However, a polyion complex of integral–pendent type can form a water-soluble complex with a ratio of [polycation]/[polyanion] = 1/3, in addition to a complex with a equimolar composition. The mechanism of formation of this specific complex is discussed.

Rapid dissolving water-soluble polymers

Abstract: WATER-SOLUBLE VINYL ADDITION POLYMERS MAY BE RAPIDLY DISSOLVED IN WATER BY FIRST DISPERSING THESE POLYMERS INTO A WATER-IN-OIL EMULSION AND THEN INVERTING THESE EMULSIONS IN WATER. THE INVERSION OF THE EMULSION RELEASES THE POLYMER INTO WATER AS A SOLUTION.

Hydrophilic polyurethane polymers

Abstract: WATER ABSORPTIVE POLYURETHANE POLYMERS PREPARED FROM RESINS HAVING A LOW RATIO OF CARBON TO OXYGEN TO NITROGEN OR HAVING IONIC, QUATERNARY AMMONIUM OR SALT GROUPS IN THE RESIN BACKBONE AND A LOW AMOUNT OF ISOCYANATE. THE WATER ABSORPTIVITY OF THE POLYURETHANE POLYMERS IS ABOUT 10%, PREFERABLY ABOVE 20%, AND THESE POLYMERS MAY RANGE TO COMPLETELY GEL-LIKE, HIGH WATER ABSORPTIVE, POLYMERS; THESE POLYMERS ARE USEFUL AS COATINGS, MEMBRANES, ETC.

Polymer adsorption and its effect on the stability of hydrophobic colloids

Abstract: As a first step in a study on the interaction between polymers and hydrophobic colloids we investigated in detail the adsorption of polyvinyl alcohol (PVA) on aqueous silver iodide sols. The adsorption is irreversible. Adsorption isotherms are of the highaffinity type. The amount adsorbed increases with molecular weight and with the fraction of acetate groups in the PVA chain. The effective thicknessΔ of the adsorbed layer was determined viscosimetrically and independently checked by an electrophoretic method. Double layer studies enabled the determination of the occupancy of the first layer on the surface by polymer segments. It was found that even at maximal coverage with polymer this layer is still about 30% void. The combination of these data enabled the assessment of the polymer segment distribution. It was found that with not too low coverages the distribution isHoeve- like. The distribution, thus obtained reflects itself in the flocculation of AgI sols by PVA.

Polymers having stable radicals. I. Synthesis of nitroxyl polymers from 4‐methacryloyl derivatives of 2,2,6,6‐tetramethylpiperidine

Abstract: Polymers having stable nitroxyl free radicals, poly-4-methacryloylamino- and poly-4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyls, were synthesized from their precursor polymers by oxidizing them in a methanolic solution of hydrogen peroxide. The precursor polymers were prepared by radical polymerization of 4-methacryloyl-amino/oxy-2,2,6,6-tetramethylpiperidines in various solvents. These polymerizations in acetic acid were found to yield polymers of high molecular weight. The copolymers of the precursor monomers with styrene and methyl methacrylate were also prepared as precursor copolymers. These precursor polymers of a piperidine type were converted to the polymers having stable nitroxyl free radicals by the hydrogen peroxide method. In this report, it was assumed that the post-oxidation reaction introduced a nitroxyl group smoothly and quantitatively at room temperature. Elucidations of the stable radical formation and the electron spin behavior of the stable radical polymers were made in terms of elemental analyses, infrared, ultraviolet, and ESR spectroscopy.

Mechanism of submicrocrack generation in stressed polymers

Abstract: Submicrocracks, free radicals, and endgroups of scissioned molecules formed in polyethylene, polypropylene, and polycaprolactam under uniaxial tension have been investigated. Measurements were carried out by small-angle x-ray scattering, electron paramagnetic resonance, and infrared spectroscopy. The concentration of submicrocracks is almost the same as that of free radicals but is smaller than the concentration of scissioned macromolecules by approximately three orders of magnitude. The number of scissions per crack proved to be close to the number of macromolecules passing through the cross section of a submicrocrack calculated on the assumption of close packing. It is concluded that submicrocracks in stressed polymers are formed as a result of chain reactions of macromolecular decomposition initiated by the active end primary free radicals.

Thermal conductivity of polymers filled with particulate solids

Abstract: The thermal conductivities of polystyrene and polyethylene containing several different particulate solids were measured over a range of solid concentrations. Experimental data were compared with results predicted by theoretical models for two-phase media. The equations of Bruggeman and Cheng-Vachon both gave reasonable agreement with measured results. The applicability of these equations does not appear to depend upon the structure of the polymer.

Thermo-optical and differential scanning calorimetric observations of mobility transitions in polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) blends

Abstract: Transition temperatures by thermo-optical analysis (TOA) and by DSC were measured on films of polystyrene (PS), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO resin) and nine homogeneous blends of these polymers. The TOA procedure consists of automatically monitoring light transmission through birefringent scratches in a film during heating at constant rate in a microscope hot stage between crossed (90°) plane polarizers. The TTOA transition temperature, defined as the temperature of birefringence disappearance in the scratches, increased monotonically from 113°C for pure PS to 222°C for pure PPO resin at a 10°/min heating rate. The Tg (DSC) similarly ranged from 99°C to 212°C at a 20°/min heating rate. The TOA technique as described should be a useful addition to thermomechanical studies of transparent polymers and polymer blends.

Surface-Chemical Criteria for Optimum Adhesion

Abstract: According to Bikerman, who attributes failure in adhints to a weak boundary layer, it is almost impossible and meaningless to correlate adhesive strength to surface-chemical properties of adhints. Though his assertion seems to be confirmed by the recent studies of Schonhorn and his coworkers on the methods of CASING and TCR, not a few results have yet been accumulated, which show a close relation between them. In this paper surface-chemical criteria for the optimum adhesion are investigated and the minimum interfacial tension or the maximum wetting pressure is deduced from the published data and our own as a first approximation. It is emphasized that, when critical surface tension γ c would be used as a measure of surface-chemical properties of solid, its variability according to liquid series (nonpolar, polar and hydrogen bonding liquids) should be carefully taken into consideration. The importance is shown for polyethylene and its fluorine substituted polymers, using newly measured contact angl...

Method for preparation of biocompatible and biofunctional materials and product thereof

Abstract: A METHOD FOR THE PREPARATION OF BIOCOMPATIBLE AND BIOFUNCTIONAL SURFACES IS PROVIDED BIOCOMPATIBLE AND ATI N GRAFTING A REACTABLE COMPOUND SELECTED FROM THE GROU CONSISTING OF POLYMERS AND COPOLYMERS ONTO AN INERT UP POL MERIC SUBSTRATE AND THEREAFTER CHEMICALLY BONDING A BIOLOGICALLY ACTIBE MOLECULE TO THE REATABLE COMPOUND SPECIFIC EMBODMENTS INCLUDE CHEMICALLY BONDING OF HUMAN SERUM ALBUMIN HEPARIN, STREPTOKINASE, PROSTAGLANDIN E-1 AND MIXTURES THEREOF TO HYDROGELS OF VARYING COMPOSITIONS WITH OR WITHOUT "ARM" SUC AS E-AMINO CAPROIC MOLECULE OR CHEMICAL "ARM" SUCAN INTERMEDIATE SMALLER ACID OR 1,4 DIAMINO BUTANE, THE HYDROGELS HAING BEEN PREVIOUSLY RADIATION-GRAFTED TO TOUGH INERT POLYMERIC SUBSTRATE. A HIGHLY SYNERGISTIC EFFECT IS ACHIEVED FOR HYDROGELS CONTAINING HIGH WATER CONTENT E.G., ABOVE ABOUT 55% WHEN THE CHEMICALLY BONDING OF THE BIOLOGICALLY ACTIVE MOLECULE IS CARRIED OUT VIA AN INTERMEDIATE SMALLER MOLECULE OR CHEMICALL ARM. FOR THIN FILM SUBSTRATES HAVING RAIATION-GRAFTED THERETO HYDROGELS WITH -CO2 PENDANT FUNCTIONAL GROUPS WHICH ARE ACTIVATED WITH A CARBODIIMIDE SOLUTION A QUICK WASH OF THE THIN FILM WITH ICE WATER IS REQUIRED TO EFFECT SUBSEQUENT CHEMICAL BONDING OF THE BIOLOGICALLY ACTIVE MOLECULES TO THE ACTIVATED SURFACE. THE SAME TECHNIQUE IS ALSO REQUIRED WHERE A CHEMICAL ARM IS EMPLOYED WHICH HAS -CO2H PENDANT FUNCTIONAL GROUPS.