Showing papers on "Polymer published in 1977"

Principles of Polymerization

Abstract: All syntheses that proceed from low-molecular-weight compounds (monomers) to produce high-molecular-weight compounds (polymers) are termed “polymerizations” (i.e., polyreactions). Polymerizations only occur when the appropriate chemical, thermodynamic, and mechanistic requirements are fulfilled.

Diffusion in polymer—solvent systems. I. Reexamination of the free-volume theory

Abstract: The free-volume theory describing diffusion in polymer–solvent systems is reexamined. Calculation of the specific free volume for such systems is discussed, and equations are presented for the determination of the self-diffusion coefficients of the polymer and the solvent. Conditions under which the mutual diffusion coefficient can be deduced solely from free-volume considerations are clarified, and a more general version of the free-volume diffusion theory proposed by Fujita is presented. The further restrictions needed for the theory of Fujita are discussed, and it is concluded that these additional restrictions are responsible for failures of the Fujita theory.

Physical properties and supermolecular structure of perfluorinated ion‐containing (nafion) polymers

Abstract: The supermolecular structure and viscoelastic and diffusion properties of a perfluorinated polymer containing sulfonic acid (Nafion) were investigated. The breakdown of time–temperature super-position for the dry salt and and acid in the presence of 0.5 H2O/SO3H as well as the results of small-angle x-ray scattering suggest that the ions in this material are clustered. Above 180°C, the reestablishment of the time–temperature superposition in the salt suggests that ions in the clusters become mobile. Dynamic mechanical studies were performed over a temperature range from −190°C to above the glass transition temperatures Tg of the materials. The Tg of the salts is found at ca. 220°C, while in the acid it occurs at 110°C. A β peak in the acid is found at ca. 20°C, while in the salts it occurs between 140°C and 160°C. The β peak shifts to a lower temperature with the addition of water in both the acid and the salts, while the α and γ peaks are unaffected. The latter is located at ca. −110°C at 1 Hz. Dielectric behavior has also been studied as a function of water content for the acid sample and the potassium salt at frequencies of 100 Hz to 10 kHz. Two relaxations with different activation energies were observed. The position of both peaks shifts to a lower temperature as the water content increases. Finally, the diffusion of water in Nafion in the acid form has been determined. The diffusion coefficient can be represented by the equation

Stabilization of tetragonal phase in polycrystalline zirconia

Abstract: It is shown that the tetragonal phase can be stabilized in the sintered body of a partially stabilized zirconia (PSZ) containing low concentrations of yttria. Such sintered body containing the metastable phase undergoes stress-induced phase transformation by the absorption of thermal or mechanical stress and exhibits strengths in excess of 690 MPa (100ksi).

Solid-state polymerization mechanisms

Abstract: Mechanisms of topochemical polymerizations are described using the four-center-type photopolymerization of diolefins and the polymerization of diacetylenes as actual examples. Solid-state polymerizations can be treated as a special case of phase change which may proceed homogeneously or heterogeneously. Special consequenses of the mechanism of phase change are described. The scope of the four-center-type and of diacetylene polymerization is discussed and some rules relating molecular shape and packing into a reactive modification are discussed. Photoresponse curves for diacetylenes are reported and the relation between molecular structure and photosensitivity is discussed. Finally, the nature of chain growth is considered. Four-center-type photopolymerization proceeds in an stepwise manner along the same mechanism which is also true for dimerization of cinnamic acids and derivatives. Diacetylene polymerization proceeds via carbenoid intermediates which add to polymer chain ends with carbene character.

Tough thermoplastic nylon compositions

Abstract: Toughened multi-phase thermoplastic composition consisting essentially of one phase containing 60 to 99 percent by weight of a polyamide matrix resin of number average molecular weight of at least 5000, and 1 to 40 percent by weight of at least one other phase containing particles of at least one polymer having a particle size in the range of 0.01 to 3.0 microns and being ahdered to the polyamide, the at least one polymer having a tensile modulus in the range of 1.0 to 20,000 p.s.i., the ratio of the tensile modulus of the polyamide matrix to tensile modulus of said at least one polymer being greater than 10 to 1. Said at least one polymer is either a branched or straight chain polymer. The toughened compositions are useful for making molded and extruded parts. Such parts possess greater ductility, less reduction in toughness from scratches and molded in notches and reduced susceptibility to catastrophic failure when compared to known melt fabricated materials.

Mechanism of emulsion polymerization of styrene in soap‐free systems

Abstract: The formation and growth of monodisperse polystyrene latex particles in the absence of added surfactant has been studied by sampling polymerization reactions at different times and determining the surface and bulk properties of the latex. A large number of nuclei in excess of 5 × 1012/ml were generated during the first minute of reaction, but this fell due to coagulation until a constant number (1011−1012/ml) was reached. The rate of polymerization per particle was then found to be proportional to the particle radius. Gel-permeation chromatography has shown that the initial particles consist mainly of material of MW 1000 with a small amount of polymer up to MW 106, and the presence of this low molecular weight polymer, which in many cases can still be detected after 100% conversion, is taken as being indicative of particle formation via a micellization-type mechanism involving short-chain (MW 500) free-radical oligomers. Mn values determined for the latex particles throughout the course of reactions show that the molecular weight increases to a maximum of about 105 as the particles grow. The presence of anomalous regions within the particles has been confirmed by transmission electron microscopy, scanning electron microscopy, and gas adsorption studies. It has also been found possible to re-expose these regions within apparently homogeneous particles by stirring with styrene monomer; this is indicative of a molecular weight heterogeneity within the latex particles. The presence of sulfate, carboxyl, and hydroxyl groups upon the latex particle surfaces has been determined by conductometric titration.

Cross-linked, water-swellable polymer microgels

Abstract: Discrete, spheroidal microgels of a water-swollen or water-swellable, cross-linked polymer such as cross-linked polyacrylamide are particularly useful as thickening agents for aqueous dispersions to be subjected to high shear and as agents for reducing the permeability of porous structures.

Process for preparation of spontaneously-crosslinked alkali metal acrylate polymers

Abstract: Spontaneously cross-linked alkali metal acrylate polymers having a high water-absorbing property and which are safe for contact with the human skin are prepared by a water-in-oil suspension polymerization process, using a sorbitan fatty acid ester having an HLB value of 3 to 6 as a dispersing agent.

Some aspects of plasma polymerization investigated by pulsed R.F. discharge

Abstract: The polymerization of organic compounds in glow discharge (plasma polymerization) was investigated by using pulsed R.F. discharge (100 μsec on, 900 μsec off). The effects of pulsed discharge on polymer deposition rate, pressure change in plasma, ESR signals of free spins in both plasma polymer and substrate, and the contact angle of water on the plasma polymer surface were investigated for various organic compounds. The results are correlated to the mechanisms of polymer formation in plasma (plasma polymerization) which has been postulated as repeating processes of stepwise (propagation) reactions. The effect of the pulse is different from one group of organic compounds to another depending on whether or not they contain an olefinic double bond and/or a triple bond. The main difference seems to be the addition polymerization which can occur exclusively during the off-period of pulsed discharge. Ultraviolet emission from pulsed discharge is much less than from continuous discharge. Consequently, the fragmentation of the monomer and the free-radical formation in the substrate are less with the pulsed discharge. Properties of polymers from some organic compounds formed in continuous and in pulsed discharge were found to be significantly different, and the differences were postulated from the changes of polymerization mechanisms in the pulsed discharge.

High resolution NMR in randomly oriented solids with homonuclear dipolar broadening: Combined multiple pulse NMR and magic angle spinning

Abstract: The first combined multiple pulse‐magic angle experiment is reported in which both homonuclear dipole interactions and chemical shift anisotropies are removed to resolve chemically shifted fluorines. The sample selected was KEL‐F.(AIP)

Multicomponent polyester- block copolymer- polymer blends

Abstract: A multicomponent polymer blend composition is prepared by intimately mixing a thermoplastic polyester, a selectively hydrogenated monoalkenyl arene-diene block copolymer, and at least one dissimilar engineering thermoplastic resin under such conditions that at least two of the polymers form at least partial continuous network phases which interlock with the other polymer networks and therefore results in a desirable balance of properties. These blends have an unobviously high heat distortion temperature relative to the improved impact strength.

Polyurethane polymers characterized by lactone groups and hydroxyl groups in the polymer backbone

Abstract: Polyurethane polymers characterized by a molecular weight above 6,000 and having lactone groups and hydroxyl groups in the polymer backbone are prepared by reacting a mixture of polyols, a polyfunctional lactone and a polyfunctional isocyanate proportioned so as to provide the desired polymer properties. The product is soluble in alkaline solutions and may be used for light sensitive photographic layers on films, paper or glass; in drug delivery systems, as burn dressings, in body implants such as vascular prosthesis, in molding compositions, and in the manufacture of catheters. The novel polymers also find use in the manufacture of artificial finger nails, finger cots, adhesives, and in protective and hdyrostatic drag resistant coatings. The water absorptivity of the polyurethane lactone polymers is above 10%, preferably in the range of about 20% to 60%, and these polymers may range in their physical properties from rigid solids to completely gel-like high water absorptive polymers. The polymers of the present invention can provide a leachable substrate wherein the leaching agent may be water, gases, alcohols, esters and body fluids, e.g., animal or human.

ESCA Study of Polymer Surfaces Treated by Plasma

Abstract: Surfaces of polymers [polyethylene, polystyrene, poly(ethylene terephthalate), poly(oxymethylene), cellulose acetate, polyacrylonitrile, nylon 6, and polytetrafluoroethylene] treated with argon (inert) and nitrogen (reactive) plasma were examined by ESCA (electron spectroscopy for chemical analysis). Argon plasma treatment generally introduces oxygen functionalities into the polymer surface. Nitrogen treatment generally incorporates nitrogen and oxygen functionalities into the treated surface. The extent of oxygen incorporation is typically less than that produced by argon plasma. When nitrogen and oxygen functional groups are already in a polymer structure, the extent of additional incorporation of these two elements as a result of plasma treatment is very much less than with other polymers. Polymers which contain only one of the elements tend to incorporate the other element to much the same degree as polymers without either element initially present.

Polyolefinic copolymer additives for lubricants and fuels

Abstract: Graft copolymers wherein the backbone polymer is a polymeric hydrocarbon such as ethylene/propylene copolymer and the grafted units are the residues of a monomer system comprising maleic acid or anhydride and one or more other monomers copolymerizable therewith, the monomer system being post-reacted with a polyamine compound. The graft copolymers impart combined detergent, viscosity index improvement and other useful properties to lubricating oils and hydrocarbon motor fuels.

A novel type of polycondensation of polyhalogenated organic aromatic compounds producing thermostable polyphenylene type polymers promoted by nickel complexes.

Abstract: Nickel complexes (NiCl2 (2,2′-bipyridine) and NiBr2(triphenylphosphine)2) catalyze polycondensation of di- and polyhalogenated aromatic compounds including p-dibromobenzene, p-dichlorobenzene, m-dichlorobenzene, bis (4-bromophenyl)ether, p-chlorobenzyl chloride and 1,3,5-trichlorobenzene by dehalogenation with magnesium to give polyphenylene type polymers in high yields.

Processes of making a porous membrane material from polyvinylidene fluoride, and products

Abstract: Covers processes for making microporous membranes and molecular filtration membranes from vinylidene fluoride polymers, and the products so produced. A continuous version of the process consists of applying a layer of a solution of a polyvinylidene fluoride polymer to a rigidly supported surface of a backing belt to form a film, then passing the belt through a formation bath, in which the membrane is formed. To form the polymer solution, the polymer is dissolved in a liquid vehicle that will dissolve up to about 25% by weight of the polymer at a temperature of at least 50° C. but that dissolves substantially less of the polymer at about 20° C. (room temperature). The polymer solution is formed at 50° C. or higher, and the formation bath is maintained at about room temperature. The formation bath is a mixture of the liquid vehicle solvent with a second liquid that is miscible with the solvent but that is not itself a solvent for the polymer. The film is maintained immersed in the formation bath until it has been converted to a porous membrane whose pore structure is essentially fully formed, by leaching of the solvent from the film and its replacement with the non-solvent liquid. Thereafter the residual solvent is extracted from the porous membrane, and after separation of the membrane from the backing belt, the membrane is dried. The preferred solvent - non-solvent system for the formation bath is acetone-water. A preferred formation bath composition is from about 70% to about 80% acetone by volume.

Polymer cryoprotectants in the preservation of biological ultrastructure. I. Low temperature states of aqueous solutions of hydrophilic polymers.

Abstract: The solid states formed by vitrified and frozen aqueous solutions of some hydrophilic polymers, able to act as biological cryoprotectants, have been studied by differential scanning calorimetry and freeze fracture electron microscopy. Glass transitions, devitrification, recrystallization and melting behaviour of aqueous solutions of polyvinylpyrrolidone, hydroxyethyl starch and dextran have been established. The vitrified polymer solutions exhibit a characteristic microspheral morphology which is not induced by the quench cooling process but is an inherent feature of the solutions themselves.

Plastic deformation in polyimides, with new implications on the theory of plastic deformation of glassy polymers

Abstract: The plastic deformation behaviour of a series of glassy aromatic polyimides, derivatives of resorcinol, hydroquinone, oxydiphenyl, and pyromellitic acid, have been investigated between room temperature and a temperature 20 K below their respective glass transition temperature The results are analysed by means of a theory due to Argon (1973) for plastic flow in glassy polymers, and show that, as the spacing between natural hinges on polymer molecules increases with increasing chemical complexity, the thermally activated complex grows in size, and plastic deformation becomes less local

The concentration dependence of transport processes: A general description applicable to the sedimentation, translational diffusion, and viscosity coefficients of macromolecular solutes

Abstract: The transport coefficients of macromolecular solutes are normally extrapolated to “infinite dilution” to remove the effects of concentration-dependence terms, for which no satisfactory general treatment has been available. It is shown that a simple general treatment for the concentration-dependence effect can be derived, applicable to limiting concentrations in the absence of charge effects or other forms of specific interactions between the solute particles. The relationships derived are of considerable practical significance for the characterization of the size and conformation of natural and synthetic polymers.

Secondary Loss Peaks in Glassy Amorphous Polymers

Abstract: A short description is given of the determination–as a function of frequency and temperature–of secondary mechanical loss peaks in glassy amorphous polymers. The molecular motions causing secondary loss peaks are classified. The dependence on frequency of the temperature of the maximum of the loss peak is discussed. The effects on the secondary loss peaks of structural features such as plasticization, intermoleeularsteric hindrance and polarity, are illustrated by the example of the β-maximum of poly(methyl methacrylate), emphasis being laid on the difference between a glass transition and a secondary loss peak.

The energy dissipation in sheared coagulated sols

Abstract: The observed energy dissipation in coagulated sols subjected to a shear flow can be explained by assuming that the basic units of flow are elastic flocs which are slightly deformed during collisions because of the stretching of the particle bonds within a floc by a few tenths of a nanometer. Liquid inside perforated structures is generally considered immobile, but during the deformation of the flocs some internal liquid movement occurs. Although the amount of internal liquid movement is rather small, of the order of 1%, it is sufficient to account for the observed energy dissipation.

Mechanical properties of mixtures of two compatible polymers

Abstract: The properties of mixtures of poly(2, 6-dimethyl p-phenylene oxide) and poly(styrene) have been measured by DSC, density gradient, dynamic mechanical response, and tensile testing. The mixtures are found to have single glass trasitions that vary continuously with the composition. They also have small negative excess volumes of mixing, indicative of strong polymerpolymer interaction. The dynamic mechanical response of the mixtures shows that the low temperature secondary relaxations are suppressed whereas those at high temperatures are enhanced. These observations imply that mixing on the segmental levc l has occurred. A plot of tensile strength vs composition at different strain rates reveals two regions of failure behavior. The high PS, high strain rate region is brittle, and the high PM2PO, low strain rate region is ductile. When the tensile yield data are treated according to the Ree-Eyring equation, the addition of PS to PM2PO is found to reduce the flow volum, e of the mixture. The overall effect on mechanical properties of adding small amounts of one component to the other is similar to that of anti-plasticization. Our experimental observations are consistent with the shifting of the relaxation mechanisms to longer times due to the negative excess volume of mixing.