Showing papers on "Polymerization published in 1985"

Encyclopedia of polymer science and engineering

Abstract: Cellular Materials Cellulose Cellulose, Biosynthesis Cellulose, Graft Copolymers Cellulose, Microcrystalline Cellulose Derivatives Cellulose Esters, Inorganic Cellulose Esters, Organic Cellulose Ethers Cement Additives Chain-Reaction Polymerization Chain Transfer Characterization of Polymers Charge-Transfer Complexes Chelate- Forming Polymers Chemical Analysis Chemically Resistant Polymers Chitin Chloroprene Polymers Chlorotrifluorethylene Polymers Chromatography Classification of Polymerization Reactions Coating Methods Coatings Coatings, Electrodeposition Cold Forming.

Polymerization of Propene and Butene with a Chiral Zirconocene and Methylalumoxane as Cocatalyst

Abstract: Hitherto, only atactic polypropylene could be prepared with soluble bis(cyclopentadienyl)zirconium(iv)/methylalumoxane Ziegler-Natta catalysts.".'' E ~ e n [ ~ ' has recently shown that mixtures of, e.g., 63% isotactic and 37% atactic polypropylene are formed with the sterically rigid ethylenebis( I-indeny1)titanium dichloride (mixture of meso form and ra~emate) . '~ ' If, however, the chiral ethylenebis(4,5,6,7-tetrahydro-lindeny1)zirconium dichloride 1 (Fig. 1) is used in combination with methylalumoxane ([AI(CH3)-O],) as cocatalyst, highly isotactic polypropylene is obtained. The racemate of 1 was used for this polymerization. The fraction of polymer soluble in toluene can be reduced to 0.2 wt.45, which is considerably lower than the 2-7% achievable with heterogeneous TiCI,/MgC12/AI(C2H5)3/ C,H,CO,C,H,-based catalysts.1h1

Polymers of N-vinylpyrrolidone: Synthesis, characterization and uses.

Abstract: Polyvinylpyrrolidone (PVP) having molecular weights (Mw) from 2500 to about 1 million is mainly obtained by radical polymerization in solution The higher molecular weight type products are polymerized in aqueous solution mostly using hydrogen peroxide as initiator The polymers thus obtained have hydroxyl and carbonyl end groups More stable end groups can be obtained by polymerization in solvents, which may act as chain transfer agents and which produce low molecular weight type products Copolymers especially with monomers such as vinyl acetate and with various acrylic compounds may also be produced by solution polymerization Popcorn polymerization leads to insoluble PVP Thereby VP is polymerized without initiator in the presence of small amounts of bifunctional monomers The polymeric flakes thus formed are highly cross-linked, mainly due to entanglements The molecular weight distribution of soluble PVP is broad due to transfer reactions An unusual property of PVP is its solubility in water as well as in various organic solvents The glass transition temperature of high molecular weight polymers (Mw=1 million) is about 175°C and falls to values under 100°C with decreasing molecular weight Mw=2500) PVP forms complexes with various compounds, especially with H-donors such as phenols and carboxylic acids The complex formed with cross-linked PVP and polyphenols is used commercially for the clarification of beverages Another commercial use is the complexation of iodine with linear PVP, which leads to effective disinfectants of very low toxicity Further important applications of PVP in the pharmaceutical field are their use as binding or film forming agents for tablets, and as solubilizing agents for injections The swelling ability of cross-linked PVP in water is used in disintegrating agents for tablets In the cosmetic field VP polymers are used as film formers for hair dressing products Examples of technical applications are adhesives, textile auxiliaries and dispersing agents

Silica diagenesis; II, General mechanisms

Abstract: Amorphous silica phases (opal-A) precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions. Opal-A dissolves and yields solutions of still relatively high silica content. In pore waters containing abundant cations, open framework polymers form which flocculate to yield opal-CT. Opal-CT becomes increasingly ordered, primarily due to preferential growth of cristobalite relative to tridymite and crystal size increase. Opal-CT dissolves to yield pore waters of low silica concentration, which allows slow growth of quartz crystals from monomeric solution. The quartz crystals then slowly increase in size and crystallinity. Carbonates appear to enhance opal-CT formation, possibly due to the activity of positively charged hydroxyl complexes. Hence, polymerization in relatively pure systems is involved in opal-A formation and polymerization in impure systems is involved in opal-CT formation, and slow growth from monomeric (low silica concentration) solutions is involved in precipitation of quartz in sedimentary realms.

High-temperature stabilities of hydrocarbons

Abstract: Analyse thermodynamique chimique de molecules d'hydrocarbures de 1500° a 3000°K pour les especes C 2n H 2m (n=1-21, m=1-8)

Particle size control in dispersion polymerization of polystyrene

Abstract: In a dispersion polymerization process, the reaction mixture starts out as a homogeneous solution and the resulting polymer precipitates as spherical particles, stabilized by a steric barrier of di...

The crystallization of ultralong normal paraffins: the onset of chain folding.

Abstract: The nature of chain folding in polymers and the determination of the chain length at which folding occurs have been central questions in polymer science. The study of the formation of lamellar polymer crystals through chain folding has received a new impetus as a result of the recent synthesis of normal alkanes of strictly uniform chain lengths up to C390 H782. Chain folding is found in all such paraffins starting with C150H302. As with polyethylenes obtained by conventional polymerization, the fold length in the normal alkanes varies with crystallization temperature, but it is always an integral reciprocal of the full chain length. This behavior indicates that the methyl end groups are located at the lamellar surface and that the fold itself must be sharp and adjacently reentrant.

Recent advances in liquid crystalline polymers

Abstract: I: Synthesis, Structure, Properties Relationships.- 1. Synthetic Routes to Liquid Crystalline Polymers.- 2. Chiral Thermotropic Liquid Crystal Polymers.- 3. Solid State Physics of Thermotropic Polyesters: Internal Friction of Mesomorphic Structures.- 4. Thermotropic Liquid Crystal Aromatic Copolyesters Containing Cycloaliphatic Units.- 5. Polymerization of Allyldimethyldodecylammonium Bromide Liquid Crystalline Monomer to Its Liquid Crystalline Polymer.- II: Theory.- 6. Theoretical Basis for Liquid Crystallinity in Polymers.- 7. Nematic Liquid Crystals Formed from Flexible Molecules: a Molecular Field Theory.- 8. Order and Odd-Even Effects in Thermotropic Nematic Polyesters.- III: Characterization.- 9. Structure and Characterization of Thermotropic Liquid Crystalline Polymers.- 10. Observations on the Rheology of Thermotropic Polymer Liquid Crystals.- 11. Rheo-Optical Studies of the Thermotropic Aromatic Copolyesters of Poly(Ethylene Terephthalate) and p-Acetoxybenzoic Acid.- 12. Electron Microscopy of Thermotropic Copolyesters.- 13. Nuclear Spin-Label Studies of Liquid Crystal Polymers.- 14. Viscosity and the Thermodynamic Properties of Liquid Crystalline Polymers with Mesogenic Side Groups.- 15. Measurement of Orientational Order in Liquid Crystalline Samples by NMR Spectroscopy.- 16. Phase Behaviour of Dye-Containing Liquid Crystalline Copolymers and Their Mixtures with Low Molecular Weight Liquid Crystals.- 17. Dielectric Relaxation Measurements and X-ray Investigations of Liquid Crystalline Side-Chain Polymers.- 18. Structural Investigations on Liquid Crystalline Side-Chain Polymers.- 19. Macromolecular Order and Conformation in the Solid and Nematic Phases of Semi-Rigid Polymers and Polymer-Monomer Mixtures-NMR Study.- IV: Applications.- 20. Aramids-Bridging the Gap between Ductile and Brittle Reinforcing Fibres.- 21. Towards a Photoconductive Liquid Crystal: Carbazole-Containing Systems.- 22. Electro-Optic Effects in a Smectogenic Polysiloxane Side-Chain Liquid Crystal Polymer.

Hydrogel-forming polymer compositions for use in absorbent structures

Abstract: The present invention relates to improved hydrogel-forming polymer compositions which can be used as absorbents in absorbent structures and absorbent articles such as diapers, sanitary napkins and the like. Such hydrogel-forming polymer compositions are substantially water-insoluble, slightly cross-linked, partially neutralized polymers which are prepared from unsaturated polymerizable, acid group-containing monomers and cross-linking agents. These hydrogel-forming polymer materials, upon imbibing fluids, form hydrogels. Such polymer materials have relatively high gel volume and relatively high gel strength as measured by shear modulus of the hydrogel which forms therefrom. Such polymer materials also contain relatively low levels of extractable polymer material which can be extracted therefrom by contact with synthetic urine. Preferred hydrogel-forming polymers having these characteristics can be prepared by polymerizing the acid group-containing monomers in their free acid form at relatively low monomer concentrations, preferably using relatively low polymerization temperatures. Absorbent structures and absorbent articles containing these dried hydrogel-forming polymer materials are also disclosed.

Supported Chromium Catalysts for Ethylene Polymerization

Abstract: Publisher Summary This chapter discusses supported chromium (Cr) catalysts for ethylene polymerization. The Phillips Cr/silica polymerization catalyst is prepared by impregnating a Cr compound onto wide pore silica and then calcining in oxygen to activate the catalyst. This leaves Cr in the hexavalent state, monodispersed on the silica surface. Chromium trioxide (CrO3) has been impregnated most commonly, but even a trivalent Cr salt can be used because oxidation to Cr(VI) occurs during calcining. Dichromate is the main species in CrO3 solutions. Trivalent Cr salts, notably CrCl3, impregnated onto silica and calcined under vacuum, are found to polymerize ethylene. Three processes are used commercially to make linear polyethylene—namely, solution, slurry, and gas phase. All these processes are called “low-pressure processes” to distinguish them from the free radical or high-pressure process that makes highly branched polyethylene. The slurry process is very convenient for batch polymerization studies. The diluent permits precise control of the temperature and serves to dissolve ethylene and other reactants that must contact the catalyst during polymerization.

Syntheses with Radicals—C ? C Bond Formation via Organotin and Organomercury Compounds [New Synthetic Methods (52)]

Abstract: CC bond formation is one of the most important synthetic steps in the construction of organic molecules. In the last few years it has been increasingly achieved by radical addition to alkenes. In such reactions the adduct radicals have to be trapped by an donor subsequent to the CC bond formation in order to prevent polymerization. This task can be accomplished with organotin and organomercury hydrides, the use of which has led to new synthetic methods. The occurrence of radical chain reactions in which reactions take place between radicals and nonradicals is decisive for the success of the synthesis. In these cases small amounts of radical initiators suffice and numerous functional groups may be used in the CC bond-forming reactions. The yields and selectivities of these radical reactions are often very high.

Morphology of latex particles formed by poly(methyl methacrylate)-seeded emulsion polymerization of styrene

Abstract: Poly(methyl methacrylate)–polystyrene composite particle latexes were prepared by poly(methyl methacrylate)-seeded emulsion polymerization of styrene employing batch, swelling-batch, and semibatch methods. The changes in particle morphology taking place during the polymerization reaction were followed by electron microscopy. Anchoring effect exerted by ionic terminal groups introduced by ionic initiator was found to be the main factor in controlling the particle morphology. The polymer particles obtained by oil-soluble hydrophobic initiators such as azobisisobutyronitrile and 4,4′-azobis-(4-cyanovaleric acid) gave the inverted core-shell morphology. Water-soluble hydrophilic initiator, K2S2O8, also gave the inverted core-shell morphology. However, in this case the occurrence of the halfmoonlike, the sandwichlike, and the core-shell morphologies were also observed depending upon the polymerization conditions. The distribution of terminal SO groups on the surface area of polystyrene particles could be controlled by initiator concentration and polymerization temperature. Viscosity of polymerization loci dictated the movement of polymer molecules, thus causing the unevenness of particle shape and phase separation at high viscosity state. Viscosity was controlled by the styrene/poly(methyl methacrylate) ratio, the addition of a chain transfer agent or a solvent which is common to polystyrene and poly(methyl methacrylate).

Method for continuous production of cross-linked polymer

Abstract: A method for the continuous production of a cross-linked polymer having a low proportion of large particles, comprising the steps of continuously feeding the aqueous solution of a monomer capable of being converted by aqueous solution polymerization into a water-containing cross-linked gel polymer and a polymerization initiator to a vessel provided with a plurality of mutually parallel rotary stirring shafts each fitted with stirring blades, finely dividing a water-containing gel polymer issuing from the polymerization in progress by the shearing force of stirring blades generated by the rotation of said stirring shafts while allowing the radical aqueous solution polymerization to proceed without interruption, and continuously discharging the resultant finely divided water-containing gel polymer out of said vessel.

Surgical articles of copolymers of glycolide and ε-caprolactone and methods of producing the same

Abstract: Novel copolymers of e-caprolactone and glycolide useful in making surgical articles and particularly surgical sutures having Young's modulus of less than 250,000 psi. New and improved polymerization methods for producing the novel e-caprolactone and glycolide copolymers.

Gas permeability of polyacetylenes carrying substituents

Abstract: The gas permeabilities of three polyacetylene films, prepared from poly[1-(trimethylsilyl)-1-propyne], poly(tert-butylacetylene), and poly(1-chloro-2-phenylacetylene), were studied. Although depending on conditions of polymerization and membrane preparation, typical permeability coefficients P of the polymers to oxygen and nitrogen at 25°C were as follows: poly[1-(trimethylsilyl)-1-propyne], PO2 = 40 × 10−8, PNr2 = 20 × 10−8; poly(tert-butylacetylene), PO2 = 3.0 × 10−8, PN2 = 1.0 × 10−8; poly(1-chloro-2-phenylacetylene), PO2 = 9.4 × 10−10, PN2 = 2.0 × 10−10 cm3(STP) · cm/(cm2 · s · cm Hg). Thus PO2 of a poly[1-(trimethylsilyl)-1-propyne] film is the largest among those ever known, and the values of poly(tert-butylacetylene) and poly(1-chloro-2-phenylacetylene) films are also fairly large. Influences of polymer structure, measuring temperature, and so forth on the PO2 and PN2 of these polyacetylene films were studied. The possibility of applying these films to oxygen enrichment of air are being discussed.

Homogeneous Ziegler–Natta catalysis. II. Ethylene polymerization by IVB transition metal complexes/methyl aluminoxane catalyst systems

Abstract: Homogeneous Ziegler-Natta systems for the ethylene polymerization, deriving from R2R2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization The catalytic activity of the systems under investigation was strongly affected also by changing both the σ-alkyl and the π-cyclo-pentadienyl ligands Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ-alkyl derivatives of IVB transition metals, such as Zr(CH2C6H5)4, are also able to polymerize ethylene with a fairly high productivity Active species containing ZrOAl bonds have been postulated

Method of forming shaped hydrogel articles

Abstract: A method for forming shaped hydrogel articles such as soft contact lenses wherein hydrophilic monomers are mixed with an inert diluent prior to polymerization, and the diluent is replaced with water following the polymerization. Diluents yielding optically clear hydrogels with good mechanical properties are selected on the basis of their viscosity and their Hanson cohesion parameters relative to the cohesion parameters of the polymeric component of the hydrogel.

Polymerization of 1-(trimethylsilyl)-1-propyne by halides of niobium(V) and tantalum(V) and polymer properties

Abstract: Polymerisation dans le toluene a 80°C. Influence du solvant et de la temperature. Conformation twist. Polymere blanc amorphe, soluble, stable a l'air, dielectrique solide non paramagnetique

The Structure and Mechanical Properties of Polypyrrole

Abstract: The evidence for the presence of the pyrrole moiety in electro-chemically prepared polypyrrole is reviewed together with structural and IR data obtained for the crystalline dimer and trimer of pyrrole. The modification of the mechanical properties of polypyrrole by formation of graft copolymers with polystyrene, by polymerization of the pyrrole monomer within the matrix of a swellable polymer film and by polymerization of the pyrrole on vitreous carbon electrodes is described.