Showing papers on "Polymerization published in 1979"

Impregnated polymerization catalyst, process for preparing and use for ethylene copolymerization

Abstract: A catalyst formed from selected organo aluminum compounds and a precursor composition of the formula Mg.sub.m Ti.sub.l (OR).sub.n X.sub.p [ED].sub.q wherein ED is a selected electron donor compound m is ≧0.5 to ≦56 n is 0, 1 or 2 p is ≦2 to ≧116 q is ≧2 to ≦85 R is a C 1 to C 14 aliphatic or aromatic hydrocarbon radical, or COR' wherein R' is a C 1 to C 14 aliphatic or aromatic hydrocarbon radical, and X is selected from the group consisting of Cl, Br, I or mixtures thereof, which catalyst is in particulate form and impregnated in a porous inert carrier material. A process for preparing such catalyst. A process for using said catalyst to readily prepare ethylene copolymers having a density of about ≧0.91 to ≦0.94 and a melt flow ratio of ≧22 to ≦32 in a low pressure gas phase process at a productivity of ≧50,000 pounds of polymer per pound of Ti. Novel polymers and molded articles are prepared.

Absorption of low molecular weight compounds in aqueous dispersions of polymer-oligomer particles, 2. A two step swelling process of polymer particles giving an enormous increase in absorption capacity

Abstract: A novel method for preparation of stable emulsions of slightly water soluble compounds is described. The method implies that the slightly water soluble compound diffuses through water and becomes absorbed into polymer particles which in a previous step have been brought to absorb a water insoluble, relatively low molecular weight compound. By this two step swelling process the polymer particles can be brought to absorb more than 100 times their own volume of the low molecular weight compounds to form stable o/w emulsions of the latter, with high oil content, and with a droplet size and size distribution which is completely determined by the size of the polymer particles in the latex applied initially. Monodisperse emulsions with large droplet size could easily be prepared. When the slightly water soluble compound added in the second step is a vinyl monomer which may subsequently be polymerized, the method represents a seed technique which is especially favourable for preparation of latexes with large particles size, including monodisperse latexes, with high solid content.

Monolithic glass formation by chemical polymerization

Abstract: Historically, glasses have been formed by solidification of oxide melts from elevated temperatures. Recently it has been demonstrated that monolithic oxide glasses can be formed by chemical polymerization at low temperatures. By the use of this technique, high-temperature reactions such as crystallization, phase separation, etc., which restrict glass formation in certain systems and regions, can be largely avoided. Thus, the technique not only permits investigation of glass structure from a fundamentally different point of view, but also allows the formation of new glasses which can not be formed by thermal means.

Plasma cell immunoglobulin M molecules. Their biosynthesis, assembly, and intracellular transport.

Abstract: Immunoglobulin M (IgM)-secreting murine plasmablasts have been used to explore the cytologic site(s) of the successive modifications of the polypeptide H and L chains (steps of glycosylation, chain assembly, and polymerization) which occur during intracellular transport (ICT) and the interrelationships between these events. A combination of pulse-chase biosynthetic labeling protocols (using amino acids and sugars), subcellular fractionation, and electron microscope autoradiography was used in conjunction with inhibitors of glycosylation and agents (carboxyl cyanide m-chlorophenyl hydrazone [CCCP] and monensin) which block Ig exit from the rough endoplasmic reticulum (RER) or Golgi cisternae. The data are consistent with the following conclusions: (1) Sugar addition and modification occur in three main steps: (a) en bloc addition of core sugars to nascent H chains, (b) partial trimming of these oligosaccharide chains in the RER, (c) quasiconcerted addition of terminal sugars (galactose, fucose, and sialic acid) in a very distal compartment between monensin-sensitive Golgi cisternae and the cell surface. (2) H and L chain assembly occurs between nascent H chains and a pool of free light chains present in the RER, followed by interchain disulfide bonding and rapid assembly of monomers into J chain-containing pentamers in the RER. Small amounts of various apparently non-obligatory intermediates in polymerization are also formed. (3) Carbohydrate addition is not required for chain assembly, polymerization, and secretion since completely unglycosylated chains (synthesized in the presence of deoxyglucose or tunicamycin) undergo polymerization and are secreted (although at a reduced rate). (4) Surface 8s IgM molecules do not represent a step in the IgM secretory pathway.

Polymerization of diacetylenes in multilayers

Abstract: The synthesis of extended and oriented very thin layers of polymers by solid-state polymerization of multilayers built up from monomolecular films of suitable monomers by means of the Langmuir-Blodgett (LB) technique has been felt to be a particular challenge for a long time. Attempts to make use of radiation-induced free radical polymerization of long-chain vinyl derivatives have been successful only in part (1–5).

A calorimetric study of acrylate photopolymerization

Abstract: The kinetics of the photoinitiated polymerization of lauryl acrylate (LA), 1,6-hexanedioldiacrylate (HDDA) and pentaerythritol tetraacrylate (PET4A) have been investigated using differential scanning calorimetry (DSC). An autoacceleration phenomenon is observed with the multifunctional acrylates, but not with lauryl acrylate. The empirical dependences of reaction rate on such parameters as incident light intensity, initiator concentration, and temperature have been established and are in general found to vary with monomer conversion. Apparent activation energies for the photopolymerizations have been determined from rate versus temperature data. The multifunctional acrylates show an increasing activation energy with monomer conversion, whereas the apparent activation energy for lauryl acrylate not only decreases with conversion, but becomes negative at conversions greater than about 30%. The ratio kp/k is calculated from rate versus conversion data under constant illumination and the (independently determined) initiation rate. Analysis of rate versus time data under nonsteady-state conditions (light turned off) yields the ratio kt/kp. With these two ratios the rate constants for propagation (kp) and termination (kt) may be separated and their respective values calculated. Both kp and kt are found to decrease substantially with monomer conversion, indicating a significant change in the rates of both the propagation and termination steps as the polymerization advances. These observations are explained in terms of a radical isolation phenomenon and diffusion control of the propagation step.

Molecular dynamics study of a polymer chain in solution

Abstract: The behavior of a polymer chain in solution has been simulated by means of molecular dynamics techniques. The polymer itself is represented by a freely linked chain of hard spheres and the solvent by a hard sphere fluid. Both the equilibrium configurational properties of chains of various lengths and their time‐dependent autocorrelation functions are studied. The equilibrium behavior agrees with the results of previous work. The decay of the autocorrelation functions is exponential over a considerable range and the relaxation times, thus defined, appear to scale with the chain length. The effect of the solvent density is also examined.

Polyglutaraldehyde synthesis and protein bonding substrates

Abstract: Polyglutaraldehyde (PGL) is polymerized in aqueous base or in aqueous highly polar solvent basic media to prepare powders, castable films or coatings for substrates such as amine substituted microbeads. PGL microspheres can be prepared by suspension polymerization in presence of a surfactant or by precipitating PGL from solution containing surfactant. Magnetic PGL microspheres are formed by suspension polymerization in the presence of magnetic particles such as iron oxide. Polyglutaraldehyde can be converted to a fluorescent polymer by reaction with m-aminophenol or other reagent. Proteins can be readily covalently bound to the polyglutaraldehyde.

Self-assembly of microtubules in extracts of cultured HeLa cells and the identification of HeLa microtubule-associated proteins.

Abstract: Microtubule protein from HeLa cell extracts was purified by multiple cycles of polymerization and depolymerization in the absence of glycerol or other exogenous polymerization-stimulatory agents. Approximately 4-5% of the extract protein was tubulin, of which more than one-half was competent to participate in polymerization-depolymerization cycles. The purified HeLa microtubule protein preparations contained 95% tubulin after the second cycle of polymerization and depolymerization. Additional protein species bound specifically to and copurified quantitatively with microtubules throughout at least four cycles of polymerization and depolymerization. These microtubule-associated proteins (MAPs) were separated from tubulin by DEAE column chromatography. When added to purified brain or HeLa tubulin, these MAPs stimulated the polymerization of microtubules as assayed by electron microscopy and a quantitative sedimentation assay. The most prominent HeLa MAPs had molecular weights of approximately 210,000 and 120,000.

Advances in Indolizine Chemistry

Abstract: Publisher Summary This chapter discusses the synthetic routes, physical properties, and reactions of indolizines. One of the synthetic routes presented is Tschitschibabin reaction involving the quaternization of a 2-substituted pyridine, normally using an α -halo carbonyl compound, followed by intramolecular cyclization of the quaternary salt with a mild base, usually aqueous sodium bicarbonate. Another route is ring closure reactions providing indolizines unsubstituted in the five-membered ring. Several physical properties including electronic spectra, acid–base properties, mass spectra, infrared spectra, nuclear magnetic resonance (NMR) spectra and X-ray diffraction are described. The most widely investigated reaction of the indolizine nucleus is electrophilic substitution. The other reactions of indolizines discussed are cyclizations, reduction, oxidation, and polymerization. Cyclization is concerned with reactions that result in the fusion of one or more additional rings to the indolizine system. Various indolizines containing vinyl groups in the pyridine ring are synthesized by polymerization reactions.

Polysiloxane/acrylic acid/polcyclic esters of methacrylic acid polymer contact lens

Abstract: Monomeric polysiloxanes end-capped with activated unsaturated groups polymerized with acrylic acid and a comonomer comprising a polycyclic ester of acrylic acid or methacrylic acid to form a hydrophilic, water absorbing contact lens is disclosed. These polysiloxane polymer contact lenses are unexpectedly capable upon hydration of retaining from 1 percent to about 99 percent by weight of water, based upon the total weight of the dry, i.e., unhydrated polymer.

Ultraviolet polymerization of acrylate monomers using oxidizable tin compounds

Abstract: Pressure-sensitive adhesive tape having a photopolymerized adhesive coating of a mixture of alkyl acrylate and/or methacrylate and preferably also copolymerizable monoethylenic monomer such as acrylic acid in which is dissolved an oxidizable tin salt such as stannous octoate. The tin salt permits thick layers of the mixture to be photomolymerized in air and allows an unusual tolerance of oxygen when photopolymerizing thin layers to provide pressure-sensitive adhesive coatings.

Biodegradable submicroscopic particles containing a biologically active substance and compositions containing them

Abstract: Biodegradable particles, with a diameter smaller than 500 nanometers, formed by the micellar polymerization of an alkyl-cyano-acrylate where the term "alkyl" means a lower alkyl radical having 1 to 4 carbon atoms and containing a biologically active substance.

Kinetics of silica polymerization and deposition from dilute solutions between 5 and 180°C

Abstract: Between 5 and 90°C the maximum rate of silica polymerization in dilute neutral solutions at constant supersaturation, increases only slowly (formal Energy of Activation = 3 kcal/mole). From 90 to 180°C the maximum rate decreases to below the rate at 5°C. The reactions show induction periods, whose lengths increase with temperature and decrease with supersaturation. The maximum reaction rates after the period of induction obey approximate 4th order kinetics. As the reaction temperature increases from 5 to 180°C, the average molecular weight of the polymers formed increases from approximately 105 to 109. A model is proposed, which is consistent with these kinetics. It assumes a slow bimolecular reaction between monomers; as polymers are formed, active sites on them react rapidly with further monomer. Because fewer, but larger, polymers are formed at higher temperatures, the reaction rate is little affected by temperature. Between 5 and 90°C the total silica concentration remains constant throughout the polymerization reaction. Above 90°C, the total silica concentration progressively decreases with rising temperature, as formation of larger polymers leads to silica deposition. Deposition is accelerated by rocking the reaction vessel. At 180°C, in an Incoloy-lined vessel, the total silica concentration falls to below the quartz solubility; possibly some iron or nickel silicates are formed. At 180°C in a gold reaction vessel, the total silica concentration falls to the quartz solubility; the deposit consists of amorphous silica, cristobalite, and a trace of quartz. It is suggested that at elevated temperatures, especially in iron pipes, aerated geothermal waters could deposit silica scales, even though the silica concentration of the water is near, or even below, the amorphous silica solubility at that temperature.

Supported Organometallic Catalysts for Olefin Polymerization

Abstract: The concept of the basic role of the transition metal-carbon bond in the catalytic polymerization of olefins was formulated in the early stages of the study of Ziegler-Natta catalysts (see Ref. 1). In this connection, attempts to use the individual organometallic transition metal compounds as catalysts for olefin polymerization have been made regularly when such compounds were synthesized[2–10]. Polymerization of ethylene in the presence of organometallic compounds containing [sbnd]CH3[2, 3], [sbnd]C6H5[7], [sbnd]CH2C6H5[5, 6], [sbnd]C3H5[4, 10], [sbnd]CH2-C(CH3)3[10], and [sbnd]CH2-Si(CH3)3[10] as organic ligands have been reported. In some cases such compounds were considered to be “models of the active centers.” However, considering the experimental results from this point of view led to a discrepancy with the following observations:

Calculation of molecular parameters for stepwise polyfunctional polymerization

Abstract: Our recursive method is extended to calculate several new parameters for stepwise polyfunctional polymerization. In the pregel region we calculate weight average molecular weight, Mw, for polydisperse reactants and effective average functionality, fe, of a reacting mixture. These quantities are useful for systems employing reactive oligomers. We also calculate weight average number of branches per molecule, Bw, and the weight average of a longest chain. These should be useful for viscosity relations. In the postgel region we give relations for the extent of reaction in the soluble fraction. This result can be used to calculate sol properties directly from existing pregel relations. We also calculate the weight fraction of pendant chains on the gel, wp, and the average molecular weight of the elastically effective network chains, Mc,w.

Molecular interactions and macroscopic properties of polyacrylonitrile and model substances

Abstract: The relationships between intra- and intermolecular forces in polyacrylonitrile on the one hand, and the macroscopic behavior of the polymer and fibers thereof on the other, are reviewed Characteristic properties such as the very high polymerization rate constant in water, the dissolution of the polymer in concentrated inorganic salt solutions, the high melting point, the strong depression of melting point and glass transition temperature by water, the plasticization by polar additives, etc, are traced back to their molecular origins, in particular to the strong intra- and intermolecular noncovalent bonding caused by the highly polar nitrile group The effects of dipole-dipole interaction, hydrogen bonding and electron-donor-acceptor complex formation are discussed separately

Spheroidal polymerization catalyst, process for preparing, and use for ethylene polymerization

Abstract: A catalyst composition formed from selected organoaluminum compounds and a precursor composition of the formula Mgm Ti1 (OR)n Xp [ED]q [Filler]r wherein ED is a selected electron donor compound R is a C1 to C14, aliphatic or aromatic hydrocarbon radical, or COR' wherein R' is a C1 to C14 aliphatic or aromatic hydrocarbon radical, X is Cl, Br, I, or mixtures thereof, Filler is an inert organic or inorganic compound, and, based on the total weight of such composition m is ≧0.5 to ≦56 n is 0 or 1 p is ≧6 to ≦116 q is ≧2 to ≦5 r has a value such that the percent filler is from about 10 to about 95 weight percent based on the total weight of the precursor composition. A process for preparing such precursor composition by spray drying it from a slurry or solution in said electron donor compound, using atomization. A process for using said catalyst to readily prepare ethylene polymers having a density of about ≧0.91 to ≦0.97, a melt flow ratio of ≧22 to ≦32 and a bulk density of about 18 to 32 lbs/ft3 and controlled particle shape and size in a lower pressure gas phase process at a productivity of ≧50,000 pounds of polymer per pound of Ti.

Dental Resins with Reduced Shrinkage During Hardening

Abstract: Unsaturated spiro-orthocarbonates are monomers that expand on polymerization and will co-polymerize with conventional BIS-GMA based resins. This combination has good physical properties and bonding to enamel with some polymerization expansion evident at 50 C. Dispersion of the carbonate in microcrystalline form in liquid monomer appears to be a method to allow its reaction in the initial polymerization.

Steady-state kinetics of mouse DNA polymerase beta

Abstract: DNA polymerase beta from mouse myeloma has been purified to near homogeneity, and its properties have been examined. The enzyme did not catalyze a detectable level of dNTP turnover, pyrophosphate exchange, pyrophosphorolysis, 3'-exonuclease degradation, or 5'-exonuclease degradation. Steady-state kinetic studies point to an ordered bibi mechanism for the polymerization reaction. Metal activation, which is required for polymerization, did not alter the Km for either the dNTP or the template--primer.

The Polymerization of β-Propiolactone by Calcined Synthetic Hydrotalcite

Abstract: The calcination of synthetic hydrotalcites of different compositions gave aluminium magnesium double oxides with strong basic sites and a high catalytic activity towards the polymerization of β-propiolactone. The strong basic sites were determined and compared with the apparent polymerization rates, suggesting that the strong basic sites are active sites towards the reaction.

A new method for investigating the mechanism of initiation of radical polymerization

Abstract: The mechanism of initiation of polymerization of methyl acrylate by di-t-butyl peroxalate at 60°C, has been investigated using 2,2,6,6-tetramethylpiperidine-1-oxyl as a radical trapping agent and isolation of the resulting products. The following processes were identified: Tail addition of t-butoxy radicals to monomer, hydrogen abstraction from the methyl group of the monomer and fragmentation of the t-butoxy radicals to methyl radicals followed by tail addition of these to the methyl acrylate.

Structural Properties of Calcium Silicate Pastes: II, Effect of Curing Temperature

Abstract: The chemical and physical properties of C3S pastes cured at 4°, 25°, and 65°C were investigated. The 65°C paste had lower H2O surface area and larger capillary pore volume than the 25°C paste. The structure of the gel in the 4°C paste changes markedly with increased hydration. These changes were reflected in an increase in H2O surface area, decrease in C/S ratio, and decrease in the diameter of the mesopores. The degree of silicate polymerization increased with time and temperature of curing. In addition, the 4°C paste had a significant amount of monomer in the gel, which polymerizes with time.

Compatibility of various materials with oral tissues. I: The components in composite restorations

Abstract: The basic ingredients in composite restorative materials include: monomers, polymerization stabilizers, color stabilizers, polymerization initiators, polymerization accelerators, inorganic reinforcing fillers, and coupling agents. Typical members of each category are discussed.