Showing papers on "Polymer published in 1971"

Textbook of polymer science

Abstract: The Science of Large Molecules POLYMERIZATION Step-Reaction (Condensation) Polymerization Radical Chain (Addition) Polymerization Ionic and Coordination Chain (Addition) Polymerization Copolymerization Polymerization Conditions and Polymer Reactions CHARACTERIZATION Polymer Solutions Measurement of Molecular Weight and Size Analysis and Testing of Polymers STRUCTURE AND PROPERTIES Morphology and Order in Crystalline Polymers Rheology and the Mechanical Properties of Polymers Polymer Structure and Physical Properties PROPERTIES OF COMMERICAL POLYMERS Hydrocarbon Plastics and Elastomers Other Carbon-Chain Polymers Heterochain Thermoplastics Thermosetting Resins POLYMER PROCESSING Plastics Technology Fiber Technology Elastomer Technology Appendixes Author and Subject Indexes.

Biodegradable poly(lactic acid) polymers

Abstract: The synthesis of poly(lactic acids) from the cyclic lactides and properties of the polymers prepared have been described. Degradation rates in vitro under homogeous and heterogeneous conditions have been measured. The kinetics of deesterification under homogeneous conditions is second order and an activation energy of 11 Kcal/mol has been calculated. This is comparable to the value found for the hydrolysis of alkyl acetates. A biological in vitro method for determining the degradation of poly(lactic acids) has been described. The method indicates, in accordance with expectations, that poly(dl-lactic acid) degrades at a faster rate than L(+) lactic acid. Initial results of medical evaluation of the polymers in suture, rod, and film form are presented.

A Transition to a Compact Form of DNA in Polymer Solutions

Abstract: In the presence of over-threshold concentrations of simple neutral polymers and salts, DNA undergoes a cooperative change in its solution structure Sedimentation studies at low DNA concentrations show that phage DNA molecules collapse into particles approaching the compactness of the contents of phage heads The interaction between DNA and polymers is thought to be nonspecifically replusive

Elements of polymer degradation

Abstract: A survey of the degradation of polymer structures through thermal, oxidative, radiative, mechanical, chemical and biological means is presented. Examples, data and equations are largely based on synthetic polymer analyses, but the essential theories of polymer degradation are presented. -- AATA

Pressure‐Volume‐Temperature Properties and Transitions of Amorphous Polymers; Polystyrene and Poly (orthomethylstyrene)

Abstract: An apparatus based on Bridgman's bellows method, originally devised for fluids, has been constructed for use with solid samples. Mercury is employed as the confining liquid. The operating range is 0≤t≤200 °C and 1≤P≤2000 bar. Calibration with benzene and mercury shows an accuracy of ±2×10−4 cm3/g in the measurement of the specific volume change. A detailed investigation of two systems, polystyrene and poly(orthomethylstyrene) in the glassy and liquid states is undertaken. The P‐V‐T results in both states can be well represented by the Tait equation, with the single parameter B as an exponentially decreasing function of T. Similar to the earlier result for polystyrene, a β‐relaxation region is observed in terms of the isothermal compressibility of the methylated polymer with Tβ/Tg≃0.70 for both. The pressure coefficients for the two transition temperatures are discussed. For the glass transition, the Ehrenfest‐type equation appears to be obeyed by the low‐pressure glasses (formed by cooling the liquid at a...

Laminates of ethylene vinyl acetate polymers and polymers of vinylidene chloride

Abstract: A multiply laminate useful as a packaging film having a first layer of a cross linked ethylene vinyl acetate polymer, a directly joined middle layer of a polymer of vinylidene chloride and a third layer directly joined to the middle layer of an ethylene/vinyl acetate polymer. Especially preferred for the middle layer are blends of emulsion polymerized and suspension polymerized vinylidene chloride and an epoxy resin.

Lubricants containing oil-soluble graft polymers derived from degraded ethylene-propylene interpolymers

Abstract: GRAFT POLYMERS ARE PREPARED FROM VARIOUS POLYMERIZABLE UNSATURATED MONOMERS AND AN OXIDIZED, DEGRADED INTERPOLYMER OF ETHYLENE AND PROPYLENE. THESE POLYMERS ARE USEFUL AS VISCOSITY INDEX IMPROVES, DISPERSANTS AND POUR POINT DEPRESSANTS FOR FUELS AND LUBRICANTS.

Reinforcement of elastomers by carbon black

Abstract: The reinforcement of elastomers by carbon black is governed by the morphology of the black and its physical and chemical interactions with the polymer. The latter are strongly affected by ...

Dynamic mechanical properties of polyurethane block polymers

Abstract: The dynamic mechanical properties of polyester and polyether urethane block polymers have been investigated at four frequencies (3.5, 11, 35 and 110 Hz) in the temperature range of — 150 to 200°C. The existence of a two phase structure was demonstrated in these systems by the observation of two major transition regions corresponding to (1) the glass transition temperature (Tg) of the ester or ether soft segments, and to (2) the softening temperature of the aromatic-urethane hard segments. Several secondary relaxations were observed in addition to the two major relaxations. It was possible to assign molecular mechanisms to each of these relaxations. All relaxation phenomena were greatly influenced by the molecular weight of the prepolymer, weight percent of hard segments, and thermal history. An increase in the molecular weight of the prepolymer above 1,000 at constant hard segment content resulted in a semi-crystalline material, which possessed a lower Tg for the macroglycol segments. Annealing to enhance crystallinity increased the Tg of the soft segments, consistent with the usual observation in semicrystalline homopolymers. These findings suggest that the relaxation mechanisms of polyurethane block polymers are not only influenced by the degree of crystallinity, but also by the nature of the domain structure.

Particle Formation in Polymer Colloids, III: Prediction of the Number of Particles by a Homogeneous Nucleation Theory

Abstract: The formation of particles in polymer colloids ordinarily is accomplished by the free radical polymerization of an organic monomer in a liquid which is a non-solvent (diluent) for the polymer. A surface active material, such as a soap or other amphipathic molecule, is usually added to stabilize the colloidal particles as they are formed. The particle size distribution varies from very narrow to extremely broad depending primarily upon the solubility of the monomer in the diluent, the stabilizer concentration and the ionic strength.

Ethylene/carbon monoxide polymer compositions

Abstract: COPOLYMERS OF CERTAIN AMOUNTS OF ETHYLENE, CARBON MONOXIDE AND ONE OR MORE TERMONOMERS COPOLYMERIZABLE THEREWITH TO PRODUCE SOLID PRODUCTS. THE COPOLYMERS ARE USEFUL AS MOLDING RESINS AND AS BLENDING RESINS. BLENDS OF THESE COPOLYMERS WITH SOLID ORGANIC POLYMERS SUCH AS POLYVINYL CHLORIDE WAX, ETC., ARE COMPATIBLE AND ARE USEFUL AS MOLDING RESINS. THESE BLENDS MAY BE USED, FOR EXAMPLE, TO PRODUCE FLEXIBLE FILMS AND RIGID OR SEMIRIGID ARTICLES.

Bistable Electrical Switching in Polymer Thin Films

Abstract: Reproducible bistable switching has been observed in Au‐Polymer‐Au junctions. The polymer is formed by a glow‐discharge polymerization technique. The resistance ratio is more than 107 and structures can be switched more than 2000 times. When the polymer thickness is lower than 1500 A, the threshold voltage increases linearly with the polymer thickness. A scanning electron microscope picture of a junction that has been switched shows circular dots, ranging between 5‐ and 10‐ μm diameter, on the surface. These dots are probably due to current‐carrying filaments.

Molecular Motion in the Glassy State: The Effect of Temperature and Pressure on the Dielectric Relaxation of Polyvinyl Chloride

Abstract: The dielectric β relaxation of polyvinyl chloride has been studied in the ranges of temperature, pressure and frequency, 296 to 353 K, 1 × 105 to 3 × 108 N m–2 and 1 to 105 Hz. Detailed results are discussed in terms of current concepts of the α, β and (αβ) relaxations which occur in amorphous polymers and in small molecule glass forming systems.

Synthesis and characterization of poly‐β‐hydroxybutyrate. I. Synthesis of crystalline DL‐poly‐β‐hydroxybutyrate from DL‐β‐butyrolactone

Abstract: The polymerization of β-butyrolactone was investigated as a possible monomer for a proposed synthesis of the naturally occurring polyester, D-poly-β-hydroxybutyrate (D-PHB). The racemic DL-monomer was used in this initial study to determine the best conditions and catalyst system for use in a subsequent study of the polymerization of optically active β-butyrolactone. In so doing it was found that certain organometallic catalysts (Et2Zn and Et3Al) plus a cocatalyst of water produced highly crystalline samples of polyester from the racemic monomer. This paper describes the synthesis and characterization of the racemic polymer obtained using these catalyst systems, and compares the results obtained with certain other catalysts that were also investigated for this purpose. Examination of the DL-PHB by infrared, NMR, x-ray, and electron microscopy shows that it is possible to synthesize a crystalline racemic polymer that is virtually identical (excepting optical activity) to the naturally occurring polymer, D-PHB.

Polymerization in expanding catalyst particles

Abstract: Four models are presented to describe polymerization in expanding catalyst particles. The globules are presumed to be expanding with accumulating polymer, and catalytic reaction sites are dispersed throughout the polymer matrix which is forming about them. Monomer must diffuse through the polymer to polymerize at the catalyst sites. The Thiele modulus (α), , is a ratio of characteristic diffusion time to reaction time which is a measure of the importance of diffusion relative to reaction. Polymerization rates are predicted by the models which are generally dependent on the controlling mechanism. Broad molecular weight distributions are predicted for cases of diffusion control (large α) for those models in which catalyst sites are not equally accessible to monomer. Polymerization rates decline toward an asymptotic final value as the particles expand in diffusion-controlled cases. Most of the decline which would be readily observable in a laboratory experiment would have occurred by the time the particle radii had increased to about three times their original value.

Relation of particle size of colloidal silica to the amount of a cationic polymer required for flocculation and surface coverage

Abstract: This is a study of the flocculation of colloidal silicas of known uniform particle sizes by a quaternary ammonium substituted methacrylate polymer, of which the cations are adsorbed on the anionic sites of the silica surface by ion exchange. The unusual observation is reported that as increasing amounts of polymer are added to a silica sol of a given particle size, all of the polymer is precipitated, carrying down with it a constant ratio of silica to polymer. When sufficient polymer has been added to precipitate all of the silica, further amounts of polymer are then adsorbed on the precipitate until the silica surface is saturated, after which free polymer remains in solution. For particles smaller than 40 nm, the amount of polymer required to precipitate 1 unit weight of silica varies inversely with particle diameter; for larger silica particles, it varies inversely with the square of the diameter. These different relationships are consistent with calculations based on two models: (1) With particles smaller than 40 nm diameter, only a segment of a polymer chain, which is 150 nm long, is required to bridge one pair of particles; thus a single chain can extend through the bridging points of several pairs of particles. (2) With larger particles, one or more polymer chains are required to form the bridge at one contact point between a single pair of particles. A new spot test technique for detecting either excess silica or polymer in the supernatant liquid is employed, based on adsorption of a monolayer on a black glass test plate, and making its presence or absence visible by the interference color developed by a subsequently applied monolayer of 150 nm silica particles.

Polylactide fabric graphs for surgical implantation

Abstract: Absorbable surgical sutures that are dimensionally stable within the body may be prepared by the extrusion of polylactide polymer, including copolymers of L(-) lactide with up to 35 mole percent of glycolide. Said polymers are characterized by an inherent viscosity of at least 1.0, and the extruded filaments are oriented by drawing at a temperature of about 50* to about 140* at a draw ratio of up to 11 X , and annealed. Sutures so prepared have a tensile strength of from 25,000 p.s.i. to 100,000 p.s.i.

Rheological properties of molten polymers. II. Two‐phase systems

Abstract: A study is carried out for characterizing two-phase systems of molten polymers by their viscous and elastic properties. The two-phase systems chosen for study are blends of polystyrene and polypropylene, and blends of polystyrene and high-density polyethylene. For the study, measurements of wall normal stresses are made by use of a capillary melt rheometer described in part I of this series. The concept of the “exit pressure” is used to determine the elastic properties of the two-phase polymer systems. The present study shows anomalous viscous and elastic properties of two-phase systems, which are difficult to predict from knowing the viscous and elastic properties of their individual components. A detailed discussion is given on the state of dispersion of two incompatible polymer systems in the molten state, by presenting pictures of the microstructure of the extrudate samples. The state of dispersion appears to vary depending on the blending ratio, extrusion temperature, melt viscosities of individual components, and blending method.

Thermoplastic Polyurethane Hydrolysis Stability

Abstract: This paper describes the monomer types commonly used in making thermoplastic polyurethane elastomers. It gives chemical structure of the polymers and their general properties. Also de scribed are s...

Dilute Solution Theory of Polymer Crystal Growth: A Kinetic Theory of Chain Folding

Abstract: A kinetic theory of polymer crystallization from dilute solution is formulated for linear chain molecules of finite molecular weight (monodisperse). Two models of crystal growth are considered; both are essentially “regular” chain folding type models. Formulas for the crystal growth rates are derived as a function of the fundamental rate constants associated with the various states of molecular crystallization. These rate constants are evaluated as a function of polymer concentration, molecular weight, crystallization temperature, and crystal thickness. Consideration of finite molecular weight molecules requires an understanding of how these molecules are incorporated into the crystal and what happens to chain ends. Attention is focused on these problems and a description of how “cilia” are formed in polymer crystals is given. A remarkable aspect of cilia formation is that the uncrystallized portion of a chain molecule which dangles in the solution can participate in nucleating a new growth strip (fold pl...

Structure of crystalline polymers with unbranched long side chains

Abstract: The structure and thermodynamic properties of atactic and isotactic acrylic and methacrylic polymers containing 16–18 carbon atoms in the n-aliphatic side chains, and of copolymers of hexadecyl acrylate with isopropyl acrylate were studied by means of x-ray and differential thermal analysis. The crystallization of branched acrylic and methacrylic polymers and of acrylic copolymers proceeds in the form of a hexagonal crystal, regardless of the configuration of the backbone chain. Methods of ordering branched macromolecules are proposed, and the melting points, heats and entropies of fusion determined. The role of flexibility of the backbone chains in ordering and the crystallization processes was determined. In the case of poly(n-alkyl acrylates) the backbone chain is involved in the crystalline lattice; this is not the case in methacrylates and copolymers of hexadecyl acrylate with isopropyl acrylate. Some similarity was assumed between the structure of biopolymers and synthetic branched polymers.