Showing papers on "Polymer published in 1973"

The Physics of Glassy Polymers

Abstract: (The Nature of Polymer Glasses, Their Packing Density and Mechanical Behaviour).- The Nature of Polymeric Glasses.- The common glassy polymers.- The softening of polymer glasses.- Polymer melts and rubbers.- The crystallisation of polymers.- Amorphous isotactic polymers.- The morphology of amorphous polymers.- Packing Volume in the Glassy State.- The expansion volume of amorphous polymers.- Free volume concepts derived from viscosity theories.- Viscosity and free volume in polymers.- Geometrical factors affecting the possible value of the free volume at Tg.- Bernal's random close packed volume.- The Rigidity of Polymer Glasses.- Large Deformations and Fracture.- References.- 1 The Thermodynamics of the Glassy State.- 1.1 Introductory Thermodynamic Considerations.- 1.2 Glassy Solidification and Transition Phenomena.- 1.2.1 General considerations and transitions of different order.- 1.2.2 Glassy solidification with one or several internal parameters.- 1.2.3 Experimental results.- 1.2.4 Position of the equilibrium curve below the glass temperature.- 1.2.5 Zero point volume of a polymer.- 1.3 Results of the Thermodynamic Theory of Linear Relaxation Phenomena.- 1.4 Glassy Mixed Phases.- 1.4.1 The glassy solidification of polymer solutions.- 1.4.2 The glassy solidification of cross-linked systems. The coexistence of glassy phases with phases in internal equilibrium.- 1.5 The Mobility and Structure of Glassy Phases.- References.- 2 X-Ray Diffraction Studies of the Structure of Amorphous Polymers.- 2.1 Introduction.- 2.2 The Interaction of X-rays With Matter.- 2.2.1 Scattering by a free electron.- 2.2.2 Interference among scattered waves.- 2.2.3 Atomic scattering factor.- 2.2.4 Compton scattering.- 2.3 Order and Orientation in Polymers.- 2.3.1 Order.- 2.3.2 Orientation.- 2.4 Diffraction of X-rays by Amorphous Materials.- 2.5 Small Angle X-ray Scattering.- 2.5.1 Introduction.- 2.5.2 Experimental requirements for SAXS.- 2.5.3 Outline of the theory of SAXS.- 2.5.4 Some applications of SAXS.- 2.6 The Radial Distribution Function for Amorphous Polymers.- References.- 3 Relaxation Processes in Amorphous Polymers.- 3.1 Introduction.- 3.2 Molecular Motion in Polymeric Melts and Glasses.- 3.2.1 General description of relaxational processes.- 3.2.2 Relaxational processes at the crystal melt temperature.- 3.2.3 Relaxations in the amorphous state above Tg and below Tm.- 3.2.4 Relaxational processes at the glass transition.- 3.2.5 Relaxations in the glassy state.- 3.3 Secondary Relaxation Regions in Typical Organic Glasses.- 3.3.1 Secondary relaxation regions in Polyvinylchloride.- 3.3.2 Secondary relaxation regions in polystyrene.- 3.3.3 Secondary relaxations in polymethylmethacrylate.- References.- 4 Creep in Glassy Polymers.- 4.1 Introduction.- 4.2 Phenomenological Theory of Creep.- 4.2.1 Linear theory.- 4.2.2 Nonlinear theory-creep equations.- 4.2.3 Nonlinear theory-superposition rules.- 4.3 Apparatus and Experimental Methods.- 4.3.1 General principles.- 4.3.2 Special experimental requirements.- 4.3.3 Special experiments.- 4.4 Creep Phenomena in Glassy Polymers.- 4.4.1 Typical creep behaviour.- 4.4.2 Creep at elevated temperatures.- 4.4.3 Creep in anisotropic samples.- 4.4.4 Recovery behaviour.- 4.4.5 Creep under intermittent stress.- 4.4.6 Creep under abrupt changes of stress.- 4.5 Final Comments.- References and Bibliography.- 5 The Yield Behaviour of Glassy Polymers.- 5.1 Introduction.- 5.2 Exact Definitions.- 5.2.1 Stress.- 5.2.2 Strain.- 5.2.3 The deformation-rate tensor.- 5.2.4 The yield point.- 5.2.5 Nomenclature for deformation processes.- 5.3 Mechanical Tests.- 5.3.1 The tensile test.- 5.3.2 The uniaxial compression test.- 5.3.3 The plane strain compression test.- 5.3.4 Tests in simple shear.- 5.3.5 Machine elasticity.- 5.3.6 Drawing at constant load.- 5.4 Characteristics of the Yield Process.- 5.4.1 The yield point and the yield stress.- 5.4.2 The yield strain.- 5.4.3 Strain softening and orientation hardening.- 5.4.4 The strain-rate dependence of the yield stress.- 5.4.5 The temperature dependence of the yield stress and the yield strain.- 5.4.6 The effect of hydrostatic pressure on the yield stress and yield strain.- 5.4.7 The effect of polymer structure on the yield stress.- 5.4.8 Volume changes at yield.- 5.4.9 The Bauschinger effect.- 5.5 Inhomogeneous Deformation.- 5.5.1 The reasons for inhomogeneous deformation.- 5.5.2 The principle of maximum plastic resistance.- 5.5.3 The geometry of inhomogeneous deformation.- 5.5.4 Strain inhomogeneities in polymers.- 5.6 Structural Observations.- 5.6.1 Birefringence.- 5.6.2 Electron microscopy.- 5.7 Yield Criteria for Polymers.- 5.7.1 The Tresca yield criterion.- 5.7.2 The von Mises yield criterion.- 5.7.3 The Mohr-Coulomb yield criterion.- 5.7.4 The modified Tresca criterion.- 5.7.5 The modified von Mises criterion.- 5.7.6 Choice of a yield criterion for polymers.- 5.8 Molecular Theories of Yielding.- 5.8.1 Reduction of the Tg by the applied stress.- 5.8.2 Stress-induced increase in free volume.- 5.8.3 Break-down of entanglements under stress.- 5.8.4 The Eyring model.- 5.8.5 The Robertson model.- 5.8.6 The theoretical shear strength-Frank's modification of the Frenkel model.- 5.8.7 Disclinations.- References.- 6 The Post-Yield Behaviour of Amorphous Plastics.- 6.1 General.- 6.2 The Phenomena of' strain Softening'.- 6.2.1 Stress hardening.- 6.3 Plastic Instability Phenomena.- 6.3.1 Plastic instability in tension.- 6.3.2 Plastic instability in different stress fields.- 6.4 The Adiabatic Heating of Polymers Subject to Large Deformations.- 6.4.1 Reversible thermoelastic effect.- 6.4.2 Thermal effects in large plastic deformation.- 6.4.3 The experimental measurement of temperature changes during deformation.- 6.5 Orientation Hardening.- 6.5.1 Orientation hardening as a physical process.- 6.5.2 Factors affecting orientation hardening.- 6.5.3 A model for large polymer deformations.- 6.6 Large Deformation and Fracture.- 6.6.1 Crack propagation as a deformation process.- 6.6.2 Crazing as a plastic instability phenomenon.- 6.6.3 The growth of voids in a polymer glass.- 6.6.4 The nucleation of voids.- References.- 7 Cracking and Crazing in Polymeric Glasses.- 7.1 Introduction.- 7.2 Fracture Mechanics.- 7.2.1 Linear fracture mechanics.- 7.2.2 Measurements of KIC for glassy polymers.- 7.2.3 Crack-opening displacement.- 7.2.4 Energy balance approach.- 7.2.5 Measurements of surface work.- 7.2.6 Fracture stress.- 7.3 Fatigue Fracture.- 7.3.1 Fatigue failure by heat build-up.- 7.3.2 Fatigue crack propagation.- 7.4 Crazing.- 7.4.1 Crazing of glassy plastics in air.- 7.4.2 Environmental crazing.- 7.4.3 Theoretical aspects.- 7.5 Molecular Fracture.- 7.5.1 Kinetic theories of fracture.- 7.5.2 Experimental evidence for bond fracture.- 7.6 Conclusion.- References.- 8 Rubber ReinForced Thermoplastics.- 8.1 Introduction.- 8.2 Rubber Reinforced Glassy Polymers of Commercial Importance.- 8.2.1 Based on polystyrene.- 8.2.2 Based on styrene acrylonitrile copolymer (SAN).- 8.2.3 Based on Polyvinylchloride.- 8.3 Methods of Manufacture.- 8.3.1 Physical blending.- 8.3.2 Interpolymerisation process.- 8.3.3 Latex interpolymerisation.- 8.4 Incompatibility in Polymer Mixtures.- 8.5 Identification of Two Phase Rubber Reinforced Systems.- 8.6 Dispersed Phase Morphology.- 8.6.1 Toughened polystyrene.- 8.6.2 ABS copolymers.- 8.6.3 Polyvinylchloride.- 8.7 Optical Properties.- 8.7.1 Matching of the refractive index.- 8.7.2 Reduction in particle size.- 8.8 Mechanical Properties.- 8.8.1 Tensile properties.- 8.8.2 Dynamic mechanical properties.- 8.8.3 Impact properties.- 8.8.4 Structure-property relationships.- References.- 9 The Diffusion and Sorption of Gases and Vapours in Glassy Polymers.- 9.1 Introduction.- 9.2 Ideal and Non-ideal Sorption and Diffusion of Fixed Gases.- 9.2.1 Ideal diffusion and sorption of fixed gases.- 9.2.2 Non-ideal sorption and diffusion of fixed gases.- 9.3 The Effect of the Glass Transition on Gas and Vapour Diffusion in Polymers.- 9.4 Relaxation Controlled Transport and Related Crazing of Polymeric Glasses by Vapours.- 9.4.1 Introduction ..- 9.4.2 Relaxation controlled transport and solvent crazing.- 9.5 Some Effects of Crystallinity and Orientation on the Transport of Gases and Vapours in Glassy Polymers.- 9.5.1 Effect of crystallinity.- 9.5.2 The effect of orientation.- References.- 10 The Morphology of Regular Block Copolymers.- 10.1 Introduction.- 10.1.1 General.- 10.1.2 Microphase separation.- 10.2 Techniques Used for the Study of the Morphology of Block Copolymers.- 10.2.1 Low angle X-ray scattering.- 10.2.2 Electron microscopy.- 10.2.3 Other techniques.- 10.3 Variables Controlling the Morphology.- 10.3.1 Chemical variables.- 10.3.2 Physical variables.- 10.4 Studies with Specific Systems.- 10.4.1 Systems with liquid.- 10.4.2 The pure copolymers.- 10.5 Theories of the Morphology of Block Copolymers.- 10.5.1 Objectives.- 10.5.2 Principles of calculation.- 10.6 Implications of Theories and Comparison With Experiment.- 10.6.1 Influence of block molecular weight ratio.- 10.6.2 Effect of block molecular weights.- 10.6.3 Molecular orientation in the phases.- 10.6.4 Interfacial region.- 10.6.5 Effect of temperature on domain size.- 10.7 Mechanical Properties and Deformations.- 10.8 Crystallinity.- References.- Appendix I Glass Transition Temperatures and Expansion Coefficients for the Glass and Rubber States of some Typical Polymeric Glasses.- Appendix II Conversion Factors for SI Units.

On the transport of compact particles through solutions of chain-polymers

Abstract: The problem is discussed of providing a theoretical explanation for the empirical equation of Laurent, Bjork, Pietruszkiewicz & Persson (1963) which relates the relative retardation of the sedimentation of compact particles in solutions of hyaluronic acid to the radius of the particle and the concentration of hyaluronic acid. From published and original data, the same relation is shown to apply also to sedimentation and diffusion in solutions of a number of linear and branched chain-polymers. Of several approaches to the problem, only one, based on the stochastic model of diffusional migration, yields the empirical relationship, and predicts a value of the numerical constant close to that observed. This treatment is shown to apply to other forms of migration, including the case where the chain-polymer is itself migrating. The theory is tested by calculation, from migration data, of the effective radii of the polymer chains. The results are consistent and comparable with values deduced from equilibrium experiments.

Glass transition temperature as a guide to selection of polymers suitable for PTC materials

Abstract: It has been shown that the only way to predict the size of the PTC effect displayed by a crystalline polymer when filled with conductive particles is through the knowledge of the glass transition point of the polymer. The size of the PTC anomaly is found to decrease sharply with rise in glass transition temperature and for a polymer to be a useful PTC material its glass transition must be below 0°C. It has not been possible to explain this relationship by any of the current theories of the PTC mechanism in filled polymers.

Water and hydrogels.

Abstract: The apparent biocompatibility of many synthetic and natural aqueous gel materials has encouraged their study and testing for a wide variety of biomedical device applications. Many of the physical and in particular the interfacial properties of such gels are highly dependent on the organization of water within and on the surface of the hydrogel. Water is an important component of such gels, varying from about 30 to nearly 100 wt-%, yet the role of water in the gels has been virtually ignored. This paper briefly reviews the nature of water structure in pure bulk water, in solutions, and at interfaces. Polywater or anomalous water is also briefly reviewed. Evidence is presented that the water in many hydrogel systems can exist in at least three different, structurally distinct forms. A hypothesis is presented which can be used to evaluate and study the nature of water in bulk hydrogels. Consideration is also given to the role of organized water at the hydrogel surface on the interfacial properties of such systems.

The preparation and characterisation of polymer latices formed in the absence of surface active agents

Abstract: Methods have been devised for the formation of monodisperse polystyrene latices in the absence of added surface active agents. The particles are stabilised, as a colloidal dispersion, by surface groupings which are an integral part of the particle and are not removed by dialysis. By suitable variation of the ionic strength of the aqueous phase, the initiator concentration and the polymerisation temperature, the final particle size obtained in single-stage reactions was varied between c. 0.15 and 1.0 μm. The coefficient of variation on particle diameters was usually less than 5%. The ionic strength of the aqueous phase was found to play an important part in determining particle size; this was explained in terms of a limited coagulation process occurring at the stage involving the nucleation of polymer particles. Conductometric titration experiments revealed the presence of sulphate, carboxyl and hydroxyl groups on the particle surfaces. Molecular weight determination of the polystyrene formed showed that this was lower than that formed in conventional emulsion polymerisation.

Stabilization of synthetic polymers

Abstract: A new piperidine derivative and a synthetic polymer composition stabilized against photo- and thermal deterioration thereof wherein there is incorporated, in a sufficient amount to prevent such deterioration, said piperidine derivative.

The elasticity and related properties of rubbers

Abstract: The relation of rubbers to other classes of polymers and the molecular basis of rubber elasticity are briefly examined. The methods used in the quantitative development of the statistical-thermodynamic theory of a molecular network are outlined, and the main conclusions, in the form of stress-strain relations, etc, are presented and compared with experimental data. Also examines the photoelastic properties of rubbers from both theoretical and experimental standpoints and discusses in detail the evidence derived from photoelastic studies on the statistical segment length in the molecular chain and its relation to intramolecular energy barriers. The thermodynamic analysis of stress-temperature data for rubber and other polymers, with particular reference to the internal energy and entropy changes during extension under constant pressure or constant volume conditions is studied. The phenomena of swelling in liquids is considered.

Process for producing microporous films and products

Abstract: Microporous films are produced by a process of quenching a polymer solution cast in a quench bath containing a non-solvent system for the polymer to form micropores in the resulting polymer film

Polymerization of proteins with glutaraldehyde. Soluble molecular-weight markers.

Abstract: Glutaraldehyde is well known for its ability to react with proteins and to produce insoluble cross-linked aggregates. In contrast with this situation, conditions are described here which yield covalently linked soluble protein oligomers. The procedure is applicable to a wide range of proteins, and by slight variation in the reaction conditions, soluble polymers in the molecular weight range 3x10(4)-2x10(7) were produced. The products are valuable as molecular-weight markers, e.g. in sodium dodecyl sulphate-polyacrylamide-gel electrophoresis. The inherent similarities of these oligomers make them superior to commercial molecular-weight protein markers, which may have marked differences in composition and charge.

Poly(vinyl alcohol) hydrogels. Formation by electron beam irradiation of aqueous solutions and subsequent crystallization

Abstract: Aqueous solutions of poly(vinyl alcohol) were submitted to varying doses of electron beam irradiation. By modification of the classical Flory-Huggins equations appropriate to the initial state of solution of the polymer, the molecular weight between crosslinks, Mc, was calculated as a function of radiation dose, initial polymer concentration, and temperature. Following crosslinking in the solution state, crystallization was induced by dehydrating the network at temperatures above 90°C. Following dehydration, the polymer network was reequilibrated with water and its tensile properties compared with identically prepared hydrogels not subjected to crystallization by dehydration. Greatly enhanced values of ultimate tensile strength and resistance to tear result from the treatment producing crystallization, compared with those of the crosslinked but not previously dehydrated gels.

Review: The thermal expansion of composites based on polymers

Abstract: In the past 25 years, several approaches have been made to the theoretical study of thermal expansion of composites. These approaches range from the empirical, to sophisticated analyses based on applied mechanics. The alternatives are discussed in the following paper, after which the available experimental data are examined in the light of current theory. The approach of Kerner and similar workers shows reasonable success for those systems where the dispersed particles can be treated as spheres, but this case is of limited technological interest. On the other hand, the equation due to Turner most closely represents those systems in which the fillers are fibrous or plate-like in nature. Apart from particle shape, it appears that any general theory must take into account a number of physicochemical variables which have hitherto been omitted.

Polyaspartimides: Condensation of aromatic diamines and bismaleimide compounds

Abstract: A detailed investigation of the condensation of aromatic amines and maleimide compounds was conducted by the use of model compounds. Weak Bronsted acids were found to have a marked catalytic effect on the reaction. By using glacial acetic acid as the reaction medium, a number of model aspartimide compounds were prepared. Aromatic diamines and bismaleimide compounds were condensed to high polymers in cresol containing a small amount of a protonic acid catalyst. Polymers having a variety of novel backbone structures were prepared and their physical properties studied.

An apparent double glass transition in semicrystalline polymers

Abstract: Thermal expansion and/or specific heat and/or dynamic mechanical loss data reveal the presence of two glass-like transitions in bulk crystallized polyethylene, polypropylene, polybutene-1, polypentene-1, cis-and trans-polyisoprene (natural), poly-4-methylpentene-1, isotactic polystyrene, poly(vinyl alcohol), nylon 6, the oxide polymers ‒(CH2)nO‒, with n = 1 to 4, polyethylene terephthalate, polyvinylidene fluoride, polyacrylonitrile, and polyvinylidene chloride. We designate the lower of these as Tg(L), which appears identical with the conventional Tg at zero crystallinity. The higher one, designated as Tg(U), is strongly increased with increasing levels of cystallinity. The differnece ΔTg = Tg(U) − Tg(L) tends to approach zero as the fractional crystallinity, X, approaches zero. For a X of 0.5 [Ptilde] 0.1, ΔTg is about 50°C and Tg(U)/Tg(L) is about 1.2 with temperatures in °K. The increases in coefficient of thermal expansion, (Δα)L and (Δα)U, at these two transitions seem to depend on crystall...

Preparation of microcapsules

Abstract: Microcapsules are made by (a.) dispersing or dissolving a core substance in a film-forming polymer solution, (b.) emulsifying in fine droplets the resulting dispersion or solution in a vehicle which is poorly miscible with the solvent of the polymer solution and which doesn't dissolve said polymer to prepare an emulsion, and (c.) adding to the emulsion a non-solvent for the polymer wherein the non-solvent is miscible with the solvent, poorly miscible with the vehicle, and does not dissolve the polymer, whereby the solvent is removed by being absorbed by non-solvent emulsion droplets to precipitate the polymer film around the core substance.

Polymers and ecological problems

Abstract: Polymers with Controlled Lifetimes.- Delayed Action Photo-Activator for the Degradation of Packaging Polymers.- The Photoactivated Degradation of Polyolefins.- The Biodegradability of Synthetic Polymers.- Effluents from the Municipal Incineration of Plastics.- The Auto-Ignition of Multicomponent Fiber Systems.- Thermal Analysis of Irradiated Poly(Vinyl Chloride).- Recycling Poly(tetrafluoroethylene).- An Industry View of Plastics and the Environment.- The Plastics Issue.- The Federal Approach to Recycling of Polymers.- Who's On The Clean-Up Crew?.- Panel Discussion.

Arylene sulfide polymers

Abstract: Arylene sulfide polymers having a high extrusion rate, e.g. at least about 100g/10 min. are prepared by a process comprising: a) dehy­drating an aqueous admixture of a suitable sulfur source and a cyclic organic amide; b) admixing a dihalo-substituted aromatic compound with the dehydrated mixture to form a polymerization mixture wherein the molar ratio of sulfur source to the cyclic organic amide is about 0.39:1 to about 0.6:1, c) subjecting the polymerization mixture to reaction conditions sufficient to produce the arylene sulfide polymer; and d) recovering the arylene sulfide polymer.

Formation of an amorphous powder during the polymerization of ethylene in a radio-frequency discharge

Abstract: An investigation has been carried out to determine the influence of operating conditions on the character of the final product resulting from the polymerization of ethylene in a radio-frequency discharge. It has been found that low pressures and high ratios of discharge power to gas flow rate lead to the deposition of a powder as well as a film. From visual observations of powder deposition, it has been possible to divide the plane formed by the axis of pressure and flow rate into a region in which powder is deposited together with a film and a region in which only a film is deposited. Numerous physical measurements have been carried out in order to characterize the powder. From these measurements, it has been concluded that the powder is a relatively dense, amorphous, and highly crosslinked polymer composed of short-chain segments containing no more than two adjacent methylene groups. Many forms of unsaturation have been observed which, together with the high crosslink density, explain the measured hydrogen-to-carbon ratio of 2.7 to 2. Evidence of oxidation has been observed through the appearance of hydroxyl and carbonyl bands in the infrared spectrum of the polymer. A mechanism for the formation of the powder has been proposed which suggests that the polymerization of the powder takes place totally in the gas phase.

Chromocene‐based catalysts for ethylene polymerization: Kinetic parameters

Abstract: The chromocene catalyst for ethylene polymerization shows a high response to hydrogen which leads directly to highly saturated polyethylenes containing methyl groups as the major terminal functionality in the polymers. At a polymerization temperature of 90°C the ratio of termination rate constants for hydrogen (kH) and ethylene (kM) is kH/kM = 3.60 × 103. The ratio of kH to the chain propagation constant (kp) is kH/kp = 4.65 × 10−1 A simple relation that can be derived from polymerization kinetics and the Quackenbos equation exists between melt index and hydrogen–ethylene ratio. A deuterium isotope effect (kH/kD) = 1.2 was calculated for the termination reaction. The overall polymerization process has an apparent activation energy of 10.1 kcal/mole. Oxygen addition studies show catalyst activity is proportional to initial divalent chromium content.

Preparation of asymmetric polymer membranes

Abstract: A method is disclosed for the preparation (by the utilization of a proper solvent system) of dry asymmetric membranes comprising a porous layer of interconnected crystals of polymer material. Membranes of many polymer materials may be optionally prepared either with or without a dense surface layer as one face thereof. In either case the porous layer is structured with graded porosity. A three-component casting solution is prepared containing the polymer, a first good volatile solvent for the polymer and (relative to the first solvent) a poor less-volatile solvent for the polymer, which is miscible with the good solvent. A membrane is cast at room temperature, allowed to desolvate at room temperature for a short time and is then immersed in a precipitating agent, that is miscible with both the aforementioned solvents but is a non-solvent for the polymer. The membrane is then permitted to dry.