Showing papers on "Polystyrene published in 1968"

The influence of non-ionic surface active agents on the stability of polystyrene latex dispersions

Abstract: The influence ofn-dodecyl hexaoxyethylene glycol monoether on the stability of dispersions of polystyrene latices has been investigated by measuring the rates of flocculation, by lanthanum nitrate and hydrochloric acid, in the presence of various concentrations of the surface active agent. The adsorption isotherm for the non-ionic surface active agent on the latex surface showed that saturation adsorption was reached at about the critical micelle concentration to give a monolayer of vertically orientated molecules. A determination of the thickness of the adsorbed layer by an ultracentrifuge method confirmed the vertical orientation. In order to explain the results a theory has been developed based on the interaction between the adsorbed layers which includes a term to account for the interaction between the surface active molecule and the solvent.

Photolysis of aromatic azides. Part 4.—Lifetimes of aromatic nitrenes and absolute rates of some of their reactions

Abstract: The transients in the flash photolysis of several aromatic azides are identified as triplet nitrenes by their spectra. Their half-lives are determined over a range of concentrations in hexane, ethanol and in several polymeric matrices (polystyrene, sucrose benzoate, polymethylmethacrylate) and are interpreted in terms of three processes : nitrene recombination, hydrogen abstraction from the solvent and reaction of the nitrene with an azido group. Recombination is diffusion-controlled (rate constant ∼109 1. mole–1 sec–1); the same applies to the reaction with an azido group. In contrast, hydrogen abstraction by an aromatic nitrene is a comparatively slow process, corresponding to a life-time (in ethanol) of about 2 × 10–4 sec. This value is corroborated by experiments in soft polystyrene matrices (half-life 10–3sec) and by the rate of intramolecular hydrogen abstraction in the cyclization of 2-nitrenobiphenyl to carbazole (half-life 8 × 10–4 sec). In hard polymeric matrices, hydrogen abstraction is considerably slower (half-lives from 0.1 to 2 sec). Here the rate-determining step is configurational diffusion of CH bonds towards the electron-deficient nitrogen.

Crystallization kinetics of polymer-diluent mixtures. Influence of benzophenone on the spherulitic growth rate of isotactic polystyrene

Abstract: As an extension of earlier work on the crystallization kinetics of isotactic polystyrene, the spherulite growth rate in mixtures of isotactic polystyrene and benzophenone has been measured over a concentration range extending from pure polymer to a mixture containing about 30% benzophenone. The glass transition temperature has been measured over the entire range from pure polymer to pure benzophenone. For the mixtures the dependence of the growth rate on temperature is similar to that of the undiluted polymer. The addition of benzophenone causes a shift of the crystallization range to lower temperatures. For mixtures containing up to about 20% benzophenone, the maximum in the growth rate increases with increasing content of benzophenone. On addition of more benzophenone, the maximum rate is depressed. Taking into account the glass transition temperature of the mixtures, the influence of benzophenone on the melting point of isotactic polystyrene, and the volume fraction of polymer, we can describe the influence of benzophenone on the growth rate in a semiquantitative way.

Crystallization kinetics of isotactic polystyrene. I. Spherulitic growth rate

Abstract: The spherulitic growth rate of isotactic polystyrene has been measured in a wide range of temperature by means of a polarizing microscope provided with a hot stage. It was possible to fit the experimental data to theory by choosing a value of 75 for the constant C2 of the WLF equation. The growth rate parameters were compared with those of polyethylene and polychlorotrifluoroethylene. The slowness of crystallization of isotactic polystyrene is mainly a consequence of the lower mobility of the molecules caused by the bulky phenyl groups.

Laser‐Excited Raman Scattering in Polystyrene

Abstract: Atactic polystyrene was examined by argon ion laser‐excited Raman scattering. Depolarization measurements of oriented and unoriented polystyrene were made. An analysis is made of the depolarization measurements in terms of the orientation of the sample. Comparisons are made with dichroic measurements made by infrared. Utilizing Raman and infrared polarization data on oriented polystyrene, some changes in band assignments have been made.

Morphology of nascent polyolefins prepared by Ziegler‐Natta catalysis

Abstract: The morphology of nascent (i.e., as-polymerized) Ziegler-Natta polymers was studied by optical and electron microscopy and x-ray and electron diffraction. Observations were made on six polyolefins: polyethylene, polybutene, polypropylene, polystyrene, poly-4-methylpentene-1, and polyisoprene. These polymers were synthesized by using conventional techniques by polymerizing the undiluted monomer or monomer–diluent mixtures with a preformed heterogeneous catalyst obtained by reacting a titanium halide and aluminium alkyl. After the reactions were terminated the polymers were subjected to suitable purification treatments and stored in the wet state. Observations in the optical microscope revealed that, in most cases, the polymers is formed as discrete hollow particles with a fibrous texture, but in a few instances, depending upon experimental conditions, it could also form as fibrous sheets or webs. More detailed observations in the electron microscope showed that the polymer is composed of a profusion of fibrils 200–1000 A. in width and of indefinite length. The fibrils themselves have a fine structure as indicated by the presences of lamellae running prependicular to their length. Various interpretations of this appaerent structure are discussed. The x-ray and electron diffraction studies show that the molecular chain axis is oriented prependicular, or nearly so, to the plane of fibril lamellae and suggest that the molecules are folded within the lamellae in a manner analogous to conventional polymer single crystals. As fibril formation is observed under most conditions of polymerization it is considered to be basic to the mechanism of Ziegler-Natta catalysis. It is proposed that the fibrils are formed by the crystallization of polymer chains growing from the active sites on the catalyst surface. The process is likened to root growth in whiskers, new materials being added at the base or root. The detailed mechanism of fibril formation and of the organization of the fibrils into larger structural formations are obscure, but several possibilities are discussed.

Controllably crazed polystyrene: Morphology and permeability

Abstract: The effects of n-heptane and heat treatment on the structural and transport properties of polystyrene films (biaxially oriented and unoriented) were studied to determine whether these treatments improve the film as selective barriers for separation of molecules differing only slightly in size and shape. n-Heptane treatment of biaxially oriented polystyrene produces a sandwich structure composed of expanded, crazed, surface layers surrounding an apparently unaffected central core. The crazed layers contain a continuous network of interconnected channels. The core provides the total resistance to gas permeation, hence, the overall effect of n-heptane treatment is fabrication of a thinner more permeable membrane. By restricting the stress-cracking treatment to one face of the film, it should be possible to make high flux, anisotropic membranes—a type of membrane which is required for successful development of membrane separation processes. n-Heptane treatment of cast, annealed polystyrene results also in a crazed polymer, but the crazing is in the form of spherical voids, and the films, even with a residual uncrazed core, are too weak to be useful as separation membranes. The crazing process in both types of polymer specimens is characteristic of case II non-Fickian diffusion in which the kinetics are apparently controlled by polymer relaxation processes. Sorption of isopentane into cast, annealed polystyrene does not cause visible crazing but the kinetics are again non-Fickian. Desorption of isopentane into n-heptane-treated polystyrene releases the appreciable residual n-heptane in the film which could not be removed by long-term exposure to vacuum. Analysis of D(0) values for isopentane in n-heptane treated films indicates that the polymer surrounding the visible voids in the film is essentially unaltered polystyrene with only a small fraction of the voids being interconnected by open channels.

Variation of refractive index of polystyrene with molecular weight: Effect on the determination of molecular weight distributions

Abstract: Sensitive refractive index measurements on solutions have indicated that the narrow molecular weight polystyrene samples prepared by the Mellon Institute method exhibit a small systematic molecular weight–refractive index dependence up to 300,000 and higher. This upper limit is higher than had previously been suggested. Sensible consistency is generally assumed above a few thousand molecular weight. The effect on this molecular weight–refractive index dependence on gel permeation chromatography and light-scattering molecular weight measurements on polystyrene standards is illustrated.

Thermal degradation of polymer mixtures. I. Degradation of polystyrene–poly(methyl methacrylate) mixtures and a comparison with the degradation of styrene–methyl methacrylate copolymers

Abstract: The degradation behavior of mixtures of polystyrene and poly(methyl methacrylate) in the form of thin films cast from a solution containing both polymers has been compared with that of the individual polymers and of copolymers of the same monomer pair by means of thermal volatilization analysis (TVA) together with product analysis by gas-liquid chromatography determinations of the molecular weight of the solid polymer residues. The results indicate no interaction between the polymers when degraded together. The polymer mixtures are readily distinguished from copolymers of the same overall composition by TVA.

Infrared spectroscopic studies of polystyrene emulsion polymers: Effect of oxidation during polymerization

Abstract: Infrared spectroscopy was empolyed to study the nature of the structural changes which occurred through oxidation during the emulsion polymerization of styrene. Aliphatic carboxylic, amino, and phosphate emulsifiers and hydrogen peroxide and potassium persulfate initiators were empolyed for polymer preparation. In addition, a polystyrene dispersion prepared in the absence of any emulsifier or stabilizer was examined. Irrespective of the nature of the initiator–emulsifier combination employed, all of the polymer spectra revealed bands at 1705 and 1770 cm.−1. The band at 1705 cm.−1 was assigned in part to the carbonyl stretching mode of dimertic carboxylic acid, formed by oxidation, in the polystyrene chains. Absorption at 1770 cm.−1, which was very weak, was tentatively attributed to the carbonyl stretching mode of the monomeric form of this acid. The structure of the acid endgroup was not established, but the results obtained suggest that it was possibly a phenylacetic acid residue or a residue with a similar structure.

Detection of polymer transition temperatures by infrared absorption spectrometry

Abstract: Infrared bands in the 900–1100 cm−1 region are sensitive to thermal energy. These bands can result from intermolecular coupling, producing the crystal lattice, or from intramolecular coupling of the various atomic groups in a regular helix or coiled chain. In either case an increase in temperature will disrupt the coupling mode, resulting in a form of structural relaxation and a reduction in the integrated absorbance. It is proposed that the temperature at which the peak areas begin to decrease be assigned as the Tg. This is measured by continuously scanning a selected peak in the infrared spectrum of a polymer film while it is heated at a rate of about 1°C/min. Using this technique polyamides (nos. 6,66, and 610) exhibited transitions in the 30–50°C range, and by studying the increase in the free NH region (3440 cm−1) of nylon 66 two other transitions were detected at 80 and 137°C; the latter represents a change in the nylon 66 crystal state. An amorphous film of poly(ethylene terephthalate) displayed a transition at 58–68°C (Tg) and at 85°C, which is the crystallization temperature. Films of poly(vinyl acetate) and polystyrene exhibited transitions at 25–37°C and at 70°C, respectively.

Mechanism of reinforcement in rubber‐modified polystyrene systems studied by use of a miniature dart drop test

Abstract: A miniature dart drop test was used in a study of the mechanism of reinforcement in impact resistant rubber-modified polystyrene. A typical SBR-polystyrene system was diluted with varying amounts of polystyrene, and thin compression moldings were made from each blend. The impact-whitened areas were observed directly under the microscope and photomicrographs are presented. The whitening is caused by scattering of light from interfacial separation of portions of many rubber particles from polystyrene and by formation of a multitude of microcracks and/or crazes, starting at the partially separated particles. The absorption of energy by this mechanism can be very large. The driving force for the initial separation appears to be the triaxial tension under which the rubber particles exist, and this results from the higher volume shrinkage rate of rubber compared to that of polystyrene. Included also are photomicrographs taken of specimens after tensile stretching, and the mechanism derived from the impact case is extended to explain the increased elongation and corresponding whitening.

Electrically superior polyester film containing polystyrene or polyionomer additive polymer

Abstract: PHYSICALLY BLENDING MINOR AMOUNTS OF POLYSTYRENE OR POLYIONOMERS INTO POLYESTER RESIN WHICH IS TO BE EXTRUDED INTO A FILM AND THEREAFTER ORIENTED, IMPARTS UNEXPECTEDLY SUPERIOR ELECTRICAL PROPERTIES TO THE ULTIMATE FILM. THE FILM ALSO DISPLAYS IMPROVED "SLIP" PROPERTIES.

Energy Transfer and Quenching in Plastic Scintillators

Abstract: Luminescence quenching in polystyrene + 9,10-diphenylanthracene + quencher and polystyrene + quencher systems has been investigated. In the latter system, the residual styrene monomer is regarded as a fluorescent solute. Result show that solvent quenching observed under uv excitation is due mainly to the competition between dipole-dipole energy transfer from polystyrene to the fluor and that from polystyrene to the quencher, and that such a transfer occurs directly from an excited polystyrene segment before it forms an excimer with an unexcited segment. Solvent quenching under beta-ray excitation was generally greater than that under uv excitation. It is suggested that this phenomenon may result from the occurrence of energy transfer at higher excited state of polystyrene. Solute quenching in some series of polystyrene + 9,10-diphenylanthracene + quencher is not accounted for by usual mechanisms of quenching. Such quenching can be explained by assuming energy transfer from the singlet excited sta...

Studies of solution properties of copolymers. II. Copolymer of maleic anhydride and styrene

Abstract: Styrene and maleic anhydride were copolymerized in benzene. The whole polymer thus obtained was fractionated with acetone and petroleum ether as the solvent and precipitant, respectively. The viscosities and osmotic pressures of the fractions were determined in tetrahydrofuran. The relation between the intrinsic viscosity and the molecular weight, [η] = 5.07 × 10−5 Mn0.81, was obtained in tetrahydrofuran. The unperturbed mean square end-to-end distance was estimated by the Stockmayer-Fixman equation. A theoretical equation for the mean square end-to-end distance for a chain of repeating units of different bond lengths a and b with a fixed valence angle θ and without restriction of internal rotation was presented and applied to this copolymer. In addition, the equation of the mean-square end-to-end distance derived by Wall for trans-polyisoprene without rotational restriction was modified for application to this copolymer. The result evaluated with our equation was about 26% smaller than that from the modified Wall equation. A steric parameter for the present copolymer is defined and discussed in comparison with those of polystyrenesulfone and polystyrene.

Processes using polyperoxides affording sequential free radical generation

Abstract: ORGANIC SYNTHESES REQUIRING FREE RADICAL INITIATION IN TWO STAGES ARE CARRIED OUT USING AS THE SOURCE OF SEQUENTIAL FREE RADICALS A POLYPEROXY COMPOUND HAVING AT LEAST TWO FUNCTIONAL PEROXY GROUPS, AT LEAST ONE OF THESE HAVING A HALF-LIFE DIFFERENT FROM THE OTHER FUNCTIONAL PEROXY GROUPS. EXAMPLE: STYRENE MONOMER AND DI-T-BUTYL ALPHA(METHOXYCARBONYL)DIPEROXYSUCCINATE WERE REACTED AT ABOUT 60*C. TO OBTAIN A POLYSTYRENE CONTAINING FUNCTIONAL PEROXY GROUPS. THE POLYSTYRENE-PEROXY POLYMER WAS REACTED WITH METHYL METHACRYLATE MONOMER AT 85*C. TO OBTAIN A BLOCK COPOLYMER OF POLYSTYRENE AND POLY (METHYL METHACRYLATE).

Sulfonated polystyrene compositions and methods of treating boiler water

Abstract: COMPOSITIONS AND METHODS FOR BOILER WATER TREATMENT ARE DISCLOSED. THE COMPOSITIONS CONTAIN A SULFONATED POLYSTYRENE TO ACT AS A DISPERSIVE; IN ADDITION, THEY MAY CONTAIN A CHELATING AGENT SUCH AS NA3NTA. A USEFUL COMPOSITION COMBINES THE POLYMER WITH A SILICATE AND/OR A PHOSPHATE.

Diffusion in atactic polystyrene above the glass transition point

Abstract: Diffusivities and solubilities in the system n-pentane-polystyrene were measured for low penetrant concentrations at several temperatures above the glass transition temperature. The relatively sharp changes in the activation energy of diffusion and the heat of solution near 150°C. are interpreted tentatively as indicating that a second-order transition exists in atactic polystyrene above the glass transition temperature. Evidence indicating the existence of this transition has been obtained by other techniques and the effects observed in this study should also be present in the diffusion of other penetrants in polystyrene. Correlation of these and other available data for diffusion in polystyrene as a function of the molecular size of the penetrant indicates that specific thermodynamic interactions between polymer and penetrant have little influence on the diffusion process.

Structure and properties of cellulose graft copolymers. II. Cellulose–styrene graft copolymers synthesized by the ceric ion method

Abstract: Styrene was graft-copolymerized onto wood cellulose by the ceric ion method of Mino and Kaizerman. The grafting reaction was found to depend strongly on the concentration of ceric ion in the grafting system and maximum grafting occurred in a narrow range of concentration of initiator, 1.0 × 10−3-1.8 × 10−3 mol/l, at 58 ± 1°C. A pretreatment technique, developed to enhance the monomer diffusion into cellulose, was found to increase the grafting considerably. The structures of the cellulose-styrene graft copolymers were studied by hydrolyzing away the cellulose backbone to isolate the grafted polystyrene branches. The molecular weight and the molecular weight distributions of the grafted polystyrene were determined using gel permeation chromatography. The number-average molecular weight (Mn) ranged from 23,000 to 453,000 and the polydispersity ratios (Mw/Mn) varied from 2.5 to 8.0. The grafting frequencies calculated from the per cent grafting and molecular weight data were of the order of 0.05–0.4 polystyrene branches per cellulose chain.

Reinforced polystyrene and its copolymers

Abstract: Polystyrene and copolymers thereof can be reinforced by glass fibers having a coating of silane coupling agent and a thermosetting polymer such as epoxy, phenolic, polyester, polyacrylate and melamine, to provide superior thermoplastic injection molding compositions.