Showing papers on "Polystyrene published in 1974"

Studies on the preparation and characterisation of monodisperse polystyrene laticee: III. Preparation without added surface active agents

Abstract: Preparative methods have been developed in order to obtain monodisperse polystyrene latices in the absence of added surface active agents. By suitable adjustment of the ionic strength of the aqueous phase the initiator concentration and the polymerisation temperature it was found possible to obtain a range of particle sizes, ca. 0.1 to 1.0 ,um, by single-stage reactions. The total initial ionic strength of the aqueous phase was found to play a critical function in determining particle size. A formula has been derived from the experimental data which enables the preparative conditions required to form a latex, containing particles of a particular size, to be predicted.

Recent advances in polymer blends, grafts, and blocks

Abstract: Section I. Introduction.- An Introduction to the Synthesis of Block- and Graft Copolymers.- Practical Properties of Multi-Phase Polymer Systems.- On the Generation of Novel Polymer Blend, Graft, and IPN Structures through the Application of Group Theory Concepts.- Effects of Monomer Unit Arrangement on the Properties of Copolymers.- Block Copolymer Theory. II. Statistical Thermodynamics of the Microphases.- Cationic Grafting: The Synthesis and Characterization of Butyl Rubber-g-Polystyrene and PVC-g-Polyisobutylene.- Synthesis, Morphology, and Properties of AB Crosslinked Copolymers.- Section II. Introduction.- Polysulfone-Nylon 6 Block Copolymers and Alloys.- Dynamic Mechanical Properties of Urea-Urethane Block Polymers.- Orientation Studies of Polyurethane Block Polymers.- Butadiene-Styrene AB Type Block Copolymers.- New Developments in Block Copolymer Applications.- Polystyrene-Poly (?-Methyl Styrene) AB Block Copolymers and Alloys.- Section III. Introduction.- The Synthesis, Characterization and Physical Properties of EPM-g-Polystyrene Thermoplastic Elastomers.- The Causes of Pitting and Haze on Molded ABS Plastic Surfaces.- Poly(Butadiene-Co-Styrene)/Polystyrene IPN's, Semi-IPN's and Graft Copolymers: Staining Behavior and Morphology.- Topologically Interpenetrating Polymer Networks.- Time-Temperature Superposition in Two-Phase Polyblends.- Contributors.

Studies on the photooxidation mechanism of polymers. I. Photolysis and photooxidation of polystyrene

Abstract: A new mechanism has been proposed for the photooxidation of polystyrene as film and in benzene. The initial stage of the photooxidative degradation may involve reactions of singlet oxygen with polystyrene molecules. Singlet oxygen may be formed in the reaction between excited benzene ring in polystyrene molecule and molecular oxygen. The addition of singlet oxygen quenchers such as 1,3-cyclohexadiene or β-carotene reduces the rate of polymer degradation in benzene solution. The mechanisms of the photolysis of polystyrene as film and in benzene solution, in vacuo and in the presence of oxygen, are discussed and interpretations proposed. The pronounced yellowing of polystyrene during the photooxidation process is interpreted as a reaction involving benzene ring-opening photooxidation in polystyrene molecule. These results were obtained by comparing ultraviolet and infrared spectra in experiments of photooxidation of pure liquid benzene and polystyrene film.

Effect of Molecular Weight on Glass Transition by Differential Scanning Calorimetry

Abstract: The influence of molecular weight (900 to 1.8 × 106) on the glass transition temperature of low polydispersity polystyrene (anionically prepared) has been studied by differential scanning calorimet...

Switching in organic polymer films

Abstract: Memory and threshold switching processes are described, as observed in systems consisting of thin (∼0.5 μ) polymer films (polymethylmethacrylate, polystyrene, polyethylmethacrylate, polybutylmethacrylate) between inert electrodes (graphite, molybdenum, NESA glass). The memory off‐state is highly linear, in contrast to the corresponding characteristics of multicomponent chalcogenide glasses. Switching speeds are probably similar or, at any rate, ≪10−7 sec.

Excimer formation in vinyl polymers. II. Rigid solutions of poly(2‐vinylnaphthalene) and polystyrene

Abstract: Excimer formation has been examined in solid films of poly(2‐vinylnaphthalene) (P2VN) and polystyrene (PS) as a function of sample temperature from 373 to 4.2°K and film preparation temperature between 373 and 295°K. The concentration of suitable excimer forming sites in the solid state is fixed by the temperature at which the film is cast. A statistical model based on the rotational isomeric state approximation is used to formulate an expression for the fraction of excimer forming sites in the solid systems. This model makes use of the excimer site conformation energy, found to be 2500 cal for P2VN. Excimer sampling in solid solution is shown to be consistent with an activated exciton migration to preformed excimer sites. The mechanism for this process is attributed to a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. A semianalytical expression for the enhancement of the excitation migration is developed which has the same general form as the experimental results. The effective vibrational frequency is found to be 157 cm−1 for PS and 84 cm−1 for P2VN.

Flow visualization for injection molding of polyethylene and polystyrene melts

Abstract: Flow patterns have been observed during the injection molding of rheologically characterized low-density polyethylene and polystyrene melts under various molding conditions. Some studies of high-density polyethylene were also carried out. Various mold designs were included in the study and the flow patterns investigated under both isothermal and cold cavity wall conditions. In addition to investigating injection molding of single polymer melts, flow patterns in the sandwich molding of polyethylene and polystyrene were studied.

Phenolic resins for solid‐phase peptide synthesis: Copolymerization of styrene and p‐acetoxystyrene

Abstract: Details are given of the synthesis and purification of p-acetoxystyrene and its solution and suspension copolymerization with styrene. Reactivity ratios, evaluated by the Tidwell-Mortimer method, were r1 (p-acetoxystyrene) = 1.18, and r2 (styrene) = 0.88 for (bulk) solution copolymerization. Corresponding values of the reactivity ratios for suspension copolymerization were, within experimental error, indistinguishable from unity. Thus the copolymer composition is governed simply by the monomer feed composition. Use of a specially designed reactor vessel permits convenient suspension copolymerization of styrene, p-acetoxystyrene, and divinylbenzene to give crosslinked resins having comparatively narrow particle size distributions. Acetoxy groups in the crosslinked resin are cleaved by hydrazine hydrate under very mild conditions to give crosslinked polystyrenes having phenolic groups which, in turn, provide a useful alternative to the more usual chloromethylated polystyrene resins for solid-phase peptide synthesis.

Determination of surface car☐yl groups in styrene/itaconic acid copolymer latexes

Abstract: The modes of distribution of acid monomer in two styrene/itaconic acid copolymer latexes prepared with varying emulsifier types were estimated by conductometric titration. The concentrations of acid bound at the surface of the latex particles (“surface bound”) and “free” acid in the water phase can be determined in a single conductometric titration. The concentration of acid “buried” within the latex particles was obtained from the differences between the charge of acid during polymerization and the conductometric titration results. It was found that a larger particle size latex had much lower concentration of “total bound” and “surface bound” acids and higher “free” acid concentration than a smaller particle size latex. Although conductometric titration is suitable for determining the loci of car☐yl groups in polystyrene latexes, it may not apply to all car☐ylated latexes. Analysis of the isolated water phase of styrene/itaconic acid copolymer latexes by G.P.C. indicated the presence of oligomers containing weak acid groups with MW ranging between 2500 and 5000. These oligomers are generated “in situ” during latex polymerization and may become important in conferring adequate latex stability during preparation of car☐ylated latexes of low emulsifier content.

The phosphorescence spectrum and photodegradation of polystyrene films

Abstract: Low-temperature polarized phosphorescence spectroscopy of polystyrene polymerized under different conditions is used to detect emission from phenyl alkyl ketone endgroups in addition to triplet excimer emission from phenyl groups. The carbonyl group concentration can only be lowered by vigorous chemical reduction; and from the phosphorescence excitation spectrum, these carbonyl groups are considered responsible for the initiation of polystyrene photodegradation by solar radiation.

Influence of particle size on the stability of polystyrene latices with an adsorbed layer of nonionic surface active agent

Abstract: The coagulation of monodisperse polystyrene latices by nitric by nitric acid has been studied at different concentrations of a nonionic surface active agent, n-dodecylhexaoxyethylene glycol monoether C12H25[OCH2CH2]6OH; a range of particle sizes from 60 to 870 nm was examined. With an adsorbed monolayer of the nonionic surface active agent the small particle size latices are stable in the absence of an electrostatic charge but the larger particles cannot be stabilized under these conditions. The experimental results are consistent with a theory based on the concept that the adsorbed layer acts as a steric barrier and also modifies the van der Waals interactions.

Time-Temperature Superposition in Styrene/Butadiene/Styrene Block Copolymers

Abstract: The dynamic mechanical response of a styrene/butadiene/styrene (SBS) block copolymer with segment molecular weights of 16,000/78,000/16,000 (designated as Shell 16/78/16) was determined at various temperatures between -83 and +86°C at frequencies between 0.1 and 1000 Hz. The data were shifted into a master curve according to a procedure developed for thermorheologically complex materials and utilizing an additive compliance model. Data on two other triblock copolymers, Kraton 102, and an SBS triblock copolymer exhibiting a continuous polystyrene phase (designated NBS 10/30/10), are also presented. A noteworthy feature of all three triblock copolymers is a long-drawn-out intertransition plateau in which the modulus changes very little for many decades of time. The modulus is high because of the presence of the polystyrene phase and trapped entanglements in the polybutadiene phase. The extent of the plateau, effectively the distance between the two glass transitions, depends on temperature because ...

Method for separation of mixture of plastics

Abstract: A method for separating a mixture of plastics of at least two components selected from the group consisting of polyethylene, polypropylene and a polystyrene, which comprises placing the mixture of plastics in a separation cell containing an aqueous liquid medium containing at least one wetting agent, and introducing gas bubbles into the cell thereby to cause the gas bubbles to selectively adhere to the surface of the polypropylene and/or polyethylene and float the polypropylene and/or polyethylene when the mixture of plastics comprises a polystyrene and polypropylene and/or polyethylene or to selectively adhere to the surface of the polypropylene and float the polypropylene when the mixture of plastics comprises polypropylene and polyethylene with the polypropylene and/or the polyethylene being recovered as a float and the polystyrene being recovered as a residue when the mixture of plastics comprises a polystyrene and polypropylene and/or polyethylene, and with the polypropylene being recovered as a float and the polyethylene being recovered as a residue when the mixture of plastics comprises polypropylene and polyethylene.

Upper and lower critical solution temperatures in the cosolvent system acetone(1)+ diethyl ether(2)+ polystyrene(3)

Abstract: Phase diagrams for different molecular weight fractions of polystyrene in the mixed solvent system acetone + diethyl ether have been obtained. The system shows a variation of upper and lower critical solution temperatures with solvent composition which indicates the cosolvent nature of the mixed solvent. No solvent composition is found which can dissolve high molecular weight poly-styrene (M106). The separation of critical solution temperatures can be predicted by the Prigogine theory of polymer solution thermodynamics, but not the absolute values.

Studies on the photooxidation mechanism of polymers. II. The role of quinones as sensitizers in the photooxidative degradation of polystyrene

Abstract: During the quinone-sensitized photooxidative degradation of polystyrene film and its solution in benzene, an initial rapid decrease of average molecular weight has been observed by GPC and viscosity measurements. The reaction rates are strongly increased by quinones such as p-quinone, duroquinone, anthraquinone, and chloranil. It has been suggested that this photosensitized degradation of polystyrene occurs by a singlet oxygen reaction which might be related to an energy transfer mechanism from excited triplet states of quinones to molecular oxygen. The photooxidative degradation of polystyrene in solution can be diminished by addition of typical singlet oxygen quenchers such as 1,3-cyclohexadiene or β-carotene.

Combustion of Polystyrene and Oxygen-Styrene Copolymer/Ammonium Perchlorate Propellants

Abstract: Burning rate, heat of combustion, flame temperature, and surface temperature of the two composites have been measured. Studies on thermal degradation kinetics and differential scanning calorimetry (DSC) of the propellants have also been made. The inhibitor-free styrene was polymerized by benzoyl peroxide. To prepare the oxygen-styrene copolymer, azobis isobutyronitrile was used as the intiator and oxygen was passed at 1 atm pressure for 24 hr through the styrene. The reaction was completed by adding benzoyl peroxide and maintaining the solution in thermostat at 50°C for another 24 hr until it became sufficiently viscous. The yield of styrene peroxide was of the order of 21-22%. Styrene peroxide was characterized by microanalysis and infrared spectroscopy. Infrared spectra have weak characteristic absorption bands at 7.42 // and 11.15 n and a broad absorption band at 9.75 \i characteristic of peroxide linkage. Burning rate was measured in a manner described earlier. The products of combustion were analyzed by an Orsat Gas Analyzer. The heat of combustion of the PS and copolymer propellant was determined by a Parr Bomb Calorimeter. Thermal degradation of the propellants was determined by the weight-loss method. The flame temperature was measured by the sodium-line reversal technique. The stray light incident on the spectroscope was minimized by putting a diaphragm between the flame and the lens. The measured temperature was corrected for a shift in wavelength on account of the red filter in the pyrometer which was used for calibration. For the polystyrene +70% AP propellant, the flame temperature was found to be 1550±30°C whereas for the corresponding copolymer propellant, the value was 1850±30°C. The surface temperature of the PS and copolymer propellants during burning was determined by using a Pt-Pt (Rh 10%) thermocouple (0.45-mm-diam). The hot junction was kept touching the surface by putting a load of 60-80 g. The cold junction was kept in water at room temperature. The thermocouple was calibrated beforehand by taking measurements on the melting points of silver nitrate, potassium dichromate, and

Application of NMR to the study of molecular motion in SBS copolymers

Abstract: NMR T1 and T2 data are presented for two styrene‐butadiene‐styrene block copolymers along with results for homopolymers of polystyrene and polybutadiene. The relaxation processes in both polymers are discussed. The results indicate that the glass transition temperature for polystyrene is lower in the SBS copolymer than for the homopolymer, in agreement with earlier findings. It is concluded that the vigorous motions in the polybutadiene phase of the copolymer instigate motion in the polystyrene phase prematurely. The data further indicate that motion in polybutadiene is more hindered in SBS than in the pure polymer as a result of the cross‐linking effect of the polystyrene domains; however, there is little effect on Tg for polybutadiene. Finally, the T1 results indicate that spin diffusion is operative between the two phases in the SBS block copolymer. The principal features of this effect are satisfactorily explained in terms of a simple model which neglects the geometry of the interface between the two phases.

Wrinkle free extrusion coating of heat fusible foam sheet

Abstract: In a process for extrusion coating of both sides of a foamed polystyrene sheet with a rubber modified polystyrene the specific improvement of crushing the coated foam sheet such that it will rebound to only 30 to 70 percent of its original thickness results in a product of improved processing characteristics. This crushed sheet can be thermally formed into a wrinkle free china-like surface useful in making insulated dishes, trays, food containers and the like.