Showing papers on "Polystyrene published in 1970"

The formation of micro shear bands in polystyrene and polymethylmethacrylate

Abstract: The conditions under which amorphous polystyrene and polymethylmethacrylate deform inhomogeneously by the formation of fine shear bands have been investigated. The thermal history of the sample and the temperature and strain rate at which the deformation is carried out have been found to be critical. Stress-strain data have been obtained in order to test the criterion for inhomogeneous deformation presented in the preceeding paper. In addition, stress-birefringence measurements have been made on polystyrene and the possible influence of molecular transition processes on the plastic deformation process is discussed.

Colloid chemical studies of polystyrene latices polymerized without any surfaceactive agents: I. Method for preparing monodisperse latices and their characterization

Abstract: SummaryPolystyrene latices were polymerized in the absence of any emulsifiers using potassium persulphate as an initiator. The latex dispersions obtained consisted of particles having high monodispersity and their diameters could be varied within a wide range (350 to 1400 mμ) in response to the preparing conditions.The electrophoretic mobilities of the latices were measured according to a microelectrophoretic technique and their zeta-potential was obtained as 70–80 mV in the standard state.Average molecular weights and the distributions of the latices were determined by use of the Gel Permeation Chromatography and the mechanism of the particle growth was discussed.The critical flocculation concentrations for the latex dispersion were determined with the various salts (KCl, BaCl2 and LaCl2) by measuring sedimentation rates. These results were discussed byVerwey-Overbeek's analytical expression for the flocculation concentration.ZusammenfassungDie Polystyrol-Latices wurden ohne Emulgatoren mit Kaliumpersulfat als initiator polymerisiert. Die erhaltenen Polystyroldispersionen waren monodispers; der Durchmesser der Partikel konnte im großen Bereich (350 to 1400 mμ) variiert werden.Die elektrophoretische Beweglichkeit der Latices wurde mikroelektrophoretisch gemessen; das Zetapotential lag zwischen 70 und 80 mV. Die mittleren Molekulargewichte und die Verteilungskurven wurden durch Geldurchdringungschromatographie bestimmt. Die kritische Auflockerungskonzentration für die Polystyroldispersion wurde mit verschiedenen Salzen (KCl, BaCl2 und LaCl3) bestimmt. Die Ergebnisse werden mit der Verwey-Overbeek-Theorie diskutiert.

Dynamic mechanical properties of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐polystyrene blends

Abstract: Blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPO) and atactic polystyrene (PS) have been prepared by mechanically mixing powders of the two polymers and subjecting the mixtures to three different thermal treatments. Three different compositions were studied by the dynamic mechanical and DSC techniques. The weight fractions of PPO in the mixtures were 0.25, 0.50 and 0.75. The dynamic mechanical measurements indicate that partial mixing took place but that two distinct phases, one rich in PS and the other in PPO, exist in all the mixtures studied. Each phase exhibits a characteristic relaxation peak associated with the glass transition of that phase. DSC measurements, on the other hand, reveal only a single glass transition apparently characteristic of the PS rich phase in each case. The results indicate that a given type of experiment will indicate compatibility or incompatibility depending upon the size of the molecular process it represents.

Inferences on the mechanism of emulsion polymerisation of styrene from characterisation of the polymer end-groups†

Abstract: Solute electrolyte and adsorbed emulsifier can be removed by ion exchange from polystyrene latices prepared with persulphate initiator. Rigorous purification of the ion-exchange resins is necessary to avoid contamination by leached polyelectrolytes. These ion-exchanged latices are stabilised by strong acid surface groups - sulphate end-groups of the polymer molecules. The number of surface groups as determined by conductometric titration of the latex, plus the number buried within the particle as determined by conductometric titration of the polymer in solution (or by X-ray fluorescence), is less than the expected value of two per polymer molecule. The other end-groups are shown to be hydroxyl groups by oxidation to the carboxyl form followed by ion exchange and titration. The total number of end-groups thus determined is close to two per molecule. As the pH of the polymerisation medium is decreased, the proportion of hydroxyl end-groups increases and that of the sulphate end-groups decreases. No carboxyl groups are detected in ion-exchanged latices prepared in a nitrogen atmosphere, independent of the nature of the emulsifier. The dye partition method gives end-group concentrations that are far lower than those determined by titration or X-ray fluorescence, probably because the formation of the dye end-group ion-pair is not complete. Finally, for latices prepared at relatively low emulsifier concentrations, the contribution of the sulphate end-groups to the surface charge density is significant and cannot be overlooked, as has been done in the past.

Factors Affecting the Oxygen Tension around Cells Growing in Plastic Petri Dishes

Abstract: SummaryAnomalous observations on the survival of hamster cells irradiated while growing on polystyrene Petri dishes led to a detailed study of oxygen tension around the cells. It was found that polystyrene and other plastics held large quantities of oxygen in solution and released this slowly by diffusion. If the cells were covered by even a thin layer of liquid, this caused a build-up in oxygen concentration around the cells attached to the plastic surface. Of the several plastics tested for oxygen solubility and diffusion coefficient, only TPX and Mylar (or Melinex) seem to offer a hope that they may be suitable as a support for cells in anoxic experiments. Of these two, TPX is the better and is indeed the only one which allows 10−8 M [O2] to be reached in a reasonable gassing time, assuming a liquid layer only 100 μ thick. The effect of the meniscus is discussed and the radiation-chemical binding of oxygen in both plastic and solution has been considered. It is pointed out that monitoring the effluent ...

Impact Polystyrene: Factors Controlling the Rubber Efficiency

Abstract: The rubber phase volume (rubber + occluded polystyrene) can be widely varied in impact polystyrene by controlling the rate of agitation during polymerization. The tensile modulus and magnitude of the rubber phase mechanical loss transitions are related to the degree of polystyrene occlusion. It is shown that the occluded polystyrene can substitute for rubber in determining these parameters. Impact strength and ultimate elongation pass through maxima as the rubber phase volume is increased at constant rubber concentration due to the optimization of rubber phase volume with particle size and rubber phase modulus. Over crosslinking of the rubber and a high concentration of a low molecular weight tail of matrix polystyrene have deleterious effects on the impact strength and ultimate elongation. The optimization of these three factors is required in making efficient use of the rubber in impact polystyrene.

The preparation and properties of yeast β-fructofuranosidase chemically attached to polystyrene

Abstract: 1. A process is described for the chemical attachment of an enzyme to the surface of a polystyrene matrix. 2. By this process yeast β-fructofuranosidase was chemically attached to the surface of both polystyrene beads and polystyrene tubes. 3. The kinetics of sucrose hydrolysis by β-fructofuranosidase and polystyrene-supported β-fructofuranosidase were compared. 4. The pH–activity curve of the polystyrene-supported enzyme shows a marked difference from that of the free enzyme in solution. 5. The inhibitor dissociation constant with respect to tris is increased, whereas the inhibitor dissociation constant with respect to aniline is decreased when the enzyme is attached to polystyrene. 6. Differences between the properties of the bound and free enzyme are discussed in terms of a micro-environmental effect arising from the hydrophobic nature of the polystyrene support.

Specific Heat of Amorphous Polymethyl Methacrylate and Polystyrene Below 4°K

Abstract: Measurements of the specific heat of polymethyl methacrylate and polystyrene have been performed using the heat pulse method between 0.5 and 4.3°K. Above 2°K the specific heat is about double that expected on the basis of the Debye theory and acoustic measurements. Below 2°K the experimental data approach the Debye value. The excess specific heat can be fit by two Einstein modes. For polymethyl methacrylate the Einstein temperatures are 4.9 and 17.5°K containing 0.014% and 1.0% of all modes, respectively. For polystyrene the corresponding modes are 5.5 and 16°K with strengths of 0.038% and 1.8% respectively. The data support a model of pendant side groups near voids capable of independent low frequency torsional oscillations. The barrier to internal rotation of the pendant group is estimated.

Quantitative thermal analysis of polyblends

Abstract: A new quantitative thermal analysis technique was attempted on ABS and Noryl-type polyblends. A particular component within a polyblend was identified by its glass transition temperature and the amount of the component was determined from the increase in specific heat at the glass transition temperature. Two commercial Noryl resins were determined to be blends of high impact polystyrene and polyphenylene oxide in 47-47 and 69-17 proportions by weight, respectively. Polystyrene appears to be cosoluble with polyphenylene oxide without the formation of any complex. The PS-PPO polyblends yield single sharp glass transitions which are a function of concentration.

Anomalous transport of hydrocarbons in polystyrene

Abstract: The transport kinetics and equilibrium concentrations of n-pentane at high penetrant activities in cast, annealed polystyrene were determined and compared with similar measurements in biaxially-oriented polystyrene. The rate of Case II (relaxation-controlled) sorption in biaxially-oriented polystyrene is three to four times faster than the sorption rate in cast, annealed polystyrene. The Case II sorption process in biaxially-oriented polystyrene is more highly temperature dependent than in cast, annealed film. The higher activation energies coupled with the larger relaxation-controlled sorption rates in biaxially-oriented polystyrene imply the involvement of larger polymer segments in the rate controlling polymer relaxations. The sorption in cast, annealed polystyrene was a position-dependent relaxation controlled transport process; in contrast the sorption in biaxially oriented polystyrene, albeit relaxation-controlled, was not position dependent. The position dependence of the Case II sorption appears to be a consequence of the presence of residual benzene in the film which accelerates the rate-determining relaxations. Desorption measurements at very low penetrant activities were quite similar for both biaxially oriented and cast, annealed polystyrene. The desorption kinetics were Fickian and were only a weak function of polymer orientation at these low activities.

Characterisation of latex particles produced by emulsion polymerisation

Abstract: The emulsion polymerisation of styrene, using sodium dodecanoate as emulsifier and hydrogen peroxide as initiator, has been used to prepare a series of polystyrene latices of different sizes. The size range covered was from 600 A to 4230 A. After removal of the soap by dialysis, the surface groups on the particles were characterised by electrophoresis. The main surface groupings were found to be carboxyl groups. Number-average molecular weight determinations were carried out using osmometry and it was found that the molecular weight decreased as the particle size increased. The evidence obtained suggests that the growth of a latex particle involves a surface-phase polymerisation.

Dynamic Properties of a Model Reinforced Elastomer. Styrene-Butadiene Reinforced with Polystyrene

Abstract: The dynamic storage and loss moduli of SBR 1503 reinforced with 400 A˚ polystyrene particles were measured at 110 cps over a 200° temperature range. The effect of the polystyrene filler on the rubber was to raise the storage modulus dramatically in the rubbery zone, but only slightly in the glassy region of viscoelastic response. As a result the transition zone appeared broadened and shifted toward higher temperature. Corresponding changes were observed in the loss maximum with a shift of 4° at the highest filler content (46%) investigated. The height of the loss maximum was nearly unaffected. The loss tangent of the filled and unfilled polymers showed no systematic shift with temperature and the dilatometric glass transition was raised only 2° C at the highest filler content. All the essential features of the dynamic behavior could be described in terms of the properties of the component polymers by the phenomenological equivalent mechanical model treatment of Takayanagi. It is concluded that th...

Macronet polystyrene structures for ionites and method of producing same

Abstract: MACRONET POLYSTYRENE STRUCTURES FOR IONITES, CHARACTERIZED IN THAT THEY CONSISTS OF CROSS-LINKED POLYSTYRENE OR CROSS-LINKED COPOLYMERS OF STYRENE WITH DIVINYLBENZENE IN WHICH THE CONTENT OF THE DIVINYLBENZENE IN THE COPOLYMERS IS UP TO 1 MOLE PERCENT, AND THE LINKING BRIDGES BETWEEN THE BENZENE RINGS OF THE POLYSTYRENE CHAINS ARE AS FOLLOWS R-(1,4-PHENYLENE)N-R WHERE R=CH2, CO, N=1,2,3 THE PROPOSED MACRONET STRUCTURES CAN BE PRODUCED BY USING A METHOD PROVIDING FOR TREATING OF POLYSTYRENE OR GRANULAR COPOLYMERS OF STYRENE WITH DIVINYLBENZENE, THE LATTER BEING INCLUDED IN THE COPOLYMERS IN AN AMOUNT OF UP TO 1 MOLE PERCENT, BY A CROSS-LINKING AGENT IN A MEDIUM OF AN ORGANIC SOLVENT IN THE PRESENCE OF THE FRIEDELCRAFTS CATALYST. THE CROSS-LINKING AGENT IS COMPOSED OF BISFUNCTIONAL COMPOUNDS OF THE GENERAL FORMULA R-(1,4-PHENYLENE)N-R WHERE R=CH2CL, COCL, N=1,2,3 THESE STRUCTURES FEATURE A HIGH MECHANICAL STRENGTH AND HAVE ADEQUATELY LONG, RIGID, CHEMICALLY STABLE BRIDGES REGULARLY ARRANGED BETWEEN THE POLYSTYRENE CHAINS AND CAPABLE OF CARRYING THE SAME IONOGENIC GROUPS AS THOSE CARRIED BY THE POLYSTYRENE CHAINS. THE IONITES BASED ON THESE STRUCTURES HAVE A HIGH EXCHANGE CAPACITY (E.G. UP TO 5.35 MEQ./G. FOR SULPHOCATIONITE), HIGH OSMOTIC STABILITY AND HIGH KINETIC CHARACTERISTICS.

Thermal degradation of copolymers of styrene and acrylonitrile. I. Preliminary investigation of changes in molecular weight and the formation of volatile products

Abstract: By the use of thermal volatilization analysis (TVA), 292°C was chosen as a suitable temperature for a preliminary experimental survey of the thermal degradation of styrene–acrylonitrile copolymers. TVA also indicated that there is no fundamental change in reaction mechanism as the acrylonitrile content of the polymer is increased from zero to 33.4% although there is a progressive increase in the rate of volatilization. The increase in the rate of volatilization over that of polystyrene is directly proportional to the acrylonitrile content of the copolymer. From the changes in molecular weight which occur during the reaction it is clear that the primary effect of the acrylonitrile units on stability is to cause an increased rate of chain scission, but there is a small proportion of “weak links” which are associated with the styrene units and which are broken instantaneously at 292°C. The number of monomer molecules liberated per chain scission, the zip length, is about 40 for polystyrene in the initial stages of degradation and decreases only to the order of 20 even in copolymer containing 24.9% acrylonitrile. Thus the unzipping process is not severely affected by the acrylonitrile units; this is borne out by the fact that acrylonitrile appears among the products in very much greater concentrations than from pure polyacrylonitrile. The proportion of larger chain fragments (dimer, trimer, etc.) also increases with acrylonitrile content.

Dynamic mechanical properties, structure, and composition of impact polystyrene

Abstract: Two series of impact polystyrene were studied; they had been obtained by grafting and by mechanical mixing, at two different known polybutadiene levels. Their biphasic structure had been characterized by optical microscopy and physicochemical separation. The following factors were investigated: morphology and content of the dispersed phase and continuous phase, composition of the dispersed phase, and molecular weight of the continuous phase. The elastic shear modulus and mechanical damping were measured. It was found that the elastic shear modulus of the two series of materials does not depend on the total polybutadiene content, as is often suggested in the literature, but on the rubbery dispersed phase content. The polybutadiene concentration of this phase, although varying between 100% for the mechanical mixes and 34% for one of the grafted polymers, does not influence the mentioned correlation. The particle size of the dispersed phase and the molecular weight the continuous phase have very little or no influence. The found correlation agrees with the theories for the moduli of models consisting of dispersions of spheres or particles in a matrix, like those of Kerner,13 Hashin,14,15 and Mackenzie.18

Structure and properties of a styrene–butadiene–styrene block copolymer

Abstract: Electron-microscopic texture and physical properties of a styrene–butadiene–styrene (SBS) block copolymer obtained by casting from toluene, carbon tetrachloride, ethyl acetate, and methyl ethyl ketone are discussed. Two peaks are observed in the mechanical loss (tan delta;) curve at −70 and 100°C which are attributed to segmental motion of polybutadiene and polystyrene, respectively. The polybutadiene peak heights are in the order of solubility in the solvent used; the polystyrene peak heights are in converse order. In addition to these peaks, a third peak is observed at 10°C for specimens cast from ethyl acetate or methyl ethyl ketone. A transition corresponding to this peak is also noticed in thermal analysis. It is proposed that aggregation of styrene blocks is relatively incomplete in specimens cast from solution in poor solvents.

Electric polarization and conductivity of polystyrene in unidirectional electric field

Abstract: The present work interprets the anomalous conductivity and the discharge and recovery voltage in polystyrene as a result of the dielectric relaxation processes—the dipole-orientation polarizations. This view is based on a number of author's measurements and on some literature data. Approximate relations were derived for the time dependence of discharge and recovery voltage. The given conception is believed to be valid for other “nonpolar” and polar polymeric insulating materials, too. The activation energy of steady-state conductivity of polystyrene, measurable practically aboveTg, is 2.3 eV, i. e. the same value as given in literature for the activation energy of diffusion in polystyrene.

Glass Transition of Atactic Polystyrene by Ortho‐Positronium Decay

Abstract: In solid polymers the mean lifetime τ2 of ortho‐positronium annihilating by pickoff depends upon the free volume. τ2 has been measured for five samples of relatively monodisperse atactic polystyrene over a temperature range from room temperature to 120°C. The number average molecular weight of the samples ranged from 50 100 to 640 000. For each sample the variation of τ2 with temperature indicated a glass transition about 13 deg below that measured on a differential scanning colorimeter. An increase in the glass transition temperature with molecular weight was observed. The τ2 lifetime, which depends upon the overlap of the positron component of the ortho‐positronium atom with the lattice wavefunction, seems to be very sensitive to the cooperative motion about the chain axis which is associated with the glass transition.

The degradation of polystyrene during extrusion

Abstract: An investigation was made of the magnitude and mechanism of shear degradation of a narrow distribution, high molecular weight (Mw = 670,000) polystyrene. An Instron rheometer was used to perform the extrusion at temperatures from 164° to 250°C. The change in molecular weight distribution was studied by gel permeation chromatography. The maximum shear stress employed was 5.83 kg/cm2. It was found that degradation could be induced at high stress at temperatures of 50°C lower than degradation of polystyrene would occur exclusively due to thermal forces. An activation energy for the degradation, calculated at constant shear rate, was +20.2 kcal/mole. The direction and magnitude of this value are consistent with degradation induced through a mechanical reduced activation for thermal degradation.

Hot-melt adhesive polymer blends

Abstract: IMPROVED HOT-MELT ADHESIVES COMPRISING POLYESTERS BLENDED WITH POLYOLEFINS OR VINYL POLYMERS AND ARTICLES SECURED THEREWITH. THE POLYESTERS OF 1,4-BUTANEDICAL AND TEREPHTHALIC OR TRANS-1,4-CYCLOHEXANE DICARBOXYLIC ACID, BLENDED WITH POLYSTYRENE ARE PREFERED ADHESIVE COMPOSITIONS.

Insulation product and method

Abstract: AN INSULATION BOARD IS MADE BY LAMINATING TO THE SURFACE OF A BODY OF FOAMED PLASTIC RESIN, SUCH AS FOAMED POLYSTYRENE, A FILM OF HIGHER DENSITY FOAMED PLASTIC RESIN SUCH AS FOAMED POLYSTYRENE.