Showing papers on "Polystyrene published in 1993"

Preparation of monodisperse ellipsoidal polystyrene particles

Abstract: A method is described for the preparation of monodisperse ellipsoidal particles of polystyrene in the colloidal size range. Monodisperse polystyrene particles were dispersed in a solution of polyvinyl alcohol. This dispersion was then allowed to form, by evaporation, a thin film of polyvinyl alcohol containing spherical polystyrene particles. Strips of this film were clamped into a metal frame, heated rapidly in an oil bath to 200°C and stretched to a predetermined extent in order to convert the spherical particles into ellipsoids; the film was then cooled. A wide range of axial ratios for a variety of initial particle sizes was obtained by this method.

Polymeric materials formed by precipitation with a compressed fluid antisolvent

Abstract: Polymer microspheres and fibers are formed with a versatile new process, precipitation with a compressed fluid antisolvent. By spraying a 1 wt. % polystyrene in toluene solution into CO2 through a 100-μm nozzle, microspheres are formed with diameters from 0.1 to 20 μm as the CO2 density decreases from 0.86 to 0.13 g/cm3. The uniform submicron spheres produced at high CO2 density are due in part to the rapid atomization produced by the large intertial and low interfacial forces. Fibers, with and without microporosity, are obtained at higher polymer concentrations where viscous forces stabilize the jet. The effect of CO2 density and temperature on the size, morphology and porosity of the resulting polymeric materials is explained in terms of the phase behavior, spray characteristics, and the depression in the glass transition temperature.

Observation of temperature dependent thicknesses in ultrathin polystyrene films on silicon.

Abstract: The temperature dependent thicknesses of ultrathin polystyrene films under vacuum on Si (111) substrates were investigated via x-ray reflectivity in situ. The contraction of ultrathin polymer films was directly observed for the first time to the author's knowledge. The degree of contraction depends on the initial thickness of the ultrathin polystyrene film, with the magnitude of contraction increasing with decreasing initial film thickness. This contraction ranged from 0--17 % and occurred at temperatures well below the reported bulk polystyrene glass transition temperature.

Effects of a diblock copolymer on adhesion between immiscible polymers. 1. Polystyrene (PS)-PMMA copolymer between PS and PMMA

Abstract: We would like to acknowledge the kind donation of materials for this work by Professor Robert JBr6me and Professor Matt Tirrell.

Compatibilizing agents in polymer blends : interfacial tension, phase morphology, and mechanical properties

Abstract: The interfacial tension, phase morphology, and phase growth was determined for four polymer blend systems: polyethylene/polystyrene, polyethylene/polyamide-6, polystyrene/polyamide-6, and polystyrene/poly(ethylene terephthalate). Generally, high interfacial tension correlates with coarse phase morphology and rapid phase coalescence. The addition of various potential compatibilizing agents to these binary blend systems results in lowered interfacial tension, finer and stabilized phase morphologies. The characteristics of different compatibilizing agents were compared for several of the blend systems. We also look at the influences of compatibilizing agents on mechanical properties of the blend systems. Some compatibilizing agents are able to produce substantial improvements in ultimate properties.

Polymerization processes and toner compositions therefrom

Abstract: Disclosed is a free radical polymerization process for the preparation of a thermoplastic resin or resins comprising heating a mixture of a free radical initiator, a stable free radical agent, and at least one polymerizable monomer compound to form a thermoplastic resin or resins with a high monomer to polymer conversion; cooling said mixture; optionally isolating the thermoplastic resin or resins; and optionally washing and drying thermoplastic resin or resins. Related free radical processes are also disclosed for the preparation of mixtures and block copolymer thermoplastic resins. Resins prepared by the disclosed processes possess a narrow polydispersity and a modality that is controlled by the selection of a free radical initiator and stable free radical agent addition step or steps. The figure is a plot of percent conversion versus molecular weight of a polystyrene homopolymer product obtained from a bulk or solventless stable free radical agent moderated polymerization of styrene at 130 degrees centigrade.

Ellipsometric study of the glass transition and thermal expansion coefficients of thin polymer films

Abstract: The glass transition temperature (T g ) of thin polystyrene films (ca. 3000 A) cast on silicon wafers was determined by a new technique. An ellipsometer was used to determine the refractive index and thickness of the polystyrene films. T g was determined by measuring the temperature dependence of the refractive index. The change in thickness with temperature was used to calculate the linear and bulk thermal expansion coefficients of the material. A significant shift in T g , possibly due to strains induced in the cooled films, was observed between heating and cooling for polystyrene films

A Simple Kinetic Model of Polymer Adsorption and Desorption

Abstract: A model of the desorption and adsorption of a polymer layer at a planar surface indicates a transition from exponential kinetics at high temperatures to nonexponential kinetics (stretched exponential with index one-half) at lower temperatures where these processes are diffusion-limited. Measurements of polystyrene desorption through polyisoprene overlayers show this predicted transition. Corroborative results are obtained for polystyrene desorption through polymethylmethacrylate overlayers. This identification of two distinct kinetic regimes suggests a unifying perspective from which to analyze polymer and biopolymer mobility at surfaces.

Characterization of submicrometer periodic structures produced on polymer surfaces with low‐fluence ultraviolet laser radiation

Abstract: Periodic ripples and dot patterns with spacing smaller than 200 nm have been produced on various highly absorbing polymers [poly(ethylene terephthalate), poly(butylene terephthalate), polystyrene, polycarbonate, etc.] using a polarized beam of an ArF and KrF excimer laser. The period of the structures increases with the wavelength used and with the angle of incidence of the beam, whereas the ripple direction is parallel to the polarization direction. The fluence interval in which the pattern can be produced is far below the ablation threshold of the polymer but probably allows a local melting or photolysis of the surface. For polystyrene, a strong influence of the presence of oxygen was observed, which leads to the conclusion that photooxidative processes play a major role in the structure growing mechanisms. Due to the small size (0.1 μm) of the structure scattering techniques using visible light (0.4–0.8 μm) could not be used in this study and scanning electron microscopy and transmission electron micro...

Microphase separation of block copolymer solutions in a flow field

Abstract: Films of polystyrene–polybutadiene–polystyrene (PS/PB/PS) triblock copolymer and polystyrene-poly(ethylene/propylene) (PS/PEP) diblock copolymer were cast from toluene solutions subjected to hydrodynamic flow at room temperature using a device based on a novel casting method we term ‘roll-casting.’ Polymer solutions were rolled between two corotating eccentric cylinders while at the same time the solvent was removed at a controlled rate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. A discussion of the flow field that develops during roll-casting is presented and specific attention is given to the importance of the shear and elongation rates present. For the triblock and diblock, respectively, the processed structures consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix, and unidirectional lamellae of alternating polystyrene and polyethylene/propylene. Small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) indicated the near single-crystal structure both types of films. SAXS also showed the styrene cylinders and the alternating lamellae to be packed closer together in roll-cast films than in simple quiescently cast films. A molecular orientation mechanism is proposed to describe both these results as well as the changes in packing and in macroscopic sample dimensions measured after complete solvent evaporation and after sample annealing. © 1993 John Wiley & Sons, Inc.

Influence of the seed polymer on the chromatographic properties of size monodisperse polymeric separation media prepared by a multi-step swelling and polymerization method

Abstract: Monodisperse polymer particle-based separation media were prepared by a multi-step swelling and polymerization method with two pairs of monomers and two porogenic solvents. Their chromatographic properties were compared to those of beads prepared by a corresponding suspension polymerization method without the use of seed polymer to ascertain the influence of the seed polymer on their porous structures. A large change in porous structure was observed when the swollen particle consisting of monomers and porogenic solvents contained at least one good solvent for the polystyrene seed polymer, allowing it to remain in the polymerizing medium. In contrast, when the polystyrene seed particle was excluded from the swollen oil droplets, due to its poor solubility in the monomers and the porogenic solvents, there was no difference in the chromatographic properties such as pore volume, pore size, pore size distribution, or retention selectivity between the multi-step swelling and polymerization method and the suspension polymerization method. Since the only difference between the multi-step swelling and polymerization method and the suspension method is the use of the seed polymer, it appears that a very small amount (< 1% v/v) of seed polymers in the enlarged swollen droplets plays an important role as a porogen and affects the porous structure as well as the chromatographic properties of the monodisperse polymer particle-based separation media. © 1993 John Wiley & Sons, Inc.

Morphology transition from cylindrical to lamellar microdomains of block copolymers

Abstract: Thermally induced morphology transition from cylindral to lamellar microdomains was found for a poly(styrene-block-butadiene-block-styrene) (SBS) triblock copolymer having a 0.56 weight fraction of polystyrene blocks by SAXS and TEM. Polybutadiene (PB) cylinders with hexagonal close packing were formed in a polystyrene (PS) matrix when the SBS was cast from a methyl ethyl ketone solution. It was found that the PB cylinders were transformed into lamellae on annealing at 150°C. This is a transition from thermodynamically quasi-stable to stable morphology. The transition turned out to occur via coalescence of cylinders without their translational movements

Formation of microporous polymer fibers and oriented fibrils by precipitation with a compressed fluid antisolvent

Abstract: Polymer morphology is controlled over a continuum from microspheres to interconnected bicontinuous networks to fibers with a versatile new process: precipitation with a compressed fluid antisolvent. The results are explained qualitatively as a function of phase behavior, mass-transfer pathways, and the formation rates of skin on the flowing jet. By spraying dilute polystyrene in toluene solutions into liquid carbon dioxide, extremely small 100 nm microspheres are formed. For concentrations above the critical composition, fibers are produced that are not only microcellular, but, in some instances, even hollow. Mass-transfer pathways that cross the binodal near the critical composition produce interconnected networks, likely due to spinodal decomposition. In this region, fibers composed of highly oriented microfibrils are produced at high shear rates. Preaddition of CO2 influences the morphology because of dilution, in a similar manner as a liquid antisolvent, except that the viscosity reduction is larger due to added free volume. Because CO2 diffuses through the glassy polystyrene skin faster than does a conventional liquid antisolvent such as methanol, it produces more porous fibers, which are also more cylindrical. © 1993 John Wiley & Sons, Inc.

Sulfonation of Syndiotactic Polystyrene for Model Semicrystalline Ionomer Investigations

Abstract: Syndiotactic polystyrene was lightly sulfonated in 1,2,4-trichlorobenzene using acyl sulfate complexes. The sulfonation efficiency of the acyl sulfate increased significantly when anhydrides containing long aliphatic groups were used to complex fulfuric acid. The high sulfonation efficiencies, relative to acetyl sulfate, were attributed to the increased solubility of the longer hydrocarbon complexes in trichlorobenzene. The incorporation of small quantities (less 3.4 mol%) of sulfonic acid groups onto the syndiotactic polystyrene backbone was found to have little effect on the T g of these new materials. However, a much more pronounced effect of sulfonation was observed in the ionomer crystallization

Heterogeneous catalytic hydrogenation of polystyrene: thermodynamics of poly(vinylcyclohexane)-containing diblock copolymers

Abstract: Heterogeneous catalytic hydrogenation of 1,4-poly(isoprene) (PI), atactic poly(styrene) (PS), and two poly(styrene)-poly(isoprene) (PS-PI) diblock copolymers was performed using two palladium supported catalysts. In each case fully saturated materials were obtained with no chain degradation. The dynamic and thermodynamic properties of these materials were investigated using DSC and dynamic mechanical spectroscopy. Saturated poly(styrene), denoted poly(vinylcycloherane) (PVCH), exhibited a T that is 40 deg higher than that of poly(styrene)

Use of ATR-FTIR to study interdiffusion in polystyrene and poly(vinyl methyl ether)

Abstract: ATR-FTIR was used to measure interdiffusion in a polystyrene (PS) and poly(vinyl methyl ether) (PVME) compatible pair below and above the glass transition of PS. At 105°C, corresponding to 5°C above the glass transition of PS, the interdiffusion coefficient was of the order of 1.1x10 -12 cm 2 /s. Interdiffusion was not dominated by either component and it was controlled by the rate of swelling of PS by PVME. At 85°C, the interdiffusion was not-Fickian and time-dependent. A combination of the Fickian and case II models was used to fit the data at 85°C as well as the data at 105°C

Monosize polystyrene microbeads by dispersion polymerization

Abstract: Monosize Polystyrene microbeads were prepared by dispersion polymerization in different alcohol/ water media. Azobisisobutyronitrile and polyacrylic acid were utilized as initiator and steric stabilizer, respectively. The polymerizations were performed in three kinds of dispersion media having different polarities: isopropanol/water, 1-butanol/water, and 2-butanol/water. The effects of initiator and stabilizer concentrations, alcohol/water ratio, and monomer/dispersion medium ratio on the size and monodispersity of the polymeric microbeads were investigated. By dispersion polymerization, polystyrene (PS) microbeads were obtained in the size range of 1.0–4.0 μm with narrow size distribution or in the monosize form. The average size and size distribution of microbeads with increasing polarity of the dispersion medium. The average size and size distribution increased with increasing initiator concentration in all dispersion media. The increase in the stabilizer concentration in homogeneous dispersion media resulted in a decrease in average size and size distribution of the microbeads. A clear increase was observed in the average size with increasing monomer/dispersion medium ratio. Isopropanol/water dispersion medium provided monosize microbeads with higher values of monomer/dispersion medium ratio. © 1993 John Wiley & Sons, Inc.

Ordering by flow near the disorder order transition of a triblock copolymer styrene-isoprene styrene

Abstract: An oriented morphology has been generated by cooling a triblock copolymer styrene-isoprene- styrene (SIS) below ita order-disorder transition (ODT) temperature and annealing it there at constant quench depth AT while simultaneously shearing it. The polymer has an equilibrium microphase-separated morphology of hexagonally packed cylinders of polystyrene in a polyisoprene matrix. The evolving structure was investigated with rheology and small-angle X-ray scattering (SAXS). SAXS showed that mirophase separation occurred rapidly upon cooling below the ODT temperature while the growth of large-scale spatial order (-1-pm scale) needed long annealing times as shown with low-frequency dynamic mechanical measurements. The slow part of the structuring process gave sufficient time for flow alignment of microphase- separated domains during their growth phase. Near "single crystal" morphology was obtained through large- amplitude oscillatory shear at -25 K below ODT. The low-frequency linear viscoelastic properties of the single crystal structure were found to be affected by the domain alignment in the flow direction. The quench depth AT is an important parameter: at a small quench depth of AT 10 K, microphase separation was found to be suppressed by the oscillatory shear.

Anomalous segment diffusion in polymers and NMR relaxation spectroscopy

Abstract: The dynamics of polymer chains (polyisoprene, polyisobutylene, poly(tetrahydrofuran), polystyrene, poly(ethylene oxide), polyethylene, and poly(dimethylsiloxane)) in melts, solutions, and network was studied by the aid of NMR relaxation spectroscopy. Proton data of the spin-lattice relaxation times in the laboratory and rotating frames, T 1 and T 1ρ , respectively, and of transverse relaxation curves are reported. Frequency, temperature, concentration, molecular weight, and cross-link density dependences have been investigated.

Dependence of the Solvent Diffusion Coefficient on Concentration in Polymer Solutions

Abstract: Self-diffusion coefficients of several different solvents in polystyrene as well as methyl methacrylate in poly(methyl methacrylate) have been determined at polymer concentrations from 0 to 50 wt% at 25 o C. The solvents used for the polystyrene solutions were toluene, ethylbenzene, cumene, tert-butyl acetate, chloroform, and methyl ethyl ketone. The diffusion data were used to evaluate several theories for the concentration dependence of the solvent diffusion coefficients, and in most cases the reduced diffusion coefficients, of solvents in polymer solvent systems. In addition to the experimental data presented here, literature data for several systems were also used to test the models

Synthesis, characterization, and properties of new polystyrene-SiO2 hybrid sol-gel materials

Abstract: A new family of organic-inorganic hybrid materials has been prepared by incorporating polystyrene structure units covalently into the SiO2 glass network via the sol-gel approach. The polymer precursors were synthesized by free-radical copolymerization of styrene with 3-(trimethoxysilyl)propyl methacrylate (MSMA) at various feeds. These copolymers were then hydrolyzed and co-condensed with tetraethyl orthosilicate in tetrahydrofuran at room temperature to afford monolithic polystyrene-SiO2 hybrid sol-gel materials having SiO2 contents of 15 to 84% by weight. The hybrid materials derived from the copolymers with MSMA contents greater than 22 mol% have excellent optical transparency. In these transparent hybrid materials, the polymer chains should be uniformly distributed in and covalently bonded to the amorphous SiO2 matrices. The bulk properties of these materials including density, refractive index, and hardness were found to be related to their molecular compositions and can be tailored by varying the polymer contents.