Showing papers on "Polystyrene published in 1991"

Cloud-point curves of polymer solutions from thermooptical measurements

Abstract: Thermooptical analysis (TOA) provides a simple, rapid, and reliable experimental method to determine cloud-point curves of binary polymer/solvent systems. Phase diagrams have been obtained for different molecular weights of polystyrene in cyclohexane, methylacetate, ethylacetate, and tert-butylacetate and for poly(ethylene glycol) in water. Polystyrene solutions exhibit both upper and lower critical solution temperatures, while aqueous poly(ethylen glycol) solutions give closed-loop phase diagrams. The TOA apparatus described here uses very small samples (0.02 cm 3 )

Interfacial behavior of block polyelectrolytes. 1. Evidence for novel surface micelle formation

Abstract: Monolayers of a polystyrene/poly-4-vinylpyridine AB diblock ionomer, (PS) 260 (4-PVP) 240 , fully quaternized with decyl iodide have been studied at the air/water interface with the Langmuir film balance technique. Surface pressure/area isotherms exhibit an abrupt onset and an apparent first-order phase transition at high pressures. Transmission electron micrographs of LB films deposited on carbon-coated copper grids provide direct evidence of self-assembly of the diblock copolymers into circular surface micelles

Adsorption kinetics of block copolymers from a good solvent : a two-stage process

Abstract: The adsorption kinetics and adsorption isotherm of a polystyrene (PS)-poly(ethylene oxide) (PEO) diblock copolymer onto a silicon wafer from toluene solution was measured in situ by ellipsometry. PS-PEO behaves like an end-adsorbed chain. The adsorption kinetics shows two processes on a clearly separated time scale. The repulsion between the nonadsorbing PS blocks determines the maximal adsorbed amount. The adsorbed monolayer can be rapidly and completely displaced by PEO oligomer with a length comparable to the PEO block in the block copolymer

Critical molecular weight for block copolymer reinforcement of interfaces in a two-phase polymer blend

Abstract: The effect of a small addition of poly(styrene-b-2-vinylpyridine) block copolymer on the microstructure and mechanical properties of phase-separated blends of polystyrene (PS) and poly(2-vinylpyridine) (PVP) was investigated. Only copolymers whose PVP block degree of polymerization was above 200 were found to be effective in preventing failure at the interface. This critical value corresponds roughly to the molecular weight between entanglements M e , suggesting therefore that at least one average «entanglement» between the PVP bhlock and the PVP homopolymer is necessary to have good stress transfer at the interface

Preparation of micron-size monodisperse polymer particles by seeded polymerization utilizing the dynamic monomer swelling method

Abstract: Utilizing a new type of monomer swelling method, 6.1 μm-size monodisperse polymer particles were prepared by seeded polymerization. 1.8 μm-size monodisperse polystyrene (PS) seed particles (1.8 μm in size) were prepared by dispersion polymerization in ethanol-water (80/20, v/v) medium in the presence of poly(acrylic acid) as stabilizer with 2,2′-azobisisobutyronitrile as initiator. The PS seed dispersion was mixed with ethanol-water (60/40, v/v) solution dissolving styrene (S) monomer, benzoyl peroxide as initiator, and poly(vinyl alcohol) as stabilizer. By slow, continuous, dropwise addition of water with a micro feeder into the mixture, the PS particles absorbed the many S monomers, which were separated from the medium and swelled from 1.8 μm to 8.4 μm while keeping the monodispersity high. We named this procedure the “dynamic swelling method”. Then, the seeded polymerization of the absorbed S monomer was carried out in the presence of NaNO2 as water-solube inhibitor.

Viscoelastic Behavior of Lightly Sulfonated Polystyrene Ionomers

Abstract: The linear viscoelastic behavior of sulfonated polystyrene ionomers with as few as one sulfonate group per 1000 styrene repeat units was studied by dynamic mechanical analysis. Interactions of the sulfonate groups shifted the terminal flow region to lower frequency and produced a new low-frequency relaxation that was not present in the unmodified polystyrene. The observation of the low-frequency relaxation at very low sulfonation levels suggests that even for 0.11 mol % sulfonation, ionic clusters formeven though, no SAXS peak has been resolved for ionomers with that low a sulfonation level. The effect of the ionic groups on the viscoelastic properties can be varied for a fixed sulfonation level by weakening the ion-dipole strength of the ion pair. This can be achieved by substituting ammonium (NH4+) cations for metal cations such as Na+.

Effect of surface hydrophobicity on the conformational changes of adsorbed fibrinogen

Abstract: The extent of conformational changes of fibrinogen adsorbed on germanium, poly(hydroxyethyl methacrylate) (poly(HEMA), Biomer, and polystyrene surfaces was studied using Fourier transform infrared spectroscopy (FTIR) coupled with attenuated total reflectance (ATR) optics. The contact angles of water on the solid surfaces were 19.3°, 35.5°, 37.6°, and 90.5°, respectively. The adsorption kinetics of fibrinogen from 1 mg/ml solution showed that the amount of adsorbed fibrinogen increased as the surface became more hydrophobic. The spectra of fibrinogen in the bulk solution and of fibrinogen tightly adsorbed on germanium, poly(HEMA), Biomer, and polystyrene surfaces were treated using Fourier self-deconvolution and the synthetic single-peak fitting techniques to resolve the overlapped peaks in the amide I and II regions. It was found that some α-helical structures were changed into the unordered structures and the content of β-turns was increased upon the protein adsorption. A weighted-peak shift method was used to examine the extent of the protein conformational changes upon adsorption on hydrophobic and hydrophilic surfaces. The results indicated that the adsorbed fibrinogen underwent a larger degree of conformational changes as the surface hydrophobicity increased.

Synthesis and size control of polystyrene latices via polymerization in microemulsion

Abstract: Polystyrene latices with 10nm < R < 60 nm were prepared via microemulsion polymerization. The size of the particles was controlled only by the ratio of styrene to surfactant. Within a certain range, the relation between stoechiometry and droplet size is described by a simple geometrical model which can be generalized to other nonpolar monomers. By contrast, the microemulsion polymerization of polar monomers such as methyl methacrylate(MMA) and even copolymerization with MMA become more complex and the simple model fails.

Ordered morphologies in binary blends of diblock copolymer and homopolymer and characterization of their intermaterial dividing surfaces

Abstract: Binary blends of a lamellar poly(styrene‐b‐isoprene) diblock copolymer and homopolystyrenes of various molecular weights self‐assembled into highly ordered morphologies upon solvent evaporation. The equilibrium blend morphologies were studied by transmission electron microscopy and small angle x‐ray scattering. The type of ordered morphology (lamellae, the ordered bicontinuous double diamond morphology, cylinders on a hexagonal lattice, and spheres on a cubic lattice) observed in each blend was generally dictated by the overall polystyrene volume fraction in the blend, i.e., the homopolymer concentration. The blend morphology also depended on the homopolymer molecular weight at a single fixed composition. The intermaterial dividing surface between the polystyrene and the polyisoprene microdomains was characterized by the interfacial mean curvature (H) and the average area per copolymer junction (σj). H and σj increased as the homopolymer concentration increased and/or as the homopolymer molecular weight d...

Interfacial phenomena controlling particle morphology of composite latexes

Abstract: A thermodynamic analysis and a mathematical model were derived to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Seeded batch emulsion polymerization was carried out at 70°C using as seed monodisperse polystyrene latex particles having different surface polarity. The surface polarity was estimated by contact angle measurement at the latex “film”/water interface for octane as the probe liquid. Methyl methacrylate and ethyl methacrylate were polymerized in a second stage seeded emulsion polymerization using polystyrene particles as seed in the presence of a nonionic stabilizer, nonyphenol polyethylene oxide (Igepal Co-990). Two types of initiators, potassium persulfate (K2S2O8) and azobisiobutyronitrile (AIBN), were used to change the interfacial tension between the second stage polymer (in monomer) and water interface. The values of the interfacial tension of polymer solutions in the second stage monomer vs. the aqueous phase, measured by drop-weight–volume method under conditions similar to those prevailing during the polymerization, correlated well with the determined particle surface polarity and the observed TEM particle morphology. The results showed that, rather than the polymer bulk hydrophilicity, the surface particle polarity is the controlling parameter in deciding which phase is inside or outside in the composite particle. The variation of the polymer phase interfacial tension with polymer concentration was also estimated. Based on experimentally measured interfacial tensions, composite particle configurations were predicted. The predicted morphologies showed good agreement with the observed particle morphologies of the composite latexes.

UV absorption spectra of polystyrene

Abstract: Polystyrene (PSt) exhibits a new UV absorption band at around 290nm in comparison with ethylbenzene, which is attributed to associative interaction between pendant phenyl groups. Similar absorption bands are also observed for polymers of styrene derivatives. The UV spectra suggest charge-transfer complex formation between the polymeric and monomeric donors with electron-acceptor tetracyanoethylene (TCNE) and the equilibrium constants were estimated to be in the sequence of ethylbenzene > PSt > copolymer of St with methylmethacrylate.

Development of miscible blends of polyamide-6 and manganese sulfonated polystyrene using specific interactions

Abstract: Polyamide-6 and a functionalized polystyrene containing 10.1 mol % manganese sulfonate groups were miscible over the entire range of composition as evidenced by a single, composition-depentent T g . The T g 's for the blends exhibited positive deviation from a weight average of the two component polymer T g 's. Interaction parameters were large and negative, indicating strong interactions between the component polymers. Infrared spectra confirmed that these specific interactions were hydrogen-bonding, ion-dipole, and complexation interactions involving the manganese sulfonate and amide groups

Chemical amplified resist material containing photosensitive compound capable of generating an acid and specific polystyrene copolymer having functional groups that become alkali-soluble under an acid atmosphere

Abstract: A resist material comprising (a) a polymer having a monomer unit having a special functional group, a monomer unit having a phenolic hydroxyl group, and if necessary a third monomer unit, (b) a photoacid generator, and (c) a solvent can provide a resist film excellent in heat resistance and adhesiveness to a substrate when exposed to light with 300 nm or less such as deep UV light, KrF excimer laser light, etc., and is suitable for forming ultrafine patterns.

Ultrasonic degradation of polymer solutions. 1. Polystyrene revisited

Abstract: The results of ultrasonic irradiation of polystyrene solutions in toluene, benzene and carbon tetrachloride are described. The effect of a range of conditions such as ultrasonic intensity, solution concentration and varying solvents were investigated. The non-random nature of the degradation process was clearly demonstrated and the effect of different solvents was interpreted in terms of their thermodynamic properties.

Rheological properties of copolymer modified polyethylene/polystyrene blends

Abstract: In this study, the effect of hydrogenated styrene butadiene diblock copolymers on the rheological properties of high‐density polyethylene (HDPE)/high impact polystyrene (HIPS) blends is investigated. The blends were prepared in the melt state at 180 °C for 5 min in a batch mixer. The results show that the rheological properties of the blends were very sensitive to the copolymer concentration present in the blend mainly in the low frequency region. At low copolymer content (e.g., 1 wt. %), an important decrease of the zero‐shear viscosity (η0) was observed in the case of HIPS rich blends. For the HDPE rich blends, this decrease was not observed when modified with the pure diblock copolymer. As the copolymer content increases, and depending on the copolymer structure, an increase or a further decrease of η0 was obtained. This behavior was interpreted as due to the change in the copolymer state in the blend, i.e., saturation of the interface and micelles formation. Predictions of an emulsion model of two viscoelastic liquids including an interfacial tension (σ) contribution to the elastic properties were close to the experiments for the 90/10 and 20/80 HDPE/HIPS unmodified blends, but unsatisfactory in the other cases. According to the general features of polymer suspensions and to the predictions of this model, it is concluded that phase interactions as produced by the addition of the copolymer are very important. This aspect must be included in any rheological model for copolymer modified immiscible blends.

Polyisobutylene‐containing block polymers by sequential monomer addition. II. Polystyrene–polyisobutylene–polystyrene triblock polymers: Synthesis, characterization, and physical properties

Abstract: New linear and three-arm star thermoplastic elastomers (TPEs) comprising a rubbery polysobutylene (PIB) midblock flanked by glass polystyrene (PSt) blocks have been synthesized by living carbocationic polymerization in the presence of select additives by sequential monomer addition. First, isobutylene (IB) was polymerized by bi- and trifunctional tert-ether (dicumyl- and tricumyl methoxy) initiators in conjunction with TiCl4 conintiator in CH3Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at −80°C. After the living, narrow molecular weight, distribution PIB (Mw/Mn = 1.1-1.2) has reached the desired molecular weight, styrene (St) together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to block PSt from the living chain ends. Uncontrolled initiation by protic impurities that produces PSt contamination is prevented by the use of DtBP. PSt-PIB-PSt blocks obtained in the absence of additives are contaminated by homopolymer and /or diblocks due to inefficient blocking and initiation by protic impurities, and exhibit poor physical properties. In contrast in the presence of the strong ED N,N-dimethylacetamide (DMA) and DtBP the blocking of St from living PIB chain occurs efficiently and block copolymers exhibiting good mechanical properties can be prepared. Virgin TPEs can be repeatedly compression molded without deterioration of physical properties. The products exhibit a low and a high temperature Tg characteristic of phase separated PIB and PSt domains. Transmission electron microscopy of linear triblocks containing ∼ 34 wt % PSt also indicates microphase separation and suggests PSt rods dispersed in a PIB matrix.

Polyethylene glycol derivatives for solid-phase applications

Abstract: The present invention pertains to polyethylene glycol (PEG) derivatized graft supports, to methods for making these supports and to methods of using the supports to synthesize peptides by solid-phase synthesis techniques. The PEG-graft supports of this invention comprise functionalized PEG derivatives which are covalently attached to solid supports, such as polystyrene.

Blends of styrene/maleic anhydride copolymers with polymethacrylates

Abstract: The phase behavior of a series of styrene/maleic anhydride (SMA) copolymers with various polyacrylate and polymethacrylate homopolymers has been investigated using various techniques. None of the polyacrylates are miscible with SMA copolymers. Poly (methyl methacrylate) (PMMA) poly(ethyl methacrylate) (PEMA) and poly(n-propyl methacrylate) (PnPMA), are miscible with these copolymers over a certain range of maleic anhydride contents; whereas, the higher methacrylates apparently have no region of miscibility. For PEMA and PnPMA, the miscibility windows extend through 0% MA; hence, polystyrene is miscible with these polymethacrylates although the lower critical solution temperature is quite low. The exothermic heat of mixing styrene and ester analogs found here supports the observed miscibility of polystyrene with ethyl, n-propyl, and cyclohexyl (reported elsewhere) methacrylates. Lattice fluid interaction parameters for styrene-methacrylate obtained from the cloud points of these blends agree quite well with the Flory—Huggins parameters obtained from copolymer miscibility windows.

Styrene maleic anhydride and styrene glycidyl methacrylate copolymers as in situ reactive compatibilizers of polystyrene/nylon 6,6 blends

Abstract: The reactive type copolymers styrene maleic, anhydride (SMA) and styrene glycidyl methacrylate (SG) are used as in situ compatibilizers in polyblends of polystyrene (PS) and nylon 6, 6 (N66). Both copolymers can react with N66 to form copolymers as effective compatibilizers to reduce interfacial tension and increase phase adhesion. However, the toughness of the compatibilized blends is significantly lower than of the corresponding noncompatibilized blends. Only a small fraction of SMA is actually reacted in a typical melt blending, and SG copolymer seems to be more reactive than SMA. The unreacted copolymers are expected to be distributed mostly in the PS phase because of their structural similarity. The reacted copolymers are not exclusively distributed along the interface; some may distribute in both matrices. SMA is known as a very brittle polymer, and the way it is distributed can greatly influence the toughness of the resulting blends. PS is also very brittle relative to N66, and moreover a high amount of SMA in the N66 phase is detrimental since N66 is responsible for the toughness of PS/N66 blends. The better compatibilized blends have the tendency to bring more SMA and reacted SMA into the N66 phase. The relative detrimental effect on the inherent toughness of N66 is much more severe than in case of PS, if they contain the same amount of SMA. This study demonstrates that polyblends with good compatibilizers do not guarantee toughness improvement. The way the compatibilizers affect the inherent properties of the matrix needs also to be taken into consideration.

Effects of blending on local chain dynamics and glass transition: Polystyrene/poly(vinyl methyl ether) blends as studied by high‐resolution solid‐state 13C nuclear magnetic resonance spectroscopy

Abstract: To evaluate effects of blending on molecular motion of the individual polymer components in a compatible polymer blend, polystyrene/poly(vinyl methyl ether)(PS/PVME), the temperature dependence of 13C nuclear magnetic resonance linewidth for CH carbon resonance of PVME was studied under conditions of magic‐angle spinning and proton dipolar decoupling. The observed temperature dependence was satisfactorily explained by assuming the following effects of molecular motion: (1) averaging the dispersion of isotropic chemical shifts in the glassy state and (2) the interference between local anisotropic motion and high‐power proton decoupling. The activation parameters for motion of PVME of the blends were determined, and the compositional dependence is discussed. It is concluded that microscopically homogeneous mixing is achieved for PS/PVME blends.

Segmental adsorption energies for polymers on silica and alumina.

Abstract: Segmental adsorption energies for polymers on inorganic solids were determined from adsorption/desorption transitions in binary solvent mixtures which were measured by thin layer chromatography. Polystyrene, poly(methyl methacrylate), poly(butyl methacrylate), poly(tetrahydrofuran) and poly(ethylene oxide) were classified according to their adsorption strength on silica and alumina. A consistent trend with respect to the adsorption energy was observed for both substrates.

A spectroscopic study of phase-transition kinetics in syndiotactic polystyrene

Abstract: The degree and kinetics of the transformation of crystallites containing a helical chain conformation into those containing an all-trans chain conformation in solution cast syndiotactic polystyrene films are studied. The amount of phase transformation above the transition temperature is highly dependent upon sample morphology and therefore their thermal history. Imperfections in films cast from solution cannot be removed by annealing at low temperatures. Extensive phase transformation was observed to occur very rapidly above a critical temperature of 192 o C for cast films annealed at 150 o C