Showing papers on "Polymer blend published in 1995"

Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions

Abstract: The photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. We describe a novel phase‐separated polymer blend (composite) made with poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene], MEH‐PPV, as donor and cyano‐PPV, CN‐PPV, as acceptor. The photoluminescence and electroluminescence of both component polymers are quenched in the blend, indicative of rapid and efficient separation of photogenerated electron‐hole pairs with electrons on the acceptor and holes on the donor. Diodes made with such a composite semiconducting polymer as the photosensitive medium show promising photovoltaic characteristics with carrier collection efficiency of 5% electrons/photon and energy conversion efficiency of 0.9%, ∼20 times larger than in diodes made with pure MEH‐PPV and ∼100 times larger than in diodes made with CN‐PPV. The photosensitivity and the quantum yield increase with reverse bias voltage, to 0.3 A/W and 80% electrons/photon respectively at −10 V, comparable to results obtained from photodiodes made with inorganic semiconductors.

Monte Carlo and molecular dynamics simulations in polymer science

Abstract: 1. Introduction. General Aspects of Computer Simulation Techniques and Their Applicaitons in Polymer Physics 2. Monte Carlo Methods for the Self-Avoiding Walk 3. Structure and Dynamics of Neutral and Charged Polymer Solutions: Effects of Long-Range Interactions 4. Entanglement Effects in Polymer Melts 5. Molecular Dynamics of Glassy Polymers 6. Monte Carlo Simulations of the Glass Transition of Polymers 7. Monte Carlo Studies of Polymer Blends and Block Copolymer Thermodynamics 9. Computer Simulations of Tethered Chains

Drop Breakup and Coalescence in Polymer Blends - The Effects of Concentration and Compatibilization

Abstract: This study shows that a limiting dispersed phase particle size exists at very low concentrations for polymer blends mixed in an internal batch mixer and two types of twin-screw extruders. The Taylor limit for breakup of a single drop in a matrix underpredicts the limiting particle size; this discrepancy is attributed to viscoelastic effects. For uncompatibilized blends, the final particle size increases with the dispersed phase concentration due to increased coalescence. The particle size distribution also broadens at higher concentrations. Using in-situ reaction during blending or adding premade diblock copolymers suppresses coalescence resulting in smaller particle size and narrower particle size distribution. Using premade block copolymers is not as efficient in stabilizing morphology as using reactive polymers. It is shown that the main advantage of using compatibilizers in polymer blends is the suppression of coalescence achieved through stabilizing the interface, not a reduction in the interfacial tension. There is a critical shear rate in polymer systems where a minimum particle size is achieved. A qualitative explanation of why this occurs is given based on droplet elasticity

Design of electrical conductive composites : key role of the morphology on the electrical properties of carbon black filled polymer blends

Abstract: Effect of carbon black (CB) on the morphology of filled polyethylene (PE)/polystyrene (PS) blends has been investigated by image analysis of optical micrographs (2-D analysis) and by the selective extraction of one phase of the binary blends (3-D analysis). The macroscopic electrical resistivity of the filled polyblends strongly depends on the selective localization of CB in one phase or at the interface and above all on the double percolation, i.e. percolation of the polymer phases and percolation of the CB particles. The selective localization of CB in the PE phase has remarkable effects on the polyblend phase morphology. The phase cocontinuity is indeed extended over a much larger composition range, and the phase morphology is stabilized toward post-thermal treatment at 200 °C. In the case of double percolation and selective localization of CB at the polyblend interface, electrical conductivity is observed at a CB content as low as 0.4 wt %.

History of commercial polymer alloys and blends (from a perspective of the patent literature)

Abstract: Polymer blends are defined as mixtures of at least two polymeric species. Thus, the first patent polymer blend was a mixture of natural rubber, NR, with gutta percha patented by Alexander Parkes, an artist of Birmingham, in 1846. The first man-made polymer, nitrocellulose, NC was prepared by Braconnot in 1833. The resin was commercialized in 1868, but its first blends (with NR) were patented three years earlier. The first patent on blends of two synthetic polymers was granted in 1928 for poly(vinylchloride)/poly(vinylacetate), PVC/PVAc (latex blending). During the intervening 65 years, the polymer blend patent literature grew at an exponential rate; since 1983 the annual output has doubled, to exceed 3000 patents/year in 1993.

Chemical treatment of membranes of a polymer blend

Abstract: Sodium hypochlorite solutions are used to treat membranes prepared from a polymeric blend containing poly(vinyl pyrrolidone) (PVP) to increase their water permeability. Sodium hypochlorite affects the membrane material in such a way that PVP is selectively removed from the membrane matrix. The mechanism of the reaction between hypochlorite and PVP is investigated by several chemical analysis techniques of the reaction products. Strong indications are found that the reaction involves chain scission of PVP according to a radical mechanism.

Chemical treatment of membranes of a polymer blend: Mechanism of the reaction of hypochlorite with poly(vinyl pyrrolidone)

Abstract: Sodium hypochlorite solutions are used to treat membranes prepared from a polymeric blend containing poly(vinyl pyrrolidone) (PVP) to increase their water permeability. Sodium hypochlorite affects the membrane material in such a way that PVP is selectively removed from the membrane matrix. The mechanism of the reaction between hypochlorite and PVP is investigated by several chemical analysis techniques of the reaction products. Strong indications are found that the reaction involves chain scission of PVP according to a radical mechanism.

Polymerization of styrene in supercritical co2-swollen poly(chlorotrifluoroethylene)

Abstract: The heterogeneous (solid/supercritical fluid solution) free-radical polymerization of styrene in supercritical carbon dioxide-swollen poly(chlorotrifluoroethylene) (PCTFE) polymer film (63 mil) has been studied as an approach to polymer blend preparation Decompression followed by thermal initiation using AIBN or tert-butyl perbenzoate yields polymer blends with the polystyrene trapped inside the matrix polymer Polymerization prior to decompression yields more extensively modified products Polystyrene content and the distribution of polystyrene in the blend can be controlled by adjusting the concentration of styrene in the supercritical fluid or by controlling the time that the PCTFE film is in contact with the fluid The control imparted is consistent with the phase behavior and absorption kinetics of the styrene-CO 2 -PCTFE system Transmission electron microscopy and energy dispersive X-ray analysis (EDX) indicate that the polystyrene exists as discrete phase-segregated regions throughout the thickness of the PCTFE film Thermal analysis of blends and infrared data from extraction experiments indicate that radical grafting reactions do not occur to any significant extent EDX data indicate that blends with composition gradients of adjustable degrees of severity can be produced by using soaking periods of shorter duration than is required to achieve equilibrium solubility of the monomer in the substrate

Free-Volume Hole Properties of Polymer Blends Probed by Positron Annihilation Spectroscopy: Miscibility

Abstract: Positron annihilation lifetime (PAL) spectroscopy has been utilized to investigate the free-volume hole properties of two types of polymer blends, a miscible blend of tetramethyl-Bisphenol A polycarbonate (TMPC) and polystyrene (PS) and an immiscible blend of Bisphenol A polycarbonate (PC) and PS. Larger fractional hole volumes are observed in TMPC than in PC in order to form a miscible blend with PS. In miscible blends, the free volume shows a negative deviation due to blending. In immiscible blends, the relationship between the free volume as detected by positronium annihilation and the weight fraction is complicated due to the presence of interfaces. The free-volume hole distribution is additive in miscible blends, while a significant broadening is observed in immiscible blends. The observed negative deviation of the free-volume hole fraction in miscible blends is interpreted in terms of segmental conformation and packing between dissimilar polymers.

Polymer blend latex films : morphology and transparency

Abstract: Latex blend films were prepared from mixtures of two types of particles in dispersion, one composed of a high-T g polymer [poly(methyl methacrylate), PMMA] ; the other a copolymer of butyl methacrylate and butyl acrylate [P(BMA-co-BA)] with T g ≤ 10 °C. Transparent films were obtained under air-drying conditions if the PMMA particles had diameters less than ∼250 nm and if the volume fraction of low-T g latex polymer exceeded a certain critical fraction Φ c . Values of Φ c varied over a narrow range (0.40-0.50) with P(BMA-co-BA) particle size, and were independent of the T g of the soft latex, ranging from ca. -35 to +10 °C. Film morphologies were examined by scanning electron microscopy and by freeze-fracture transmission electron microscopy. In all films, the hard particles retain their original size and spherical shape. In the transparent films, they are uniformly distributed in a polymer matrix generated from deformed soft particles, whereas clustering of PMMA microspheres is observed in turbid films. Various factors, such as increasing the size ratio between the two types of particles, removing of surfactant in the systems, and annealing of the films after drying, disrupt the uniform particle packing required for transparent films.

Interfacial Tension Reduction in Polystyrene/Poly(dimethylsiloxane) Blends by the Addition of Poly(styrene-b-dimethylsiloxane)

Abstract: The effects of diblock copolymer addition on the interfacial tension of immiscible homopolymer blends are examined for the ternary system comprising polystyrene (PS), poly(dimethylsiloxane) (PDMS), and poly(styrene-b-dimethylsiloxane) [P(S-b-DMS)]. Interfacial tension is measured, as a function of the diblock copolymer concentration and the molecular weight of PDMS, using an automated pendant drop tensiometer. The interfacial tension of the blend initially decreases upon an increase in the copolymer concentration and then attains a constant value above a certain critical concentration. A maximum interfacial tension reduction of 82% is achieved at a critical concentration of 0.002% diblock copolymer. At a fixed PS molecular weight, the reduction in interfacial tension increases and the critical concentration decreases with an increase in the PDMS molecular weight. These results are compared to the predictions of Leibler's theory for copolymer brushes wherein the critical concentration can be attributed either to saturation of the interface (i.e., for the dry brush case) or to the onset of copolymer micelle formation (i.e., for the wet brush case). The degree of interfacial tension reduction is found to be dependent on the sample preparation procedure. When the copolymer is mixed into the PS phase, the amount of interfacial tension reduction is much less than the reduction when it is blended into the PDMS phase. This behavior suggests that the polymer blend interface may act as a kinetic trap that limits the attainment of global equilibrium in these systems.

Polyolefin compositions exhibiting heat resistivity, low hexane-extractives and controlled modulus

Abstract: The subject invention provides a polymer mixture having high heat resistivity, low hexane extractive and controllably lower or higher modulus. The mixture is comprised of at least one first substantially linear ethylene polymer, Component (A), and at least one second ethylene polymer which is a homogeneously branched polymer, heterogeneously branched linear polymer or a non-short chain branched linear polymer. When fabricated into film, the mixture is characterized by a heat seal initiation temperature which is substantially lower than its Vicat softening point as well as a high ultimate hot tack strength. When fabricated as a molded article, the mixture is characterized by high microwave warp distortion while maintaining a lower modulus. The polymer mixture is particularly well-suited for use in multilayer film structures as a sealant layer for such applications as cook-in packages, hot-fill packages, and barrier shrink films. In molding applications, the mixture is well-suited as freezer-to-microwave food storage containers and lids which maintain good flexibility at low temperature to allow easy openability of such containers.

Solvent crazing of polymers

Abstract: Part 1 Structural aspects of polymer cold drawing: conditions providing development of polymer fibrillar structure structure of solid polymers specific features of molecular mobility in glassy and semicrystalline polymers model description of polymer cold drawing the effect of surface active liquid environment on polymer fibrillar structure the role of surface active environment Part 2 Dynamics of solvent crazing: craze nucleation craze tip advance craze thickening dynamics of solvent crazing and fine structure of crazes final stage of solvent crazing - collapse of porous craze structure of solvent crazes Part 3 Solvent crazing and mechanical response of polymer: critical strain for solvent crazing fracture mechanics tensile drawing with a constant strain rate polymer drawing under constant stress Part 4 Structure and properties of the solvent-crazed polymers: mechanical properties of solvent-crazed polymers thermomechanical properties of solvent-crazed polymers adsorption properties of solvent-crazed polymers specific features of transport of non-volatile components from the craze volume of solvent-crazed polymers Part 5 Delocalized solvent crazing: specific features of solvent crazing in semicrystalline polymers delocalized solvent crazing and new ways of preparation of polymer blends Part 6 Structure and properties of low-molecular-mass compounds introduced into craze structure: direct method of preparation of polymer/(low-molecular-mass compound) blends via solvent crazing indirect method of introduction of low-molecular-mass compounds into craze structure Part 7 Applied aspects of solvent crazing: solvent-crazed polymers as porous adsorbents and membranes development of transverse relief of the surface of polymer films and fibers fibrillation of polymer films solvent crazing as a universal means of introduction of various additives into polymer films and fibers

Crystallization and compatibility of poly(vinyl alcohol)/poly(3‐hydroxybutyrate) blends: Influence of blend composition and tacticity of poly(vinyl alcohol)

Abstract: Compatibility of a crystalline/crystalline polymer blend, poly(vinyl alcohol) (PVA)/poly(3-hydroxybutyrate) (PHB), was studied by high-resolution solid-state 13C-NMR spectroscopy. The 1H T1 measurement demonstrated that both the compatibility and the domain size depend on the composition of the blend. The PVA/PHB blend is compatible only when the blend contains a large amount of PVA. The domain sizes of the compatible blend are less than 200 A. In the pulse saturation transfer (PST) MAS NMR spectra, the carbonyl carbon resonance from PHB showed a downfield shift, which indicates that the compatibility of the PVA/PHB blends is due to the hydrogen-bonding interaction in the amorphous phase. The DSC measurement showed that the compatible blends adopt low crystallinity for both PHB and PVA. The crystallization in these blends is likely to be distributed by the hydrogen-bonding interaction in the amorphous phase. The compatibility of PVA/PHB is also affected by the tacticity of PVA. The compatible composition range of the syndiotacticrich PVA/PHB blend is wider than that of the atactic-PVA/PHB blend. It is likely that the capacity to form the hydrogen bond depends on the tacticity of PVA. © 1995 John Wiley & Sons, Inc.

Supramolecular Polymer Interactions Based on the Alternating Copolymer of Styrene and Maleimide

Abstract: Supramolecular interactions between the alternating copolymer of styrene and maleimide with melamine and with the copolymer of styrene and 2,4-diamine-6-vinyl-1,3,5-triazine are investigated. The results show that multiple hydrogen-bonding can give rise to high compatibility. The polymer blends are all amorphous

Adhesive tape compositions and method for covering roofs

Abstract: An adhesive tape composition includes a polymer blend comprising at least one EPDM rubber, and preferably three EPDM rubbers in substantially equal amounts, and an adhesive-enhancing polymer selected from the group consisting of polyisoprene, polybutadiene, and ethylene-propylene copolymer and mixtures thereof. The tape adhesive composition further includes at least one tackifying additive compatible with said polymer blend and a sulfur and organic accelerator cure package for said polymer blend, the adhesive composition being devoid of butyl rubber which is found in most other adhesive tape compositions. This composition is seen as providing excellent long-term heat aging, weathering resistance, and low temperature properties as compared to adhesive tape compositions containing butyl rubber. Moreover, the adhesive tape composition provides more surface tack, better "quick-grab", and higher green strength as compared to adhesive tape compositions containing 100 percent EPDM rubber. A method is also provided for covering roofs which includes the step of employing the adhesive tape composition.

Phase behavior of linear/branched polymer blends

Abstract: The phase behavior of a linear/branched polymer blend is predicted within the framework of the Flory-Huggins theory. The linear polymer is treated as monodisperse and the branched polymer as polydisperse with power law statistics, O(N) ∞ N -(τ-1) , cut off at some upper degree of polymerization N 2 . The latter is dependent on the reacted fraction, α, and the functionality, f, of the functional groups of the branched polymer. We calculate analytically the spinodal curves for various α up to the gel point and find unusual behavior of the critical point. In particular, it is found to be very sensitive to the exponent of the power law distribution function, e.g., whether τ takes the classical value of 2.5 or the percolation value of 2.20. Example cloud point curves and coexistence curves have been calculated numerically, again for various α, and a picture of the evolution of the phase diagram during cross-linking has been constructed. The coexistence curves are surprisingly steep as χ is varied over a large range ; this is particularly evident for the parameters of the linear-rich phase. Hence it is found that although the distribution of the branched polymer in the linear-rich phase varies considerably with increasing χ, the ratio of linear and branched polymer volume fractions within this phase does not. From our results we are able to predict, at least qualitatively, a secondary phase separation that is known to occur in such blends.

The development of laminar morphology during extrusion of polymer blends

Abstract: Studies of the microstructure and permeability of extruded ribbons of polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) and polyethylene (PE)/polyamide-6 (PA-6) blends have shown that it is possible to control the flow-induced morphology to generate discontinuous overlapping platelets of EVOH or PA-6 dispersed phase in a PP or HDPE matrix phase. The effects of the following factors on morphology development and blend properties were considered: blending sequence, melt temperature, composition, compatibilizer level, die design, screw type, and cooling conditions. The impact properties and interfacial adhesion of laminar blends of PP and EVOH were improved without diminishing the barrier properties. The oxygen and toluene permeability of extruded samples with EVOH content of 25 vol% resembled values obtained with multilayer systems. Processing conditions had a major influence on the morphology of blends of high.density polyethylene and polyamide-6 (HDPE/PA-6), and, under special processing conditions, laminar morphology was obtained in this system. The toluene permeability of extruded ribbons of HDPE/PA-6 blends was in the range obtained with multilayer systems

Pressure Dependence of Polymer Fluids: Application of the Lattice Cluster Theory

Abstract: The lattice cluster theory is used to analyze the pressure dependence of the effective Flory interaction parameter X eff observed in recent small-angle neutron scattering experiments for polymer blends. A description of this pressure dependence in blends requires a theory that contains a minimum of four empirical parameters, three interactions energies and one lattice cell volume, a set smaller than in the seven- or eight-parameter treatments generally employed with other methods. The conventional liquid mixture philosophy is used for determining this minimal set of parameters as follows : The self-interaction parameters and pure component cell volumes are obtained from fits to pure melt PVT data. A common combining rule then provides the blend cell volume as functions of those for the pure melts, but the common geometric combining rule for the heterocontact interaction energy is found to be grossly inadequate. Hence, this interaction parameter is chosen by fitting to blend data. Explicit comparisons with experimental data for polystyrene (PS) and poly(vinyl methyl ether) (PVME) melts, PS/PVME blends, and PS-b-PMMA (poly(methyl methacrylate)) diblock copolymers demonstrate that this minimal lattice cluster theory provides a good representation of melt equations of state, the composition, temperature, molecular weight, and pressure dependence of the small-angle neutron scattering, the composition dependence of the volume change on mixing, the spinodal curves, and the composition and temperature dependence of the blend correlation length. Additional predictions are presented concerning the stabilization and destabilization of blends by diblock copolymers.

Separation of MTBE-Methanol Mixtures by Pervaporation

Abstract: Membranes made of a polymer blend of poly(acrylic acid) and poly(vinyl alcohol) were evaluated for the separation of methanol from methyl tert-butyl ether (MTBE) by pervaporation. The influence of the blend composition and the feed composition on the pervaporation performance were investigated. Methanol permeates preferentially through all tested blend membranes, and the selectivity increases with increasing poly(vinyl alcohol) content in the blends. However, a flux decrease is observed with increasing poly(vinyl alcohol) content. With increasing feed temperature the flux increases, and the selectivity remains constant. In addition, the influence of crosslinking on the permselectivity was investigated. The pervaporation flux decreases with increasing crosslinking density, but the selectivity is enhanced. This is due to a more rapid decrease in the component flux of MTBE compared to that of methanol.