Showing papers on "Polymer blend published in 1997"

Factors Affecting the Height and Phase Images in Tapping Mode Atomic Force Microscopy. Study of Phase-Separated Polymer Blends of Poly(ethene-co-styrene) and Poly(2,6-dimethyl-1,4-phenylene oxide)

Abstract: Blends of two polymers, poly(ethene-co-styrene) (PES) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), were examined with tapping mode atomic force microscopy (AFM) using various values of the driving amplitude A0 and set-point amplitude ratio rsp = Asp/A0, where Asp is the set-point amplitude. In height and phase images of PPO/PES blend samples, the relative contrast of chemically different regions depends sensitively on the rsp and A0 values. As the tip−sample force is increased from small to large, both phase and height images of PPO/PES blend samples can undergo a contrast reversal twice. This makes it difficult to assign the features of height and phase images to different chemical components without performing additional experiments. Phase and height images were interpreted by analyzing several factors that affect the dependence of phase shift and amplitude damping on rsp and A0.

Efficient white light-emitting diodes realized with new processable blends of conjugated polymers

Abstract: An alternative method for producing efficient white light-emitting polymer diodes based on a blend of two polymers is reported. The white light emission is composed of a broad blue emission of laddertype (polyparaphenylene) (m-LPPP) and a red-orange emission of a new polymer, poly(perylene-co-diethynylbenzene) (PPDB). The red-orange electroluminescence emission is promoted by an excitation energy and charge transfer from m-LPPP to the PPDB. A concentration of 0.05% PPDB in the polymer blend is required in order to obtain white light emission. By inserting an insulating material in the blend, so that a maximum external quantum efficiency of 1.2% is obtained.

Efficient organic electroluminescent devices using single-layer doped polymer thin films with bipolar carrier transport abilities

Abstract: Detailed studies of electroluminescent devices made from single-layer doped polymer blend thin films having bipolar carrier transport abilities are presented. The active organic layer consists of the hole-transport polymer poly(N-vinylcarbazole) (PVK) containing dispersed electron-transport molecules, as well as different fluorescent small molecules or polymers as emitting centers to vary the emission color. Both the photoluminescence and electroluminescence (EL) properties are extensively studied. In photoluminescence, very efficient transfer of energy can occur from the host to very dilute (/spl sim/1 wt.%) amounts of emitting materials. When covered with a metal layer, the intensity of photoluminescence from blend thin films was found to be dependent on the type of metal coverage. The optical and electrical properties of materials and devices were systematically studied to understand the operating mechanisms and to optimize the devices. In EL, excitons appear to be formed at doped emitting centers, rather than in the host. We show that in an optimized device, a relatively high external quantum efficiency (>1%, backside emission only) and a low operating voltage (<10 V for over 100 cd/m/sup 2/) can be easily achieved by this class of devices. It was also found air-stable Ag is as good as reactive Mg-Ag alloy for the cathode contact in devices using PVK containing dispersed electron-transport oxadiazole molecules.

Dielectric spectroscopy of polymeric materials : fundamentals and applications

Abstract: FUNDAMENTALS OF DIELECTRIC MATERIALS 1. Theory of Dielectric Properties 2. Broadband Dielectric Measurement Techniques 3. Dielectric Properties of Amorphous Polymers 4. Dielectric Spectroscopy of Semicrystalline Polymers 5. Calculation of Dipole Moments and Correlation Parameters 6. Unbiased Modeling of Dielectric Dispersions 7. Application High-Frequency Dielectric Measurements of Polymers 8. Thermally Stimulated Currents of Polymers APPLICATION OF DIELECTRIC SPECTROSCOPY TO POLYMER SYSTEMS 9. Dielectric Relaxation in Polymer Solutions 10. Dielectric Studies of Polymer Blends 11. Dielectric Monitoring of Polymerization and Cure 12. Dielectric Properties of Polymeric Liquid Crystals 13. Dielectric Properties of Fluoropolymers 14. Dielectric Studies of Polymeric Nonlinear Optical Materials 15. Broadband Dielectric Spectroscopy on Collective and Molecular Dynamics in Ferroelectric Liquid Crystals

Effect of shear history on the morphology of immiscible polymer blends

Abstract: In this paper we study how the steady state morphology during shear of an incompatible blend can be affected by the initial conditions. By means of rheological experiments it is shown that below a ...

Solution rheology of a hydrophobically modified alkali-soluble associative polymer

Abstract: Rheological and photophysical data are presented for a hydrophobically modified alkali-soluble copolymer, of a constitution similar to materials currently employed as rheology modifiers in water-borne coatings. The copolymer comprises a polyelectrolyte backbone bearing ethoxylate side chains capped with complex alkylaryl groups of a high molar volume. In aqueous alkaline media, the hydrophobes associate dynamically, the topology of the network so formed being dependent on the polymer concentration. Photophysical studies, employing pyrene as a hydrophobic fluorescent probe, indicate the presence of hydrophobic associations. At concentrations below the coil overlap concentration, c*, these associations are predominantly intramolecular. At higher polymer concentrations, intermolecular interactions become more probable. This change in network topology is in qualitative agreement with previous theoretical considerations of associative polymer systems and is reflected in an unusually high concentration dependen...

Compatibilization of polyethylene terephthalate/polypropylene blends with styrene–ethylene/butylene–styrene (SEBS) block copolymers

Abstract: Blends of polyethylene terephthalate (PET) and polypropylene (PP) at compositions 20/80 and 80/20 were modified with three different styrene–ethylene/butyl–ene-styrene (SEBS) triblock copolymers with the aim of improving the compatibility and in particular the toughness of the blends. The compatibilizers involved an unfunctionalized SEBS and two functionalized grades containing either maleic anhydride (SEBS-g-MAH) or glycidyl methacrylate (SEBS-g-GMA) grafted to the midblock. The effects of the compatibilizers were evaluated by studies on morphology and mechanical, thermal and rheological properties of the blends. The additon of 5 wt % of a SEBS copolymer was found to stabilize the blend morphology and to improve the impact strength. The effect was, however, far more pronounced with the functionalized copolymers. Particularly high toughness combined with rather high stiffness was achieved with SEBS-g-GMA for the PET-rich composition. Addition of the functionalized SEBS copolymers resulted in a finer dispersion of the minor phase and clearly improved interfacial adhesion. Shifts in the glass transition temperature of the PET phase and increase in the melt viscosity of the compatibilized blends indicated enhanced interactions between the discrete PET and PP phases induced by the functionalized compatibilizer, in particular SEBS-g-GMA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:241–249, 1997

Conjugated polymer surfaces and interfaces

Abstract: The doping of a conjugated polymer, polyacetylene, to a state of high electrical conductivity in 1977 marked a distinct step in interest in the electronic and transport properties of electrically conducting organic materials Since 1990, however, undoped semiconducting conjugated polymers have emerged as potentially useful electronic materials in a variety of electronic and optoelectronic applications In the context of polymer–based electronic device applications, it is of critical importance to understand the nature of the electronic structure of the polymer surface and the polymer–metal interface It has been shown that, especially for conjugated polymers, photoelectron spectroscopy provides a maximum amount of both chemical and electronic structural information within a single measurement technique This contribution contains an overview of some details of the early stages of interface formation with metals on the surfaces of conjugated polymers and model molecular solids, as studied using photoelectron spectroscopy The materials chosen are especially of interest in connection with polymer-based light emitting devices, or LEDs Specifically, the materials involved include poly( p –phenylenevinylene), or PPV, and a series of substituted PPVs, as well as a diphenylpolyene molecule for PPV, namely, α,ω–diphenyltetradecaheptaene Some general trends in the behaviour of light–metal atoms on the clean surfaces of conjugated polymers are pointed out Some consequences, based upon the information obtained in the studies reviewed, are highlighted Finally, two recent issues, which are studied by the methods used for the metal–on–polymer interfaces studies, are covered: the role of water vapour on the electronic structure of PPV; and the use of phase–separated polymer blends to increase the quantum efficiency of blue light emitting diodes

Polymer blends based on polyolefin elastomer and polypropylene

Abstract: A new family of homogeneous polyolefin polymers that exhibit unique molecular and rheological properties designated polyolefin elastomers (POEs) are characterized by a narrow molecular weight and high degrees of comonomer distribution. Because these copolymers are often elastomeric in nature, one of the uses for these materials is as impact properties improver for brittle polymers such as polypropylene at low temperatures. In this work a study was carried out about the effectiveness of the polyethylene elastomer (POE) as an impact modifier for polypropylene in relation to the traditional modifier EPDM. In this study the flow properties of of the POE/PP and EPDM/PP blends were also evaluated. The blends were analyzed by solid-state 13C nuclear magnetic resonance (13C-NMR) spectroscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The results showed that PEE/PP and EPDM/PP blends present a similar crystalline behavior, which resulted in a similar mechanical performance of the blends, on the composition analyzed. It was also verified that the POE/PP blend presents lower torque values than the EPDM/PP blend, which indicates a better processability when POE is used as an impact modifier. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2005–2014, 1997

Golf ball incorporating grafted metallocene catalyzed polymer blends

Abstract: The disclosed invention provides novel golf ball compositions which contain non-ionic olefinic copolymers produced by use of metallocene catalysts, wherein the metallocene catalyzed polymers have been functionalized with a post-polymerization reaction. The grafted metallocene catalyzed polymers may be blended with ionomers, non-grafted metallocene catalyzed polymers, or other non-ionomeric polymers. These compositions exhibit improved mechanical properties such as tensile and flexural properties, and can be foamed or unfoamed. Golf balls that employ at least one layer of these compositions in any of the golf ball cover, core, or a mantle situated between the cover and the core provide ball properties and performance similar to and in some cases better than the state of the art ionomer based golf balls.

pH sensitivity and ion sensitivity of hydrogels based on complex‐forming chitosan/silk fibroin interpenetrating polymer network

Abstract: A novel natural polymer blend, namely, a semi-interpenetrating polymer network (semi-IPN) composed of crosslinked chitosan with glutaraldehyde and silk fibroin was prepared. The FTIR spectra of the semi-IPN manifested that the chitosan and silk fibroin had a strong hydrogen-bond interaction and formed an interpolymer complex. The semi-IPN showed good pH sensitivity and ion sensitivity. According to the different swelling ratios of the semi-IPN in the buffer solution with different pH values or the AlCl3 aqueous solution with different concentrations, the semi-IPN could swell and shrink while being put alternately into different pH buffer solutions or AlCl3 aqueous with different concentrations. The semi-IPN could also act as an ''artificial muscle'' because its swelling-shrinking behavior exhibited a fine reversibility. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2257-2262, 1997

Polymeric Multicomponent Materials: An Introduction

Abstract: FUNDAMENTAL RELATIONSHIPS. Basic Concepts in Multicomponent Polymer Materials. Modeling Multicomponent Polymer Behavior. Fracture Behavior. POLYMER SURFACES AND INTERFACES. Basic Principles and Instruments. Polymer Chains at Surfaces and Interfaces. Strengthening the Interface. Surfaces of Advanced and Composite Systems. SELECTED ENGINEERING POLYMER MATERIAL. Rubber Toughening of Engineering Plastics. Block Copolymers and Thermoplastic Elastomers. Interpenetrating Polymer Networks. Overview and Future. Index.

Effects of coalescence and breakup on the steady-state morphology of an immiscible polymer blend in shear flow

Abstract: The steady-state morphology of an immiscible polymer blend in shear flow has been investigated by optical microscopy techniques. The blend is composed by poly-isobutylene (PIB) and poly-dimethylsiloxane (PDMS) of comparable viscosity. Experiments were performed by means of a home-made transparent parallel plate device. The two plates can be independently counterrotated, so that sheared droplets of the dispersed phase can be kept fixed with respect to the microscope point of view, and observed for long times. The distribution of drops and their average size were measured directly during flow at different shear rates and for different blend compositions. It was found that the average drop size in steady-state conditions is a decreasing function of the applied shear rate, and does not depend on blend composition for volume fractions up to 10%. Experiments have proved that, in the shear rate range which could be investigated, the stationary morphology is controlled only by coalescence phenomena, droplet breakup playing no role in determining the size of the dispersed phase. More generally, it has been shown that the steady-state morphology is a function not only of the physical parameters of the blend and of the shear rate, but also of the initial conditions applied to the blend. The steady-state results reported in this paper constitute the first direct experimental confirmation of theoretical models which describe the mechanisms of shear-induced drop coalescence.

Blends of crystalline and amorphous poly(lactide). III. Hydrolysis of solution-cast blend films

Abstract: Hydrolysis of blend films prepared from amorphous poly(DL-lactide) (a-PLA) and isotactic crystalline poly(D- or L-lactide) (c-PLA) having different c-PLA contents [X = c-PLA/(a-PLA + c-PLA)] was performed in phosphate buffered solution of pH 7.4 at 37°C. The blend films before and after hydrolysis were studied using gel permeation chromatography, tensile testing, differential scanning calorimetry (DSC), and optical rotation. The mass of the blend films remaining after hydrolysis of longer than 20 months was larger with the increasing initial X. The tensile strength of the blend films remained unchanged in the early stage of hydrolysis, followed by a rapid decrease with time, the duration of period for the tensile strength remaining unchanged was longer for the blend films of smaller X. The change in crystallinity, molecular weight, and specific optical rotation during hydrolysis of the blend films revealed that degradation took place preferentially in the amorphous region than in the crystalline region of the blend films. A double melting peak was observed in the DSC spectra of blend films with X = 0.75 and 0.5 after hydrolysis for 20 months. The time difference in the induction of reduction between the tensile strength and the mass due to hydrolysis of the blend films increased with an increase in X. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 855–863, 1997

Interfacial tension coefficient from the retraction of ellipsoidal drops

Abstract: Keywords: interfacial tension ; polymer blends ; ellipsoid retraction Reference LTC-ARTICLE-1997-011 URL: http://www3.interscience.wiley.com/cgi-bin/jhome/36698 Record created on 2006-06-26, modified on 2016-08-08

Morphological stability, interfacial tension, and dual-phase continuity in polystyrene-polyethylene blends

Abstract: The morphological stability of polystyrene high-density polyethylene (PS/PE) blend is investigated in the region of dual-phase continuity. The effect of the addition of a triblock SEBS copolymer to the blends on the stability of these morphologies, is examined. The results show that the morphology of the unmodified blends changes from co-continuous to droplet matrix for PS-rich blends whereas the morphology of a 50/50 blend maintains continuity but coarsened significantly upon annealing at 200°C. In the presence of the copolymer, these morphologies are much more stable. Selective solvent extraction of polystyrene in di-ethyl ether reveals that the level of PS continuity in the 50/50 blend is higher for the unmodified system than for the modified one. Upon annealing, the level of PS continuity significantly increases for the unmodified 50/50 PS/PE blend. The effect of the copolymer content in the blend on the interfacial tension between the two components is also investigated using the breaking thread method. The interfacial tension is found to be reduced from 5.6 to 1.1 mN/m by the addition of 20 parts of the copolymer to the blend. © 1997 John Wiley & Sons, Inc.

Method for producing a diffusion barrier and polymeric article having a diffusion barrier

Abstract: A method of forming a diffusion barrier on an article of a polymer blend of (i) a high surface energy polymer and (ii) a low surface energy polymer. Most commonly the low surface energy polymer is an organosilicon polymer, as a polysilane or a polysiloxane. The surface of the article is exposed to ozone and ultraviolet radiation to form a diffusion barrier.

Clear polycarbonate and polyester blends

Abstract: A blend of polycarbonates of dihydroxydiphenyl cycloalkanes and optionally 4,4'-isopropylidenediphenol with polyesters from terephthalic acid, isophthalic acid, 1,4-cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol, having the advantage of being colorless and providing an unexpected amount of impact strength, hardness and heat resistance. The polymer blends are especially suitable for the manufacture of clear molded articles, fibers, sheeting, and film.

Morphology Development through an Interfacial Reaction in Ternary Immiscible Polymer Blends

Abstract: We studied the morphology development of ternary immiscible blends through an interfacial reaction between components. This phenomenon was observed in two ternary blend systems; one is composed of polyamide(6) (PA6), polycarbonate (PC), and poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS), and the other is composed of PA6, PC, and polystyrene (PS), where PA6 forms the continuous matrix in both blend systems. Maleinated SEBS (SEBS-gMA) or maleinated PS (PS-gMA) is incorporated with its unmodified polymer (un-SEBS and un-PS, respectively) at various ratios into the blends of PA6/PC. The blends of PA6/PC/un-SEBS and PA6/PC/un-PS show a similar phase formation in which the two dispersed polymers are stuck together in a PA6 matrix. The use of the maleinated polymers instead of their unmodified polymers in the blends of PA6/PC changes the phase formation drastically. The maleinated polymers react with amine end groups of PA6 at the interface during the melt mixing. Through this interfacial reaction, the ...

Interpretation of a New Interface-Governed Relaxation Process in Compatibilized Polymer Blends

Abstract: We have analyzed the influence of different amounts ω be of two diblock copolymers, poly(styrene-b-methyl methacrylate) (sm blend series) and poly(cyclohexyl methacrylate-b-methyl methacrylate) (cm blend series), on the morphological and rheological characteristics of a blend containing w = 7.5 wt % polystyrene in poly(methyl methacrylate) matrix. The morphological analysis is based on the sphere size distribution function, which was determined from the image analysis of the transmission electron micrographs. Using this function and assuming that all block copolymers are located at the interface, the interfacial area per copolymer joint, Σ, was calculated. From its hyperbolic dependence on ω bc the value at the critical micelle concentration, Σ cmc , was found to be about 10 nm 2 for both systems. The rheological analysis reveals that in addition to the form relaxation process, well-known for polymer blends, a new relaxation process is observed for these systems. Its relaxation time, τ β , has been studied in dependence on the amount of added block copolymers. The observed phenomena for each blend series, i.e. constant blend viscosity, slight shift of the form relaxation times τ 1 , and systematic shift of the interface governed relaxation time τ β (τ β > τ 1 ), have been interpreted quantitatively. In contrast to τ 1 , τ β is less influenced by the interfacial tension but is mainly governed by an additional contribution, the interfacial shear modulus. Formulas were derived from an expanded version of the Palierne emulsion model which allows the determination of the proposed interfacial properties from rheological measurements. In general, the interfacial tension decreases with increasing amount of block copolymer, and the decrease is more pronounced for the cm blend series. The interfacial shear modulus increases during compatibilization from 0 to amounts which are in the range of 20-30% of the interfacial tension. The decrease of interfacial tension is in good agreement with predictions from Leibler's brush model extended by Dai et al. In conclusion, it was found that the Palierne model with an nonisotropical interfacial stress state is quantitatively correct to describe the observed phenomena for those blends.

Ethylene polymer film made from ethylene polymer blends

Abstract: Fabricated articles made from formulated ethylene polymer compositions are disclosed. Films made from such formulated compositions have surprisingly good impact and tensile properties, and an especially good combination of modulus and toughness. The ethylene polymer compositions have at least one homogeneously branched substantially linear ethylene/α-olefin interpolymer and at least one heterogeneously branched ethylene polymer. The homogeneously branched substantially linear ethylene/α-olefin interpolymer has a density from about 0.89 to about 0.92 g/cm 3 and a slope of strain hardening coefficient greater than or equal to about 1.3.

Late Stages of Phase Separation in a Binary Polymer Blend Studied by Rheology, Optical and Electron Microscopy, and Solid State NMR

Abstract: The relation between rheology and the time dependent morphology of a phase-separating binary blend of polystyrene and poly(vinyl methyl ether) was investigated by heating a sample from the single-phase (at 90 °C) into the two-phase regime (at 124 °C, 16 K above the LCST) and maintaining its temperature there while measuring the evolution of the dynamic moduli G‘ and G‘‘. Morphological changes occurred slowly so that there was sufficient time to cycle the dynamic mechanical measurements repeatedly over five decades in frequency. The morphology was observed on length scales from 1 mm down to 1 nm by conventional optical microscopy combined with digital image analysis, Hoffman modulation microscopy, TEM, and WISE NMR with spin diffusion. NMR shows that major compositional changes occur mostly in the first 20 min and then the composition remains constant at about 60:40 PS/PVME for the PS-rich matrix and 5:95 PS/PVME for the PVME-rich microdomains. The PVME-rich microdomains are separated by thin layers of the...

Conformational Entropy Contributions to the Glass Temperature of Blends of Miscible Polymers.

Abstract: Because of negligible contributions of combinatorial entropy, miscibility of polymers is attributed predominantly to favorable (exothermic) enthalpic effects of mixing, i.e., to strong interactions between the blend components, which have to overcome the cohesive forces acting within the components. Miscibility of amorphous polymers usually is associated with the presence of a single glass temperature of the blend. Although stronger hetero-contact interactions are thermodynamically required for polymer miscibility, the majority of miscible binary polymer blends exhibit negative deviations of the glass temperature from values predicted by the free volume or flexible bond additivity rules, suggesting a looser packing within those blends. A reasonable explanation assumes that binary hetero-contact formation within the blend may be accompanied by local interchain orientation contributing consequently to conformational entropy changes. The smaller the induced interchain orientation by hetero-contact formation, the larger the mobility in the neighborhood of the contacts and the probability of related conformational entropy changes, causing an equivalent increase of the "free volume" within the blend, i.e., a corresponding decrease of the blend Tg, which finally can be situated below the values predicted by the additivity rules. Vice versa, the corresponding argument will hold for blends with higher interchain orientation induced by intensive exothermic hetero-contact forces.

Dynamic–Mechanical Properties of Bioartificial Polymeric Materials

Abstract: Bioartificial polymeric materials represent a new class of polymeric materials based on blends of synthetic and natural polymers, designed with the purpose of producing new materials with enhanced properties with respect to the single components. The mechanical properties of bioartificial materials prepared using poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) as synthetic components, and collagen (SC), gelatin, starch, hyaluronic acid (HA) and dextran as biological components, were investigated by dynamic mechanical thermal analysis. The materials were prepared in the form of films or hydrogels and treated by glutaraldehyde (GTA) vapour or thermal dehydration in order to reduce their solubility in water. The results indicate that SC/PVA, gelatin/PVA and starch/PVA films behave as biphasic systems, showing good mechanical properties over a wide range of temperature. It was observed that the GTA procedure affects only the biological component of the SC/PVA and gelatin/PVA blends, whilst the thermal treatment influences mainly the synthetic polymer. In the case of HA/PVA hydrogels, a modulus variation was found with the HA content related to the organization degree and perfection of the PVA network structure. It seems evident that, in the experimental conditions used, dextran/PAA mixtures behave as miscible blends showing a glass transition intermediate between those of the pure components. With both untreated and GTA-treated gelatin/PMAA blends, it was not possible to evaluate the miscibility of the systems; it could only be affirmed that these materials show good mechanical properties over a wide range of temperature. © 1997 SCI.

Phase separation morphology of spin-coated polymer blend thin films

Abstract: We present the results of a study of the morphology of phase separation in thin films of two different polymer blend systems: polystyrene/polyisoprene and polystyrene/poly(methyl methacrylate). For each blend system, the two polymer components are dissolved in a common solvent. Spin coating of the ternary solutions (polymer blend/solvent) is used to confine the blends to a thin film geometry and to produce phase separation because of rapid evaporation of the solvent (solvent quench). As a quantitative measure of the phase separation morphology the average domain area of the minority component is measured as a function of the polystyrene mass fraction. For both blend systems we identify a small range of composition corresponding to a large increase in the average domain area. We show that the strong dependence of the average domain area on spin speed allows control over the quench time of the polymer blend thin films.