Frank E. Karasz

Bio: Frank E. Karasz is an academic researcher from University of Massachusetts Amherst. The author has contributed to research in topics: Phenylene & Miscibility. The author has an hindex of 60, co-authored 457 publications receiving 14351 citations. Previous affiliations of Frank E. Karasz include Celanese.

Phase Behavior in Copolymer Blends : Poly(2,6-dimethyl-1,4-phenylene oxide) and Halogen-Substituted Styrene Copolymers

Abstract: A recently introduced mean field theory of phase behavior in polymer/copolymer systems is extended to random copolymer/copolymer systems. Miscibility in these systems does not require any specific interaction but rather a "repulsion" between the different covalently bonded monomers of the copolymers. Conversely, immiscibility may occur in systems with specific interaction due to an "attraction" between the different covalently bonded monomers of the copolymers. Using the mean field approach, we discuss in detail the phase behavior in polymer/copolymer systems. The requirements for the occurrence of a symmetric or an asymmetric (im)miscibility window in a temperature-copolymer composition diagram are derived. Using this treatment, we calculate all the segmental interaction parameters for blends of poly(2,6-dimethyl-l,4- phenylene oxide) with poly(o-chlorostyrene-co-p-chlorostyrene), poly(o-fluorostyrene-co-p-fluorostyrene), poly(styrene-co-o-chlorostyrene), poly(styrene-co-p-chlorostyrene), poly(styrene-co-o-fluorostyrene), and poly(styrene-co-p-fluorostyrene). The absence of miscibility in blends of poly(2,6-dimethyl-l,4-phenylene oxide) with any poly(o-bromostyrene-co-p-bromostyrene) copolymer is explained.

Polaron-pair generation in poly(phenylene vinylenes).

Abstract: The effects of weak magnetic fields on the photoconductivity of poly(p-phenylene vinylene) (PPV) and two derivatives, poly(1,4-phenylene-1,2-dimethoxyphenyl vinylene) (DMOP-PPV) and poly(2-phenyl-1,4-phenylene vinylene) (PPPV), were observed within the temperature range 130\char21{}350 K. These effects are attributed to the formation of interchain pairs involving a negative polaron and a positive polaron. A polaron pair is formed as a result of interchain electron transfer from a molecular exciton. The lifetime of a pair is estimated to be within the range of ${10}^{\mathrm{\ensuremath{-}}8\char21{}}$${10}^{\mathrm{\ensuremath{-}}9}$ s. Thermal dissociation of a polaron pair produces free charge carriers, and recombination of the pair regenerates a singlet or triplet exciton on a single conjugated segment of a chain.

Solubility and properties of a poly(aryl ether ketone) in strong acids

Abstract: Proprietes des solutions diluees de poly(oxy phenyleneoxy phenylenecarbonyl phenylene-1,4) dans l'acide sulfurique et HSO 3 Cl. Modification chimique du polymere dans ces acides

Synthesis of Conjugated Polymers for Organic Solar Cell Applications

Abstract: -phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deficient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2-

Efficient photodiodes from interpenetrating polymer networks

Abstract: THE photovoltaic effect involves the production of electrons and holes in a semiconductor device under illumination, and their subsequent collection at opposite electrodes. In many inorganic semiconductors, photon absorption produces free electrons and holes directly1. But in molecular semiconductors, absorption creates electrona¤-hole pairs (excitons) which are bound at room temperature2, so that charge collection requires their dissociation. Exciton dissociation is known to be efficient at interfaces between materials with different electron affinities and ionization potentials, where the electron is accepted by the material with larger electron affinity and the hole by the material with lower ionization potential3. A two-layer diode structure can thus be used, in which excitons generated in either layer diffuse towards the interface between the layers. However, the exciton diffusion range is typically at least a factor of 10 smaller than the optical absorption depth, thus limiting the efficiency of charge collection3. Here we show that the interpenetrating network formed from a phase-segregated mixture of two semiconducting polymers provides both the spatially distributed interfaces necessary for efficient charge photo-generation, and the means for separately collecting the electrons and holes. Devices using thin films of these polymer mixtures show promise for large-area photodetectors.

Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate–polymer composites

Abstract: There have been a number of review papers on layered silicate and carbon nanotube reinforced polymer nanocomposites, in which the fillers have high aspect ratios. Particulate–polymer nanocomposites containing fillers with small aspect ratios are also an important class of polymer composites. However, they have been apparently overlooked. Thus, in this paper, detailed discussions on the effects of particle size, particle/matrix interface adhesion and particle loading on the stiffness, strength and toughness of such particulate–polymer composites are reviewed. To develop high performance particulate composites, it is necessary to have some basic understanding of the stiffening, strengthening and toughening mechanisms of these composites. A critical evaluation of published experimental results in comparison with theoretical models is given.

Alternative Polymer Systems for Proton Exchange Membranes (PEMs)

Abstract: Fuel cells have the potential to become an important energy conversion technology. Research efforts directed toward the widespread commercialization of fuel cells have accelerated in light of ongoing efforts to develop a hydrogen-based energy economy to reduce dependence on foreign oil and decrease pollution. Proton exchange membrane (also termed “polymer electrolyte membrane”) (PEM) fuel cells employing a solid polymer electrolyte to separate the fuel from the oxidant were first deployed in the Gemini space program in the early 1960s using cells that were extremely expensive and had short lifetimes due to the oxidative degradation of their sulfonated polystyrene-divinylbenzene copolymer membranes. These cells were considered too costly and short-lived for real-world applications. The commercialization of Nafion by DuPont in the late 1960s helped to demonstrate the potential interest in terrestrial applications for fuel cells, although its major focus was in chloroalkali processes. PEM fuel cells are being developed for three main applications: automotive, stationary, and portable power. Each of these applications has its unique operating conditions and material requirements. Common themes critical to all high performance proton exchange membranes include (1) high protonic conductivity, (2) low electronic conductivity, (3) low permeability to fuel and oxidant, (4) low water transport through diffusion and electro-osmosis, (5) oxidative and hydrolytic stability, (6) good mechanical properties in both the dry and hydrated states, (7) cost, and (8) capability for fabrication into membrane electrode assemblies (MEAs). Nearly all existing membrane materials for PEM fuel cells rely on absorbed water and its interaction with acid groups to produce protonic conductivity. Due to the large fraction of absorbed water in the membrane, both mechanical properties and water transport become key issues. Devising systems that can conduct protons with little or no water is perhaps the greatest challenge for new membrane materials. Specifically, for automotive applications the U.S. Department of Energy has currently established a guideline of 120 °C and 50% relative humidity as target operating conditions, and a goal of 0.1 S/cm for the protonic conductivity of the membrane. New membranes that have significantly reduced methanol permeability and water transport (through diffusion and electro-osmotic drag) are required for portable power oriented direct methanol fuel cells (DMFCs), where a liquid methanol fuel highly diluted in water is used at generally <90 °C as the source of protons. Unreacted methanol at the anode can diffuse through the membrane and react at the cathode, lowering the voltage efficiency of the cell and reducing the system’s fuel efficiency. The methanol is usually delivered to the anode as a dilute, for example, 1 M (or less), solution (3.2 wt %), and relatively thick Nafion 117 (1100 EW, 7 mil ∼ 178 μm thick) is used to reduce methanol crossover. The dilute methanol feed increases the system’s complexity and reduces the energy density of the fuel, while the thick Nafion membrane increases the resistive losses of the cell, especially when compared to the thinner membranes that are used in hydrogen/air systems. The presence of excessive amounts of water at the cathode through diffusion and electro-osmosis * To whom correspondence should be addressed. E-mail: jmcgrath@vt.edu. † Sandia National Laboratory. ‡ Case Western Reserve University. § Los Alamos National Laboratory. | Virginia Polytechnic Institute and State University. 4587 Chem. Rev. 2004, 104, 4587−4612