Frank E. Karasz

Synthesis, doping, and electrical conductivity of high molecular weight poly(p-phenylene vinylene)

Abstract High molecular weight poly( p -phenylene vinylene) (PPV) has been synthesized starting from the monomer p -xylylene- bis (dimethylsulphonium chloride). The latter was polymerized to yield a water-soluble sulphonium salt polyelectrolyte, which was converted to PPV by the thermal elimination of (CH 3 ) 2 S and HCl from films cast from aqueous solution. The elimination reaction was studied by elemental analysis and by thermogravimetric analysis and mass spectrometry. The PPV films had good mechanical properties and could be n- and p-doped to yield material with electrical conductivities approaching those of highly doped polyacetylene. The degree of conversion of the intermediate polyelectrolyte to PPV could be controlled and the conductivities of these doped films could be related to the average conjugation length.

The sodium salts of sulphonated poly(aryl-ether-ether-ketone) (PEEK): preparation and characterization

Two complementary methods were developed to produce sulphonated poly(oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene) (SPEEK) with random, homogeneous compositions over the range of zero to one sulphonate group per repeat unit. The sodium salts (Na-SPEEK) were prepared from about 5 to 100% sodium sulphonate. They displayed excellent thermal stability. The behaviour of Tg, ΔTg and ΔCp at the glass transition as a function of composition suggested the onset of ionic clustering below 25 to 30% sodium sulphonate—an observation confirmed by preliminary SAXS studies. In particular, Tg increased sigmoidally from about 150°C for 5% Na-SPEEK to 415°C for 100% Na-SPEEK. No evidence of crystallinity was observed by d.s.c. in melted and quenched samples above 9% sodium sulphonate. The equilibrium water content at room temperature and 58% relative humidity was four molecules of water per sodium sulphonate group for all compositions. For immersed films, this value increased from 8 molecules of water per sodium sulphonate group for 38% Na-SPEEK to an indeterminably large number for 100% Na-SPEEK, which slowly dissolved. Upon re-equilibration at 58% relative humidity, the water content of the films decreased to about 5.5 molecules per sodium sulphonate group. A low temperature (−80°C to −60°C) mechanical relaxation peak was present in the films conditioned at 58% relative humidity.

Fourier transform infra-red spectroscopy on the thermo-oxidative degradation of polybenzimidazole and of a polybenzimidazole/polyetherimide blend

Abstract The thermo-oxidative degradation of the polybenzimidazole material, poly[2,2′-m-phenylene)-5,5′-bibenzimidazole] (PBI), and of a blend of PBI with the polyetherimide, poly[2,2′-bis(3,4-dicarboxyphenoxy) phenylpropane-2-phenylene bisimide] (Ultem 1000), was investigated by Fourier transform infra-red (FTi.r.) spectroscopy. An experimental protocol and the necessary instrumentation were developed for real-time monitoring of the molecular changes occurring during the process. The spectroscopic data provided information about the mechanism and the kinetics of the thermo-oxidative degradation in its early stages. The FTi.r. spectra of the PBI/Ultem 1000 blend were analysed by subtraction spectroscopy, and the application of this technique allowed us to selectively follow the fate of the two components in the blend. No chemical interaction between PBI and Ultem 1000 was detectable by FTi.r. spectroscopy during the degradation process.

Electroluminescence of pure poly(N‐vinylcarbazole) and its blends with a multiblock copolymer

Electroluminescence (EL) in pure poly(N‐vinylcarbazole) (PVK) has been observed in a simple single active layer EL device with the structure of ITO/PVK/Al (or Ca). The emitted light is violet with a maximum intensity at 426 nm; a part of the spectrum lies within the UV region. Blends of PVK with a conjugated‐nonconjugated multiblock copolymer (CNMBC) previously described are also electroluminescent. In these blends a new emission peak in the EL spectra appeared and can be attributed to the emission from an exciplex formed by the two polymers. As the composition of the aforementioned blend changes from a PVK‐poor to a PVK‐rich ratio, the emitted light changes from green to blue. Further, blends containing 97 wt. % PVK and 3 wt. % CNMBC yielded an EL spectrum with a single emission peak different in location from either that of pure PVK or the pure CNMBC; the latter is blue with a maximum intensity at 476 nm. The EL output of the blends can be clearly seen in a brightly lit room at ambient temperature. An e...

Poly(p-phenylene vinylene)-silica composite: a novel sol-gel processed non-linear optical material for optical waveguides

Abstract We report here the first case (to our knowledge) of a compatible blend of an inorganic polymer, silica glass, and a π-conjugated non-linear optical polymer, poly( p -phenylene vinylene), homogeneously miscible over wide composition ranges. This composite material was prepared by combining sol-gel processing techniques applicable to the silica glass with those used for the synthesis of the organic polymer from a water/alcohol-soluble sulphonium salt precursor. In this preparation the organic polymer precursor and the inorganic sol were mixed in a common solvent and converted to the final composite material. The thermal conversion of the precursor polymer released HCl, which catalysed the gelation of the inorganic sol. The resulting composite material has been characterized by infra-red and ultra-violet/visible spectral analysis and thermogravimetric and differential scanning calorimetric analysis. The material can be cast into various forms. Thin films cast by the doctor-blading technique exhibit good optical quality and show promise for application as optical waveguides.

Blue‐light electroluminescence from p‐phenylene vinylene‐based copolymers

Electroluminescence (EL) in the blue region of the spectrum with a maximum at 465 nm was observed from polymer films sandwiched between indium‐tin‐oxide and Al electrodes. The specially designed soluble multiblock copolymers used consisted of chromophoric units that have uniform conjugation length and are spaced with polymethylene units of various lengths. EL originates from the radiative decay of the chromophore singlet excitation created as a result of the recombination of injected charge carriers.

Conductivity anisotropy in oriented poly(p-Phenylene vinylene)

SummaryThe study of charge transport mechanisms in highly conjugated conducting polymers has historically been hampered by the complex and invariant morphologies of the best conductors. We have prepared amorphous and uniaxially oriented films of poly(p-phenylene vinylene) (PPV) which exhibit a large conductivity anisotropy proportional to the degree of molecular orientation. The conductivity of the AsF5 doped PPV, together with wide angle x-ray and IR characterization of these samples is reported.

Interaction of epoxy resins with water: the depression of glass transition temperature

Abstract The depression of T g in a number of epoxy-water systems has been investigated calorimetrically. Except where an unbalanced reaction stoichiometry was used, experimental results are in good agreement with theoretical predictions based on equations developed for the composition dependent T g in polymer diluent-systems. Thermal analysis also demonstrates a complex thermal behaviour on rescanning of samples, attributed to diluent diffusing out of the sample. The importance of this behaviour in the context of solvent-induced physical ageing of epoxy resin composites is discussed.

Poly(ethylene oxide)/poly(methyl methacrylate) blends: Influence of tacticity of poly(methyl methacrylate) on blend structure and miscibility

Abstract The influence of different configurations of poly(methyl methacrylate) on the miscibility and superstructure of poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blends was examined using small-angle X-ray scattering and differential scanning calorimetry. The blends prepared by solution casting were isothermally crystallized at 48°C. The miscibility, the melting behaviour, the glass transition temperature and the structural parameters of the blends were strongly dependent on the tacticity and blend composition. The small-angle X-ray intensity profiles were analysed using a recently developed methodology. For the poly(ethylene oxide)/atactic poly(methyl methacrylate) (PEO/APMMA) and poly(ethylene oxide)/syndiotactic poly(methyl methacrylate) (PEO/SPMMA) blends, the long period and the amorphous and transition region thicknesses increased with increase of PMMA content, whereas for the poly(ethylene oxide)/isotactic poly(methyl methacrylate) (PEO/IPMMA) blends they are independent of composition. The structural properties of the blends were attributed to the presence of non-crystallizable material in the interlamellar or interfibrillar regions, depending on PMMA tacticity. From the glass transition and melting temperatures, it has been supposed that one homogeneous amorphous phase is present in the case of PEO/APMMA and PEO/SPMMA blends and that the PEO/IPMMA amorphous system is phase-separated. The free-volume contribution to the energy of mixing for the various tactic PMMAs is hypothesized to be responsible for the difference in mixing behaviour.

Molecular orientation and conductivity in highly drawn poly(p-phenylene vinylene)

Abstract Films of poly( p -phenylene vinylene), PPV, have been prepared with various degrees of uniaxial orientation by thermal conversion and drawing of cast films of a precursor polymer. Molecular orientation was determined by X-ray diffraction and infrared dichroism as a function of the draw ratio. The crystallite size transverse to the stretch direction was also estimated by X-ray line broadening. Electrical conductivities of the PPV films, doped with AsF 5 , show a substantial enhancement in conductivity in the orientation. Conductivity in the direction perpendicular to the stretch direction decreases with increased orientation. These data may be understood in terms of the relative contributions of intrachain and interchain transport of the electronic charge carriers.