Host Polymer Matrices Research Articles

Photoinduced FT-IR spectroscopy and CW-photocurrent measurements of conjugated polymers and fullerenes blended into a conventional polymer matrix

In this work we present an investigation of the photoexcited states in conjugated polymer (donor) – fullerene (acceptor) interpenetrating networks embedded into conventional polymer hosts like polystyrene (PS), polyvinylcarbazole (PVK) or polyvinylbenzylchloride (PVBC) (guest – host approach), using photoinduced FT-IR spectroscopy. We discuss the influence of the specific host polymer matrices on the photoexcited states of the photoactive guests and investigate the photoinduced electron transfer by analysis of the infrared activated vibrational (IRAV) bands of poly-3-octylthiophene (P3OT) in comparative studies. Solar cells based on mixtures of poly [2-methoxy, 5-(3′,7′-dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV), a highly soluble fullerene derivative [6,6]-phenyl C 61-butyric acid methyl ester (PCBM) and a conventional polymer (PS, PVK or PVBC) are characterized. We studied the current–voltage characteristics of devices and determined the energy conversion and electron/photon conversion efficiencies.

Photoinduced ft-ir spectroscopy of conjugated polymer/fullerene composites embedded into conventional host polymer matrices

In this work, we report on the investigation of photoexcited states in conjugated polymer (donor) - fullereae (acceptor) interpenetrating networks (polythiophene derivatives — PC61BM) embedded into conventional polymer hosts like polystyrene, polyvinylcarbazole, polycarbonate or polyvinylbenzenechloride, using photoinduced FT-IR spectroscopy. We discuss the influence of specific host polymer matrices on photoexcited states of the photoactive guests via photoinduced infrared activated (IRAV) modes.

Preparation and characterization of fluorinated hybrid electrolytes

Hybrid polymer electrolytes based on copolymers of vinylidene fluoride, (VdF) and different molar ratios of hexafluoropropylene (HFP), and an electrolyte solution ethylene carbonate (EC)/propylene carbonate (PC)/LiN(CF 3SO 2) 2 have been prepared by the solvent casting technique. Thermal analysis showed that small or no interactions exist between the electrolyte solution and the host polymer matrices. Conductivities in excess of 10 −3 S/cm at room temperature were obtained. However, on isothermal heating at 55°C under vacuum, the samples showed relevant losses of the electrolyte solution, that caused the conductivity to drop by 1–2 orders of magnitude. Cationic transport numbers, t +, ranging between 0.2 and 0.3 have been measured by the Hittorf method.

An Investigation of the Ablation Behavior of Advanced Ultrahigh-Temperature EPDM/Epoxy Insulation Composites

Abstract The influence of ultrahigh temperature and shear flow on the ablation behavior of bonded composites is studied. The various composites were fabricated by either reactive injection-molding (isotropic composites) or resin-impregnation-stacking (mat reinforcement) techniques. The host polymer matrices (EPDM or epoxy), containing either carbon/refractory fibers or inert/interactive particles, were examined following exposure to an oxidizing flame at 2750 K and a net effective heat flux of ∼25.0 W/cm2, for a specified duration. Both planer and tubular specimens in the head-on impingement (HOI) and parallel flow (PF) configurations were investigated. Scanning electron microscopy (SEM) of the residual surface morphology (RSM) of the various irradiated specimens revealed that the ablation was a function of both the resin and the reinforcement type. The resistance to ablation/erosion improved with both higher-melting substrates and greater matrix-substrate interaction. The global erosion rate was found to correlate with the geometrical, thermal, and processing parameters, and generally increased with increased thermal transport and reduced compaction pressure. These findings may have important implications in the engineering of ablative composites for possible use in the more discriminating thermal environments of certain propulsion devices.

New Developments in Thermally and Chemically Stable Nonlinear Optical Chromophores for E-O Device Applications

ABSTRACTA new class of second order nonlinear optical chromophores resulted from the replacement of the most reactive CN group in tricyanovinylthiophene derivatives with aryl units, have been designed and synthesized. It was shown that these chromophores provide excellent tradeoffs among many relevant properties such as molecular nonlinearity, linear absorption at 830 nm, inherent thermal stability, chemical stability in processing solvents as well as host polymer matrices at high temperatures and attenuation at 830 nm.

Conditional artificial dielectrics: phase and amplitude response at microwave frequencies

Conditional artificial dielectrics are considered; these are composites of small semiconductor crystallites embedded in a polymeric host material. The dielectric properties of these materials were measured at microwave frequencies and under light illumination. It was found that the light affect mostly the phase velocity of a propagating microwave beam and with almost no loss.

An electron spin resonance (ESR) and simultaneous electrochemical and electron spin resonance (SEESR) spectroscopic study of motion, stability and potential controlled release of radical guests from the β-cyclodextrin inclusion polymer

The influence of molecular inclusion and separation of radical guests inside the amorphous β-cyclodextrin host polymer (β-CDP) matrices on the motion and stability as well as controlled potential release of radicals was studied by electron spin resonance spectroscopy (ESR) and simultaneous electrochemistry and electron spin resonance (SEESR) spectroscopy. A pronounced restriction of rotational motion was observed for the included stable protonated form of the 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) free radical and a partial restriction of motion of the NN, N', N'-tetramethyl-1,4-phenylenediamine (TMPD .+) radical (generated ex situ by controlled potential electrolysis), while virtually no restriction was found in the case of the methyl (MV .+) and heptyl viologen (HV .+) monocation radicals as well as of the 2-nitrotoluene anion radical (2NT .− ). The MV .+, HV .+ and 2NT .− unstable radicals were electrochemically generated inside the β-CDP film coat at a Pt flag electrode. The rate of the open-circuit decay of the included unstable radicals was markedly decreased as compared with their decay at the bare electrode. It was also found that the extent of inclusion of alkyl viologens was governed by their ionic charge, i.e. the higher the charge of the ion the weaker its inclusion.

Oligomers containing carbocyanine/flexible chain segments as non-linear optical materials

As part of a search for new non-linear optical (NLO) materials, we have synthesized new oligomers containing carbocyanine units linked by flexible chain segments. The oligomers can be cast into films and have an improved miscibility with other host polymer matrices compared to the simple carbocyanine molecules. Degenerate four-wave mixing (DFWM) measurements showed that a pure oligomer film has a χ (3) α value of 9.0 · 10 −13 esu cm at λ = 532 nm. Furthermore, the reaction of acidic protons in a quinolidine quaternary salt with diethyl squarate has been utilized to synthesize a polymer. The polymer, containing 13 repeat units, has a diffuse and strong absorption in the visible region and does not exhibit a detectable DFWM signal at 532 or 1064 nm.

Laser behavior and photostability characteristics of organic dye doped silicate gel materials

The solgel process is a solution synthesis technique which provides a low temperature chemical route for the preparation of rigid transparent matrix materials. Luminescent organic dye molecules have been incorporated via the solgel method into organically modified silicate (ORMOSIL) polymer host matrices. Optical gain, laser oscillation, and photostability of rhodamine and coumarin dyes doped into ORMOSIL gels are reported. The gel laser materials exhibit peak gain values of 40 cm(-1) and show improved photostability with respect to comparable polymeric host materials.

The effect of flexibility on the photodegradation of aromatic diisocyanate‐based polyurethanes

AbstractThe photolytic degradation of 2,4‐TDI/aliphatic diol polyurethanes is directly dependent on the flexibility of the polymer backbone. The extent of photodegradation is accelerated above the glass transition temperature, indicating the role of chain flexibility and/or oxygen diffusion in the decomposition process. Photolysis of the model compound ethyl N‐phenylcarbamate (EPC) in neutral host polymer matrices indicates that the para photo‐Fries to ortho photo‐Fries product ratio experiences an accelerated increase with temperature above the glass transition of the polymer matrix.

Complex formation and ionic conductivity of polyphosphazene solid electrolytes

The linear poly[(alkoxy)phosphazene], [NP(OC 2H 4OC 2H 4OCH 3) 2] n (MEEP), has been synthesized and investigated as a polymeric electrolyte host material. Amorphous solvent free polymersalt complexes formed with a variety of mono-, di-, and trivalent salts and exhibit high ionic conductivity. The conductivity varies with changes in the identify of the cation, the anion and the salt concentration. It also exhibits a non-Arrhenius temperature dependence. For alkali-metal salt complexes the cations and anions both contribute to the ionic conductivity. The complex (LiSO 3CF 3) 0.25·MEEP exhibits a conductivity at room temperature which is 2.5 orders of magnitude greater that the corresponding poly(ethylene oxide) complex.

The gamma-ray response of radiochromic dye films at different absorbed dose rates

In leucotriphenylmethane radiochromic dye systems, using polymeric host materials, low-intensity rate dependence of gamma-ray response at doses >10 kGy and at dose rates <1 Gy·s −1 is observed in some dye-plastic combinations. This effect is prevalent under dry or anoxic conditions, and accompanies a shift in the optical absorption band. Whether or not the net dye yield becomes sublinear with dose and diminishes with decreasing dose rate is determined by environmental effects (e.g. relative humidity) and especially by the nature of the host material. Experiments at absorbed dose rates between 0.01 and 3 Gy·s −1 show that the apparent low-intensity dose rate dependence is due mainly to a moisture-controlled decrease in efficiency of radiation-induced dye formation at relatively low radiation intensities. For several hydrophilic dosimeters, the thinner the film, the greater the dose rate effect. With the exception of polyvinyl pyrrolidone and the very thin films, there is only slight rate dependence at intermediate relative humidity.

Possible use of electron spin resonance of polymer films containig leucodyes for dosimetry

When plastic films containing leucocyanides of triphenylmethane dyes are irradiated with large doses of 60Co gamma rays, free radicals are formed that are sufficiently stable for analysis at room temperature. It is shown that by separating the electron spin resonance spectrum due to free radical is produced in the polymeric host materials from that of the dye precursor, the number of spins associated with a free radical produced in the substituted triphenyl methyl radical can be determined as a means of dosimetry. Instabilities in the free radical populations are evaluated, and methods of preparing plastic films containing triphenylmethane leucocyanides are described. Not only can dosimetry be achieved at higher doses than are normally used with spectrophotometry of this films, but also information about the radiation chemistry of dye formation can be derived.