J.-I. Jin

Study of third-order optical non-linearity and electrical conductivity of sol-gel processed silica: poly(2-bromo-5-methoxy-p-phenylene vinylene) composite

A novel sol-gel processed silica: poly(2-bromo-5-methoxy-p-phenylene vinylene)silica composite was prepared using a soluble precursor. The optical properties of this material have been investigated using u.v.-visible and FTi.r. spectroscopy. The densification process was monitored by d.s.c. and t.g.a. The third-order non-linear susceptibility χ(3) has been investigated for both the pure polymer and its sol-gel composite at 602 nm using femtosecond degenerate four-wave mixing. A relatively large χ(3) value with a subpicosecond response is observed. The electrical conductivities of AsF5 doped polymer and composite films were studied using four-probe measurement.

Electrical properties of polyaniline and substituted polyaniline derivatives

Abstract Polyaniline and substituted polyaniline derivatives which the ortho position hydrogen is substituted with CH 3 , OCH 3 and Cl are studied. Both protonic acid doping (i.e. the addition of protons to the polymer chain without changing the number of electrons in the chain) and the acceptor doping (i.e., the number of electrons in the polymer chain is decreased by the acceptor which is iodine in this case) results on these samples show metallic conductivity. On the other hand, the signs of thermoelectric power are different. The sign of protonic acid doped polyaniline becomes negative upon doping, but the sign of the acceptor doped sample remains positive. The effect of the substitution of ortho hydrogen is more significant in the protonic acid doping than in the iodine doping. Electron affinity of the substituted molecules could affect the electronic structure of the polyaniline. The electrical conductivity and thermoelectric power measurement data as functions of doping concentration and temperature for these samples are presented.

Liquid crystal polymers: 19. Cholesteric main chain polyesters with triad aromatic ester mesogenic units and chiral polyalkylene spacers

Abstract Three series of thermotropic, main chain polyesters and copolyesters which formed cholesteric mesophases were prepared and characterized. These polymers contained triad aromatic ester mesogenic units and chiral polyalkylene spacers. Differential scanning calorimetry and observations on a polarizing microscope were used to examine the thermal properties and the nature of mesophases of these polymers. The dependence of the wavelength of reflected light for some of the cholesteric polymer melts on temperature and composition was measured spectrotrophotometrically.

Synthesis and electrical conductivity of poly(1,4-phenylenevinylene-co-2-n-butoxy-5-methoxy-1,4-phenylenevinylene)s and poly(1,4-phenylenevinylene-co-2-n-dodecyloxy-5-methoxy-1,4-phenylenevinylene)s

Abstract A series of copolymers containing 1,4-phenylenevinylene (PV) and either 2-n-butoxy-5-methoxy-1,4-phenylenevinylene (BMPV) or 2-n-dodecyloxy-5-methoxy-1,4-phenylenevinylene (DDMPV) units were prepared in the form of thin films from their water-soluble sulfonium-salt precursor polymers. The electrical conductivity of the I2- and FeCl3-doped copolymers exhibits a steep initial increase with an increase in the content of the BMPV or DDMPV units, followed by a slower increase to finally reach the values of that of the corresponding homopolymers, PBMPV and PDDMPV, respectively. The conductivities of the I2- and FeCl3-doped, drawn BMPV copolymer films ranged from 35 to 266 S cm−1, and from 10−1 to 256 S cm−1, respectively, depending on the composition. PDDMPV films could be uniaxially drawn at 150–160°C to a draw ratio of 5, and gave an electrical conductivity value of 27 S cm−1 when doped with I2, whereas I2-doped PDDMPV films, obtained from the precursor polymer that itself had been pre-drawn to the draw ratio of 5, exhibited a conductivity of 46 S cm−1. PDDMPV was found to be soluble in p-xylene, but PBMPV was insoluble in this solvent. The presence of the long dodecyloxy group enables the precursor polymer of PDDMPV to form an ordered structure. The u.v.-vis. spectra of the dialkoxy substituted homopolymers and their corresponding copolymers were red-shifted relative to the parent PPV, suggesting a decreased bandgap, which was consistent with the electron-donating nature of the alkoxy substituents. In general, the electrical conductivities of the DDMPV copolymers were lower than those of the BMPV copolymers, which can be ascribed to the presence of longer insulating alkoxy groups in the former.

Synthesis and characterization of novel polyamides carrying NLO moieties

Abstract A series of novel polyamides carrying NLO chromophores were synthesized and their general properties were characterized. The electrooptic properties of a couple of selected compositions were studied. These polyamides were synthesized by direct polycondensation at 100°C of 4,4′-methylenedianiline or 4,4′-oxydianiline with 4-nitro-[ N,N -bis(2-carboxyethyl)]aniline or 4-[ N,N -bis(2-carboxyethyl)amino]-4′-nitrostilbene in the presence of a condensing agent composed of lithium chloride and triphenyl phosphite. All of the polymers were found to be amorphous and their glass transition temperatures were about 160°C. In contrast, the polymer that does not carry the nitro group in the phenyl ring of the side group revealed a T g value of only 78°C. This difference strongly indicates that the nitro group is involved in the formation of hydrogen bonds and, thus, hinders the chain mobility resulting in the enhanced T g values. This could be confirmed by the i.r.-spectroscopic analysis of the polymers. The u.v.-vis. absorption characteristics of the polyamides also were studied. The second-order nonlinear optical properties of the thin films of two selected polymers of better solubility were studied by measuring their electrooptic coefficients after being poled at the temperatures near their T g s. When the polymer films were poled at the field strength of 0.4–0.6 MV cm −1 , their electrooptic coefficients obtained for the incident beam of 1.3 μm were about 3 pm V −1 and they showed an excellent temporal stability even at 80°C.

Comparative studies on EL performances of the OLEDs prepared by PVD, NCBD and ICBD methods

Organic light emitting diodes (OLEDs) with the structure of indium-tin-oxide glass/spin-coated poly[2-(N-carbazolyl)-5-(2-ethyl-hexyloxy)-1,4-phenylenevinylene]/8-hydroxyquinoline aluminum/Li:Al [ITO-glass/CzEH-PPV/Alq 3 /Li:Al] have been fabricated by applying three deposition methods: physical vapor deposition (PVD), neutral and ionized cluster beam depositions (NCBD and ICBD). Atomic force microscopy (AFM) measurements show that the weakly bound and highly directional cluster beam is effective in producing uniform flat film surfaces. Photo- and electro-luminescence (PL, EL) spectra demonstrate that the NCBD and PVD methods produce more efficient EL devices and the introduction of neutral buffer layer to the ICBD devices enhances the performances. DCM-doped devices show color-tuning capability and higher external quantum efficiency (EQE) compared to undoped devices.

Thermal sequence randomization of a wholly aromatic copolyester having an ordered sequence

Abstract A wholly aromatic copolyester having an ordered comonomer sequence was prepared from 2,7-naphthalenediyl bis(4-hydroxybenzoate) and terephthalic acid following a method reported previously. This polymer was subjected to thermal treatment at 305°C under nitrogen atmosphere and the sequence randomization process was quantitatively analysed by 13 C n.m.r. spectroscopy. The melting temperature of the original polymer was 290°C. According to the results of analysis for various triad formation, the ester bonds in the triad of terephthaloyl- p -oxybenzoyl-oxynaphthyleneoxy (TPN) sequence were found to undergo very fast exchange reactions at the treatment temperature. The formation of PPP triad was evident after 30 min at 305°C, whereas PP dyad was formed after only 10 min. Although the sequence changes occurred rather rapidly, complete randomization was not attained even after 1 h.

Steady state photoconductivity of poly(2-styryl-1, 4- phenylene vinylene) (PSPV)

Abstract The steady state photoconductivities of poly(2-styryl-1,4-phenylene vinylene) (PSPV) and its oxidized form poly(2-methoxy-5-styryl 1, 4-phenyIene vinylene) (PMSPV) are studied. PSPV contains styryl radical in PPV backbone chain. The spectral response of the photocurrent of PSPV shows a peak at 2.7 eV with no additional peak structure near 2.4 eV. PMSPV made by the substitution of methoxy radical to PSPV shows somewhat unusual feature. The spectral response of PMSPV does not show any peak near the absorption edge and the magnitude of the photocurrent is decreased compared to that of the PSPV. The results are discussed in terms of the different interchain distances of the two polymers as well as the existence of a conjugated double bond in the styryl radical in these PPV derivatives.

Synthesis and characterization of poly(2-methoxy-5-(2-(4-nitrophenyl)ethenyl)-1,4-phenylenevinylene) and a series of copolymers containing 1,4-phenylenevinylene units

Abstract Poly(2-methoxy-5-(2-(4-nitrophenyl)ethenyl)-1,4-phenylenevinylene) (PMNEPV) and a series of copolymers (poly(MNEPV- co -PV)) containing varying amounts of 1,4-phenylenevinylene (PV) units have been synthesized via soluble precursor polyelectrolytes. These polymers possess a unique structural feature in which the electron-donating methoxy groups are located on the phenylene rings along the main chain whereas the electron-attracting nitro groups are attached to the side chain styryl substituents. The u.v.-vis. spectra of PMNEPV and the poly(MNEPV- co -PV)s revealed two major absorptions arising from π-π * transitions of the two π-electron systems: the first peak is due to the π-system in the 4-methoxy-4′-nitrostilbene moiety and the second due to the π-system in the backbone. The maximum electrical conductivity of FeCl 3 - or I 2 -doped copolymers increased rapidly initially with the level of MNEPV unit followed by a gradual decrease when the content of MNEPV unit was > 7 mol%. The dependence of the electrical conductivity of the present series of copolymers, when doped either with I 2 or FeCl 3 , is almost the same as that observed earlier by us for poly(2-methoxy-5-(2-phenylethenyl)-1,4-phenylenevinylene) and its copolymers containing the PV unit.

Synthesis and characterization of poly(oxy-1,4-phenyleneoxycarbonyl-1,4-phenyleneoxypolymethylene)s

Abstract A multistep synthetic route for the preparation of a series of poly(oxy-1,4-phenyleneoxycarbonyl-1,4-phenyleneoxypolymethylene)s having a varying length of the polymethylene spacer from the di- to the hexamethylene group is reported. The polymers prepared were characterized particularly for their liquid crystalline properties by differential scanning calorimetry, wide-angle X-ray diffractometry and observation of their textures on a polarizing optical microscope. All the polymers, with the exception of the trimethylene polymer, formed the nematic phase in melt. They exhibited the well known odd-even effect at melting temperature as well as at isotropization temperature.