Takeshi Igarashi

Highly efficient polymer light-emitting devices using ambipolar phosphorescent polymers

We report on highly efficient polymer light-emitting devices (PLEDs) achieved using a phosphorescent polymer, which is a copolymer that has bis(2-phenylpyridine)iridium (acetylacetonate) [Ir(ppy)2(acac)], N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a side group. The phosphorescent polymer has an ambipolar charge-transport ability. An increase in PBD unit concentration allows an improvement in the efficiency of the PLEDs. Ba and Cs were used for electron-injection layers as well as Ca, to improve the electron injection. An external quantum efficiency of 11.8% and a power efficiency of 38.6lm∕W were obtained by using Cs. The results indicate that this can be attributed to an improvement in the charge balance of electrons and holes.

Recovery of acetic acid from dilute aqueous solutions using catalytic dehydrative esterification with ethanol

We have developed a direct esterification of aqueous acetic acid with ethanol (molar ratio=1:1) catalyzed by polystyrene-supported or homogeneous sulfonic acids toward the recovery of acetic acid from wastewater in chemical plants. The equilibrium yield was significantly increased by the addition of toluene, which had a high ability to extract ethyl acetate from the aqueous phase. It was shown that low-loading and alkylated polystyrene-supported sulfonic acid efficiently accelerated the reaction. These results suggest that the construction of hydrophobic reaction environments in water was critical in improving the chemical yield. Addition of inorganic salts was also effective for the reaction under not only biphasic conditions (toluene-water) but also toluene-free conditions, because the mutual solubility of ethyl acetate and water was suppressed by the salting-out effect. Among the tested salts, CaCl(2) was found to be the most suitable for this reaction system.

Preparation of fullerene/epoxy resin composite with fine dispersion and its breakdown strength

Fullerene is likely to form aggregates so that it is diificult to disperse it well in a polymer matrix, and few reports have been made on electrical insulation properties of fullerene filled composite as electrical insulating material. This paper deals with fullerene dispersion method in conventional epoxy resin (EP) and breakdown strength (BDS) of the composite with different filler loading of fullerene. Composite materials added with fullerenes of 0.1, 0.3, and 0.6 weight% were prepared in a plate shape with a thickness of 0.5 mm using two different dispersion methods, i.e. fullerene dissolved and fullerene direct mixing methods, and neat specimen was also prepared for comparison so as to investigate BDS. As a result, it was found that BDS of fullerene/EP composite with good dispersion greatly increased by 30 %. The increase in BDS of the composite is discussed in terms of the inter-particle distance as an index of the dispersion degree.