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had been evacuated by a mechanical rotary pump to a pressure of 6 10 ±2 torr, a carrier gas of argon premixed with 5 % hydrogen was kept flowing at a rate of 50 sccm from the end containing the laser ablation target to the end containing the silicon substrates. The pressure inside the tube was maintained at 200 torr by continual pumping during the experiment. The temperature of the furnace central region was increased at a rate of 30 C min ±1 to 950 C and held at this temperature. The KrF laser (length wave of 248 nm, pulse width 34 ns, and of rate 5 Hz of 450 mJ per pulse was then started and focused on the target. The laser ablation process lasted for 1 h and the laser was repeatedly turned on for 10 s and off for 10 s during this period.Samples collected from the silicon substrates were characterized by scanning electron microscopy (SEM; Philips XL 30 FEG), transmission electron microscopy (TEM; Philips, CM20 operated at 200 kV) and high-resolution transmission electron microscopy (HRTEM; CM200 FEG, operated at 200 kV). Room-temperature photoluminescence (PL) spectra were recorded with a Perkin-Elmer luminescence spectrometer (LS50B), using a xenon discharge lamp as the exciting source. Polymer Electrolyte Membranes with a Pore-Filling Structure for a Direct Methanol Fuel Cell** By Takeo Yamaguchi,* Fusae Miyata, and Shin-ichi NakaoDirect methanol fuel cells (DMFCs) have potential uses in portable devices and in automobiles, because of their low weight and simple system features. However, DMFCs do not display the current high performance of hydrogen polymer electrolyte fuel cells. We therefore need to develop a new polyelectrolyte membrane to enable this technology to be exploited. The desired membrane needs to show the following characteristics: i) the membrane should show low permeation (crossover) of methanol fuel to prevent direct oxidation on the cathode; ii) the proton conductivity of the membrane material should be high, and the membrane should be thin to minimize membrane resistance; iii) the membrane should be mechanically strong, and the change in membrane area from the dry to the swollen state should be negligible to minimize any membrane/electrode interface resistance; iv) the membrane material should be chemically stable during DMFC operation; and v) the membrane needs to be manufactured at low cost. A DMFC membrane should exhibit all the above characteristics, and to date, many membranes have been developed.[1±8] However, the membranes developed so far do not satisfy all the above criteria required for DMFC membranes. In this study, we have developed pore-filling membranes that are composed of a porous substrate and a filling polymer electrolyte, and these membranes show good perfor-COMMUNICATIONS 1198

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This article describes the syntheses and second-order nonlinear optical (NLO) properties of novel types of polyesters containing second-order NLO active chromophores with high density, which were obtained by condensation polymerization using two comonomers with the N,N-dialkyl-4-nitroaniline or N,N-dialkyl-4-((4-cyanophenyl)azo)aniline moiety. The polyesters were synthesized by condensation polymerization between isophthalic acid derivatives and N-substituted diethanolamines using triphenylphosphine and diethyl azodicarboxylate as the condensation reagents in dimethyl sulfoxide (DMSO) or 1-methyl-2-pyrrolidinone (NMP). The obtained amorphous polyesters exhibited good solubility in common organic solvents and provided optical-quality films by spin-coating. The SHG measurements of the spin-coated films of the resulting polyesters were carried out by the Maker fringe method using a Q-switched Nd:YAG laser (1064 nm) as an exciting beam after corona-poling. One of the polyesters, which was prepared from 5-[2-(N-methyl-4-nitroanilino)ethoxy]isophthalic acid and N-[4-((4-cyanophenyl)azo)phenyl]diethanolamine, exhibited the large second-order NLO coefficient, d 33, of 202 pm/V. On the other hand, a polyester containing chromophore moieties with the highest density, which was prepared from 5-{[1,3-bis[4-((4-cyanophenyl)azo)-N-methylanilino]-2-propyl]oxy}isophthalic acid and N-[4-((4-cyanophenyl)azo)phenyl]diethanolamine, exhibited good temporal stability of the second-order nonlinearity at ambient temperature.