Synthesis and properties of polyimides bearing acid groups on long pendant aliphatic chains

A series of novel polyimide electrolytes having long pendant sulfo‐ or phosphoalkoxy groups were synthesized for fuel‐cell applications. Sulfodecyloxy‐, phosphodecyloxy‐, and sulfophenoxydodecyloxy‐substituted benzidine monomers were synthesized from dihydroxybenzidine. These monomers were copolymerized with naphthalene tetracarboxylic dianhydride and fluorenylidene dianiline to give the corresponding polyimides. A flexible, ductile, and self‐standing membrane was obtained via casting from the polyimide solution. Because the acid groups were on long pendant side chains and away from the main chains, the polyimide membrane showed improved oxidative and hydrolytic stability in comparison with the polyimides with sulfonic acid groups on the main chains or on the short side chains. High thermal stability (no glass‐transition temperature and a decomposition temperature > 200 °C) was also obtained. The polyimide membrane displayed high proton conductivity of 10^?1 S cm^?1 at 120 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3995–4005, 2006     

Effects of d.c. potential patterns on the performance of ion‐exchange polymer based molecular actuators

The dynamic performance (i.e. displacement, current, velocity, and force) of ion‐exchange polymer based actuators (the Nafion?/platinum electrodes) have been examined by developing instrumentation. The CCD imaging technique was examined to evaluate the displacement under the various d.c. potential patterns. Two different d.c. potential patterns with or without a rest were applied to the electrodes at 0.1 Hz. It was better to take a rest at 0 V for the polarization back and forth between +2 and ?2 V to give lower current consumption and longer displacement. The actuator produced the force of ca. 0.95 g at 3.25 V in air. The result also demonstrated that higher overpotential has to be avoided to maintain the maximum force. The generative force is in inverse proportion to the length of the actuators. The dimension of the film strongly governs the force production and its performance. Copyright © 2006 John Wiley & Sons, Ltd.     

Laser-active colour centres with functional periodic structures in LiF fabricated by two interfering femtosecond laser pulses

We report a new technique to fabricate both laser-active F₂ and F₃⁺ colour centres in lithium fluoride and permanent periodic gratings with fringe spacings as fine as sub-micron size simultaneously by two interfering infrared femtosecond (fs) laser pulses. In particular, the optical properties of such colour centres produced by a single fs laser pulse are compared with those created by damage from radiation such as X-rays. Moreover, the present technique is applied to the first production of three-dimensional active channel waveguide and a pulsed distributed-feedback (DFB) laser at around 700 nm in LiF containing F₂ colour centres with fine-pitched micro-grating structures.     

Arithmetically independent integers and values of rational functions

We prove the existence of arithmetically independent integers and their properties and apply them to values of rational functions on algebraic varieties.     

Heat transfer in composite materials with Stefan–Boltzmann interface conditions

In this paper, we discuss nonstationary heat transfer problems in composite materials. This problem can be formulated as the parabolic equation with Stefan–Boltzmann interface conditions. It is proved that there exists a unique global classical solution to one‐dimensional problems. Moreover, we propose a numerical algorithm by the finite difference method for this nonlinear transmission problem. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and characterization of new fluorescent poly(arylene ether)s

The poly(arylene ether)s were prepared by the nucleophillic aromatic substitution polymerization of phenolphthalin and its derivatives with activated aromatic difluorides. The polymers had glass transition temperatures ranging from 210 to 240°C. Though the monomers have no fluorescence, the resulting polymers fluoresced a light green color in solid and solution states. The maximum excitation and emission wavelengths are 420 nm and 470 nm, respectively. In the polymer solutions, the fluorescence intensity decreased gradually, but the intensity was recovered by heating the polymer at 220°C for a few minutes. The fluorescent polymer had a stable radical. A model compound having the same repeating unit of the polymer was also prepared. The fluorescence properties of this model were almost the same as those of the polymers. © 1994 John Wiley & Sons, Inc.