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Kei Saito

Publications and source records attributed to Kei Saito.

4 recordsLinked to original sources
PubMed2003

Depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) under oxidative conditions.

Depolymerization of an engineering plastic, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), was accomplished by using 2,6-dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (M(n)=1.0x10(4), M(w)/M(n)=1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to M(n)=4.9x10(2) (M(w)/M(n)=1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.

Journal Article↗
PubMed2002

A complex-valued version of Nagumo-Sato model of a single neuron and its behavior.

The Nagumo-Sato model of a single neuron was extended so that it can handle complex numbers and the behavior of the complex-valued model was investigated. The model neuron receives its past outputs through a complex-valued weight and fires when the absolute value of the membrane potential exceeds a threshold. Some of the basic features of the model, such as associated with fixed points and period-two orbits, were derived. The main purpose of the paper is to show the model's chaotic behavior which is the result of the extension to the complex numbers and different from that of the original real-valued model. The apparently chaotic orbits were numerically shown to have positive Lyapunov exponents and high sensitivity to the initial conditions. Some of the chaotic orbits seem to be related to the saddles of period-two and their associated stable and unstable manifolds.

Action Potentials↗