Yoshio Imai

Bio: Yoshio Imai is an academic researcher from Tokyo Institute of Technology. The author has contributed to research in topics: Condensation polymer & Polyimide. The author has an hindex of 37, co-authored 389 publications receiving 6625 citations. Previous affiliations of Yoshio Imai include Dow Corning & Honda.

Preparation of a New Class of Polyimide-Silica Hybrid Films by Sol-Gel Process

Abstract: A new class of polyimide-silica hybrid films were successfully prepared by the sol-gel reaction starting from tetraethoxysilane (TEOS) in the solution of polyamic acid in N,N-dimethylacetamide. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS in the polyamic acid solution, followed by heating at 270°C. Fairly flexible films were obtained up to 70 wt% of silica content. The films containing the silica less than 8 wt% were yellow and transparent, whereas the films with higher silica content were yellow and opaque. The density of the silica in the hybrid films was estimated to be 1.65 gcm−3. The 29Si nuclear magnetic resonance spectrum indicated that the silica in the films consisted of non-hydroxy, monohydroxy, and dihydroxy siloxane structures. Silica particles with diameter of around 5 μm were observed in the hybrid films by scanning electron microscopy. The density, decomposition temperature, and modulus of the hybrid films increased with increasing the silica content, whereas the tensile strength and elongation at break of the films decreased in this order. The glass transition temperature of the hybrid films showed the minimum at 8 wt% of silica content. The linear thermal expansion coefficient of the silica in the hybrid films was estimated to be 1.3×10−5 K−1.

Feature article. Preparation of new polyimide–silica hybrid materials via the sol–gel process

Abstract: After a description of the preparation of polymer-metal oxide hybrid materials via the sol-gel method, recent results on the preparation of new polyimide-silica hybrid materials are reviewed. Tetraethoxysilane (TEOS) can be hydrolysed and polycondensed to form a three-dimensional silica-gel network in a solution of polyamic acids, the precursor polymers of polyimides, and N,N-dimethylacetamide (DMAc). Films of the polyamic acid-silica gel mixtures can be cast onto glass plates, and can then be heated to 300 °C to convert the component matrix polymers to polyimides. Five kinds of polyamic acid have been designed and prepared. One of them was the usual polyamic acid, having no connection site with silica, whereas others had ethoxysilyl groups in the polymer backbone. The polyimide-silica hybrid films containing 70 wt.% of silica were self-standing and tough. The transparent-opaque changing points shifted to higher silica content with increasing ethoxysilyl-group content of the matrix polyimides. The silica particles were dispersed homogeneously in the matrix polyimides, as observed by scanning electron microscopy. The size of the silica particles increased with increasing silica content, and decreased with increasing ethoxysilyl content. Results of the dynamic-mechanical analysis indicate that movement of the polyimide chain in the matrix is restricted, especially when the polyimides contain higher amounts of ethoxysilyl. The tensile strength of the hybrid films showed no decrease with increasing silica content, whereas the tensile modulus increased in all cases except that where the matrix polyimide did not contain any ethoxysilyl groups.

Preparation and properties of novel soluble aromatic polyimides from 4,4′‐diaminotriphenylamine and aromatic tetracarboxylic dianhydrides

Abstract: New aromatic polyimides containing triphenylamine unit were prepared by two different methods, i.e., a conventional two-step method starting from 4,4′-diaminotriphenylamine and aromatic tetracarboxylic dianhydrides and the one-step thioanhydride method starting from the aromatic diamine and aromatic tetracarboxylic dithioanhydrides. Both procedures yielded high-molecular-weight polyimides with inherent viscosities of 0.47–1.17 dL/g. Some of these polymers were soluble in organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, m-cresol, and pyridine. All the polyimides afforded transparent, flexible, and tough films, and the color varied from pale yellow to dark red, depending markedly on the tetracarboxylic acid components. The glass transition temperatures (Tgs) of these polyimides were in the range of 287–331°C and the 10% weight loss temperatures were above 520°C in air. The polyimides prepared by the one-step method exhibited better solubility in organic solvents and had somewhat lower Tgs than the polymers prepared by a conventional two-step method.

Synthesis of novel organic-soluble high-temperature aromatic polymers

Abstract: This paper reviews our current work on the synthesis of new organic-soluble aromatic polyamides and polyimides having high glass transition temperatures above 300 °C. Our strategy to achieve this goal is to introduce a bulky pendant phenyl group along the polymer backbone and to incorporate a crank and twisted non-coplanar structure into the polymer main chain.

Preparation of mono- and multilayer films of aromatic polyimides using langmuir–blodgett technique

Abstract: Monolayer film of polyamic acid alkylamine salt at air–water interface was successfully deposited onto appropriate plates. Subsequent treatment of the multilayer film with a mixture of acetic anhydride and pyridine afforded the multilayer film of polyimide. The distance between two layers of the polyimide multilayer film was estimated to be 4 A.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Abstract: A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Carbon-Carbon Coupling Reactions Catalyzed by Heterogeneous Palladium Catalysts

Abstract: 4.4. Pd on Modified Silica 159 4.5. Pd on Clay and Other Inorganic Materials 159 5. Stille, Fukuyama, and Negishi Reactions 159 5.1. Stille Reactions 159 5.1.1. Pd on Carbon (Pd/C) 159 5.1.2. Palladium on KF/Al2O3 159 5.1.3. Pd on Modified Silica (SiO2/TEG/Pd) 159 5.2. Fukuyama Reactions 159 5.2.1. Pd on Carbon (Pd/C) 159 5.2.2. Pd(OH)2 on Carbon (Perlman’s Catalyst) 160 5.3. Pd/C-Catalyzed Negishi Reactions 160 6. Ullmann-Type Coupling Reactions 161 6.1. Pd/C-Catalyzed Aryl−Aryl Coupling 161 6.2. Pd/C-Catalyzed Homocoupling of Vinyl Halides 162

On the Nature of the Active Species in Palladium Catalyzed Mizoroki–Heck and Suzuki–Miyaura Couplings – Homogeneous or Heterogeneous Catalysis, A Critical Review

Abstract: A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true “catalysts” in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano- and macroparticles, soluble palladium nanoparticles, soluble ligand-free palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.

The electroluminescence of organic materials

Abstract: This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.