Tsutomu Takeichi

Polybenzoxazine-montmorillonite hybrid nanocomposites : synthesis and characterization

Polybenzoxazine–clay hybrid nanocomposites were prepared from a polybenzoxazine precursor (B-a) and organically modified-montmorillonite (OMMT) as a type of layered silicates. OMMTs were prepared by surface treatment of montmorillonite (MMT) by octyl, dodecyl or stearyl ammonium chloride. The curing behavior of B-a in the presence of dispersed OMMT was followed by IR and DSC. DSC showed that the onset of the ring opening polymerization of pristine B-a started at 223°C. The ring opening polymerization of B-a in the presence of OMMT started at 177–190°C, however, suggesting the catalytic effect of the OMMT surface on the ring opening polymerization. DSC and IR indicated that the curing of B-a was completed by the end of the 230°C cure cycle. The dispersion of OMMT in the polybenzoxazine matrix was confirmed by XRD, which indicated the collapse of the registry of the OMMT. The absence of basal spacings diffractions of OMMTs from the XRD patterns suggests the dispersion of OMMT layers on the molecular level when the surface was pretreated with long chain surfactants like dodecyl or stearyl ammonium chloride. However, in case of OMMT, which was pretreated with short chain surfactants like octyl ammonium chloride, the intercalation of polybenzoxazine into the clay galleries occurred with a regularly stalked layered structure. Viscoelastic measurements showed that the Tgs of the hybrid materials were higher than that of the pristine resin. In addition, the storage modulii of the hybrid materials were maintained up to higher temperatures suggesting the reinforcement attained by OMMT. Isothermal and dynamic TGA showed that nanocomposites have delayed decomposition temperatures when compared with pristine polybenzoxazine indicating the enhancement in the thermal stability.

Synthesis and characterization of poly(urethane-benzoxazine) films as novel type of polyurethane/phenolic resin composites

Poly(urethane-benzoxazine) films as novel polyurethane (PU)/phenolic resin composites were prepared by blending a benzoxazine monomer (Ba) and PU prepolymer that was synthesized from 2,4-tolylene diisocyanate (TDI) and polyethylene adipate polyol (MW ca. 1000) in 2 : 1 molar ratio. DSC of PU/Ba blend showed an exotherm with maximum at ca. 246 °C due to the ring-opening polymerization of Ba, giving phenolic OH functionalities that react with isocyanate groups in the PU prepolymer. The poly(urethane-benzoxazine) films obtained by thermal cure were transparent, with color ranging from yellow to pale wine with increase of Ba content. All the films have only one glass transition temperature (Tg ) from viscoelastic measurements, indicating no phase separation in poly(urethane-benzoxazine) due to in situ polymerization. The Tg increased with the increase of Ba content. The films containing 10 and 15% of Ba have characteristics of an elastomer, with elongation at break at 244 and 182%, respectively. These elastic films exhibit good resilience with excellent reinstating behavior. The films containing more than 20% of Ba have characteristics of plastics. The poly(urethane-benzoxazine) films showed excellent resistance to the solvents such as tetrahydrofuran, N,N-dimethyl formamide, and N-methyl-2-pyrrolidinone that easily dissolve PUs. Thermal stability of PU was greatly enhanced even with the incorporation of a small amount of Ba.

Sample preparation with fiber‐in‐tube solid‐phase microextraction for capillary electrophoretic separation of tricyclic antidepressant drugs in human urine

Solid‐phase microextraction (SPME) is a solvent‐free sample preparation technique using a thin coating attached to the surface of a fused silica‐fiber as the extraction medium, which has been successfully applied to the analysis of a wide variety of compounds by coupling to gas chromatography (GC). In recent years, in‐tube SPME using GC capillary column as the extraction medium has also been developed and coupled with liquid chromatography (LC) for the preconcentration of nonvolatile compounds. In this study, an on‐line interface between the fiber‐in‐tube SPME and capillary electrophoresis (CE) has been developed, and the preconcentration and separation of four tricyclic antidepressant (TCA) drugs, amitriptyline, imipramine, nortriptyline, and desipramine, were performed with the hyphenated system. Under the optimized condition, a better extraction performance than conventional in‐tube SPME was obtained, even the length of the extraction medium was much shorter. The results clearly indicated that the fiber was working effectively as an extraction medium. For the separation of these four TCAs, capillary electrophoretic separation with β‐cyclodextrin as the buffer additive has been employed and the application of the developed system to the analysis of complex sample mixtures in a biological matrix is also demonstrated.

Polybenzoxazine/clay hybrid nanocomposites: influence of preparation method on the curing behavior and properties of polybenzoxazines

Abstract Several types of polybenzoxazine/clay hybrid nanocomposites have been prepared from organically modified montmorillonite (OMMT) and mono- or bifunctional benzoxazine, 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine (Pa) or bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) isopropane (Ba), respectively. OMMT was prepared by a cation exchange of montmorillonite (MMT) with ammonium salts of amines such as tyramine, phenylethylamine, aminolauric acid, and dodecyl amine. Polybenzoxazine/clay nanocomposites were prepared by two different methods, namely melt method and solvent method. Melt method employs the blending of benzoxazine and OMMT above the melting point of benzoxazine without solvent. In the solvent method, OMMT was dispersed in an organic solvent and then blended with benzoxazine. XRD measurements of the polybenzoxazine/clay hybrid nanocomposites showed that the blending method and the kind of solvent play crucial roles in the dispersion of OMMT in the polybenzoxazine matrix. DSC showed that the inclusion of any type of OMMT significantly lowered the curing exotherm of benzoxazines. The hybrid nanocomposites exhibited higher T g values than the pristine resins. Dynamic and isothermal TGA clearly showed that the thermal stability was improved by the inclusion of clay.

Preparation and characterization of poly(urethane–imide) films prepared from reactive polyimide and polyurethane prepolymer

Abstract A novel type of poly(urethane–imide) was prepared by a reaction of a polyurethane prepolymer and a soluble polyimide containing hydroxyl functional group. Polyurethane prepolymer was prepared by a reaction of polyester polyol and 2,4-tolylenediisocyanate and then end-capped with phenol. Soluble polyimide was prepared by the two-step synthesis from 2,2′-bis (3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3′-diamino-4,4′-dihydroxybiphenyl (AHBP). Soluble polyimides having various content of hydroxyl functional groups were prepared similarly by using diamine mixtures of AHBP and oxydianiline. Cast films were obtained from blend solutions of the polyurethane prepolymer and the polyimide. The cast films were thermally treated at various temperatures to give a series of transparent poly(urethane–imide) films. By changing the ratio of polyurethane and polyimide components, poly(urethane–imide) films having various properties from plastic to elastomer were prepared. Dynamic mechanical analysis showed that lower glass transition temperature (Tg) of the films shift to high temperature with the increase of polyimide component, suggesting that the two polymer components are miscible to some extent. Thermogravimetric analyses indicated that the thermal degradation of poly(urethane–imide) occurs at ca. 270°C, which is ca. 30°C higher than the conventional polyurethane, confirming that the introduction of polyimide component improved the thermal stability of polyurethane.

High Performance Polybenzoxazines as Novel Thermosets

Polybenzoxazine as a novel phenolic type thermoset has been developed to overcome the shortcomings associated with the use of the traditional phenolics. It can be prepared from cyclic benzoxazines via thermally induced ring-opening polymerization. Various benzoxazine monomers can be synthesized from mono-or diamines and mono-or bisphenols with formaldehyde. Polybenzoxazines have not only the advantageous properties of conventional phenolic resins such as high thermal properties, but also other interesting advantages that are not found in the traditional phenolic resins such as excellent dimensional stability. The disadvantages of the typical polybenzoxazines are the high temperature needed for complete cure and the brittleness of the cured materials. Further improvement of thermal properties is also expected for application in harsh conditions. Herein we report on various approaches for performance improvement of polybenzoxazine. These approaches include alloying with other high performance polymers, hybridization with inorganics, and designing of novel monomers as well as high molecular weight polymeric precursors. By these approaches, lowering of the cure temperature, improvement of toughness, and enhancement of thermal and mechanical properties were achieved.

Preparation of porous carbon films by the pyrolysis of poly(urethane-imide) films and their pore characteristics

Abstract Porous carbon films were prepared by the pyrolysis of poly(urethane-imide) films that were prepared by a reaction between phenol-terminated polyurethane prepolymer and poly(amide acid) obtained from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA). Upon thermal treatment of the poly(urethane-imide) films at 300 to 400°C, the thermally less stable urethane domains decomposed, leaving porous polyimide films. The porous polyimide films were further pyrolyzed at 900°C for 1 h to give porous carbon films. The formation of macropores was confirmed from scanning electron microscopy (SEM) of the surface and the cross-section of the films. The size distribution of the macropore was relatively narrow. With the increase of urethane content, the size of the macropore increased. The average pore size was found to be controlled between 0.6 μm and 10 μm by changing the ratio of the imide and the urethane components. It was also revealed from nitrogen adsorption isotherms that macroporous carbon films also contain micropores that were formed during the pyrolysis of the polyimide films. The progress of the micropore formation was studied by measuring nitrogen adsorption isotherms of the carbonized films treated at various temperatures.

Synthesis and characterization of epoxy film cured with reactive polyimide

Abstract Reactive polyimide containing hydroxyl functionalities was prepared from the reaction of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and 3,3′-diamino-4,4′-dihydroxybiphenyl. Commercial epoxy resin was cured in the presence of different ratios of the reactive polyimide, giving a series of polyimide modified epoxy films. The transparent films had excellent solvent resistance. The tensile measurements of the films showed that, with the increase of the polyimide content, tensile modulus of the film increased but there was almost no change in the elongation at break. Viscoelastic measurements showed that glass transition temperature shifted with the increase of the polyimide content; 127°C for 13.5%, 220°C for 29.4%, 260°C for 45.4% and 290°C for 62.5%. Thermogravimetric analysis showed the increase of the thermal stability with the increase of the polyimide content.

Novel method for the preparation of poly(urethane–imide)s and their properties

A polymer blend consisting of polyimide (PI) and polyurethane (PU) was prepared by means of a novel approach. PU prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate (2,4-TDI) and then end-capped with phenol. Poly(amide acid) was prepared from pyromellitic dianhydride (PMDA) and oxydianiline (ODA). A series of oligo(amide acid)s were also prepared by controlling the molar ratio of PMDA and ODA. The PU prepolymer and poly( amide acid) or oligo( amide acid ) solution were blended at room temperature in various weight ratios. The cast films were obtained from the blend solution and treated at various temperatures. With the increase of polyurethane component, the films changed from plastic to brittle and then to elastic. The poly(urethane-imide) elastomers showed excellent mechanical properties and moderate thermal stability. The elongation of films with elasticity was more than 300%. The elongation set after the breaking of films was small. From the dynamic mechanical analysis, all the samples showed a glass transition temperature (Tg) at ca. -15°C, corresponding to T g of the urethane component, suggesting that phase separation occurred between the two polymer components, irrespective of polyimide content. TGA and DSC studies indicated that the thermal degradation of poly( urethane-imide) was in the temperature range 250-270°C.

Effect of Hydroxyphenylmaleimide on the Curing Behaviour and Thermomechanical Properties of Rubber-Modified Polybenzoxazine

Hydroxyphenylmaleimide (HPMI) and/or amine terminated butadiene acrylonitrile (ATBN)-modified polybenzoxazine were prepared by mixing benzoxazine monomer (Ba), HPMI and ATBN. The onset of the ring opening of the pristine Ba started with differential scanning calorimetry at 223°C with a maximum at 247°C. The incorporation of ATBN lowered the onset and the maximum of the exotherm to 180°C and 216°C respectively. The incorporation of HPMI initiated the ring opening of Ba at a temperature as low as 160°C with a maximum at 200°C. Viscoelastic measurements showed that the incorporation of HPMI increased the T g and the storage modulus compared to that of the unmodified polybenzoxazine and ATBN-modified polybenzoxazine. Tensile property measurements indicated that the tensile modulus was enhanced with the addition of HPMI to ATBN-modified polybenzoxazine accompanied with little decrease in the elongation at break. Thermogravimetric analysis showed that the addition of HPMI enhanced the thermal stability of polybenzoxazine.