Apirat Laobuthee

Thermal decomposition processes in polybenzoxazine model dimers investigated by TGA-FTIR and GC-MS

The thermal decomposition processes of a model compound containing Mannich bridge and a series of polybenzoxazine model dimers are investigated using TGA–FTIR and GC–MS. The 2,4-dimethylphenol-based benzoxazine dimers degraded into smaller and highly volatile compounds, leaving no char at the end of degradation. The p-cresol-based benzoxazine dimers degraded into smaller and highly volatile products as well, nevertheless some of which are able to undergo crosslinking and aromatization processes and form char. The major decomposition products for modified p-cresol-based dimers are amines and ester compounds. # 2002 Published by Elsevier Science Ltd.

MgAl2O4 spinel powders from oxide one pot synthesis (OOPS) process for ceramic humidity sensors

Abstract MgAl 2 O 4 spinel powders can be prepared via the oxide one pot synthesis (OOPS) process. Porous ceramic oxide bodies can be produced with these powders and used as humidity-sensing materials. Pellets were characterized by SEM and their electrical properties were measured using impedance spectroscopy in the frequency range from 10 −2 to 10 5 Hz at different relative humidity (RH) levels in the range 4–90%. The spinel pellets made of powder from the OOPS process exhibited good humidity sensitivity with a linear response of the logarithm of resistance with RH in the whole RH range tested.

A novel ion extraction material using host-guest properties of oligobenzoxazine local structure and benzoxazine monomer molecular assembly

Bisphenol-A based benzoxazine monomer (BA-m) and its oligomer are applied as an ionophore to study by Pedersens technique, the ion interaction with alkali and alkaline earth ions. Ion extraction efficiencies are significant when the solubility parameter of the organic phase is close to that of BA-m or the x-parameter is 0.34. Ionophore concentration controls the amount of metal ion extraction. Both BA-m and its oligomer show high entrapment efficiency over 70% extraction, for all types of ions.

Metal Ion Guest Responsive Benzoxazine Dimers and Inclusion Phenomena of Cyclic Derivatives

A series of benzoxazine dimers (1–9),esterified benzoxazine dimers (10–18),and benzoxazine dimer based macrocyclic derivatives(19–22) are prepared. The metalion guest responsive properties of the benzoxazine dimersobtained are clarified by using Pedersens technique.The ion extractions of the benzoxazine dimers are controlledby the bulkiness of the functional group at the aza position.The ones with cyclohexyl bulky groups at the aza position,7–9, are two times higher than thosewith methyl groups, 1–3. The extractionsare close to 100% for esterified dimers (10–18).For the macrocyclic derived dimers, the ether cyclic derivatives,21-22, interact with sodium, potassium and cesium ionsat stoichiometric ratios 2:1 and 1:1 depending on themetal species, as evidenced from 1H-NMR.

Novel Recovery of Nano-Structured Ceria (CeO2) from Ce(III)-Benzoxazine Dimer Complexes via Thermal Decomposition

N,N-bis(2-hydroxybenzyl)alkylamines, benzoxazine dimers, are the major product produced from benzoxazine monomers on mono-functional phenol by the one step ring opening reaction. Due to the metal responsive property of benzoxazine dimers, in this present work, N,N-bis(5-methyl-2-hydroxybenzyl)methylamine (MMD), N,N-bis (5-ethyl-2-hydroxybenzyl)methylamine (EMD), and N,N-bis(5-methoxy-2-hydroxybenzyl) methyl amine (MeMD), are considered as novel ligands for rare earth metal ion, such as cerium(III) ion. The complex formed when the clear and colorless solutions of cerium nitrate and benzoxazine dimers were mixed, results in a brown colored solution. The metal-ligand ratios determined by the molar ratio and the Job’s methods were found to be in a ratio of 1:6. To clarify the evidence of the complex formation mechanism, the interactions among protons in benzoxazine dimers both prior to and after the formation of complexes were determined by means of 1H-NMR, 2D-NMR and a computational simulation. The single phase ceria (CeO2) was successfully prepared by thermal decomposition of the Ce(III)-benzoxazine dimer complexes at 600 °C for 2 h, was then characterized using XRD. In addition, the ceria powder investigated by TEM is spherical with an average diameter of 20 nm.

The Effect of Alkali and Ce(III) Ions on the Response Properties of Benzoxazine Supramolecules Prepared via Molecular Assembly

A series of benzoxazine monomer supramolecules with different substituted groups on their benzene ring was prepared with a Mannich reaction and characterized by FTIR, 1H-NMR and MS. The obtained products were 3,4-dihydro-3-(2’-hydroxyethylene)-6-methyl-2H-benzoxazine (BM1), 3,4-dihydro-3-(2’-hydroxyethylene)-6-ethyl-2H-benz-oxazine (BM2), and 3,4-dihydro-3-(2’-hydroxyethylene)-6-methoxy-2H-benzoxazine (BM3). The efficiency of alkali metal ion extraction from the products was determined with Pedersen’s technique, while the complexation of the Ce(III) ion was confirmed by the Job’s and the mole ratio methods. The evidence of complex formation between benzoxazine monomers and Ce(III) ions was obtained with FTIR and a computational simulation. Single phase ceria (CeO2) as observed with XRD was successfully prepared by calcinating the Ce(III)-benzoxazine monomer complexes at 600 °C for 2 h. In addition, the geometry of the ceria nanoparticles confirmed by TEM is spherical, with an average diameter of 10‑20 nm.

Silica surface modified with benzoxazine-functional silane

Silica surface modified with silylbenzoxazine monomers having different bulky groups at ortho and para positions on the oxazine ring, i.e. 3-triethoxysilyl-n-propyl-3,4-dihydro-2H1,3-benzoxazine coupled with silica (4), 3-triethoxysilyl-n-propyl-3,4-dihydro-6-methyl-2H-1,3-benzoxazine coupled with silica (5), and 3-triethoxysilyl-n-propyl-3,4-dihydro-6,8-dimethyl-2H-1,3- benzoxazine coupled with silica (6) are synthesized to obtain a series of ion extraction resins. Fourier transform infrared spectroscopy (FT-IR) and elemental analysis support the successful coupling of benzoxazine-functional silane onto silica surface. The ion extraction studies of various alkali and alkaline earth metal ions from aqueous phase via the surface treated silica column chromatography shows the significant ion extraction ability of (6) compared to those of (4) and (5).

Mono-Substituted Phenol-Based Benzoxazines: Inevitable Dimerization Via Self-Termination and Its Metal Complexation

Publisher Summary This chapter explains molecules and chemistry of Benzoxazines that describe that benzoxazines are a type of heterocyclic compounds consisting of benzene and oxazine rings. The eight isomers are dependent on the position of the methylene group by supplementary H. They are obtained via Mannich reaction from phenols, formaldehyde, and amines. Benzoxazines received much more attention when their superb thermosetting property with simple preparation steps from bisphenol A-based benzoxazine monomers, namely, polybenzoxazines. It is proposed that the mechanism initiated by phenol approaching benzoxazines via an intermolecular hydrogen bond results in an intermediary complex. This complex provides electron movement from the nitrogen atom to the hydroxyl group. Polymerization of monosubstituted benzoxazines by varying types of phenols, reaction temperatures, molar ratios, and phenol initiator concentrations is explored in this chapter. The degree of polymerization is limited to low oligomers. This chapter describes that bisphenol A-based benzoxazines give thermosetting polybenzoxazines via a ring opening reaction; monofunctional phenol-based benzoxazines do not perform polymerization. The detailed studies on the reaction conditions declared that the self-termination after a single ring opening reaction occurred based on the formation of a six-membered ring between the aza-methylene and hydroxyl groups of the phenol ring. This mechanism was favored under the stoichiometric ratio between the benzoxazine monomer and phenol in nonpolar solvent at 65 °C. The single crystal structure of the host–guest compound declared a dimeric framework of benzoxazine imers in which metal ions were entrapped under lone-pair electrons of two nitrogen atoms and four oxygen atoms.

Barium ferrite prepared by modified Pechini method: effects of chloride and nitrate counter ions on microstructures and magnetic properties

Barium hexaferrite powders were successfully prepared by the modified Pechini method using citrate and glycerol. The materials were prepared employing different Ba:Fe ratios, iron(III) precursors and calcination temperatures. The obtained powders were characterized by XRD, VSM, SEM, EDX and FT-IR. The Ba:Fe molar ratio of 1:11, for both chloride and nitrate series, is observed to be the optimal ratio to attain the phase-pure barium hexaferrite. Moreover, these barium hexaferrite powders synthesized with the Ba:Fe ratio of 1:11 showed the highest saturation magnetization among the samples in the same series. Interestingly, the powders formed from chloride precursors had significantly lower coercive fields than those from nitrate precursors, highlighting the role of counter ions. The reasons were likely to be the smaller particle sizes in materials obtained from the nitrate precursors and possibly the distortion of the barium hexaferrite structure due to the substitution of some oxide with the chloride species within the materials obtained in the chloride series.

Preparation of Palladium-Impregnated Ceria by Metal Complex Decomposition for Methane Steam Reforming Catalysis

Palladium-impregnated ceria materials were successfully prepared via an integrated procedure between a metal complex decomposition method and a microwave-assisted wetness impregnation. Firstly, ceria (CeO2) powders were synthesized by thermal decomposition of cerium(III) complexes prepared by using cerium(III) nitrate or cerium(III) chloride as a metal source to form a metal complex precursor with triethanolamine or benzoxazine dimer as an organic ligand. Palladium(II) nitrate was consequently introduced to the preformed ceria materials using wetness impregnation while applying microwave irradiation to assist dispersion of the dopant. The palladium-impregnated ceria materials were obtained by calcination under reduced atmosphere of 10% H2 in He stream at 700°C for 2 h. Characterization of the palladium-impregnated ceria materials reveals the influences of the metal complex precursors on the properties of the obtained materials. Interestingly, the palladium-impregnated ceria prepared from the cerium(III)-benzoxazine dimer complex revealed significantly higher BET specific surface area and higher content of the more active Pdδ