Mechanism of formation of YBa2Cu4O8 superconductor in the sol-gel synthesis

It was shown that a single phase YBa₂Cu₄O₈ (124-phase) could be formed from gels at 1 atm oxygen pressure, and the mechanism of its formation was elucidated. It was found that there are two key routes for the sol-gel formation of the 124-phase, one involving the tetragonal YBa₂Cu₃O _y with a low concentration of oxygen defects (tetra-I phase) and the other involving the Ba₂Cu₃O_5.9 as important intermediates of the 124-phase. The rapid formation of these intermediate compounds from the gel was attributed to the small particle size of the oxides and carbonates precipitating at the initial stage of heating. It was thought that the small particles characteristic of sol-gel processing lead to the rapid formation of the intermediate compounds and subsequent precipitation of the 124-phase.     

Cationic polymerization of vinyl compounds in the presence of tetra-n-butylammonium salts

The effects of salts were examined in cationic polymerization of vinyl compounds. Cationic polymerization of styrene was carried out at 0°C, with acetyl perchlorate, stannic chloride, stannic chloride–trichloroacetic acid and boron trifluoride etherate as catalysts. Tetra-n-butylammonium perchlorate, fluoroborate and iodide were used as salts. The presence of small amounts of the salts changed both the polymerization rate and the molecular weight of polymer considerably. The consideration of various effects led to the conclusion that the results are explicable principally on the basis of counterion exchange. To confirm this, the copolymerization of 2-chloroethyl vinyl ether with γ-methylstyrene was investigated at ?78°C. The copolymer composition curve when stannic chloride was used as catalyst was changed and coincided with that of polymer obtained with acetyl perchlorate catalysis when the perchlorate salt was added. This supports the concept of counterion exchange.     

Copolymerization of 1-(trimethylsilyl)-1-propyne with disubstituted hydrocarbon acetylenes

Copolymerization of 1-(trimethylsilyl)-1-propyne (MeC ≡ CSiMe₃) with several aromatic and aliphatic disubstituted acetylenes (MeC ≡ CPh, n-BuC ≡ CPh, 2-octyne, and 4-octyne) were examined by using Ta and Nb catalysts. The TaCl₅–Ph₃Bi catalyst was effective in copolymerization with the aromatic acetylenes, whereas the NbCl₅–Ph₃Bi catalyst was preferable in copolymerization with the aliphatic acetylenes. The copolymerization products were not mixtures of homopolymers but copolymers. The relative reactivity of monomer tended to decrease with increasing steric effect of monomer: 2-octyne > MeC ≡ CSiMe₃ > 4-octyne > MeC ≡ CPh > n-BuC ≡ CPh. The copolymers of MeC ≡ CSiMe₃ with MeC ≡ CPh [copoly(TMSP/PP)s] had high molecular weight (M _w > 1 × 10⁶), and provided thermally stable tough films. With increasing MeC ≡ CPh content of copoly(TMSP/PP), the oxygen permeability coefficient (P) decreased, while the separation factor (P/P) increased.     

Hydrolysis and condensation reactions of Si(OC2H5)4 related to silica fiber drawing

The hydrolysis and condensation reactions of Si(OC₂H₅)₄ (TEOS) at 80°C in the TEOS---H₂O---C₂H₅OH---HCl solutions with H₂O/TEOS molar ratios (r) from 1.0 to 2.0 were followed by gas chromatography (GC) and measurement of molecular weight ( ) of the hydrolyzates, in order to explain the viscosity change of the solutions. It has been found that the siloxane oligomers with average polymerization degree (n) from 2 to 7 are formed in the early stage of reaction and undergo condensation to form higher polymers. The n and the number of silanol groups of the oligomers are increased with increasing r. The fact that the solution viscosity increased once rapidly around the so-called gelation point followed by a sluggish increase with the increase of reaction time for an r of 1.7, while it increased rapidly without a break till gelation for an r of 2.0, was attributed to fewer silanol groups and higher steric hindrance as a result of more −OC₂H₅ groups remaining in the oligomers for an r of 1.7.     

Synthesis of transparent BaTiO<Subscript>3</Subscript> nanoparticle/polymer hybrid

Transparent BaTiO₃ nanoparticle/polymer hybrid was synthesized by polymerization and hydrolysis of barium titanium alkoxide modified with 2-vinyloxyethoxy ligand. Barium alkoxide, titanium alkoxide and 2-vinyloxyethanol were reacted affording a BaTiO₃ precursor, which was then hydrolyzed and polymerized to form BaTiO₃ particle/polymer hybrids below 100°C. BaTiO₃ particles increased in crystallinity with increasing water amount for hydrolysis. The absorption edge of the hybrid film on silica plates shifted to shorter wavelength with decreasing crystallite size. Nano-sized BaTiO₃ particle/polymer hybrid polymerized with methyl methacrylate (MMA) was shaped into a transparent and self-standing film with a refractive index of 1.595 at 589 nm.     

Synthesis of transparent BaTiO3 nanoparticle/polymer composite film using DC field

Transparent BaTiO₃ nanoparticle/polymer composite films were synthesized from titanium-organic film and barium ion in aqueous solution under direct current (DC) field. Titanium-organic precursor was synthesized from titanium isopropoxide, acetylacetone and methacrylate derivative. The UV treatment was effective to increase the anti-solubility of the titanium-organic film during DC processing. BaTiO₃ nanoparticles were crystallized in the precursor films on stainless substrates without high temperature process, as low as 40°C. The crystallite size of BaTiO₃ increased with increasing reaction temperature from 40 to 50 °C at 3.0 V/cm. BaTiO₃ nanoparticles also grew in size with increasing reaction time from 15 min to 45 min at 3.0 V/cm and 50 °C. Transparent BaTiO₃ nanoparticle/polymer films were synthesized on stainless substrates at 3.0 V/cm and 50°C for 45 min.     

Acylation of heteroaromatic amines. II dibenzoylation of aminopyridines

Three isomeric aminopyridines were reacted with an excess of benzoyl chloride in the presence of an excess of triethylamine, giving the corresponding dibenzoylaminopyridines in high yields. As an application of the dibenzoylation, the aminopyridines were also reacted with phthaloyl dichloride, resulting in appreciable yields of the respective N-pyridylphthalimides. The rate of the conversion under various conditions was studied with high pressure liquid chromatography in order to investigate the difference in reactivity among the three isomers.     

Polymerization of 1-chloro-2-phenylacetylene induced by UV irradiation of Mo(CO)6

Polymerization of 1-chloro-2-phenylacetylene was effected by the catalyst formed by UV irradiation of Mo(CO)₆ in carbon tetrachloride to provide in high yield a polymer whose weight-average molecular weight reached 2 × 10⁶. UV irradiation and an appropriate halogenated hydrocarbon were essential for the formation of active species. The formation of a metal carbene as active species was inferred. Poly(1-chloro-2-phenylacetylene) was a light-yellow solid having the structure $ \rlap{--} ({\rm CCl\dbondCPh\rlap{--} )}_n $. The polymer was soluble in aromatic and halogenated hydrocarbons, and a film could be formed from polymer solution.