Kuniharu Kojima

Polymerization of methyl methacrylate by tri-n-butylborane in the presence of amino acid esters☆

Abstract The polymerization of methyl methacrylate by tri-n-butylborane in the presence of amino acid esters was investigated. The binary systems of tri-n-butylborane and amino esters were found to be more effective for initiating the polymerization than tri-n-butylborane alone. Co-catalytic effects of amino acid esters were in the order: tyrosinate > glutamate > aspartate ⪢ phenyl alaninate > serinate > glycinate. The rate of polymerization in a mixture of dimethylsulphoxide and toluene was proportional to the square root of the concentration of the initiator system, to the monomer concentration, and to the concentration of dimethylsulphoxide in the solvent. The overall energy of activation was estimated to be 4.6 kcal/mol for the tri-n-butylborane/methyl tyrosinate system. Copolymerization curves gave a typical free-radical character.

Stabilization of Ba2YCu3O7-δ by Surface Coating with Plasma Polymerized Fluorocarbon Film

High-Tc superconducting Ba2YCu3O7-δ pellets were coated with polyfluorocarbon thin films prepared by plasma polymerization of tetrafluoroethene (C2F4). The polymer-coated Ba2YCu3O7-δ preserved its high-Tc superconductivity even after it had been kept standing in water at 60°C, whereas the superconductivity of noncoated pellets was completely destroyed under the same condition. The high hydrophobicity of the film originated from high fluorine content is considered to be primarily responsible for the protection of the superconductor from chemical deterioration by preventing the hydrolysis at the surface.

A quantum chemical study on hydrogen radical reactions with methane and silane

A quantum chemical study on the reaction of CH4 , CF4 , SiH4 , and SiF4 with a hydrogen radical is performed on the basis of an ab initio molecular orbital calculation to predict the photochemical reactivity of methane, silane, and their analogues. The transition state geometry of the reactions is determined by employing a 3‐21G basis set. The total energies of reactant molecules at the initial, transition, and final states are calculated by employing a 6‐31G** basis set. The exponential parts of the rate constants of these reactions determined from these energies on the basis of the transition state theory are in good agreement with the experimentally obtained relative rates of the reaction. The present calculation was consistent with the experimental results of photochemical reactions for methane and silane derivatives.

Selective transport of amino acids across a crosslinked poly(l-glutamic acid) membrane

Abstract Poly( l -glutamic acid) (PLG) membranes were prepared by crosslinking poly[γ-(2-chloroethyl) l -glutamate] with diethylenetriamine and subsequently hydrolysing the side-chain esters. Selective amino acid transport across the membrane was examined using l -phenylglycine, l -phenylalanine and l -tryptophan. Transport selectivity increased with increasing pH of the solute solution, i.e. from 2.0 to 5.7. When pH was raised to 8.0 or when CaCl 2 was added, transport selectivity was lost. Conformational changes of PLG and electrostatic interactions between the solute and the membrane are suggested to cause the observed permselectivity behaviour.

Photo-oxidation-reduction sensitized by copolymers of [2-(9,10-anthraquinonyl)]methyl methacrylate

Abstract Copolymers of [2-(9,10-anthraquinonyl)]methyl methacrylate (AQMMA) with (2-naphthyl)-methyl methacrylate (NMMA) and benzyl methacrylate (BMA) were prepared. The photo-sensitizing efficiencies of these polymers for the oxidation-reduction of l -ascorbic acid and Fast Red A were examined in dimethylformamide. AQMMA-BMA copolymers with 6 and 14 mole% of AQMMA afforded nearly equal quantum yields, 1.6 times as large as that of a low molecular model compound, [2-(9,10-anthraquinonyl)]methyl acetate (AQMAc). The observed increase in the quantum yield is discussed in terms of energy delocalization, decreased rate of diffusion and cage effect by polymer segments. AQMMA-BMA-NMMA copolymers gave decreased quantum yields owing to intramolecular quenching of the anthraquinone triplet by the naphthalene unit. The intramolecular quenching was interpreted according to Perrins model of static quenching. With the radius of quenching sphere assumed to be 13 A, the local naphthalene concentration around the anthraquinone unit was suggested to be approximately 20 times as small as that in solid films.

Polymerization of Methyl Methacrylate Initiated byjributylborane-Pyridine System

The polymerization of methyl methacrylate (MMA) by the catalysts systems of tributylborane (TBB) with pyridine and its derivatives, such as hydroxypyridine, cyanopyridine, nicotinic acid, nicotinamide, nicotinic ester, picoline, lutidine and quinoline was studied. The relative initiating activities of the pyridine and its derivatives were found to be in the following order: nicotinic acid> nicotinic ester> nicotinamide> pyridine>3-hydroxypyridine>3-cyanopyridine> quinoline > 3-picoline > acridine > 2, 6-lutidine In the polymerization of MMA initiated by TBB/methyl nicotinate (MN) system, the rate of polymerization was found to be proportional to the concentration of MMA and to the square root of TBB/MN concentrations, respectively, and the apparent activation energy was 4.1 kcal/ mol. And the reaction of TBB with pyridine was also studied by NMR and ESR methods. From these results, it was found that the polymerization proceeds via a radical mechanism involving a co-ordination between TBB and pyridine or its derivatives.

Special articles on chemistry and technology of energy conversion. Synthesis of amphiphilic surfactants containing porphyrin and their photosensitizing effect on the reduction of Fast Red A by ascorbic acid.

Amphiphilic surfactants containing porphyrin with one or four poly(oxyethylene) chains were prepared by an immortal_polymerization. The photosensitizing effect of these polymers on the oxidation-reduction of L-ascorbic acid and Fast Red A(FRA) was examined in acetate buffer solution. The polymer having four poly(oxethylene) chains photosensitized the reduction better than the polymer with one poly(oxyethylene) chain which formed association. The effects of pH and of surfactant concentration on the photosensitized reaction were examined.

Photooxidation-Reduction Sensitized by Copolymers of [2-(9,10-Anthraquinonyl) methyl Methacrylate. II. Intramolecular Chemical Quenching by 2-Hydroxyethyl Methacrylate Units

Abstract Copolymers of [2-(9,10-anthraquinonyl)] methyl methacrylate (AQMMA) with 2-hydroxyethyl methacrylate(HEMA) were prepared, and their photosensitizing efficiencies were examined with respect to oxidation-reduction between L-ascorbic acid and Fast Red A in dimethylformamide. The photosensitizing efficiency was found to decrease with increasing HEMA content in the polymer. Intramolecular chemical quenching of anthraquinone triplet by HEMA units leading to the formation of O-alkylated anthra-hydroquinone derivatives (photoadducts) was found to be responsible for the observed decrease in photosensitizing efficiency. The linear relationship between the quantum yield ratio of photo-adduct formation to photosensitization and the mole ratio of HEMA to AQMMA suggests that triplet energy delocalization is effected in the AQMMA sequence where the initial excitation takes place and that the HEMA sequences nearest to the AQMMA sequence are involved in photoadduct formation.