Susumu Iwabuchi

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.

Initial elementary processes in tetrafluoroethylene plasma: An ab initio molecular orbital study

Initial elementary processes in tetrafluoroethylene plasma are studied by using an ab initio molecular orbital method. The energy‐surfaces at excited states are obtained by the Hartree–Fock method with a double zeta basis set, plus Rydberg orbitals. A π‐π* transition is low‐lying both at singlet and triplet excited states. Vinyl‐polymerization‐type reactions are expected in the presence of some radical species via these transitions. The C=C bond cleaves via a triplet π‐σ* transition to form CF2. The predicted elementary processes via these states are compatible with experimental results that C2F4* and CF2 are primary precursors. No excited states that bring about a C—F bond cleavage are obtained within 10 eV of the ground state. As a path for a C—F bond cleavage, a dissociative electron attachment process is found in a low energy region. This process is considered to be important for producing fluorine anions.

A selection rule in SiHn(n=1-4)+F reactions : an ab initio molecular orbital study

Reactions of SiHn(n=1–4) with a fluorine atom were studied by using an ab initio molecular orbital method [fourth‐order Mo/ller–Plesset (MP4/6‐21G**//second‐order Mo/ller–Plesset MP2/6‐21G**)]. Structures of the transition states were determined. In the cases of SiH3+F and SiH+F, fluorine atom addition to a silicon atom was a favorable reaction at the singlet state and abstraction of a hydrogen by a fluorine atom was a favorable route at the triplet state. Abstraction of a hydrogen was also favorable at the doublet state in the case of SiH2+F. A selection rule of these reactions on the basis of the atomic spin density on each atom was proposed. The selection rule proposed was proved to also be applicable to the reaction CH3+F.

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.

Control of vinylsilane plasma by changing the pressure: Correspondence with a quantum chemical prediction

The pressure dependence of the chemical structure and the optical band gap of the films produced by the glow discharge decomposition of vinylsilane was studied on the basis of infrared and ultraviolet absorption spectroscopies. There was a significant structural difference between the films prepared at pressures below and above 0.08 Torr. The results are discussed in relation to the initial step of gas phase reactions predicted on the basis of an ab initio molecular orbital calculation. Good consistency between the experiment and the theoretical calculation was obtained by taking a pressure dependent transition in the excited state through which the decomposition of vinylsilane predominantly proceeded into account. That is, the contribution of the transition to the lowest triplet and singlet excited states becomes larger with the increase of pressure.

Anomalously low-lying lowest excited triplet state of SiH2FCHCH2: an ab initio molecular orbital study

Abstract The anomalously low vertical excitation energy from the ground state to the lowest excited triplet state (T1) is predicted for SiH2FCHCH2 (4.6 eV) by the quantum chemical calculation using ab initio MP3/3-21+G*//HF/3-21+G* molecular orbital methods. The steric effect of the fluorine which alters the symmetry of the molecule is considered to be responsible for the low-lying T1 state.

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.

SiH3CH3+F: A Potential Reaction System for Preparing Uniform SiC Film Predicted by Using an Ab Initio Molecular Orbital Method.

Abstraction reactions and substitution reactions on SiH3CH3 by an F atom were studied on the basis of an ab initio molecular orbital method. The structures and the total energies of the reactants, the transition states, and the products were obtained at a third order Moller Plesset (MP3)/D95**//Har-tree Fock (HF)/D95** and an MP3/6-21+G//HF/6-21+G level. The activation energies for hydrogen abstractions from Si and C were -5.20 kcal/mol and 1.65 kcal/mol, respectively, while those for substitution reactions caused by Si attack and C attack were 20.96 kcal/mol and 25.58 kcal/mol, respectively. The activation energies for hydrogen abstraction reactions which retained an Si–C bond were much lower than those for substitution reactions by which an Si–C bond was cleaved. Thus, the SiH3CH3+F system was proven to be promising for preparing a uniform SiC film at relatively low temperatures.

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.

A QUANTUM CHEMICAL REACTION DESIGN OF A PLASMA CHEMICAL REACTION OF VINYLSILANE

Plasma reaction modes of vinylsilane at excited states were estimated on the basis of the two-center bond energies and the localized orbital energies obtained by using the MNDO molecular orbital method and a state energy diagram obtained by using an ab initio molecular orbital method. The vinyl π bond is activated at the lowest excited states, while the Si-C bond is weak at the second lowest excited states. A substantial energy difference exists between the lowest and the second lowest excited states. The experimental results of the rf plasma reaction of vinylsilane is consistent with this prediction. XPS of the film produced by a plasma CVD of vinylsilane show that a carbon-carbon skeletal network is formed via the cleavage of vinyl π bond when the supplied power is low. The excitation with a higher power facilitates the cleavage of the Si-C bond.