Enantiomer‐selective polymerization of (RS)‐(phenoxymethyl)thiirane with diethylzinc/L‐amino acid

Enantiomer‐selective polymerization of (RS)‐(phenoxymethyl)thiirane (RS‐ 1 ) was carried out with ZnEt₂/L ‐α‐amino acid as an initiator system, and the effect of the initiator system on the enantiomer selectivity was examined with various amino acids. All polymerizations heterogeneously proceeded, and every initiating system was effective in producing optically active polymers. For the polymerization of RS‐ 1 with diethylzinc (ZnEt₂)/L ‐leucine (1/1), the conversion was 43.7% in 12 days, and the number‐average molecular weight of the polymer was 18,000. The enantiomer selectivity was maximum when the molar ratio of the two components in the ZnEt₂/L ‐α‐amino acid system was 1:1. When the ZnEt₂/L ‐leucine (1/1) system was used in the polymerization, the best result was obtained with an enantiomer‐selectivity value of 5.36. During the polymerization, the S enantiomer was preferentially consumed, and the isotactic‐rich polymer was enriched in the S configurational units produced. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3443–3448, 2002     

Synthesis and properties of polymers containing sprio(indoline-isoxazoline)

Polymers containing spiro(indoline-isoxazoline) nuclei were prepared by 1,3-dipolar cycloaddition reactions of N,N′-alkylene-bis-3,3-dimethyl-2-methyleneindolines with bis-hydroxamic chlorides. Irradiation of the polymers with UV in solution resulted in novel skeletal rearrangements and resulted in polymers containing benzo-1,5-diazocine-2-one nuclei. Photoconductivities of the polymers were also studied.     

Antioxidants from rape (Brassica campestris vir. Japonica Hara) oil cake

A simple but novel compound, S-1-methoxy-1-(3,5-dimethoxy-4-hydroxyphenyl)ethane, was isolated as a moderately antioxidative compound from rape (Brassica campestris L. subsp. napus) oil cake together with 5 known compounds. Three of these compounds, indolacetonitrile, 4-hydroxyindolacetonitrile, and 4-hydroxyphenylacetonitrile, showed strong antioxidative activity evaluated by the ferric thiocyanate method.     

Adsorption behavior of polymers having phosphoric acid group on γ-Fe2O3 and magnetic characteristics in magnetic coatings

Polymers having phosphoric acid groups were prepared as a model binder for magnetic coatings, and the correlation among the adsorption behavior of the polymers onto-Fe₂O₃ particles and the dispersibility, the orientation, and the packing density of-Fe₂O₃ particles in the magnetic coatings was investigated.PMMA homopolymer molecules hardly adsorbed on-Fe₂O₃, and the interfacial tension at a water/polymer solution (toluene) interface ( _W/T) was scarcely changed compared with a water/toluene interface. Increasing with the content of polymeric phosphoric acid group, the adsorbance of polymer increased and the interfacial tension ( _W/T) decreased. When the content of polymeric phosphoric acid groups was over 0.4 mol%, the adsorbance of polymer and interfacial tension ( _W/T ) remained constant. When these polymers were used as a binder for magnetic tapes, the dispersibility of-Fe₂O₃ in the magnetic coatings was improved, increasing with the content of polymeric phosphoric acid group; however, when the content of phosphoric acid group was over 0.2 mol%, its dispersibility decreased abruptly.Studies on Recording Magnetic Materials and Magnetic Composite. XVIII.     

End‐functionalization of polystyrene by malto‐oligosaccharide generating aggregation‐tunable polymeric reverse micelle

This article describes that glucose, maltose, maltotriose, maltotetraose, maltopentaose, and maltohexaose ( a , b , c , d , e , and f , respectively) were introduced into the initiating chain‐end of polystyrene (PSt) through the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO)‐mediated radical polymerization. A series of glycoconjuaged TEMPO‐adducts, 1a–f , was synthesized and used as the initiators for the polymerization of styrene (St) for 6 h at 120 °C to afford the end‐functionalized PSt's with the acetyl saccharides, 2a–f , in the yields of 37–43%. For 2a–f obtained by the polymerizations using the [St]/[ 1 ] of 125, 250, and 500, the number‐average molecular weights determined by size exclusion chromatography (SEC), M_n,SEC's, were 4800–6300, 8800–10,600, and 18,400–25,200, respectively, which fairly agreed with the predicted values. The end‐functionalized PSt's with saccharides, 3a–f , which were obtained from the deacetylation of 2a–f using sodium methoxide in dry THF, formed the polymeric reverse micelles consisting of a saccharide‐core and a PSt‐shell in chloroform and toluene. The static laser light scattering (SLS) measurements provided the average molar mass of the aggregates in toluene, M_w,SLS's, which ranged from 7.50 × 10⁴ to 1.77 × 10⁵ for 3a , from 1.90 × 10⁵ to 4.93 × 10⁵ for 3b , from 4.41 × 10⁵ to 7.21 × 10⁵ for 3c , from 5.85 × 10⁵ to 8.51 × 10⁵ for 3d , from 7.55 × 10⁵ to 8.53 × 10⁵ for 3e , and from 8.54 × 10⁵ to 9.26 × 10⁵ for 3f . The aggregation numbers, N_agg's, which were calculated from the M_w,SLS's, were from 7 to 24 for 3a , from 20 to 37 for 3b , from 34 to 89 for 3c , from 39 to 116 for 3d , from 41 to 145 for 3e , and from 31 to 146 for 3f . It was confirmed that the aggregation property, such as the M_w,SLS or N_agg values, was strongly related to the polymerization degrees of St (DP's) or the number of the glucose residues (n's) for 3a–f . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4864–4879, 2006     

Defects in separation by implanted oxygen wafer probed by monoenergetic positron beams

Defects in the separation by implanted oxygen (SIMOX) wafers were studied by monoenergetic positron beams. For the as-implanted specimen, vacancies introduced by ion implantation were found to form vacancy-oxygen complexes. After high temperature annealing, a drastic increase in the formation probability of positronium was observed. This suggests an introduction of open-spaces by the formation of an amorphous SiO₂. The present investigation shows that positrons provide a nondestructive probe for the detection of defects in SIMOX wafers and microstructures of SiO₂.     

Variation of the Alexander-Conway polynomial under Dehn surgery

Let ε₁ and ε₂ belong to {±1}. When the ε₁-surgery along a knot K₁ in S³ produces the same homology sphere as the ε₂-surgery along a knot K₂ in S³, then the Casson surgery formula implies that ε₁Δ_K1″(1)=ε₂Δ_K2″(1), where Δ(t) denotes the symmetric Alexander polynomial. For any pair (Λ₁(t),Λ₂(t)) of possible knot Alexander polynomials such that ε₁Λ₁″(1)=ε₂Λ₂″(1), we exhibit a pair (K₁,K₂) of knots in S³ such that Δ_K1(t)=Λ₁(t), Δ_K2(t)=Λ₂(t) and the ε₁-surgery along K₁ produces the same homology sphere as the ε₂-surgery along K₂.     

Preparation of48V source for measurements of lineshapes of annihilation radiations and positron lifetimes

The preparation of the⁴⁸V positron source induced in a 1 μm thick Ti foil by (³He, pxn) reaction with a cyclotron is described. This source is very convenient for measurements of lineshapes of annihilation radiations and positron lifetimes at low or high temperatures, in a vacuum or for liquid metals. The absence of the mixing of long lifetime components is also convenient for the study of defects.     

On a general treatment for coupled thermal stress problems in a cylindrical coordinate system

Summary In this paper, we study the three-dimensional coupled thermoelastic problem governed by the cylindrical coordinate system under the consideration of the thermo-mechanical coupling effect. The basic relations for the three-dimensional displacement field and the corresponding stress components are derived from the field equations of motion. These expressions enable us to determine both the temperature and the stress distributions simultaneously. As an illustration, numerical calculations are carried out for an axisymmetrical coupled thermoelastic problem. From the numerical results it is shown that the thermomechanical coupling term appearing in the corrected heat conduction equation gives a fairly large difference between the coupled theory and the uncoupled one.

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Zur allgemeinen Behandlung gekoppelter Wärmespannungsprobleme in Zylinderkoordinaten

Übersicht Es wird das dreidimensionale Wärmespannungsproblem unter Berücksichtigung der thermomechanischen Kopplung untersucht. Ausgehend von den Bewegungsgleichungen werden Temperatur und Spannungen angegeben. Zur Illustration der Methode wird ein axialsymmetrisches Problem numerisch behandelt und der Einfluß der thermo-meehanischen Kopplung auf die Wärmeleitgleichung gezeigt.

     

Evaluation of the formation entropy of a single vacancy by means of positron annihilation

Analyzing positron annihilation data it was found that the formation energy of a single vacancy is proportional to the characteristic temperature T_c in f.c.c. metals. Assuming that the equilibrium fractional concentrations of single vacancies at T_c are constant, one finds that the formation entropy of a single vacancy is (1.6 ± 0.1)k for all f.c.c. metals. For zinc and cadmium, the formation entropies are 2.5k and 3.3k respectively.