Catalysis of poly(urethane imidine) copolymer formation from amine‐blocked isocyanate and bisphthalide

The catalysis of imidine formation between an amine‐blocked polyurethane prepolymer and bisphthalide was studied with a series of metal alkoxides, phenoxides, and organotin compounds and tertiary amines. The carbon dioxide released during the reaction was followed for monitoring of the reaction. The metal alkoxides and phenoxides catalyzed the imidine formation reaction but did not catalyze the deblocking reaction, whereas the organotin compounds and tertiary amines showed no catalytic activity in the reaction between isocyanate and phthalide. With tin catalysts, the imidine formation reaction depended on the deblocking of the blocked prepolymer, but it was independent of deblocking with amine catalysts. The resultant poly(urethane imidine) copolymers were characterized with Fourier transform infrared, ¹H NMR, ¹³C NMR, gel permeation chromatography, and thermogravimetric analysis techniques. The thermal stability of polyurethane increased significantly with the incorporation of imidine groups. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4236–4242, 2001     

Mn2(AsS4)4]8- and [Cd2(AsS4)2(AsS5)2]8-: discrete clusters with high negative charge from alkali metal polythioarsenate fluxes

The reaction of Mn and Cd in alkali metal polythioarsenate fluxes afforded four new compounds featuring molecular anions. K(8)[Mn(2)(AsS(4))(4)] (I) crystallizes in the monoclinic space group P2/n with a = 9.1818(8) A, b = 8.5867(8) A, c = 20.3802(19) A, and beta = 95.095(2) degrees. Rb(8)[Mn(2)(AsS(4))(4)] (II) and Cs(8)[Mn(2)(AsS(4))(4)] (III) both crystallize in the triclinic space group P1 with a = 9.079(3) A, b = 9.197(3) A, c = 11.219(4) A, alpha = 105.958(7) degrees, beta = 103.950(5) degrees, and gamma = 92.612(6) degrees for II and a = 9.420(5) A, b = 9.559(5) A, c = 11.496(7) A, alpha = 105.606(14) degrees, beta = 102.999(12) degrees, and gamma = 92.423(14) degrees for III. The discrete dimeric [Mn(2)(AsS(4))(4)](8-) clusters in these compounds are composed of two octahedral Mn(2+) ions bridged by two [AsS(4)](3-) units and chelated each by a [AsS(4)](3-) unit. Rb(8)[Cd(2)(AsS(4))(2)(AsS(5))(2)] (IV) crystallizes in P1 with a = 9.122(2) A, b = 9.285(2) A, c = 12.400(3) A, alpha = 111.700(6) degrees, beta = 108.744 degrees, and gamma = 90.163(5) degrees. Owing to the greater size of Cd compared to Mn, the Cd centers in this compound are bridged by [AsS(5)](3-) units. The [Cd(2)(AsS(4))(4)](8-) cluster is a minor component cocrystallized in the lattice. These compounds are yellow in color and soluble in water.     

Effects of periodic masker interruption on the intelligibility of interrupted speech

When listeners hear a target signal in the presence of competing sounds, they are quite good at extracting information at instances when the local signal-to-noise ratio of the target is most favorable. Previous research suggests that listeners can easily understand a periodically interrupted target when it is interleaved with noise. It is not clear if this ability extends to the case where an interrupted target is alternated with a speech masker rather than noise. This study examined speech intelligibility in the presence of noise or speech maskers, which were either continuous or interrupted at one of six rates between 4 and 128 Hz. Results indicated that with noise maskers, listeners performed significantly better with interrupted, rather than continuous maskers. With speech maskers, however, performance was better in continuous, rather than interrupted masker conditions. Presumably the listeners used continuity as a cue to distinguish the continuous masker from the interrupted target. Intelligibility in the interrupted masker condition was improved by introducing a pitch difference between the target and speech masker. These results highlight the role that target-masker differences in continuity and pitch play in the segregation of competing speech signals.     

Dose determination by ESR in an accident,using cotton fabric

Accidental exposure dose assessment by electron spin resonance (ESR) technique from the free radicals generated in a cotton handkerchief has been attempted in this investigation. The cotton handkerchief, a common material carried by individuals, was taken as the medium for free radical estimation. About 55 mg of the irradiated piece of cloth was loaded into a quartz tube and the dose dependence of the ESR signal at g=2.0026 was measured at room temperature, using a Bruker ESP-300 ESR spectrometer in X-band (9.74 GHz). The intensity of this signal was found to be proportional to the dose in the range of 1–1000 Gy. The stability of the free radicals with time of storage was followed. Dependence of dose rate as well as the presence of water on the yield of free radicals were also investigated.     

Ni[P(OPh)3]4 Catalyzed Transfer Hydrogenation Using Hcoonh4

Ni[P(OPh)₃]₄ was found to catalyze the transfer hydrogenation of various organic functional groups using HCOONH₄.

     

An Improved Synthesis of Oxazinones Using Molecular Sieves

Abstract: Oxazinones are important chiral reagents in the synthesis of both proteinogenic and nonproteinogenic amino acids. Large scale synthesis of oxazinones has been a problem. The use of molecular sieves in the final step to remove ethanol has helped to obtain the cyclized product in three hours.     

Superconductivity characteristics of the system Y1.2Ba0.8CuO4−δ

Abstract

Superconducting behaviour of the multiphase system Y_1.2Ba_0.8CuO_4?δ has been studied, as a function of annealing conditions. These investigations strongly suggest the existence of an underlying superconducting phase with T_C = 90K. A series of annealings lead to a successive sharpening of the superconducting transition, the suppression of the localization effects (in the normal state) and the enhancement of the Meissner effect.