EPR spectra and structure of 1,2-dihydroxy- and 1,2,4-trihydroxy-anthrasemiquinones

Conclusions Radicals of hydroxyanthrasemiquinones were generated by chemical and electrochemical reduction and their probable structures established by EPR.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 822–827, April, 1986.     

Course of bromination of thiazole and 2-methylthiazole

Bromination of thiazole by bromine in the presence of aluminum chloride in neutral solvent or without solvent takes place at the 2-position. Such an orientation contradicts the traditional addition-cleavage mechanism, and agrees with the ylid mechanism of electrophilic substitution. 2-Methylthiazole brominates at the 5-position, and the reaction is impeded in the presence of aluminum chloride; this is due to heterocycle deactivation by complexation with the Lewis acid at the nitrogen atom.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 837–840, June, 1986.     

Instrumental neutron activation analysis of semiconductor grade silicon

The single comparator method in neutron activation analysis has been applied to the investigation of the purity of silicon single-crystals of different origins. The following impurities were determined: Au, Sb, Co, Cu and Na. Studies were also carried out on the surface contamination of silicon samples introduced through steps of sample preparation and irradiation. Up to nineteen elements on the surface of samples were analysed and found to be easily reduced to low levels or detection limits by washing and etching.     

Azo initiators for the preparation of hydroxyl-terminated polybutadienes

Azo compounds such as di(4-hydroxybutyl)-2,2′-azobisisobutyrate, di(3-hydroxybutyl)-2,2′-azobisisobutyrate, di(2-hydroxypropyl)-2,2′-azobisisobutyrate, and di(2-hydroxyethyl)-2,2′-azobisisobutyrate were prepared and used as initiators for the preparation of hydroxyl-terminated polybutadienes (HTPBs) of molecular weight (M?_n) ranging from 2000 to 7500 and functionality between 1.90 and 3.0. The polymers were prepared by free-radical solution polymerization in dioxane and toluene. The polymers obtained were characterized for their molecular weight, hydroxyl number, functionality, and instrinsic viscosity.     

Modellrechnungen zum Dendriten-Wachstum in partiell-kristallinen Hochpolymeren

Zusammenfassung Überstrukturen in partiell-kristallinen Thermoplasten liegen oft in Gestalt von Sphärolithen vor. Es wird versucht, ihre Entstehung auf behindertes Dendritenwachstum zurückzuführen. Die durch das Simulationsmodell beschriebenen Strukturen werden mit experimentell beobachteten verglichen.

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Superstructures in partial-crystalline thermoplastics often show the shape of spherulites. The reason of this can be a handicapped growth of dendrites. The structures obtained by a simulation model are compared with those obtained by experiments.

     

Error analysis of surface area determinations by the chromatographic technique

The systematic and random errors in the determination of the surface area of adsorbents and catalysts by argon thermodesorption chromatography are analyzed.

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