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The processes involved in the solution combustion synthesis of a-Al 2 O 3 using urea as an organic fuel were investigated. The data describing the influence of the relative urea content on the characteristic features of the combustion process, the crystalline structure and the morphology of the aluminium oxide are presented herein. Our data demonstrate that the combustion of stable aluminium nitrate and urea complexes leads to the formation of a-alumina at temperatures of approximately 600-800 1C. Our results, obtained using differential thermal analysis and IR spectroscopy methods, reveal that the low-temperature formation of a-alumina is associated with the thermal decomposition of an a-AlO(OH) intermediate, which was crystallised in the crystal structure of the diaspore.

Urea (URE) and guanidine hydrochloride (GHC) possessing strong chaotropic properties in aqueous media were added to DMSO solutions of poly(vinyl alcohol) (PVA) to be gelled via freeze–thaw processing. Unexpectedly, it turned out that in the case of the PVA cryotropic gel formation in DMSO medium, the URE and GHC additives caused the opposite effects to those observed in water, i.e., the formation of the PVA cryogels (PVACGs) was strengthened rather than inhibited. Our studies of this phenomenon showed that such “kosmotropic-like” effects were more pronounced for the PVACGs that were formed in DMSO in the presence of URE additives, with the effects being concentration-dependent. The additives also caused significant changes in the macroporous morphology of the cryogels; the commonly observed trend was a decrease in the structural regularity of the additive-containing samples compared to the additive-free gel sample. The viscosity measurements revealed consistent changes in the intrinsic viscosity, Huggins constant, and the excess activation heat of the viscosity caused by the additives. The results obtained evidently point to the urea-induced decrease in the solvation ability of DMSO with respect to PVA. As a result, this effect can be the key factor that is responsible for strengthening the structure formation upon the freeze–thaw gelation of this polymer in DMSO additionally containing additives such as urea, which is capable of competing with PVA for the solvent.

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Titanium(IV) coordination compounds are effectively used as precatalysts for ethylene polymerization and copolymerization with other olefins. New titanium(IV) complexes 3b-d with ligands containing two diphenylcarbinol fragments linked by the perfluorinated hydrocarbon units-CF 2or-C 2 F 4were synthesized. The structures of complexes 3b and 3d were determined by X-ray diffraction. Titanium atoms in 3b have a distorted trigonal-bipyramidal coordination environment while spiro-complex 3d is characterized by tetrahedral molecular geometry. The catalytic behavior of complexes activated by mixtures of Bu 2 Mg and alkylaluminium chlorides from among Me 2 AlCl, Et 2 AlCl, EtAlCl 2 , and Et 3 Al 2 Cl 3 were studied. The resulting catalytic systems catalyze ethylene polymerization to afford ultra-high molecular weight polyethylene, suitable for modern processing methods, and the solvent-free solid state formation of super high-strength (1.37-2.75 GPa) and high-modulus (up to 138 GPa) oriented film tapes. The same catalytic systems catalyze ethylene copolymerization with 1-hexene to afford high molecular weight semicrystalline elastomeric polymers containing up to 20% of comonomer units.

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