Cyclo-oligomers, structure

Cyclo-oligomers c-(R2E)j(x > 2) with E—E bonds are known for Ge and Sn only cycloplumbanes c-(R2Pb)j had never been detected, although according to quantum-chemical calculations they should form exothermically from appropriate plumbylenes and may adopt very unusual structures . 

Pyrolysis of Preceramic Polysilazanes Prepared by the Dehy-drocyclodimerization Reaction. Whatever the structure of the polysilazanes obtained by KH treatment of the cyclo-(CH3SiHNH) oligomers, these polymers are excellent ceramic precursors. Examination of the polymers from various preparations by TGA (thermogravimetric analysis) showed the weight loss on pyrolysis to be between only 15 and 20%. Pyrolysis appears... 

The yellow orthorhombic modification of sulfur is the thermodynamically most stable one. The crown-like structure of a-cyclo-Sg was discovered in 1935. fi-Cyclo-Sf, is monoclinic and is formed slowly above 95 °C, the transition temperature of orthorhombic sulfur. The third crystalline modification is y-cyc/o-Sg, which melts at 106.8 C on rapid heating and can be prepared as discussed above. There is a large number of well-studied cyclic oligomers of sulfur here we refer the reader to a standard textbook. When sulfur heated to about 400°C is subjected to quenching the product is polycatenasulfur, which exhibits rubber-like properties. 

Peptides consisting exclusively of fS- or y-amino acids (amino acids) have emerged as a promising new class of nonnatural oligomers (foldamers) that are able to fold into well-defined secondary structures [41--47]. So far, three different helical secondary structures and two turn motifs [177-181] as well as a parallel [177,179] and an antiparallel [179,182] sheet structure have been identified by two-dimensional NMR spectroscopy, circular dichroism (CD), and/or X-ray diffraction studies. In addition, cyclo- -tetrapeptides have been found to form nanotubes in the solid state [183] and have been used as transmembrane ion channels [184]. All these studies have demon-... 

Another type of epoxy oligomers are the cyclo-aliphatic ones, obtained by oxidation of cyclic diolefins with various peroxidic compounds (organic or inorganic hydroperoxides), hypochlorous acid, halogenhydrines and their derivatives, and oxygen or ozone. At present, the main industrial procedure for their production uses peracetic acid. In keeping with initial cycloolefin structure, diepoxides with different structures are produced, with the peculiarity that peroxidic oxygen is bound to the aliphatic cycle. 

FTIR-MALDI polymer and dendrimer characterisation and structure isotacticity, cyclo and oligolactides, polymerisation kinetics, molecular weight evaluations, diblock polymers-oligomer studies and cis-trans structures. 

Kaman and Hodge [28] used SEC and MALDI-ToF-MS and other techniques in their structural study of cyclo depolymerised polyurethanes. Upon cycle depolymerisation, polyurethanes yield a series of cyclic urethane oligomers, where n = 1-4 for the monomer, dimer, trimer and tetramer ... 

Method 3. Reaction of Sodiobis(cyclic dienes) with Inorganic Salts Polymerization of some a,tu-bis(cyclopentadienyl)alkanes with iron salts has been reported (10, II). Reaction of the disodio derivatives of the bis(cyclo-pentadienes) with ferrous chloride in tetrahydrofuran led to polymers and oligomers possessing the ferrocene structure. The polymers were qualitatively described as viscous, brown oils. No quantitative molecular weight data on the polymeric products were obtained. 

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