Amorphous glasses synthesis

Properties. One of the characteristic properties of the polyphosphazene backbone is high chain dexibility which allows mobility of the chains even at quite low temperatures. Glass-transition temperatures down to —105° C are known with some alkoxy substituents. Symmetrically substituted alkoxy and aryloxy polymers often exhibit melting transitions if the substituents allow packing of the chains, but mixed-substituent polymers are amorphous. Thus the mixed substitution pattern is deUberately used for the synthesis of various phosphazene elastomers. On the other hand, as with many other flexible-chain polymers, glass-transition temperatures above 100°C can be obtained with bulky substituents on the phosphazene backbone. 

Most Kaminsky catalysts contain only one type of active center. They produce ethylene—a-olefin copolymers with uniform compositional distributions and quite narrow MWDs which, at their limit, can be characterized by M.Jratios of about 2.0 and MFR of about 15. These features of the catalysts determine their first appHcations in the specialty resin area, to be used in the synthesis of either uniformly branched VLDPE resins or completely amorphous PE plastomers. Kaminsky catalysts have been gradually replacing Ziegler catalysts in the manufacture of certain commodity LLDPE products. They also faciUtate the copolymerization of ethylene with cycHc dienes such as cyclopentene and norhornene (33,34). These copolymers are compositionaHy uniform and can be used as LLDPE resins with special properties. Ethylene—norhornene copolymers are resistant to chemicals and heat, have high glass transitions, and very high transparency which makes them suitable for polymer optical fibers (34). 

As it was mentioned above, there is no unanimous opinion concerning the nature of precursors obtained in Pechini-type syntheses, and these are called polymeric resins (glasses) or gels. Clearly, this contradiction has little to do with technical aspects of the synthesis. On the other hand, its clarification will be of great value for the physics of amorphous state. 

V. Deimede, J.K. Kallitsis, and T. Pakula, Synthesis and properties of amorphous blue-light-emitting polymers with high glass-transition temperatures, J. Polym. Sci., Part A Polym. Chem., 39 3168-3179, 2001. 

Haushalter RC, O Connor CM, Haushalter JP et al (1984) Synthesis of new amorphous metallic spin-glasses Ct2SnTe4, Mu2SnTe4, Ee2SnTe4, Co2SnTe4 - solvent induced metal-insulator transformations. Angew Chem hit Ed 23(2) 169-170... 

Fine crystalline quartz or amorphous substances (gel, quartz glass, etc.) are used as one of initial components for the synthesis [19]. Depending on temperature, pressure, pH of the medium and the presence of salts, silica can exist in solution both as simple ions or molecules, and as more complicated polymer particles. Under normal conditions silica passes into solution in monomer form, as silicic acid Si(OH)4 at large pH, silicate ions SiOj - are formed. Monosilicic acid is a very weak acid however, at increased temperature its dissociation constant increases substantially. The amount of monomer form also increases with temperature. The dissolution of Si02 is due to hydration as well as to depolymerization. 

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