Melt transition temperature polymers

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. 

Melt transition temperature, Tm (Section 31.5) The temperature at which crystalline regions of a polymer melt to give an amorphous material. 

The rates of chemical reactions increase with temperature due to the greater proportion of molecules which have energies in excess of the activation energy and this will apply to radiation-induced secondary reactions in polymers. However, solid polymers are also characterized by their glass and melting transition temperatures. Substantial changes in molecular mobility occur across these transitions and the rates of chemical reactions are frequently greatly affected. 

Koehler MG, Hopfinger AJ (1989) Molecular modeUing of polymers 5. Inclusion of inter-molecular energetics in estimating glass and crystal-melt transition temperatures. Polymer 30 116-126... 

Fig. 2.18. Schematic DSC thermogram of a semicrystalline polymer = glass transition temperature = crystallization temperature = melting temperature = decomposition temperature...

Griffith, J. H., and B. G. RA.nby Dilatometric measurements on poly (4-methyl-l-pentene), glass and melt transition temperatures, crystallization rates and unusual density behavior. J. Polymer. Sci. 44, 369—381 (1960). 

M. G. Koehler and A. J. Hopfinger. Polymer, 30, 116 (1989). Molecular Modelling of Polymers 5. Inclusion of Intermolecular Energetics in Estimating Glass and Crystal-Melt Transition Temperatures. 

Tm, the melt transition temperature, is the temperature at which the crystalline regions of the polymer melt to become amorphous. More ordered polymers have higher values. 

The main processing technique in the automobile industry is injection molding in which pressure is applied to make the polymer flow into a preferred form [3]. Plastics must be cooled below the Tm (melt transition temperature) before removal from the mold [3], The molding process follows a basic injection cycle consisting of mold close, injection carriage forward, injection of material, metering, retraction of carriage, mold open, and part ejection. This cycle has been in place basically since 1946,... 

This is also the case for PGSS, where the SCF is applied to lower the melting temperature of a solid, or a solid solution, in order to finally obtain solid particles as a result of the subsequent pressure reduction. The difference is that, here, the solubility of the SCF in the HC is needed, rather than the opposite. Data of this kind are still scarce, but it is well known that the amount of SCF soluble in a HC can be significant. For instance, we recall the plasticizing effect of CO2 on many polymers, which lowers the polymer glass transition temperature, so that a liquid solution can be formed, provided that a suitable pressure is applied. 

For amorphous polymers, the viscosity at a given temperature is a function of the and of the material. For many polymers, the Williams-Landry-Ferry (WLF) equation provides a good estimate of melt viscosity where -qj is melt viscosity, polymer viscosity at 7g, T is the melt temperature, the polymer glass-transition temperature, and b and/ are parameters ... 

Two examples of the use of localised thermal analysis are provided in order to illustrate the generic applications of this approach. Figure 8 shows localised thermomechanical analysis of the surface of the multi-layer film in Figure 4. Measurements were made at points within this image describing the bulk polymer, the central gas-barrier layer and the thin tie-layer between this and the bulk film. The melting transition temperatures are consistent with high density polyethylene, poly(ethylene-co-vinyl alcohol) and medium density polyethylene for the bulk, gas barrier and tie layers, respectively [101],... 

Polymer Glass transition temperature Tg (°C) Melting temperature Tm ( 0... 

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