Polymer glass transition temperatur

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. 

In another smdy, the introduction of an adamantyl group to the poly(etherimide) structure caused polymer glass transition temperature, Tg, and solubility enhancements in some solvents like chloroform and other aprotic solvents [92]. 

Probably the best understood and most commonly used property of polymers, glass transition temperatures are important in virtually... 

Katritzky AR, Rachwal P, Law KW et al. (1996) Prediction of polymer glass transition temperatures using a general quantitative structure-property relationship treatment. J Chem Inf Comput Sci 36 879-884... 

Afantitis A, Melagraki G, Makridima K et al. (2005) Prediction of high weight polymers glass transition temperature using RBF neural networks. J Mol Struct THEOCHEM 716 192-198... 

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

A second class of polarizers uses dichroism to produce linearly polarized light. Techniques to produce dichroic polarizing sheets were pioneered by Land [52], These are made by dissolving a strongly dichroic, small molecule into an amorphous, transparent polymer. The dichroic molecules are then oriented by a uniaxial stretching of the polymer matrix. Since this is accomplished below the polymers glass transition temperature, this ori-... 

If the reaction temperature is below the polymer glass transition temperature and the amount of monomer in the particle decreases far enough, the glass effect may become important. The polymerization rate virtually goes to zero because the particle becomes so internally viscous, essentially glasslike, that the diffusion of monomer to the radicals is limited. The glass transition point varies for different polymers. This effect has also been studied by several authors [34,39,40]. 

The residual monomer content will by external plasticization cause a considerable lowering of the polymer glass transition temperature. A correlation between stability and softness of the polymer particles may exist. The hydrophobic part of the emulsifier molecules may partly penetrate the particle surface and thus be anchored to the surface to some extent. The resistance to deformation of such a stabilizing layer, when subjected to mechanical shear, is assumed to be dependent on the polymer particle softness. With soft particles polymer chain entanglement may also occur on particle-to-particle contact, making redispersion of agglomerates more unlikely. 

Polymer glass transition temperatures (Tgs) were determined with a Per-kin-Elmer DSC-2 analyzer at a heating rate of 20 °C/min with liquid nitrogen as... 

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 ... 

In this part of the chapter we discuss (a) the controlled thermolysis of thiolate solutions in polystyrene matrix at temperatures above the polymer glass transition temperature and (b) the reaction mechanism in the case of silver-polystyrene nanocomposite systems. However, the same reaction mechanism is probably involved in the thermolysis of other mercaptide-polystyrene systems. This technique has proven to be an excellent new preparative scheme for the generation of both metal and sulfide clusters in polymers. In particular, high-molecular-weight n-alkanethiolates have shown to be the most effective compound class since the low volatility of thermolysis by-products avoids film foaming during the annealing process. 

Duske [6] discussed the use of thermomechanical analysis (TMA) in assessing the quality of wire insulation materials. This is particularly important for characterization of the polymer glass transition temperature, Tg, and for curing process control. TMA has been known to be a very sensitive technique for the... 

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