Glass transition temperatures values

As-polymerized PVDC does not have a well-defined glass-transition temperature because of its high crystallinity. However, a sample can be melted at 210°C and quenched rapidly to an amorphous state at <—20°C. The amorphous polymer has a glass-transition temperature of — 17°C as shown by dilatometry (70). Glass-transition temperature values of —19 to — 11°C, depending on both method of measurement and sample preparation, have been determined. 

Table 5 Glass transition temperature values for selected poly(organophosphazenes)...

As provided by Equation (1), glass transition temperature (values look in Table 1)... 

In EP07708077A3 (Dabou et al. 1996), gas separation polymer membranes were prepared from mixtures of a polysulfone, Udel P-1700 and an aromatic polyimide, Matrimid 5218. The two polymers were proven to be completely miscible as confirmed by optical microscopy, glass transition temperature values and spectroscopy analysis of the prepared mixtures. This complete miscibility allowed for the preparation of both symmetric and asymmetric blend membranes in any proportion from 1 to 99 wt% of polysulfone and polyimide. The blend membranes showed significant permeability improvements, compared to the pure polyimides, with a minor change in the selectivity. Blend membranes were also considerably more resistant to plasticization compared with pure polyimides. This work showed the use of polysulfone-polyimide polymer blends for the preparation of gas separation membranes for applications in the separation of industrial gases. 

Natural rubber based-blends and IPNs have been developed to improve the physical and chemical properties of conventional natural rubber for applications in many industrial products. They can provide different materials that express various improved properties by blending with several types of polymer such as thermoplastics, thermosets, synthetic rubbers, and biopolymers, and may also adding some compatibilizers. However, the level of these blends also directly affects their mechanical and viscoelastic properties. The mechanical properties of these polymer blended materials can be determined by several mechanical instruments such as tensile machine and Shore durometer. In addition, the viscoelastic properties can mostly be determined by some thermal analyser such as dynamic mechanical thermal analysis and dynamic mechanical analysis to provide the glass transition temperature values of polymer blends. For most of these natural rubber blends and IPNs, increasing the level of polymer and compatibilizer blends resulted in an increase of the mechanical properties until reached an optimum level, and then their values decreased. On the other hand, the viscoelastic behaviours mainly depended on the intermolecular forces of each material blend that can be used to investigate the miscibility of them. Therefore, the natural rubber blends and IPNs with different components should be specifically investigated in their mechanical and viscoelastic properties to obtain the optimum blended materials for use in several applications. 

Care must be taken to use the appropriate activation energy value [3,4] and the appropriate glass-transition temperature value in the respective equations. The value of must be determined [3] wit a nanow temperature band around the temperature of interest, so that the obtained value has higher accuracy. In tile case of copolymms [4], extra caution has to be exercised because of the presence of dual values so that the iqqprtqnriate value alone is diosen. 

Jungnickel B J (1996) Poly(vinylidene fluoride) (overview) in Polymeric Materials Encyclopedia, (Ed. Salamone J C) CRC Press, Boca Raton, Vol. 9, pp. 7115-7122. 37. Fakirov S, Balta Calleja F J and Boyanova M (2003) On the derivation of microhardness of amorphous blends of miscible polymers from glass transition temperature values, J Mater Sci Lett 22 1011-1013. 

Most polyphenylquinoxalines show no crystallinity in wide-angle X-ray diffraction studies. Their amorphous nature is primarily due to the configurational disorder carried out in the backbone of the polymer chains by the presence of different isomers. Glass transition temperature values decrease from 360 °C for polymer 15 to 320 °C for 16 and 290 °C for 17. However, the Tg significantly increases when the polymers are heated at... 

Searching product specifications on the internet (from glass manufacturers and suppliers websites), a number of values for thermal conductivity for alkali borosilicate glasses have been quoted. It seems that below the glass transition temperature, values for thermal conductivity are quoted around 1.0 0.25 W m K at around room temperature, increasing to a value of about 2.5 0.25 W m K at about 1400 K. These values seem reasonably insensitive to composition and so may be used as markers for our glass thermal conductivity. 

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