Polymeric composites above glass transition temperature

The polymerization was studied at different temperatures. Figure 1 shows the conversion curves obtained with a 30% solution of acrylonitrile in DMF at —196°, —155° and —150°C. It appears that at —196°C. the conversion reaches a limiting value, whereas above the glass transition temperature (—156 °C.) the polymerization proceeds with a constant rate up to high conversions. This observation is discussed below. Figure 2 shows the relation between the composition of the binary mixtures and the rate of conversion at —196 °C. In all cases, the rate is highest in... 

Thermal analysis has been used extensively to characterize resin composites, which have been under development for several decades. Conventional DSC is an excellent method for investigating polymerization of the composites [53-57]. The glass-transition temperature, which is highly relevant for the mechanical properties of the composites, can be readily foimd by dynamic mechanical analysis (DMA) [58-61], as shown in Figure 22, and by thermomechanical analysis (TMA) [62,63], where there is a discontinuity in the slopes of the plot of length change as a function of temperature below and above Tg. 

Guided by the above studies, we have developed a number of experimental rubbers, and blends of rubbers, for application in tire treads. The experimental rubbers consist of vinyl BR s, SBR s, and high trans SBR s prepared by the anionic polymerization techniques, previously described in this paper. Tan 6 and Tg results for some of these rubber compositions are plotted in Figure 19. Also shown are the corresponding results for rubber compositions based on conventional rubbers used in the past. These data show that the experimental compositions have significantly lower lYO tan 6, and have simultaneously higher glass transition temperatures, when compared to compositions based on conventional rubbers. 

To summarize the ferroelectric and piezoelectric properties of the discussed polymers, some important ferroelectric and piezoelectric parameters are tabulated in Table 4. As discussed in the previous sections, the ferroelectric and piezoelectric properties of polymeric and polymeric composite systems depend on various factors, such as crystallinity, pohng conditions, glass transition temperature, and before and after electrical poling treatments (electrical, mechanical, and thermal treatments). In addition to the factors mentioned above, for composite systems, laminates or blends, fraction of constituents, and interfacial polarization are also important. Therefore, the... 

The thermal behaviour of materials can also provide important information about the structure and morphology of a material. For example, while most synthetic polymers have a glass transition temperature (Tg) associated with amorphous structure in the material, only polymers with regular chain architecture can crystalhse and so have a melting temperature (IJn). These in turn can have a direct effect on the mechanical performance of the materials since below Tg polymers tend to be glassy and become more rubbery above 7. These thermal properties can also be used to identify or verify the nature of the composition. For example, random copolymers will only exhibit one Tg that will be somewhere in between the 7 s of the individual homopolymers, whereas block copolymers will exhibit 7 s characteristic of each homopolymer but will be slightly shifted due to imperfect phase separations. Similarly this can be applied to polymeric blends, which are essentially two polymeric systems mixed together. 

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