Glass transition temperature, glassy and

In the glassy region, the polymer is below its glass transition temperature, Tg, and typically has a modulus of 1010 dynes/cm2. The transition region includes the Tg, which is taken as the point of inflection of the modulus or the maximum in the damping curve. The modulus drops by a factor of 1000 in this region. The... 

Amorphous polymers generally exist as hard, rigid, glassy plastics below their glass-transition temperature Tg and as soft, flexible, rubbery materials above their Tg. Comparison of the densities of the glassy state (pg) and the rubbery state (pj) for various amorphous polymers indicates that Pg Pr [5]. 

Polyvinyl acetate is a glassy, amorphous polymer with Glass transition temperature about 28 °C. The effect of increasing the proportion of ethylene is to reduce the strong forces between the chains, which, in the homopolymer, are associated with a high concentration of polar acetate groups. Consequently, the glass transition temperature falls and is as low as 25 °C for a VA content of 65%. The properties at room... 

The model is attractive since the six parameters required above can be obtained independently and thus no fitting to the data is required. Of these six parameters, only two relate directly to the individual polsrmer, namely the glass-transition temperature, Tg, and the parameter v, the average voliune of chain segments containing two bonds (though in practice Robertson took this to be the volume of a monomer imit in the glassy state at room temperature). 

Figure 4.24 illustrates a correlation between the expansion coefficient and degree of cure for a typical thermoset. In general, the glass transition temperature increases and CLTE decreases in both the glassy and rubbery states as the degree of cure increases (Prime 1997 Cassel 1976 and 1980). 

The relationship between chemical composition, structure and properties for the copolymers has been described in det elsewhere [68,69]. In general it is found that the glass transition temperature T, and the Young s modulus increase with hard segment content and heat treatment temperature. It was found that the material with the optimum composition and properties had a value of T, of 80°C and a Young s modulus (isotropic) of 1.7 GPa, both of which are typical of a conventional glassy polymer. 

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