The Glassy and Polymer Melt Phases

To this point, we have focused on the behavior of polymer chains in a solvent, concentrating on the dilute case, in which the individual chains do not strongly interact with each other. In this section, we now turn to more concentrated states in polymeric materials and their mechanical properties. Polymers take a variety of forms in everyday objects, but there are really only two significant states that are relevant to our understanding of everyday materials the glassy state and the melt state. In this section, we are focusing on polymer materials containing very little or no solvent. 

Glassy behavior is not just confined to macromolecules such as polymers but is a fairly general phenomenon observed in many amorphous 

FIGURE 4.15 Polymers below the glass trarasition Tg are hard. They do not flow and can be molded into durable items. 

The glass transition point is typically not sharp and may take place over a range of more than 10 C. You should think of the glass transition more as a change in physical properties (specific heat capacity, volume) than a thermodynamic phase transition. 7 can be determined by two main methods Differential scanning calorimetry (see Chapter 2 for more 

FIGURE 4.16 Cross-linked polymer melts, such as the latex used in balloons and elastic bands, are soft and elastic. 

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