Relaxations for amorphous and crystalline polymers

Polymers can be divided into two broad classes, amorphous and semicrystalline. If observations are made at a fixed frequency, or isochronally, crystalline polymers often exhibit three major transitions as the temperature is varied, usually labelled a, p and y in decreasing order of temperature, whereas amorphous polymers generally exhibit two major transitions, labelled a and p in decreasing order of temperature. If other relaxations are seen at lower temperatures, they are labelled y or 8, respectively. 

At the outset it must be understood that a relaxation can manifest itself in mechanical measurements only if the jump or more complex rearrangement to which it corresponds contributes to a change in shape or dimen- 

In trying to identify relaxations it is often useful to consider their relative strengths. The standard definition of the relaxation strength for mechanical relaxations is that it is the difference between the unrelaxed and relaxed modulus or compliance, or — J. Determination of 

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