Non-ideal dynamic mechanical relaxation behaviour

The above theory describes processes which conform to ideal relaxation behaviour and can be described accurately by a property decaying exponentially with 

Unfortunately, the behaviour observed in dynamic mechanical relaxation rarely conforms to the simple ideal. Usually the data have to be fitted to equations that allow for the breadth to be increased, so accommodating a distribution of relaxation times and the possibility of more than one distinct process being involved. 

One special relaxation process is worthy of note this is the glass to rubber transition. Because the movement of the backbone segments depends on the availability of free volume, the temperature dependence is controlled not solely by the activation energy (as was shown in Chapter 4). As a consequence, the Arrhenius plots are curved and the processes are described by a relaxation equation where the parameter a is not unity. 

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