Effect of molecular mass and cross-linking

The length of the main chain does not affect the dynamic mechanical properties of polymers in the glassy state, where molecular motions are of restricted extent, but the glass transition temperature is depressed at very low relative molecular masses as a consequence of the additional free volume introduced by the increased proportion of chain ends [14], 

As already discussed (see Section 7.1.1), molecular mass has a large effect in the glass transition range, where viscous flow transforms to a plateau range of rubber-like behaviour due to entanglements between the longer molecular chains. 

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