4. Aging affecting side clusters

In the absence of welds or cuts, side-group modification reactions have no influence (at reasonable transformation rates) on mechanical properties.

We have seen that in the case of crucial mechanical properties, such as toughness, ageing results in an abrupt variation when a threshold is crossed, which naturally offers the best choice of end-of-life criteria. In the case of properties affected by changes in lateral groupings, no such discontinuities are generally observed: properties vary linearly or quasi-linearly with the structure. End-of-life criteria must therefore be chosen more or less arbitrarily.

Apart from color, almost all properties related to the nature of the side groups, such as electrical properties, refractive index, surface properties or water absorption, are linked to the electrical polarity of the groups. We will therefore...