It has been assumed for some time that cross-linking will always enhance the thermal stability of polymers, simply because the presence of a cross-link means that at least one additional bond must be broken to enable the elimination of a volatile fragment from a polymer.
We have investigated cross-linked polyamide-6, butadienes, styrenes, and methyl methacrylates.
A variety of techniques has been used to achieve cross-linking, including:
In the vast majority of cases, the thermal stability has not been enhanced and in many cases it has actually been reduced. The one case in which we have seen enhanced thermal stability has been in those systems in which aromatic cross-links have been involved. This leads to the conclusion that it is not the number of cross-links that is important but rather it is the type of cross-link. Aromatic cross-links offer inherent advantages compared to aliphatic systems.