In the context of condensation polymers, how does an increase in polymer chain length typically influence the thermal stability compared to addition polymers?

In condensation polymers the backbone contains polar linkages such as esters or amides, and each additional repeat unit adds another bond that can break when heated, so a longer chain usually lowers the temperature at which the polymer starts to degrade. By contrast, addition polymers have only C–C bonds in their backbone, which are much stronger and less affected by chain length, so their thermal stability is less sensitive to how long the chain is. Thus, as a condensation polymer grows longer, its overall thermal stability tends to decrease more noticeably than for an addition polymer of the same length. For example, a long poly(ethylene terephthalate) chain will start to decompose at a lower temperature than a short one, whereas a long polyethylene chain remains stable at roughly the same temperature as a short chain. This difference comes from the weaker, thermally labile bonds that are repeatedly introduced in condensation polymer chains.