Why do polyamides usually have higher melting points than similar polyesters?

Polyamides generally exhibit higher melting points than similar polyesters because of the presence of amide (CO–NH) groups, which are capable of forming hydrogen bonds between polymer chains.1

While ester (CO–O) groups in polyesters do not facilitate this specific type of interaction, the hydrogen bonds in polyamides act similarly to the covalently bonded cross-links found in network polymers. Although these are not true covalent cross-links, they significantly increase the thermal stability of the material. The strength of these hydrogen bonds can be diminished by heat or solvents, which allows the polymers to be processed, but their presence remains the primary reason for the higher melting points observed in polyamides compared to their polyester counterparts.1