Abstract The catalytic conversion of esters to amides represents new opportunities in the synthetic diversification and upcycling of polymers, as esters are commonly featured in various polymer structures. Yet, direct amidation is typically hampered by poor reaction kinetics and the effects of polymer structure on the reactivity remain poorly understood. We report the accelerated amidation for amines with additional hydrogen bond donating or accepting groups. These amines facilitate the expeditious (co)amidation of polymers with pendant ester groups, displaying at least a 400‐fold higher reactivity relative to polyesters with esters in the main chain. Furthermore, a positive correlation between the reactivity and degree of polymerization for poly(methyl acrylate) suggests a hydrogen‐bond mediated intramolecular activation of the esters, which was confirmed by FT‐IR spectroscopy and basic molecular mechanics modeling. The reported method paves the way to synthesize diverse (co)polymers with amide side chains from readily available polymeric precursors.