AbstractStarting from the thermodynamic properties of some polyamidoamines, showing a protonation behaviour similar to that of small molecules, a relationship with the ability to form polymer‐polymer complexes with heparin or heparin‐like macromolecules was found.In the light of these results, new heparinisable materials (PUPA and EVAPA) were synthesised, and the surface and bulk structures were understood on the basis of the enhanced hydrophilic characters when these materials are protonated at physiological pH.