An exception is the aPMA solution with added MgCl2, where the aggregates grow upon cooling (so as the iPMA-Mg2+ ones).This similar behavior for systems with added Mg2+ is attributed to strong binding of water molecules by Mg2+ ions and to monodentate binding of Mg2+ to carboxylates, and actually rules the interaction in case of both PMAs. This is also very clearly demonstrated in calorimetric measurements.