Macroinorganics. 7. Property-structure relationships for polymeric bases whose monomeric units behave independently toward protonation

The protonation of some new poly(amidoamines) and their nonmacromolecular model compounds has been studied in aqueoussolutionby potentiometricand viscosimetrictechniques. Sharpbasicityconstants havebeenobtained,thusconfirmingthepeculiarbehaviorofthisfamilyofpolymericbases. Thebehavior of the models is similar to that of the corresponding polymers even if the former are slightly more basic. In order to rationalizethe unusualbehavior of poly(amidoamines),13C NMR titrations and quantum chemical computationshave been performed on some representative poly(amidoamines). The resulting model stresses the importance of the stiffening of each monomeric unit upon protonation,due to the formation of intramolecular hydrogenbridgesandtoelectrostaticrepulsionbetweenpositively chargedoniumions,indeterminingthe physicochemicalproperties of poly(amido amines)even in the absence of direct interactionsbetween groups belongingtodifferentmonomericunits. Infact,thisstiffeningcouldaffectthepropertiesofthewholepolymer (conformationaltransitions) because the joints between different units are very rigid.