Syntheses and thermodynamic studies on the protonation behaviour of polymers containing acylpiperazinyl units in the backbone or in the side chain of a vinyl polymer

Linear poly(1,4-piperazinediyl-1-oxotrimethylene) (1), in which amido and tertiary amino groups regularly alternate along the macromolecular chain, the isomeric poly[1-(1-piperazinyl-carbonyl)ethylene] (8) for polyvinylic structure and its N-methylated derivative, poly{1-[(4-methyl-1-piperazinyl)carbonyl]ethylene} (3), were prepared and characterized. Their protonation behaviour was investigated in aqueous solution by potentiometric and calorimetric techniques. In all cases the basicity constants were found to decrease linearly with α (the degree of protonation), whereas the enthalpy changes show a different behaviour toward protonation. The thermodynamic values indicate the important role of hydrophobic interactions