Poly(N-acryloyl-N '-propylpiperazine): A new stimuli-responsive polymer

A new water-soluble stimuli-responsive poly(N-acryloyl-N'-propylpiperazine) (PAcrNPP) was synthesized and characterized. The polymer exhibited a lower critical solution temperature (LCST) in water at 37 degreesC. The phase tr ansition temperature was highly sensitive to pH changes. The effects of som e simple salts and cationic surfactants were studied. The enthalpy of phase separation determined by microcalorimetry was 21.4 kJ mol(-1). This value corresponds to the breaking of one hydrogen bond per monomer unit. Dynamic light scattering studies indicated some aggregations of polymer chains belo w the LCST. No such aggregations were observed for the lower analogues, pol y(N-acryloyl-N'-methylpiperazine) (PAcrNMP) and poly(N-acryloyl-N'-ethylpip erazine) (PAcrNEP) which exhibited no LCST. The cross-linked polymer gels w ere sensitive to both pH and temperature. Their response time to swelling a nd deswelling was 150 min. The water sorption of the gels was non-Fickian u nder both acidic and neutral conditions.