A novel positively thermo-sensitive hydrogel based on ethylenediaminetetraacetic dianhydride and piperazine: Design, synthesis and characterization

A new positively thermo-sensitive hydrogel was designed and synthesized by a condensation polymerization reaction of ethylenediaminetetraacetic dianhydride (EDTAD) and piperazine (PA) to give poly (ethylenediaminetetraacetic dianhydride-co-piperazine) (PEP). The obtained polymers’ structure was characterized by FTIR and 13C NMR. The backbone of the polymer linked by amide bond and abundant of carboxyl groups as pendant group could form strong intermolecular and intramolecular hydrogen bond at lower temperature and dissociate at higher temperature, resulting in the polymer with thermo-sensitivity. The aqueous solution of PEP at lower temperature (<20 °C) showed micro-gel formation and transformed to transparent solution at higher temperature (>40 °C). Transition temperature shifted to higher value with the increasing of concentration. The hydrogel exhibited reversible phase transition and the transmittance change was not weakened by multiple temperature changes.