Synthesis and characterization of a novel temperature-pH responsive copolymer of 2-hydroxypropyl acrylate and aminoethyl methacrylate hydrochloric salt

In this investigation, a novel temperature-pH responsive copolymer was prepared by the radical copolymerization between 2-hydroxypropyl acrylate (HPA) and aminoethyl methacrylate hydrochloric salt (AMHS). The molecular structure of the corresponding copolymer has been confirmed by 1H NMR and FTIR measurements. The results indicated that the lower critical solution temperature (LCST) of the resulting copolymer has shown a considerable dependence on the monomer ratio and pH value in the medium. When the molar ratio of HPA to AMHS unit on polymer chain was fixed at 1.56, 2.25, and 3.01, the LCSTs of copolymers were observed at 36.5, 28.2 and 17.8°C, respectively. For the effect of additive salts, the LCST change of the copolymer was affected by both cations and anions in the following order of Al(NO3)3 > KNO3 > Mg(NO3)2 > NaNO3 and KCl ≈ KSCN > KBr > KNO3 > KI. The copolymer seems to be useful as a candidate for the controlled-drug release carrier by pH and temperature external stimuli.