Synthesis and Characterization of Temperature and pH Responsive Poly(N-isopropylacrylamide) Copolymer

Poly (N-isopropylacrylamide) (PNIPAM) has temperature responsive, exhibits a lower critical solution temperature (LCST) of approximately 32 °C in aqueous solution, below which the polymer is water soluble and above which it becomes water insoluble. The LCST of PNIPAM copolymer increase responsed to hydrophilic block acrylic acid(AA). Thus，the copolymer has pH and temperature dual responsive. The duel responsive copolymer poly(N-isopropylacrylamide-co-acrylic acid) was synthesized via solution polymerization, and characterized by IR, GPC, and assay the composition of copolymer by titration. The lower critical solution temperature (LCST) of the copolymer rose to a higher temperature not only with the ratio of AA segments increasing, also with the pH increasing. When the ratio of AA segments of the copolymer is higher, LCST rose remarkable with the pH increasing. Therefore, by changing the ratio of AA segments and pH value, the LCST of the copolymer will be 37 °C, which has application in drug delivery.