pH- and temperature-responsive hydrogels from crosslinked triblock copolymers prepared via consecutive atom transfer radical polymerizations

Well-defined poly((2-dimethyl amino)ethyl methacrylate-co-2-hydroxyethyl methacrylate)-b-poly(N-isopropylacrylamide)-b-poly((2-dimethyl amino)ethyl methacrylate-co-2-hydroxyethyl methacrylate), or P(DMAEMA-co-HEMA)-b-P(NIPAAm)-b-P(DMAEMA-co-HEMA), triblock copolymers were synthesized by consecutive atom transfer radical polymerizations (ATRPs), using ethylene glycol di-2-bromoisobutyrate (Br–EG–Br) as the starting ATRP initiator. The hydroxyl groups of the incorporated HEMA units were used as crosslinking sites for the preparation of smart hydrogels. The so-prepared hydrogels exhibited both temperature- and pH-sensitive behavior derived, respectively, and independently, from the P(NIPAAm) blocks and P(DMAEMA) units, in the crosslinked matrices. The hydrogels exhibited a lower critical solution temperature (LCST) of 31–32 °C in aqueous media of pH 1–7, not unlike that of the P(NIPAAm) homopolymer. The swelling ratios and swelling/deswelling kinetics of the hydrogels depended strongly on pH and temperature of the medium. The copolymers were characterized by gel-permeation chromatography, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The resultant stimuli-responsive hydrogels were characterized by differential scanning calorimetry (DSC). These stimuli-responsive hydrogels will have potential applications in biomedical areas, such as tissue engineering and drug delivery.