Tetra-sensitive graft copolymer gels with high volume changes

Abstract

For the preparation of multi-responsive graft copolymer gels for hydrogel-based microsystem technologies, a poly(4-vinylbenzoic acid) macromonomer was prepared in a three-step synthesis. At first, a chain transfer agent was functionalized with an azide group, followed by a reversible addition fragmentation chain transfer polymerization to give an azide bearing poly(4-vinylbenzoic acid) macromonomer. Subsequently, an acrylamide functionalized macromonomer was prepared by Cu-catalyzed alkyne and azide 1,3-dipolar cycloaddition. With this acrylamide functionalized poly(4-vinylbenzoic acid) macromonomer, various graft copolymer gels composed of a temperature-sensitive poly(N-isopropylacrylamide) backbone and pH-sensitive poly(4-vinylbenzoic acid) graft chains were prepared by radical polymerization. Moreover, the swelling behavior of the hydrogels was investigated with respect to pH, temperature, solvent and salt. It was shown that the graft copolymer gels respond to these stimuli independently with a sharp transition and a high volume change. Additionally, the swelling behavior was reversible over various cycles. This behavior is fundamental for applications of smart gels in microfluidic platforms.