Aqueous polymeric micelles of poly[N-isopropylacrylamide-b-sodium 2-(acrylamido)-2-methylpropanesulfonate] with a spiropyran dimer pendant: quadruple stimuli-responsiveness

Abstract

Poly[N-isopropylacrylamide-b-sodium 2-(acrylamido)-2-methylpropane sulfonate] tagged with a spiropyran dimer at the poly(N-isopropylacrylamide) end (SP₂-b-NIPAM₁₅₄-b-AMPS₁₄₈) was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization to investigate multiple stimuli-responsive micelles. The micelles formed in aqueous solutions were stimulated by various chemical and physical stimuli and characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy and ζ-potential measurements. It was found that the block copolymer is responsive to four different types of stimulus viz. light, temperature, metal ion and pH. The NIPAM₁₅₄ block gives thermo-responsiveness to the block copolymer and the AMPS₁₄₈ block shows metal ion responsiveness. Due to the presence of the photochromic spiropyran moiety, the block copolymer also shows light and thermo-responsiveness. To the best of our knowledge this is the first report that deals with quadruple stimuli-responsive polymeric micelles. Such quadruple stimuli-responsive block copolymer micelles are expected to open up new applications in a variety of fields.