Complex micelle morphology of DNA block copolymer and ionic liquid

Abstract

DNA block copolymers are hybrid polymers that contain both DNA and synthetic polymer linked into a blocky chain structure. They also represent a special class of charged-neutral block copolymers that can potentially interact with cationic molecules to form polyelectrolyte complexes. In this study, we prepare DNA-poly(N-isopropylacrylamide) (DNA-PNIPAM) block copolymer and investigate its complexation with ionic liquid (IL). The block copolymer is synthesized via the coupling reaction of N-hydroxylsuccinimide ester functionalized PNIPAM and amine functionalized DNA. The DNA-PNIPAM block copolymer is then combined with 1-butyl-3-methylimidazolium hexafluorophosphate at different charge ratios to form polyelectrolyte complexes. We find that stable nano-sized complex micelles are formed over a range of charge ratios. The micelles prepared by following salt annealing at room temperature exhibit string-like morphology. Further treatment of the micelles at higher temperatures leads to the breakup of the string morphology into spheres and rods. Finally, we prepare complex micelles by conducting salt annealing at different temperatures to illustrate the interplay of DNA and IL charge interaction and PNIPAM thermoresponsive behavior on the micelle morphology.