Reversible hierarchical structure induced by solvation and temperature modulation in an ionic liquid-based random bottlebrush copolymer

A solvent and temperature responsive random copolymer having a polyacrylate backbone with emanating ionic liquid side chains of 1-decyl-3-methylimidazolium chloride and 1-(2-carboxyethyl)-3-imidazolium bromide grafted poly- N -isopropylacrylamide (PNIPAM) possessing bottlebrush architecture is synthesized. The bottlebrush copolymer is prepared using an uncommon route that exploits the co-assembly of two amphiphilic ionic liquid acryloyl-based monomers in 30% (w/w) water to form a lyotropic mesophase followed by photo-initiated free radical polymerization. The copolymer adopts a temperature-invariant 2D hexagonal structure as determined by SAXS in the dehydrated (de-swollen) state. The absence of thermoresponsivity is attributed to a combination of confinement coupled with insufficient solvation of the grafted PNIPAM chains. In a water-swollen state (hydrogel), loss in long range translational ordering is observed while short range temperature-dependent ordering dominates. Below the LCST of PNIPAM (