Synthesis and aggregation behaviour of thermo-responsive-b-poly(ionic liquid) diblock copolymers in aqueous solution

Stimuli-responsive di-block copolymers viz. poly(N-isopropylacrylamide)m-block-poly(butyl-3-vinylimidazolium bromide)n [abbreviated as PNIPAMm-b-PBVIBn m = 50 and 100, n = 54 and 115] were synthesized using RAFT (Reversible addition−fragmentation chain-transfer) polymerization. Gel permeation chromatography (GPC) and nuclear magnetic resonance (1H NMR) spectroscopy were used to characterize the block copolymer. Turbidity data shows that the lower critical solution temperature (LCST) of PNIPAM is independent of the molecular weight. No LCST behavior was estimated for PBVIB58 in an aqueous media. The addition of 2.75 M NaCl brings LCST of PBVIB58 to room temperature. The cloud point temperature (CPT) of both the block copolymers increases with an increase in the degree of polymerization of PBVIB. Scattering techniques confirm the molecular state of all the homopolymers at 28 °C in the dissolved condition. With an increase in temperature and the presence of sodium chloride (NaCl), both the copolymers remain as aggregates with PNIPAM as a core and PBVIB as a shell. The reverse structure is formed via the addition of 10 mM sodium dodecyl sulfate (SDS) into PNIPAM100-b-PBVIB54 solution.