Precise synthesis of UCST-type amphiphilic diblock copolymers with pendant imidazolium ionic liquid segments and their thermosensitive physical gelation at extremely low concentrations in water

Abstract

Amphiphilic diblock copolymers with an upper critical solution temperature-type thermosensitive segment ([Me₂Im][BF₄]) were synthesized by living cationic polymerization and subsequent chemical modifications and they exhibited thermosensitive physical gelation behavior at very low concentrations in water. Precise synthesis of precursor diblock copolymers of isobutyl vinyl ether and 2-chloroethyl vinyl ether was achieved by suppressing side reactions using an initiating system consisting of Et_1.5AlCl_1.5, SnCl₄, and di-tert-butylpyridine at 0 °C. An aqueous solution of IBVE₅₀-b-[Me₂Im][BF₄]₄₀₀ was demonstrated to undergo thermosensitive physical gelation at a 1 wt% concentration. Interestingly, a block copolymer with 800 units of [Me₂Im][BF₄] exhibited physical gelation at 0.2 wt% in water. The formation of large micelles with extended corona chains based on electrostatic repulsion and hydration of the ionic [Me₂Im][BF₄] segment is most likely responsible for physical gelation via micelle packing at a very low concentration.