Photoreversible gelation of a triblock copolymer in an ionic liquid.

The reversible micellization and sol-gel transition of block copolymer solutions in an ionic liquid (IL) triggered by a photostimulus is described. The ABA triblock copolymer employed, denoted P(AzoMA-r-NIPAm)-b-PEO-b-P(AzoMA-r-NIPAm)), has a Bblock composed of an IL-soluble poly(ethylene oxide) (PEO). The Ablock consists of a random copolymer including thermosensitive N-isopropylacrylamide (NIPAm) units and a methacrylate with an azobenzene chromophore in the side chain (AzoMA). A phototriggered reversible unimer-to-micelle transition of a dilute ABA triblock copolymer (1wt%) was observed in an IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim]PF6), at an intermediate bistable temperature (50 degrees C). The system underwent a reversible sol-gel transition cycle at the bistable temperature (53 degrees C), with reversible association/fragmentation of the polymer network resulting from the phototriggered self-assembly of the ABA triblock copolymer (20wt%) in [C(4)mim]PF6.