Supramolecular amphiphilic star-branched copolymer: from LCST–UCST transition to temperature–fluorescence responses

Abstract

The novel and well-defined supramolecular amphiphilic star-branched copolymer poly((caprolactone)-star-(poly(2-N,N-dimethylamino)ethylmethacrylate)₇ (PCL-(PDMAEMA)₇) with a porphyrin core was prepared via the combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and supramolecular host–guest inclusion complexation. After reaction of PDMAEMA with excess 1,3-propane sultone, the quaternized star-PCL-(PDMAEMA)₇ was obtained. The amphiphilic star-PCL-(PDMAEMA)₇ and quaternized star-PCL-(PDMAEMA)₇ can self-assemble into spherical nano-micelles by directly dissolving in water. This thermoresponsive micelles solution shows a transition from a lower critical solution temperature (LCST) of star-PCL-(PDMAEMA)₇ to an upper critical solution temperature (UCST) of quaternized star-PCL-(PDMAEMA)₇, indicating that the LCST–UCST transition of micellar solutions can be accomplished by the transition of PDMAEMA to quaternized PDMAEMA. Due to the presence of porphyrin molecules in the micelles core, the micelle solutions present obvious fluorescence and the fluorescent intensity can be adjusted by altering the temperatures. For the star-PCL-(PDMAEMA)₇ micelle solution, the fluorescent intensity decreases with the increase of temperature, while the fluorescent intensity increases with the increase of temperature for the quaternized star-PCL-(PDMAEMA)₇ micelle solution, indicating unique temperature–fluorescence responsive behavior.