Hydrogel composed of acrylic coumarin and acrylic Pluronic F-127 and its photo- and thermo-responsive release property

Hydrogels comprising acrylic coumarin (AC) and acrylic Pluronic F-127 (APF) were prepared by a free radical reaction and its photo- and thermal-responsive release property was investigated using methylene blue as a solute. AC and APF were prepared successfully, confirmed by ¹H NMR spectroscopy. The molar ratio of Pluronic F-127 chain to vinyl group of APF was 1:1.3, suggesting that diacrylic Pluronic F-127 which could act as a cross-linker for the formation of polymer networks was produced. The coumaryl groups of AC were dimerized as much as 60.1% by 2 h-UV irradiation. On the DSC thermogram, APF exhibited its melting point around 55.4°C, about 0.9°C lower than the melting point of Pluronic F-127. The gelling temperature of Pluronic F-127 solution (25% (w/v)) was about 40°C, determined by a viscometric method. The swelling ratio of the hydrogels increased up to greater than 8 in 30 min. The maximum release degree at 23 and 50°C of dye loaded in the hydrogels was suppressed by UV irradiation, possibly because of the photo-dimerization of coumaryl groups. The release degree at 50°C of dye loaded in the UV-treated hydrogels was lower as the content of APF was higher, possibly because the thermally induced gelation of the polymer chains could suppress the payload release from the hydrogels.