Photodependent release from poly(vinyl alcohol)/epoxypropoxy coumarin hydrogels

To obtain a photoresponsive hydrogel, poly(vinyl alcohol) (PVA) having coumarin residue as a pending group was crosslinked by photodimerizing the coumarin pendants. PVA having coumarin pendants was prepared by reacting the polymer with epoxypropoxy coumarin (EPC) in a strong alkali condition with EPC/PVA molar ratio of 200/1. According to the 1H NMR spectrum of PVA-EPC conjugate, the molar ratio of EPC residue to PVA was about 4.3/1, indicating that EPC was attached to PVA every 444 repeating units of vinyl alcohol. An aqueous solution of PVA-EPC (5%, w/v) became a semi-solid hydrogel by the irradiation of a light ( = 365 nm; 400 W) for 1 hr. The dimerization degree of EPC residues of the hydrogel decreased and increased in a periodical manner under the cyclic irradiation between two UV lights ( = 365 nm and = 254 nm). The release of 5(6)-carboxyfluorescein (CF) from PVA-EPC hydrogel was significantly enhanced by the 5 min-irradiation of = 254 nm (6 W), possibly due to the photodedimerization of EPC residues of the hydrogel. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012