Photo-responsive microspheres prepared using hydrophobically modified poly(vinyl alcohol)-coumarin conjugate

Photo-responsive microspheres were prepared by dispersing hydrophobically modified poly(vinyl alcohol)-epoxypropoxy coumarin conjugates (HmPVA-EPC) in an aqueous phase. These conjugates were prepared by subsequent covalent attachment of decanoyl chloride (DC) to PVA, and then EPC to HmPVA. The air/water interfacial activities of HmPVA-EPC were higher than unmodified PVA, due to the hydrophobicity of DC moiety. Under a cyclic irradiation by 365 and 254 nm light, the degree of photo-dimerization of EPC residues of HmPVA-EPC was as high as that of free EPC. The obtained HmPVA and HmPVA-EPC were immobilized into submicron-sized microspheres. The degree of Nile Red release from HmPVA-EPC microspheres was more than 75% within 24 h that was higher than the value of 40% for HmPVA microspheres. This difference is most likely due to the less compact packing of HmPVA-EPC in the microspheres due to the smaller number of hydrophobic DC residues. The dye release from HmPVA-EPC microspherses was inhibited by the irradiation with 365 nm light, possibly due to the photo-induced cross-linking of the polymer.