Per-Olof Wahlund

Photosensitive copolymer of N-isopropylacrylamide and methacryloyl derivative of spyrobenzopyran

The copolymer of N-isopropylacrylamide (NIPAM) and methacryloyl derivative of spirobenzopyran (MSBP) with a molecular weight of 21 000 g/mol and the average molar MSBP content of 1.9% was prepared by free radical polymerization. The copolymer displayed its phase transition in water in the temperature range of 30-50 degreesC. UV irradiation of its aqueous solution caused photoinduced transformation of MSBP units into their coloured merocyanine forms, while the cloud point of the irradiated copolymer shifted by ca. 10 degreesC to lower temperatures. During a long-term exposure to daylight (20 days) the copolymer gradually elapsed to its colourless spiropyran form, the process being ca. 100-times slower than that for monomeric MSBP. Due to the slow reverse isomerization of its merocyanine form and low solubility in water at room temperature the UV irradiated copolymer could be quantitatively separated from aqueous solution by centrifugation