Poly(N-isopropyla, crylamide) with pendant azobenzene groups was synthesized with the aim of inducing isothermal phase separation of the aqueous polymer solution by photoirradiation. The phase separation temperature Tc of a 1wt% aqueous solution of the copolymer (content of azobenzene units, 2.7mole%) increased from 19.4°C to 26.0°C by UV (350<λ<410nm) irradiation. On standing overnight in the dark, or by visible (λ>470nm) irradiation, Tc again returned to 19.4°C. At 19.5°C, UV irradiation caused the isothermal phase transition from the phase separated to homogeneous state, while visible irradiation induced the phase separation. The maximum phase separation temperature change by UV irradiation was observed for the aqueous solution of the copolymer with 2.7mole% pendant azobenzene units. Below and above the content, the phase separation was not affected by photoirradiation.
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Irie et al. (1992) studied this question.