STIMULI-RESPONSIVE POLYMERS - PHOTOSTIMULATED REVERSIBLE PHASE-SEPARATION OF AQUEOUS-SOLUTIONS OF POLY(N-ISOPROPYLACRYLAMIDE) WITH PENDANT AZOBENZENE GROUPS

Poly(N-isopropylacrylamide) 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 Te of a 1 wt% aqueous solution of the copolymer (content of azobenzene units, 2.7 mole%) increased from 19.4-degrees-C to 26.0-degrees-C by UV (350 < lambda < 410 nm) irradiation. On standing overnight in the dark, or by visible (lambda > 470 nm) irradiation, Tc again returned to 19.4-degrees-C. At 19.5-degrees-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 2.7 mole% pendant azobenzene units. Below and above the content, the phase separation was not affected by photoirradiation.