PROPERTIES AND APPLICATIONS OF PHOTORESPONSIVE POLYMERS

Several proposals to construct artificial photoresponsive polymer systems have been described. Polyamides with azobenzene chromophores in the backbone reversibly changed the conformation by ultraviolet light irradiation(410 > ⋋ > 350 nm), which causes the trans to cis isomerization of the chromophores. Aqueous solutions of poly(N-isopropylacrylamide) with pendant azobenzene chromophores showed a photostimulated phase separation on exposure to ultraviolet light. A large effect, a large turbidity change in this case, was induced by a small number of photons. Polyacrylamide gels with triphenylmethane leucocyanide groups reversibly dilated as much as 18 time by ultraviolet irradiation. Photodissociation of the chromophores generated the osmotic pressure difference between the gel and the outer solution, and the osmotic effect caused the gels to expand. When a rod-shaped gel was irradiated from one side, the gel showed a bending motion. Electric field accelerated the bending rate. Poly(N-isopropylacrylamide) gels with triphenylmethane leucocyanide groups underwent a discontinuous swelling-shrinking switching upon irradiation and removing ultraviolet light. © 1990 IUPAC