Photochemical modification of the lower critical solution temperature of cinnamoylated poly(N-2-hydroxypropylmethacrylamide) in water

Partial modification of the nonionic polymer poly(N-2-hydroxy-propylmethacrylamide) by cinnamate produces stimuli-responsive copolymers. The hydrophobic character of the cinnamate chromophore induces not only a lower critical solution temperature (LCST) in water, but renders additionally the polymers photoresponsive. For moderate cinnamate contents of 9 mol-%, the photoisomerization of the trans-cinnamate to cis-cinnamate groups allows to switch the LCST by irradiation, whereas for higher cinnamate contents of 21 mol-%, irradiation leads to intra- and intermolecular photocrosslinking.