Poly(N-isopropylacrylamide) copolymers:: Hydrogel formation via photocrosslinking

Recent results on the photocrosslinking of temperature sensitive polymers are reviewed. Polymers with temperature dependent degrees of swelling, especially polymers which exhibit lower critical solution temperature (LCST) behaviour in aqueous solutions, are of interest for applications in microsystems, e. g. in microvalves. For these applications it is necessary to form and pattern thin films in the pm-range. This has been achieved through the photocrosslinking of linear prepolymers. Copolymers based on N-isopropylacrylamide (NIPAAm) were modified with a stilbazolium salt or acridizinium salt chromophore to yield photocrosslinkable temperature sensitive polymers. The photocrosslinking properties of the two chromophores were compared. Patterned networks in the pm-range (20 mum space width and > 50 mum line width) were prepared through irradiation of thin films using a mask. The polymers exhibited LCST, which was measured using DSC. The patterned networks had temperature dependent swelling properties in aqueous media. (C) 2003 American Chemical Society.