Photocrosslinking of thin polymer films - Materials for sensors and actuators

Polymers with temperature dependent degrees of swelling, especially polymer s which exhibit lower critical solution temperature (LCST) behaviour in aqu eous solutions, are of interest for applications in microsystems. For these applications it is necessary to form and pattern thin films in the mu m-ra nge. This has been achieved through photocrosslinking of linear prepolymers . Copolymers based on N-isopropylacrylamide (NIPAAm) were modified with a s tilbazolium salt chromophore to yield photocrosslinkable temperature sensit ive polymers. The chromophore reacts via a [2+2]-cycloaddition under irradi ation, this can be used to crosslink the polymer. The photocrosslinking pro perties were studied by UV irradiation of thin films and measuring the chan ges in UV absorption spectra. Through irradiation of thin films through a m ask it was possible to obtain patterned networks in the mu m-range (20 mu m space width and > 50 mu m line width). The polymers exhibited LCST behavio ur, which was measured using DSC. The resulting patterned networks had temp erature dependent swelling properties in aqueous media.