Photocrosslinking of thin films of temperature-sensitive polymers

Abstract

The use of polymeric materials with temperature‐dependent degrees of swelling (especially polymers that exhibit lower critical solution temperature (LCST) behaviour in aqueous solutions) in microsystems requires the preparation and patterning of layers in the µm range. Copolymers based on N‐isopropylacrylamide were modi‐fied with a stilbazolium salt chromophore to yield photocrosslinkable temperature‐sensitive polymers. The chromophore and the polymers were characterized by UV, IR, 1H‐NMR (nuclear magnetic resonance) and 13C‐NMR spectra. The resulting polymers showed LCST behaviour, which was measured by differential scanning calorimetry. The photocrosslinking properties were studied by UV irradiation of the thin films and measurement of the changes in the UV absorption spectra. By irradiation of thin films through a mask it was possible to obtain patterned networks in the µm range (20 µm space width and ≥50 µm line width). The resulting patterned networks showed temperature‐dependent swelling properties in aqueous media. Copyright © 1999 John Wiley & Sons, Ltd.

Preparation and properties of thin films of photocrosslinkable hydrophilic polymers

“…At this moment, we cannot give an explanation for this unusual behaviour. An analogous behaviour of PNIPAAm-based copolymers modified with the same chromophore, but shifted to higher chromophore contents, was observed for their photoreactive films cast from butanone [5,34].…”

Photo-Cross-Linkable PNIPAAm Copolymers. 4. Effects of Copolymerization and Cross-Linking on the Volume-Phase Transition in Constrained Hydrogel Layers

“…However, for these particular materials the annealing process causes the thioxanthone sensitizer to phase separate, and the resulting films cannot be photo-cross-linked. Other photo-cross-linking schemes that do not include a sensitizer have been used with PNIPAAm polymers, , and these systems may be useful for further studies. However, NIPAAm5 samples can also be prepared by dip coating, which is known to produce some anisotropy, but this should be less than the corresponding spin-coated samples .…”

Fundamentals of Hydrogel‐Based Valves and Chemofluidic Transistors for Lab‐on‐a‐Chip Technology: A Tutorial Review

“…The gelling photopolymerization of hydrogel precursor solutions achieve resolutions of up to 20 µm. [196,[198][199][200] To promote the adhesion of the hydrogels on the substrate surface, prior functionalization of the glass with reactive groups, e.g., methacrylate groups, can be performed. Upon polymerization of the hydrogel, reaction with these groups results in covalent bonds between the hydrogel and the substrate.…”