Preparation and properties of thin films of photocrosslinkable hydrophilic polymers

New hydrophilic photocrosslinkable polymers were prepared from water-soluble copolymers and photodimerizable chromophores. Water-soluble prepolymers were obtained by copolymerization of N-isopropylacrylamide (NIPAAm) or N,N-dimethylacrylamide (DMAAm) with acrylic acid (AAc). The polymers were then modified with hydrophobic or hydrophilic photoreactive groups, trans-4-hydroxystilbene and styrylpyridinium (stilbazolium) salts, in polymer analogous reactions. Thereby water-soluble photoreactive polymers with or without temperature-sensitive solubility were obtained. The glass transition temperatures of the polymers and the cloud points of their solutions in water were determined and found to depend on the content of the photoreactive groups. Thin films of the materials on quartz plates were prepared from solutions in different solvents such as butanone, chloroform, ethanol, tetrahydrofuran, and water, and the photocrosslinking properties of these films were studied. The nature of the chromophores as well as the solvents used for the film preparation were found to influence the photocrosslinking behaviour.