(55b) Characterization of Cationic Poly(N-isopropylacrylamide- co-N- 3-aminopropyl(methacrylamide)-Co- Methacryloyoxybenzophenone) Thin Film Hydrogels

Poly(N-isopropylacrylamide) or PNIPAAm in aqueous solution is known to display a lower critical

solution temperature (LCST) undergoing a reversible coil-to- globule transition at 32-33°C. Above this

temperature, the polymer switches from being hydrophilic to hydrophobic, and coalesces out of

solution. It is well known that small amounts of salts copolymerized with PNIPAAm can raise or lower

the LCST of NIPAAm significantly. Moreover, copolymerization of NIPAAm with other monomers can

introduce reactivity to stimuli other than temperature, such as pH, ultraviolet (UV) light, magnetism,

electric current, etc. In the present work, the influence of a cationic co-monomer, N-3-

aminopropyl(methacrylamide) (3AMA), was investigated on the swelling properties of thin film

hydrogels of PNIPAAm copolymerized with methacryloyoxybenzophenone. The copolymers showed

reactivity to both pH and temperature depending on the percentage of the 3AMA. The cloud point

properties of the bulk solutions were measured and compared to the swelling response of the

corresponding hydrogel film. The films were prepared by spin coating the copolymer and then

irradiation with UV light was used to induce cross-linking of the benzophenone groups. The swelling

behavior of the thin hydrogel films was characterized with both ellipsometry and FTIR.