Thermoresponsive Swelling Properties of Poly(N-isopropylacrylamide) Gels Synthesized Containing a Hydrophilic Crosslinker

We investigated the effect of the hydrophilicity of a crosslinker on the thermoresponsive swelling properties of poly(N-isopropylacrylamide) (PNIPAAm) gels. The gels were prepared with a variety of feed concentration of a crosslinker, poly(ethylene glycol) diacrylate (PEGDA) having a different number of ethylene glycol (EG) units. The swelling curves of the obtained gels indicate a strong relation of swelling behavior with the number of EG units in the network. The swelling degree at 10 degrees C decreased with lower number of EG units, indicating that the crosslinking density of the gels increased. Moreover, the swelling degree at 40 degrees C and the shrinking temperature showed almost the same value below 30% of EG content and increased linearly above this threshold value. This indicates that the hydrophilicity of the crosslinker has an effect even in the shrunken state of PNIPAAm gels.