Estimation of Temperature‐Dependent Pore Size in Poly( N ‐isopropylacrylamide) Hydrogel Beads

The pore sizes of various temperature‐sensitive hydrogel beads have been estimated at different temperatures by a gel filtration method using several probe molecules of known molecular weight. The hydrogel beads were prepared by inverse suspension copoly‐merizations of a series of N ‐isopropylacrylamide (NIPAAm) and acrylamide (AAm) monomers with a small amount of cross‐linker. These hydrogel beads exhibit LCST (lower critical solution temperature) behavior in aqueous solution, that is, expanding and swelling when cooled below the LCST and shrinking and collapsing when heated above the LCST. The pore sizes of these temperature‐sensitive hydrogel beads are affected significantly by both the temperature and the gel composition, but not much by cross‐linker concentration.