Synthesis of porous poly(N-isopropylacrylamide) gel beads by sedimentation polymerization and their morphology

Sedimentation polymerization of aqueous solutions of N-isopropylacrylamide (NIPA) was carried out to prepare porous poly(N-isopropylacrylamide) (PNIPA) beads. When small amounts of DMF and a radical accelerator were added to the monomer solution, the polymerization proceeded smoothly to give polymer beads with a very narrow size distribution. The rate of swelling of the resulting bead increased with increasing crosslinker content and was also affected by the type of crosslinker used. When amounts higher than 1 mol % N,N'-methylenebisacrylamide or 3 mol % diethylene glycol diacrylate (DEGDA) were used as a crosslinker, the resulting beads underwent rapid swelling in water at 20 degrees C, reaching the equilibrium within 5 min. A cross-sectional photograph of a typical dried bead showed that it had a very complex morphology consisting of a large and irregular void, highly porous region, and nonporous region. The swelling rate was directly dependent on the morphology of the beads. PNIPA beads with well-developed porous areas show a high swelling rate. Although PNIPA beads produced from DEGDA had well-developed porous structures, they were able to effectively concentrate blue dextran from the dilute aqueous solution. (c) 2007 Wiley Periodicals, Inc.