ABSTRACT:The simplified method for the synthesis of thermosensitive porous hydrogels by a radical polymerization was presented and their swelling properties were examined experimentally. N,N-Diethylacrylamide (DEAAm) or N-isopropylacrylamide (NIPAm) as primary monomers and N,N-methylenebisacrylamide (BIS) as a crosslinker were used. They were polymerized in water at various temperatures above the lower critical solution temperature (LCST) of poly-DEAAm (ca. 32ЊC) or poly-NIPAm (ca. 31ЊC) by using N,N,N ,N-,tetramethylethylenediamine (TEMED) and ammonium peroxsodisulfate (APS) as the polymerization accelerator and initiator, respectively. From the observation by a scanning electron microscope, it was found that these gels consisted of aggregated microgel particles, namely, a porous structure. The gels swelled below their LCSTs, and the swelling degree increased with lowering temperature. Furthermore, the gels swelled or shrank very fast in response to the change in temperature, and the shrinking rate was larger than the swelling rate. Such swelling properties and mechanical properties depended on the porous structure of the gels such as the size of the microgels and the pore volume, which largely changed with the synthesis temperature and the component of the primary monomer.
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 0 -methylenebisacrylamide or 3 mol % diethylene glycol diacrylate (DEGDA) were used as a crosslinker, the resulting beads underwent rapid swelling in water at 208C, 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 welldeveloped porous structures, they were able to effectively concentrate blue dextran from the dilute aqueous solution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.