Preparation and characterization of thermosensitive beads with macroporous structures

Thermosensitive copolymers of poly(N-isopropyl acrylamide)-co-2-hydroxyethyl methacrylate (NIPA-co-HEMA) macroporous resins were synthesized in the form of beads by inverse suspension polymerization. The copolymerization was carried out in aqueous solutions of the comonomers dispersed by cyclohexane with stabilizers. A series of resins with different molar ratios of NIPA : HEMA, and different crosslinking degrees was obtained. The compositions of the copolymers were determined by elemental analysis. The results showed that the content of HEMA in a copolymer was higher than that of the corresponding feed mixture from which the copolymer was made. IR spectra also confirmed the structure of the copolymers. The porous parameters such as true densities, apparent densities, pore volumes, and porosities of the resins were measured by means of pycnometry. The determination of equilibrium swelling ratios and measurement of differential scanning calibration indicated that the resins exhibited thermosensitivity in aqueous solutions. Finally, the loading of hydroxyl groups was determined by titration. The resins have potential applications as supports in solid-phase synthesis after being functionalized. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1792–1797, 2004