In Situ Surface-Selective Modification of Uniform Size Macroporous Polymer Particles with Temperature-Responsive Poly-N-isopropylacrylamide

A new in situ surface-selective modification procedure for the incorporation of temperature-responsive poly-N-isopropylacrylamide (poly-NIPAM) into porous polymer beads has been developed. This procedure allows the incorporation of the poly-NIPAM either on the internal surface of the macroporous beads or on their external surface selectively. The process involves the addition of NIPAM monomer and a water-soluble radical initiator to a polymerizing mixture consisting of uniformly sized monomer and porogen particles prepared by a two-step swelling and polymerization method. NIPAM polymerizes in the aqueous phase but soon precipitates out because the upper critical solution temperature of poly-NIPAM is exceeded. If cyclohexanol is used as the porogen for the monodispersed beads, poly-NIPAM dissolves in the cyclohexanol and is able to penetrate all pores of the beads where it becomes grafted at their surface. With toluene as the porogen, poly-NIPAM being insoluble in the porogen cannot penetrate the pores but only becomes grafted onto the external surface of the beads. The characteristics of the poly-NIPAM-modified particles were confirmed by a simple chromatographic process.