Synthesis of Core-Shell Type Gel Beads Consisting of Two Different Poly(N-alkylacrylamide) Gel Layers, and Their Thermosensitive Behavior

Abstract

Mm-size monodispersed poly(acrylic acid) gel-1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) salt (DAA) beads were prepared via a two-step procedure involving the sedimentation copolymerization of acrylic acid with 0.5 mol % of MBAA and neutralization of the resulting gel with excess DBU in methanol. When the resulting DAA beads were placed in N-methyl-2-pyrrolidone containing an excess of alkylamine and triphenylphosphine, selective amidation occurred from the outside to give the corresponding DAA-poly(N-alkylacrylamide) (PNAA) core-shell type gel bead, consisting of an unreacted DAA core and an amidated shell layer. The thickness of the shell layer could be controlled by the reaction time. Second amidation of the obtained DAA-PNAA core-shell type gel bead with another alkylamine resulted in a novel mm-size monodispersed core-shell type bead consisting of two different PNAA layers, poly(N-n-propylacrylamide) and poly(N-isopropylacrylamide). The swelling and de-swelling of the gel bead shell layer and core occurred independently in response to temperature changes. The amidation of the DAA beads and the swelling/de-swelling of the amidated gel beads occurred isotropically, and they maintained their spherical shapes.