ABSTRACT:When poly(acrylic acid) gel-1,8-diazabicyclo-[5,4,0]-7-undecene salt (DAA) was placed in N-methyl-2-pyrrolidone containing an excess of alkylamine and triphenylphosphine, selective amidation occurred from the surface to give the corresponding DAA-poly(N-alkylacrylamide) (PNAA) core-shell type gel, consisting of an unreacted DAA core and a quantitatively amidated shell layer. Further amidation of the DAA-PNAA core-shell type gel with a second alkylamine afforded a novel core-shell type gel consisting of two PNAA layers: PNAA(2) and PNAA(1). Thermal properties of the resulting core-shell type gels, such as swelling/de-swelling behavior, were measured in water at various temperatures. The resulting cylindrical PNAA(2)-PNAA(1) core-shell type gels were resistant to marked deformation caused by swelling/de-swelling because of their axial symmetry. In contrast, the semi-cylindrical double-layer gel prepared from the cylindrical poly(N-isopropylacrylamide)-poly(N-n-propylacrylamide) core-shell type gel was markedly bent in water at temperatures between the lower critical solution temperatures of both layers.

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.KEY WORDS: Double Thermosensitive Gel / Sedimentation Polymerization / Poly(Nalkylacrylamide) Gel / Core-Shell Type Gel / Sedimentation polymerization has attracted attention as a synthetic method for the production of mm-size monodispersed beads.1 These beads can usually be obtained from a classification of the beads prepared by suspension polymerization. The yield is so low that pellet-type gels have often been used instead of these beads. However, sedimentation polymerization can effectively produce mm-size monodispersed beads. The polymerization mechanism has been described as follows: when an aqueous monomer solution is injected dropwise to an immiscible heat medium (liquid paraffin or silicone oil), surface gelation of droplets descending in the medium takes place to give a stable skin, which prevents coalescence at the base of the reactor, and the polymerization is completed at the base.Improved sedimentation polymerization systems such as oilin-water-in-oil sedimentation polymerization; 2 compressed fluid sedimentation polymerization using supercritical carbon dioxide as a heat medium; 3 nonaqueous sedimentation polymerization using an aprotic polar solvent; 4 application to the crosslinking reaction of poly(vinyl alcohol) with glutaraldehyde; 5 and, polycondensation of tetraethyl orthosilicate 6 have been investigated. Mm-size functional polymer beads such as composite polymer beads, 5 interpenetrating polymer network beads, 5 and porous polymer beads 2,7 have been prepared by these methods. However, the chemical modification of beads prepared by sedimentation polymerization has rarely been reported. In the sedimentation polymerization of an aqueous Nalkylacrylamide solution, phase-separation occurred to give porous hollow particles. 7,8 These results support the polymerization mechanism described a...