Synthesis of thermosensitive poly(N-alkylacrylamide) gels and core–shell type gels

When the poly(acrylic acid) (PAA) 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 took place from the outside to give the corresponding poly(N-alkylacrylamide) gel containing a C3 alkyl chain through a DAA–poly(N-alkylacrylamide) type gel capsule consisting of a hydrophilic unreacted core part and an amidated shell layer. The amidation proceeded by a reaction mechanism similar to the unreacted-core model. Thermal properties of the resulting poly(N-alkylacrylamide) gels such as deswelling behavior and equilibrium swelling ratio in water as a function of temperature were measured. The release of methyl orange from a poly(N-alkylacrylamide) gel and the gel capsule was also examined. PAA–poly(N-alkylacrylamide) type gel capsules containing a PAA core part and thermosensitive poly(N-alkylacrylamide) shell layer, prepared by the neutralization of DAA–poly(N-alkylacrylamide) type gel capsules, showed on–off chemical release characteristics in response to stepwise temperature changes across the LCST.