KEY WORDSThermo-Sensitive Polymer Gel / 1,8-Diazabicyclo-[5,4,0]-7-undecene / Amidation / Poly(acrylic acid) Gel / Poly(N-alkylacrylamide) Gel / Poly(N-isopropylacrylamide) (PNIPA) gel is famous thermo-sensitive polymer gel which has lower critical solution temperature (LCST) in the vicinity of 32 • C. [1][2][3] Since it shows relatively quick and large volume change caused by a small temperature change around LCST and its monomer N-isopropylacrylamide (NIPA) is commercially available, many applications of PNIPA gel were proposed. [4][5][6][7] However, the applications may be restricted because the operation temperatures depend on the LCST and cannot freely be configured. Therefore, polymer gels which show different LCST from and equal thermo-sensitivity to PNIPA gel are needed for practical use. Ito 8 reported LCST of numerous linear poly(N-alkylacrylamide)s and poly(N, N-dialkylacrylamide)s. The thermo-sensitive behavior of some poly(N-alkylacrylamide) gels such as poly(N-ethylacrylamide) gel 9 and PNIPA gel was also observed. The LCST of poly(N-alkylacrylamide)s and the gels depends primarily on their chemical structure. However, the swelling behavior of gel was strongly affected by the network structure as well as the chemical structure. Since poly(N-alkylacrylamide) gels with the same network structure were not prepared from the polymerization of the corresponding monomers, relative thermo-sensitivity of poly(N-alkylacrylamide) gels could not been determined.Recently, we have studied heterogeneous reaction of poly(acrylic acid)-1,8-diazabicyclo-[5,4,0]-7-undecene (DBU) salt (DAA) with some reagents such as alkyl halide and alkylamine. [10][11][12][13][14] It is found that almost quantitative amidation of DAA with isopropylamine (IPA) occurred in the presence of triphenylphosphite (TPP) as an activating agent to give PNIPA gel. The reaction of DAA with alkylamines would be expected to proceed without any relation to structure of alkylamines † To whom correspondence should be addressed. and give poly(N-alkylacrylamide) gels with the same network structure.In this communication, a series of thermo-sensitive poly(N-alkylacrylamide) gels containing C 3 alkyl chains with the same network structure is prepared from the amidation of DAA with alkylamines such as n-propylamine (NPA), IPA, allylamine (AA), cyclopropylamine (CPA), and mixtures of NPA and IPA (Scheme 1). Also, we discuss LCST and relative thermo-sensitivity of the obtained polymer gels. EXPERIMENTALCylindrical DAA (length and diameter; about 5 mm) was prepared via two-steps; the copolymerization of acrylic acid with 0.5 mol% of N, Nmethylenebisacrylamide in Teflon tubes (internal diameter; 6 mm) and neutralization of the resulting gel with excess DBU in methanol according to the previous papers. 12,13 The samples were sufficiently washed with methanol by a Soxhlet extractor, and dried in vacuo at 60 • C until constant weight.A typical amidation of DAA is as follows. Mixed solution (50 mL) of NPA (2.0 mol L −1 ) and TPP (1.0 mol L −1 ) in N-methyl-2-pyrr...