Preparation of asymmetric thermosensitive double-layer gel
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1129-V04-06
Preparation of asymmetric thermosensitive double-layer gel Takashi Iizawa1, and Akihiro Terao 1
Department of Chemical Engineering, Graduate School of Engineering, Hiroshima
University, 1-4-1 Kagamiyama Higashi-Hiroshima 739-8527, Japan.
ABSTRACT Heterogeneous amidation of poly(acrylic acid) gel-1,8-diazabicyclo-[5,4,0]-7-undecene salt (DAA) in N-methyl-2-pyrrolidone containing an excess of alkylamine and triphenylphosphite occurred from the surface to give the corresponding DAA-poly(Nalkylacrylamide) (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). 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. This paper proposes a new approach to the preparation of asymmetric thermosensitive PNAA(2)PNAA(1) double-layer gels by several procedures using the synthetic method of the core-shell type gels containing of poly(N-isopropylacrylamide) and poly(N-n-propylacrylamide) layers. Among the obtained asymmetric double-layer gels the model I type gel (cylindrical grooved PNNPA-PNIPA core-shell type gel) was markedly bent in water at temperatures between the lower critical solution temperatures of both layers.
INTRODUCTION Poly(N-alkylacrylamide) (PNAA) gels containing C2-C3 alkyl groups such as ethyl, npropyl, isopropyl, allyl, and cyclopropyl groups are thermosensitive with lower critical solution temperatures (LCST).1 They swell in water at temperatures below the LCST and de-swell at temperatures above the LCST. The LCST varies, depending on the alkyl groups. They can be used in a variety of applications such as polymer actuator,2 extraction,3 absorption,4 drugdelivery,5 and enzyme immobilization.6 Since the swelling/de-swelling of these simple gels occur isotropically in response to the water temperature changes across the LCST, their volume changes; however, their shapes are not markedly deformed. On the other hand, thermosensitive composite gels consisting of two different PNAA layers, which have similar structure to bimetal, would be suitable for actuator because they can be bent effectively. However, few studies have been reported on thermosensitive double-layer actuator, because it is difficult to bond two kinds of hydrogel plates together inseparably. Recently, we reported a new synthetic method of PNAA(2)-PNAA(1) core-shell type gels containing two different PNAA: poly(N-n-propylacrylamide) (PNNPA) and poly(Nisopropylacrylamide) (PNIPA) layers by the heterogeneous two-step amidation of the poly(acrylic acid) gel-1,8-diazabicyclo-[5,4,0]-7-undecene (DBU) salt (DAA) with alkylamines using triphenylphosphite (TPP) as an activating reagent.7 Since the resulting core-shell type
gels have essentially the same main chain structure and shape as the original DAA samples, 1) a d
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