Chiral chemical absorption property of a cross-linked poly(N-isopropyl acrylamide-co-sodium acrylate) thermoresponsive smart gel.

This investigation leads to the chiral chemical absorption property of a thermoresponsive gel material. D-(+)-α-phenyl ethyl amine was taken as the chiral chemical. The gel material was synthesized by polymerizing 1:1 mole ratio of N-isopropyl acrylamide and Na-acrylate along with methylene bisacrylamide (2 wt.% of total monomer) as a cross-linker using ammonium persulfate as an initiator and N, N, N', N'-tetra-methyl ethylene diamine as an accelerator. The microporous nature of the gel material is observed by scanning electron microscope as well as by surface analysis. It is a pH as well as thermoresponsive gel. The highest gel swelling is observed at around pH 8.2 at room temperature (30 °C). The gel contains carboxylate (-COO(-)) group in this slightly alkaline condition. In the ionic state, the mutual repulsion of the ionic groups helps in swelling the gel. The lower critical solution temperature (LCST) of the gel is observed to be about 38 °C, which is higher than that of poly N-isopropyl acrylamide itself (32 °C). This corroborates with the theory and other reported results that LCST increases with the incorporation of ionic moiety in the cross-linked copolymer. The chiral chemical absorption of the gel material was monitored by measuring circular dichroism of the chiral compound in the presence and absence of gel using a circular dichroism spectropolarimeter (J-810 L) (JASCO International Co., Ltd., Tokyo, Japan). About 18% of D-(+)-α-phenyl ethyl amine is absorbed from its aqueous solution by 0.01 g of dry gel material (particle size: 106-212 µm) at room temperature. The absorption of the chiral compound is reversible with temperature having a sudden jump at LCST (38 °C) of the gel material.