Two-Step Imprinting Procedure of Inter-Penetrating Polymer Network-Type Stimuli-Responsive Hydrogel-Adsorbents

Abstract

We prepared an imprinted hydrogel-adsorbent, which consists of poly(N-isopropylacrylamide (NIPAm)) and poly(sodium acrylate (NaAAc)) gel. We used an inter-penetrating polymer network (IPN) system in the preparation of thermosensitive hydrogel in order to overcome the fundamental defect that the PNIPAm hydrogel loses the thermosensitive volume-phase transition behavior in the presence of polyelectrolyte. Our imprinting strategy of the hydrogel-adsorbent is the following two-step procedure; (1) Firstly, we prepared a soft PNaAAc gel that can bind a guest molecule and change its conformation in accordance with the guest molecule, and then the hydrogel was incubated in heavy metal ion solution to bind the template molecules. (2) Secondly, we tightly fasten the metal bound hydrogel with a secondary gel-network of NIPAm by means of IPN system in order to memorize the coordination structure for the metal ions on the PNaAAc gel. The imprinted hydrogel-adsorbent selectively bound the template ion above a lower critical solution temperature (LCST) of PNIPAm. The memory was fixed by shrinking above the LCST, and was deleted by swelling below the LCST.