Highly Responsive Hydrogel Prepared Using Poly(N‑isopropylacrylamide)-Grafted Polyrotaxane as a Building Block Designed by Reversible Deactivation Radical Polymerization and Click Chemistry

We prepared building blocks with the ability to form a polymer network, a polyrotaxane (PR) structure that enhances the flexibility of the polymer network, and thermosensitive dangling chains that impart the polymer network with rapid sensitivity. First, thermosensitive poly­(N-isopropyl­acrylamide) (PNIPA) was grafted from α-cyclodextrin, a cyclic molecule of PR, via controlled radical polymerization. The terminal chlorinated alkyl group of the grafted PNIPA was then modified with azide or alkyne. As a result, we obtained two types of PNIPA-grafted PR molecules with different terminations of PNIPA as building blocks. We then prepared a polymer network in which PR molecules with several dangling PNIPA chains were connected by PNIPA chains using a click reaction. Because of the presence of the dangling PNIPA chains, the obtained hydrogel exhibits rapid responses to changes in water temperature; it also exhibits flexibility due to the presence of the PR structure.