Molecular Characteristics of Poly(N-isopropylacrylamide) Separated from Nanocomposite Gels by Removal of Clay from the Polymer/Clay Network.

The extraordinary mechanical and swelling/deswelling properties of nanocomposite (NC) gels are attributed to their unique organic (polymer)/inorganic (clay) network structure. In this study, poly(N-isopropylacrylamide) (PNIPA) was successfully separated from an NC gel network by decomposing the clay (hectorite) using hydrofluoric acid (HF). A very low HF concentration (0.2 wt.-%) was adequate for the decomposition of the clay without causing any damage to PNIPA. The separated PNIPA had a high $\overline M _{\rm w}$ (=5.5 × 10(6) g · mol(-1) ). Also, $\overline M _{\rm w}$ was almost constant regardless of the clay concentration (C(clay)  = 1-25 × 10(-2) mol · l(-1) ), even though the properties of the NC gel varied widely over this C(clay) range. Comparisons of NC gels, PNIPA, and SiO(2) -NC gels indicated that the clay platelets specifically play an important role in NC gels.