Grafting of thermosensitive poly(N-isopropylacrylamide) from wet bacterial cellulose sheets to improve its swelling-drying ability

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) is grafted from wet bacterial cellulose (WBC) sheets using atom transfer radical polymerization (ATRP). WBC is recognized as a highly swollen biocompatible material with broad application potential. However, native WBC undergoes drying relatively fast and its reswelling ability diminishes after losing a substantial amount of water. In this work PNIPAM is grafted from WBC to slow down its drying, especially at elevated temperatures, which is relevant for biomedical applications. As a primary step, initiator molecules, 2-bromoisobutyryl bromide, are attached to WBC through linkers that are covalently bound to the cellulose hydroxyl groups. Grafting of PNIPAM is then realized via surface-initiated ATRP in a water/methanol mixture leading to WBC-g-PNIPAM. The modification steps are followed via FT-IR, XRD, elemental analysis, and atomic force microscopy. It is concluded that PNIPAM contributes to ca. 22% of the dry mass of WBC-g-PNIPAM. The samples are subjected to repeating swelling and drying steps at 25 A degrees C and drying at 40 A degrees C. The obtained results indicate that grafted PNIPAM significantly reduces drying of the modified WBC and enables better reswelling after treatment at 40 A degrees C with respect to native WBC. The reported synthetic method may also be used for grafting other polymers bringing additional functionalities to WBC.