Preparation of a Thermoresponsive Lignin-Based Biomaterial through Atom Transfer Radical Polymerization

Copolymerization of N-isopropylacrylamide (NIPAM) with technical hardwood kraft lignin (HWKL) was achieved by atom transfer radical polymerization (ATRP) using a selectively modified lignin-based macroinitiator. The degree of polymerization (DP) of polyNIPAM graft side chains was affected by varying the ratio of the DMF/water solvent system from 5:0 to 0:5, and an estimated DP(NIPAM) of >40 was obtained using a ratio of 1:4 (v/v). The thermal decomposition temperature of the lignin-g-polyNIPAM copolymers significantly increased with increasing DP(NIPAM). Likewise, the solubility of the lignin-g-polyNIPAM copolymers in water changed depending on copolymer structure. In both the water-soluble and suspended copolymers, at temperatures above 32 degrees C, the g-polyNIPAM component underwent the typical hydrophilic-to-hydrophobic transition, resulting in the precipitation of the copolymer.