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The preparation of value-added, chemically modified lignin-based copolymers for the use of technical lignin is crucial for green and sustainable development. Herein, we synthesized alkali-lignin-grafted polyacrylamide by atom transfer radical polymerization (ATRP). As alkali lignin (AL) has the highest total hydroxyl group content, it was modified with 2-bromoisobutyryl bromide to synthesize a lignin macroinitiator (lignin-Br) at different ratios of [OH group in AL]:[TEA]:[BiBB] = 1:1:1, 1:1.5:1.5, and 1:2:2. Acrylamide was grafted from lignin-Br with the most Br-initiating sites via ATRP. The ratios of monomer to lignin-Br used were 50:1, 100:1, and 200:1, and the synthesized copolymers (L- g -PAM) were denoted as L- g -PAM50, L- g -PAM100, and L- g -PAM200, respectively. These copolymers were characterized by Fourier transform infrared (FT-IR) and  1 H nuclear magnetic resonance (NMR) spectroscopies. The FT-IR and  1 H NMR results indicated that polyacrylamide was introduced into the lignin backbone of all L- g -PAM copolymers. Gel permeation chromatography of L- g -PAM showed that the  Mw  of L- g -PAM200 was the highest at 427,383 g/mol. Photographs and scanning electron microscopy images of L- g -PAM showed that L- g -PAM appeared as a soft sponge and contained interwoven fibers. The maximum degradation temperature ( Tmax ) of L- g -PAM increased with increasing monomer-to-lignin-Br ratio. Moreover, the glass transition temperature ( Tg ) of L- g -PAM was higher than that of AL. The alkali-lignin-grafted polyacrylamide, synthesized by ATRP, in our study has a narrow molecular weight distribution, and its soft sponge properties make it a hydrogel or another surfactant.

Characterization of alkali-lignin-grafted polyacrylamide synthesized by atom transfer radical polymerization