Synthesis and characterization of water-soluble PEGylated lignin-based polymers by macromolecular azo coupling reaction

Water-soluble PEG grafted lignin-based polymers (AL-azo-PEG) were efficiently synthesized by macromolecular azo coupling reaction between alkali lignin and PEG based macromolecular diazonium salts in alkaline water. This one-step PEGylation method showed many advantages such as high efficiency, controllable grafting radio, extremely mild conditions and without organic solvents. The prepared AL-azo-PEG polymers were well characterized by using various spectroscopic methods including UV–vis, FTIR and ¹H NMR spectra. Experimental results showed that the synthesized polymers had good solubility both in water over a wide pH range (pH 2–12) and in the majority of organic solvents, which helped to easily fabricate self-assembly colloidal particles and nanofibers by vapor diffusion method and electrospinning method, respectively. The azobenzene linkages generated by the macromolecular azo coupling reaction also brought photo-responsive properties to the prepared polymers.