Alkali lignin was used as raw material to prepare sulfomethylated alkali lignin (SAL).SAL was then further incubated by horseradish peroxidase (HRP) to obtain the products (HPSAL) with high degree of sulfonation and high molecular weight.The gel permeation chromatography (GPC)

infrared spectroscopy (IR)

nuclear magnetic resonance (NMR)

ultra violet-visible spectrum (UV-Vis) and headspace gas chromatography (HS-GC) were used to investigate the structural characteristics of HPSAL.Compared with SAL

the molecular weight (Mw) and the sulfonation degree of HPSAL increased by above 20-fold and 30% after HRP incubation

respectively.It was also indicated that the carboxyl content increased while the phenolic and methoxyl groups decreased after HRP incubation.HRP incubation could oxidize phenolic group to form phenoxyl radicals.The free electron of the phenoxyl radicals could transfer to the ortho-

para-positions of phenolic groups and C of SAL side chains

inducing the increase of sulfonation reactivity.On the other hand

the increase of sulfonic group content was beneficial to the polymerization of SAL by HRP incubation.The polymerization was achieved by radicals coupling

including -O-4'

-'

-1' and -5' linkages.The results of molecular simulation indicated that the chances of -O-4' linkage increased significantly due to the decrease of methoxyl content and increase of sulfonic group content.