Synthesis of β-O-4-type artificial lignin polymers and their analysis by NMR spectroscopy

We describe the synthesis and NMR spectroscopic analysis of three artificial lignin polymers containing only the β-O-4 substructure: syringyl-type homopolymer, p-hydroxyphenyl-type homopolymer and guaiacyl/syringyl-type heteropolymer. Using gel permeation chromatography, the weight-average degree of polymerization (DP_w) of the three polymers was determined as 19.2, 38.6, and 13.9, respectively. The polymers were prepared based on the synthetic methodology of guaiacyl-type homopolymer, and were fully characterized using ¹H-, ¹³C-, and ¹H–¹³C NMR spectroscopy of the acetylated and non-acetylated forms. The spectra of guaiacyl/syringyl-type heteropolymers were in good agreement with those of the β-O-4 substructure of milled wood lignin obtained from the hardwood of Japanese white birch.