Solubility and structures of β- <i>O</i> -4 type lignin model compounds with different molar masses in aqueous 1,4-dioxane

Abstract Despite its macromolecular nature, the impact of the molecular sizes on the physicochemical behavior of lignin remains poorly understood. In this study, guaiacyl-type β- O -4 model compounds with varying chain lengths, corresponding to number–average degrees of polymerization (DP n ) ranging from 2.2 to 35.8, and narrow molar mass dispersity were prepared to serve as simplified lignin models. The solubility of these model compounds was evaluated in a 1,4-dioxane/H 2 O (96:4, v / v ) solvent system. Results showed that saturation dissolution concentrations ( C sat ) significantly decreased with increasing chain length; specifically, the compound with a DP n of 3.0 exhibited a C sat of 289.7 g dm −3 , whereas that with a DP n of 35.8 showed a C sat of only 0.9 g dm −3 . Ultraviolet absorption and fluorescence spectroscopy indicated that J-aggregation-type π–π interactions occurred with increasing chain length. These findings offer novel insights into the conformational behavior of β- O -4 chains in solution and the solubility limitations imposed by lignin chain elongation.