2. Methylation and Oxypropylation of Kraft Lignins.
2.2.1. Methylation of Softwood Kraft Lignin with Dimethyl Sulfate. A total of 1.0 g of softwood kraft lignin was dissolved
in 15 mL of aqueous 0.7 M NaOH at room temperature. An appropriate amount of 0.25−2.5 mmol of dimethyl sulfate per
each 1 mmol of total phenolic hydroxyl groups was added, and the solution was stirred for 30 min at room temperature. Then the mixture was heated to 80 °C for an additional 2 h (Scheme 1, I). Detailed information of these methylation reactions is shown in Table 1.