## 2 Results and Discussion
### Acetylated and Methylated Lignin  
The degree of substitution of the acetylated and methylated lignin was determined by \({}^{31}\)P-NMR (see Supporting Data). The acetylated lignin contained no free hydroxyl groups and the HSQC-spectrum showed characteristic correlation peaks for acetylated structures (see Supporting Data). For the analysis of the thermal properties we used Me\({}_{2}\)SO\({}_{4}\) in alkaline aqueous media to selectively methylate the phenolic hydroxyl groups in the lignin and to leave the aliphatic hydroxyl groups and carboxyl groups unmodified (see Table 2). The small amounts of remaining free phenolic groups seen in Table 2 seemed, based on \({}^{31}\)P-NMR shifts of the peaks, to originate from hydroxyl groups in 5-condensed structures. To fully methylate one lignin sample, CH\({}_{3}\)I was used as methylation agent and NaH as base in anhydrous DMF (Figure 3c). This sample was only used to compare the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Lignin** & **Aliphatic** & **5-subs** & **G-units** & **Ph-OH** & **OH** & **COOH** \\  & **(150.0-145.5 ppm)** & **(145.1-140.5 ppm)** & **(140.5-136.8 ppm)** & **Pb-OH** & **Total** & **(136.8-133.4 ppm)** \\ \hline Pine MWL & 4.7 & 0.8 & 1.2 & 2.0 & 6.7 & 0.3 \\ Pine BLN & 2.2 & 2.0 & 1.9 & 3.9 & 6.1 & 0.6 \\ Pine MHE & 0.7 & 1.2 & 2.5 & 3.7 & 4.4 & 1.6 \\ Pine iPOH insol & 1.9 & 1.8 & 1.5 & 3.3 & 5.2 & 0.4 \\ Pine iPOH sol & 1.7 & 1.8 & 2.3 & 4.0 & 5.7 & 0.8 \\ Spruce MWL & 4.6 & 0.8 & 1.3 & 2.1 & 6.7 & 0.2 \\ Spruce BLN & 2.2 & 1.9 & 1.9 & 3.9 & 6.1 & 0.6 \\ Spruce MHE & 1.0 & 1.3 & 2.3 & 3.6 & 4.6 & 1.4 \\ Spruce iPOH insol & 2.1 & 1.9 & 1.6 & 3.5 & 5.6 & 0.5 \\ Spruce iPOH sol & 1.6 & 1.7 & 2.1 & 3.8 & 5.4 & 0.8 \\ OMe Pine BLN & 2.0 & & & 0.8 & 2.8 & 0.7 \\ OMe Sprace BLN & 1.9 & & & 0.6 & 2.5 & 0.6 \\ OMe Birol BLN & 1.3 & & & 0.5 & 1.8 & 0.7 \\ \hline \hline \end{tabular} \({}^{1}\) 150.0–145.5 ppm when c-hexanol was used as internal standard.  
\end{table} 
Table 2: Amount of free hydroxyl groups in mmol/g based on \({}^{31}\)P NMR analysis. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Lignin** & **M\({}_{\mathbf{n}}\) (g/mol)** & **M\({}_{\mathbf{w}}\) (g/mol)** & **PDI** \\ \hline Pine MWL & 1500 & 2700 & 1.7 \\ Pine BLN & 3200 & 6700 & 2.1 \\ Pine MHE & 380 & 480 & 1.3 \\ Pine iPOH insol & 4200 & 8000 & 1.9 \\ Pine iPOH sol & 860 & 1500 & 1.7 \\ Spruce MWL & 2100 & 3000 & 1.5 \\ Spruce BLN & 2100 & 5500 & 2.7 \\ Spruce MHE & 460 & 570 & 1.2 \\ Spruce iPOH insol & 3800 & 7000 & 1.9 \\ Spruce iPOH sol & 890 & 1200 & 1.3 \\ \hline \hline \end{tabular} \({}^{1}\) 150.0–145.5 ppm when c-hexanol was used as internal standard.  
\end{table} 
Table 3: The molar mass of the different lignin fractions and elemental analysis of the unmodified lignin and the MWLs. structural differences between the unmodified (Figure 3a), methylated phenolic (Figure 3b), and fully methylated lignin (Figure 3c). The HSQC correlation peaks in the oxygenated aliphatic area can be seen in Figure 3. The selectively methylated lignin (Figure 3b) remained similar to the starting material (Figure 3a), with no changes detected in the structures originating from natively occurring lignin linkages. The only difference between Figure 3a,b is the slightly higher chemical shift, in the \({}^{13}\)C-NMR spectrum, of the 4-OMe in structures that has been condensed on the 5-position. This change in chemical shift can also be seen in model compounds with the same type of structure [34]. In the fully methylated derivative (Figure 3c) all the traditionally occurring C-H correlation peaks, besides the \(\beta\)-\(\beta\) signals that lack hydroxyl groups in the structure, were shifted to a higher ppm value due to the methylation of the aliphatic hydroxyl groups. The methyl ester group and the aliphatic methyl ether groups were also clearly detected separately (Figure 3c).