Comparative Study on Mild Depolymerization of Lignin Model Dehydrogenation Polymers and Milled Wood Lignin

Dehydrogenation polymers (DHPs) of coniferyl alcohol prepared in three different ways (bulk, end-wise and membrane) and spruce (Picea mariana) milled wood lignin (MWL) were depolymerized with dry hydrogen iodide. The amounts of the only monomeric product, 1,3-diiodo-1-(4-hydroxy-3-methoxyphenyl)propane and oligomeric products resulted from this procedure were compared. All DHPs differ noticeably from MWL in their structural organization, the bulk one being the best approximation. Yields of the diiodide were high in all cases (end-wise DHP: 45%, membrane DHP: 55%, MWL and bulk DHP: 20%). Molecular mass distributions of higher molecular mass products were similar in all the cases except end-wise DHP which demonstrated lesser degree of polymerization of high molecular mass fraction.