Polymeric structure of spruce lignin.

From the Flory-Stockmayer theory and molecular weights of successive fractions of lignin obtained by extraction of spruce wood with a mixture of water, dioxane, and hydrochloric acid and by sulfonation, the average length of the primary chains was estimated to be 18 phenylpropane units. From data on the acid-catalyzed cleavage of model compounds in various solvents the degrees of cross-linking in four extraction processes were calculated. The average degree of cross-linking of intact lignin was found to be 0.277; that is, 5 out of every 18 phenylpropane units bear cross-linking benzyl ether groups. Of the five, three are also etherified at their phenolic ends (B groups), and two are not (X groups).