A study of the molecular-weight distribution of biosynthetic lignins and milled spruce and reed lignin
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1. Molecular-weight distribution (MWD) curves of biosynthetic lignins and of spruce and reed milled wood lignins (MWL) have been obtained, and their molecular weights have been calculated. The MWD curves of the dehydropolymers are bimodal, unlike the unimodal MWD curves of the natural lignins.
2. An analysis of the MWDs has shown that the process of preparation of the biosynthetic lignins consists of a heterophase suspension polymerization taking place by a radical mechanism, the growth of the live radicals not being the result of a single mechanism.
3. From a comparison of the MWDs of the “dehydropolymers,” the results of their cleavage by sodium in liquid ammonia and of their oxidation by alkaline nitrobenzene it follows that aromatic radicals of types R1 and R2 play a principal part in the chain propagation reactions, leading to an increase in the mean MWs of the biosynthetic lignins.
KeywordsConiferyl Liquid Ammonia Coniferyl Alcohol Milled Wood Lignin Natural Lignin
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